VSEP Produced Water Treatment for Beneficial Use Technical Article

 

A Summary of Options Available for the Beneficial Use of Oilfield Produced Water using Membrane Treatment.

Greg Johnson, Brad Culkin Ph.D.

New Logic Research, Incorporated 2527 Aviation Way Minden, NV 89423

Presented: To be Determined

Keywords: Membrane, Produced Water, Reclamation, VSEP, Scaling Control, Reverse Osmosis, and Filtration

Abstract

Reverse Osmosis membranes have been used for many years to produce drinking water from seawater and brackish well water. This process has been readily accepted by regulatory agencies and by the public. Although a new technology only used since the early 1980’s, membranes have already experienced widespread use and have proven to be reliable and affordable for desalination. During more recent years with the passage of stricter discharge regulations to comply with the CWA (Clean Water Act) and other laws, membranes have now also been used effectively to treat many industrial and commercial wastewater for discharge to surface waters that are parts of drinking supply watersheds. Populations in many areas of the world, especially the arid Southwestern United States, have grown dramatically in the last 20 years outstripping the available water supply. Local water utility districts are now searching for ways to augment strained sources of drinking water. Many studies are being conducted to explore the use of “reclaimed” water from various wastewaters as a possible method of stretching the use of water and limiting the need for additional expansion of watershed depletion. [8], [9]

VSEP membrane technology has been used for many years to treat high dissolved solids bearing wastewater to produce clean water for discharge or reuse. Recent pilot trials have been conducted using the VSEP technology to examine its use in treating oilfield Produced Water for discharge into sensitive drinking water aquifer. This method of indirect introduction into the drinking water supply is only one of many ways that Produced Water can be converted from a waste product to a source of fresh water to augment strained public water supplies. This paper will discuss the variety of current water reuse applications employing membranes that are currently operating or are being considered.

Water Supply Background

As our society has become more mobile, populations have shifted and are increasingly settling in areas of the world that don’t have enough water resources to support the number of people living there. Many areas of the Southwestern United States would be deserts if it were not for irrigation and huge municipal projects to divert water. For example, the city of Los Angeles gets its water from Northern California through a huge aqueduct traveling the length of the state. In addition, its water supplies are drawn from the Colorado River, which borders the next state of Arizona. The depletion of Mono Lake in central California has reached perilous levels. In response to this, many water utilities in Southern California have been working on new sources of water including reclaimed water from wastewater.

Other states in the Southwest have experienced similar growing pains. The US Census Bureau estimates that the population of Arizona will double within the next 25 years. [3] The population of Houston has tripled since 1950. Clearly this trend cannot continue with water resources that are fixed. Other sources of water will need to be found. Texas, California, and Florida in particular have already started desalination of seawater in significant quantities using reverse osmosis membranes as a new source of drinking water. This treated water is directly introduced to the drinking water supply and is mixed with natural waters.

Texas has also started importing water from Mexico receiving 210,785 acre-feet of water into the Amistad International Reservoir. [20] Now that most sources of potable well water have been accessed, Texas has begun sourcing water from brackish water sources where the dissolved solids content can be 5000 mg/l or higher. Currently there are about 100 brackish water desalination plants using reverse osmosis membranes for drinking water production.

The subject of this case study, which will be discussed later in detail, involves the Paso Robles Aquifer located in the Salinas Valley in Central California. The Salinas Valley is an elongated valley between two large coastal mountain ranges. The Salinas River travels down the center of the Valley and discharges into the Pacific Ocean to the Northwest. The Paso Robles aquifer is fed by percolation from the rivers, rainfall, and irrigation water. It generally follows the same path as the Salinas River, and the edge of the aquifer joins the Pacific Ocean at its northern edge.

This aquifer supports thriving agriculture and industry as well as an increasing population of inhabitants. The load on the basin and aquifer has now surpassed the capacity. In 1995, inflows to the basing were estimated at 532,000 acre-feet while outflows were estimated at 550,000 acre-feet. As a result, the alluvial prism has decreased in size and seawater intrusion has steadily increased at the northwestern boundary. As of 1995, the seawater intrusion has extended 6 miles inland from the coast making ground water unusable in this area. The Monterey County Water Resource Agency is planning for the future and has several projects in the planning stages including the storage and use of recycled water.

With populations rising and water sources becoming stretched, increasing attention is being paid to how water is used and reused. Industry, agriculture, and domestic water users are all competing for this most precious natural resource. The EPA’s Office of Water recently estimated the capital required over the next 20 years for both water and wastewater upgrades is nearly $500 Billion USD (EPA, The Clean Water and Drinking Water Gap Analysis, 2002). These estimates are not adjusted for inflation and use current value terms. The EPA attributes these costs to retrofitting treatment plants and infrastructure that are obsolete, more stringent drinking water and wastewater standards, and increasing expense and controversy associated with capital improvement projects. [2]

During the 1970s and 1980s, the EPA provided more than 60 billion Dollars for construction of public water treatment projects through its Construction Grants Program. The Clean Water Act (CWA) of 1987 changed the Construction Grants Program and through an amendment to the CWA, the grant program was terminated in 1990. Under the new procedure, the EPA initiated the State Revolving Fund (SRF). Through the SRF, the EPA provides capitalization seed money to the states, which in turn offer low interest loans to local communities for municipal projects. The net effect is that although local municipal districts receive low-cost loans, they now must pay for 100% of capital improvement projects. Under the Construction Grants Program, the EPA paid about one-half of these costs directly.

Now that local water utility companies are responsible for 100% of the cost of capital projects, the construction of large mega projects such as Dams and large aqueducts will be greatly curtailed. Faced with aging infrastructure and limited current capacity, Municipal water districts are working on ways to optimize existing systems and supplement conventional sources of drinking water using relatively small capital projects. Increasingly, reclaimed water is being used as a source of water for direct or indirect distribution to the drinking water supplies. These relatively small capital projects can be implemented quickly to supplement water supplies, and the cost of these projects is more in line with what local water districts are able to manage.

Water Recycling

Through the natural water cycle, the earth has been recycling water since the beginning of time. The system that has evolved produces an infinite replenishable source of clean water for human consumption. Evaporation of water and then redistribution by the clouds and rainfall ensures an extremely pure water source. For centuries, man has used engineering practices to manipulate the natural distribution of water supplies to suit his needs. During the earlier centuries, the efforts focused on controlling the direction and volumes of water sources. Only within about the last century, have recycled water techniques been used. These types of uses have mostly been reusing water for non-potable uses such as irrigation for farming. Now with advances in water treatment technology and with burgeoning populations, man is working on more advanced methods of recycling water including potable uses.

Water recycling can either be planned or unplanned. Reuse of treated wastewater for irrigation is an example of planned water reuse. As an example of unplanned water recycling, many cities that draw drinking water supplies from the Mississippi or Colorado rivers are in a sense reusing some treated wastewater that has been discharged and blended into the river water further upstream. This has been done for many years. The fact that wastewater treated from municipal sewage and from industrial wastewater is being blended with the drinking water supply has been readily accepted since regulators and the public have assurances that the treated water will not have a negative impact on downstream operations. Large cities such as Philadelphia, Cincinnati, and New Orleans have been practicing indirect potable water reuse.

Water recycling can also be done directly into the drinking water supply just prior to water treatment or it can be done indirectly where it would be introduced further upstream in the watershed collection process. There are currently only a few examples of treated wastewater that is directly introduced into the drinking water supplies. Most reclaimed water reuse is indirectly introduced. Although there are many instances of unplanned indirect reuse as in the example above, there are also increasing numbers of planned indirect water reuse applications. When indirect water reuse is planned, the purpose of introduction to the water supply is to augment the volume of water source. Sometimes, there may be dual purposes in eliminating wastewater and at the same time creating a water resource, but generally, planned water reuse is done primarily for the purpose of replenishing water supplies.

Recycling water for non-potable use is very common and has been done safely and efficiently for many years. As the cost of water has increased and as discharge requirements have gotten tighter, industry has been at the leading edge of internally reusing its water. Many industrial plants have been able to completely close their water loop and have achieved Zero Liquid Discharge and only intakes of water to be used as make up water for system losses and evaporation.

Treated wastewater has been used for irrigation for agriculture, public parks, and golf courses for many years. Other non-potable water reuse applications include cooling water for power plants, process water for paper plants, and decorative or recreational water landscaping features.

Most water reuse projects have involved non-potable. However, an increasing number of projects are being completed where the objective is direct or indirect reuse of treated wastewater for potable purposes. Even though there are many cases of unplanned indirect water reuse as in the case of New Orleans getting its water from the Mississippi river, the number of planned cases of indirect reuse is smaller by comparison. Treated wastewater can be indirectly introduced into the water supply by percolating or injection into a drinking water aquifer or by discharge to surface waters such as lakes or rivers. Even though water is a renewable resource, the amount available to local communities can be limited. Recycled water is truly renewable, and the supply can be inexhaustible. Several converging circumstances will drive the movement towards water recycling including:

1. Existing fixed supplies of natural water will or have been used to the maximum extent possible.
2. Technology is constantly improving and evolving in wastewater treatment methods.
3. Analytical detection methods are improving to measure contaminants.
4. The scientific and medical communities are compiling a vast resource of relevant health effects studies.

Guidelines for Potable Water Reuse

In September 2004, the EPA (Environmental Protection Agency) issued its guidelines for water reuse. [1] The EPA has not made regulations concerning treated wastewater reuse and has only issued guidelines. So far, there are five states, which have issued formal regulations on reusing wastewater for potable purposes. These states include California, Florida, Hawaii, Massachusetts, and Washington. Indirect water reuse involves the planned augmentation of surface waters or aquifers that serve as water supplies. Unplanned indirect water reuses happen all the time in many rivers around the country. The result of both is the same, but the differentiation between the two depends on the intent of discharge and the proximity to withdrawal points for drinking water supplies.

There are no regulations in any of the other states across the country. For the states that have regulations on planned indirect water reuse, most are determined on a case-by-case basis. Only Washington requires the use of reverse osmosis treatment prior to discharge. The other four do not specify a treatment method. Florida requires a minimum of 500 feet of separation between the discharge point and the intake for fresh water supply. Florida also requires that all discharge to “Class 1” surface waters that are ultimately sources for drinking water must meet the EPA’s primary and secondary drinking water standards.

Water Rights and Legal Implications

Just as the guidelines and regulations for water reuse can be a little perplexing as in the case of unplanned and planned indirect water reuse, the legalities of water can be equally as confusing. Just because water exists on your property, you may not own it. In many cases, you are granted the right to use water and there are regulations on it use. It is not clear who owns reclaimed water. Some water users have subordinate rights to others when it comes to water usage. Recycled water could provide a reliable unlimited supply of unregulated water. However, this is up for debate. For example, on public lands, an oil company may have the right to the oil, while other entities may have pre-eminent water rights. Does this mean that once produced water that comes from oil production, once it is treated, can become the property of others?

Even wastewater once it is discharged into surface waters can become the property of others. There have been several cases where a wastewater generator is required to discharge effluent. One case is the City of Walla Walla in Washington State, where an irrigation district receiving water from the Mill Creek sued the city. The city had diverted its wastewater effluent discharge from Mill Creek affecting the volume available for irrigation. The irrigation district brought legal action and successfully received an order requiring the City to discharge all of its wastewater effluent into the Mill Creek. In a completely opposite direction, in 1984, the Sierra Club filed a complaint with the California State Water Resources Board. The petition stated that by discharging 1.6 MGD of treated wastewater to the Ocean, the Fallbrook Sanitation District was practicing an unreasonable use of water that is prohibited by law and that the discharge constitutes a waste of water. The board required the district to evaluate the feasibility of reclaimed water uses.

Quality Criteria for Potable Recycled Water

The Safe Water Drinking Act (SDWA) and the National Primary Drinking Water Regulations (NPDWR) were written assuming that natural water bodies would be the source for drinking water. No uniform quality criteria currently exist for water that is reused. Even though it can be proved that wastewater treated with reverse osmosis filtration can easily meet the EPA’s Primary and Secondary Drinking water standards, these standards were not designed for water where treated wastewater is the source. In many cases it can be shown that effluent treated with membranes is cleaner by far than treated surface water, however, adequate precedent and appropriate quality criteria do not exist.

The drinking water standards written have been developed to account for the known harmful chemicals that can be found in natural sources of drinking water such as Arsenic. When your source of water is treated wastewater, there are many more possible chemicals that are present and the effects of these are often unknown. There are thousands of natural and manmade chemicals that can be present in wastewater and the SDWA only accounts for a fraction of these.

Even still, if these unknown chemicals that can be hazardous are in wastewater, they will eventually end up in the drinking water supply as in the case of the Mississippi River. It will be necessary for regulators to expand the list of known contaminants and to develop standards for these whether they are intended to measure treated effluent or drinking water from a river. Amendments in 1986 and 1996 to the SWDA require the EPA to consider regulating up to 5 new contaminants every 5 years. As the knowledge about contaminants grows and as the ability to detect these hazardous chemicals at very low levels expands with the advance of science, the acceptance of treated effluent for reuse will become easier.

There cannot be a test for every hazardous contaminant, however. Even in drinking water analysis from natural sources, surrogates are used. For example, coliform counts are used to measure microbiological water quality. There are millions of species of bacteria including Cryptosporidium and Giardia that are very dangerous and can go undetected. Another advance that will help to promulgate the use of reclaimed water is the use of toxicology assays. The only way to definitively measure the health effects of potentially hazardous chemicals is to rely on actual empirical data. There have been many studies of the use of reclaimed water and its possible effects on the health of a population. As the number of reclaimed water reuse projects goes forward and as more of these studies are completed, gradually, effective guidelines can be written, and the idea of water reuse will be more accepted.

The idea of indirect water reuse takes into account the fact that the reclaimed water will undergo the same natural percolation and natural purification process that naturally occurring water sources experience. Most regulations for indirect reuse include provisions for residence time so that the treated water can also experience the natural purification process. Once that happens, it is more appropriate to apply the standards for drinking water mentioned above.

There are fewer guidelines available for direct reuse of reclaimed water, and these are generally determined on a case-by-case basis. [19] There have been toxicological studies even on direct reclaimed water reuse and this body of work will add to the growing case for direct reuse where advanced treatment methods such as reverse osmosis are employed.

Reuse of treated effluents will always have its own risks. However, so does even the use of natural sources of drinking water. Cryptosporidium and Giardia bacteria come from excrement of wild game and livestock that can find its way into the waterways. Chlorination and conventional treatment methods do not remove these bacteria. There have been many cases of contamination and even fatalities. Similarly, cruise ships have experienced problems with unknown vectors of virus transmission that may be related to drinking water supplies stored onboard.

The case for reusing treated wastewater for potable purposes would even be greater in countries that have poor drinking water supplies to begin with. In Peru, only 5% of the municipal effluent is treated with the remainder being discharged to the waterways where it is indirectly reused as drinking water. The city of Karachi Pakistan receives its drinking water from the Indus River, which winds its way through Pakistan accepting large volumes of untreated wastewater from many sources.

Examples of Indirect Water Reuse

There are many examples of unplanned indirect reclaimed water reuse. Most large rivers serve as a location for discharge of wastewater effluents and for intake of drinking water supplies. In some countries wastewater has been treated prior to discharge, and in other countries, little if any treatment has been done. Another example of unplanned indirect water reuse would be many private septic systems where effluent wastewater is sent to a holding basin underground. Some biological degradation and cleansing occur and then the water percolates down eventually into any aquifers that may exist below. Indirect water reuse that is consequential or unplanned is nothing new. Planned indirect reclaimed water reuse is a fairly new idea where the intent of discharge is to augment the existing supplies of drinking water.

1] Orange County Water District

With groundwater levels dropping, seawater intrusion into the aquifer, and few other sources of natural water supplies, the Orange County Water District (OCWD) has implemented an indirect reclaimed water reuse program where treated municipal effluent is injected into the drinking water aquifer. The Groundwater Replenishment (GWR) system was intended to recharge the groundwater basin to augment the existing supplies and to halt the seawater intrusion that was affecting the water supply. The low TDS water is injected into the seawater barrier and also allowed to percolate through the ground into the aquifer.

The treatment process involves initial treatment using an activated sludge process followed by a trickling filter to remove biodegradable contaminants. Then the water is purified using Micro-filtration followed by reverse osmosis membrane filtration and finally by ultraviolet disinfection. Analytical data shows that this treated water is much cleaner than the receiving body of water found in the aquifer. The treated water also exceeds the primary and secondary EPA drinking water standards for tap water.

The treated water blends with Santa Ana River water, rainwater, and ground water from other sources. Because the treated water has only about 100 mg/L of dissolved solids, which is much lower than the underlying groundwater, eventually the salinity of the groundwater source will be reduced. It also takes less energy to treat and distribute this reclaimed water that it would take to import natural water from great distances away. The GWR system produces about 70 million gallons per day (26,500 m3/yr) of sustainable clean water or about the equivalent of the consumption of 200,000 families. Eventually, the production rate is planned to increase to about double that amount.

2] Belgium

Belgium is a country with very limited water supplies. Only about 45% of sewage is currently treated. Reclaimed water reuse has been studied in three cases and implemented in one case. The Wulpen wastewater treatment plant treats about 2 MGD of municipal effluent using Micro-filtration followed by reverse osmosis membrane filtration. This water is introduced into a local aquifer where it is stored for up to 2 months prior to reusing as drinking water.

3] Saudi Arabia

Water is even more scarce in Saudi Arabia where the only available sources are from depleted groundwater sources and from desalination of seawater. About 70% of potable water in Saudi Arabia is produced by desalination. The government recently implemented its National Water Plan to economize and regulate its valuable water resources. Saudi Arabia has designed a 10-MGD activated sludge facility in Jeddah where the effluent is treated with Micro-filtration followed by reverse osmosis filtration and then used to recharge depleted groundwater supplies.

Examples of Direct Water Reuse

1] Namibia

Namibia is a small country in Africa, which is also located in a desert. In 1960, water supplies to the capital city of Windhoek fell well short of the need. After that, the Country implemented an emergency water plan. At first this involved construction of large reservoirs and importation of 80% of its water from great distances. Local aquifers were also tapped and depleted at a rapid rate. With this temporary fix in place, a water reclamation project was then begun. In 1968, the Gammans Treatment Plant started treating municipal effluent for reclaimed use. An activated sludge process followed by aging in maturation ponds for 4-12 days accomplishes the treatment of wastewater. This water is then blended at a ratio of 1:3.5 with water from the Goreangab Dam. This blended water is then treated using conventional water treatment methods to meet drinking water standards and again blended into the drinking water reservoir. [23]

The Tertiary treatment is accomplished by dissolved air floatation, sedimentation, and rapid sand filtration. More recently ozonation and activated carbon filtration have been added. Recently, additional membrane treatment and an additional 140 days storage are being considered as additional process improvements.

There have been toxicity studies completed for this project and a wealth of data exists from this plant that has been in operation since 1968. The studies have shown that the facility provides water that is safe and that no health effects from reclaimed water reuse have been observed. Plant capacity is currently being upgraded to 11 MGD (41,667 m3/day).

2] Singapore

Singapore is a densely populated city/state with no water resources of its own. Previously water supplies were imported from Malaysia. In 2003, Singapore has begun a process of reclaiming wastewater effluent using the advanced treatment methods of reverse osmosis filtration followed by ultraviolet disinfection. In 2003, about 2.4 MGD of treated water was introduced and blended with the other water supplies in storage reservoirs. The plans are for 12-MGD output by the year 2011. [22]

History of Membrane Filtration

The Sartorius Company in Germany first made membrane filters commercially available in 1927. [4] For many years it was used to remove microorganisms by micro-filtration. Then in 1960, researchers at the University of California at Los Angeles (UCLA) developed the first reverse osmosis membrane. The first full-scale commercial installation of these membranes was accomplished in 1965 in Coalinga California. Between 1965 and about 1980, these membranes were developed primarily for seawater desalination and specialized separations. By 1980 membrane use had become well established and during the 1980s several new membrane technologies were developed including Memtec’s hollow fiber microfiltration membrane and New Logic’s vibratory VSEP® membrane system developed in 1987. The creation of these new membrane delivery systems that were more resistant to fouling when used for wastewater applications has extended the scope of use of membranes. Today, membranes are used commercially for almost any liquid solid separation including very difficult to treat wastewater. The creation of membrane and more advanced delivery systems has made it possible for industrial plants to completely recycle wastewater and become closed loops with zero liquid discharge.

Membrane Technology

There are four basic types of membranes having to do with pore size or rejection characteristics. Microfiltration (MF) is the most open media with pore sizes from 0.05 micron and larger. Ultrafiltration (UF) membranes have pores ranging in size from 0.005 micron to 0.05 micron. These are typically rated according to the minimum nominal molecular weight size that the membrane will reject. This range for UF membranes is from 2,000 mwco (molecular weight cut off) to 250,000 mwco.

Nanofiltration (NF) and Reverse Osmosis (RO) membranes don’t have pores as such and work by diffusion. Ionic charge and size play a role in the permeation through the membrane. Monovalent ions will pass more freely than multivalent or divalent ions.

For the purpose of water filtration to remove suspended solids, Microfiltration is generally good enough. There is a correlation between pore size and throughput. Generally, the larger the pore, the higher the flow rate through a given area of membrane. Since filtration is needed to remove silt, suspended particles, bacteria, and other microorganisms, a Microfilter is normally used, as it will provide the highest throughput and best economics. If the water source is especially colored or turbid or if taste complaints are a problem, Ultrafiltration can be used which is tighter than Microfiltration. UF membranes can remove very small organic matter, humic substances, and even viruses. UF membranes can improve color, taste, and odor of the drinking water.

In the case of dissolved solids removal, as in the case of desalination or seawater or brackish water, tighter membranes including Nano-filtration and Reverse Osmosis are used. In the case of brackish water, MF or UF would not reduce the high levels of dissolved solids and could not provide filtrate meeting the primary drinking water standards. Brackish water is a term that covers a very broad range of water quality. Brackish water can have anywhere from 1000 ppm to 10,000 ppm of TDS. Above 10,000 ppm is considered Saline Water. The most appropriate membrane for brackish water still depends on the concentration of TDS. For slightly brackish waters, (1,000 to 3,000 ppm), nano-filtration would probably yield an acceptable water quality. For high level brackish water, (>3,000 ppm), reverse osmosis is probably needed as in the case of seawater desalination.

Most membranes used today are made of polymeric materials including polyamide, polysulfone, regenerated cellulose, kynar (PVDF) and Teflon® (PTFE). The pores on most polymer membranes are so small they cannot be seen even with a scanning electron microscope. The pore sizes are determined by how well the membrane rejects particles of known size. The membrane itself allows water to pass through the physical pores or through the matrix of the polymer and does not allow larger molecules or suspended solids to pass. Selection of the proper membrane depends on the separation required.

Membrane treatment has been used for the past two decades for wastewater treatment. This use has been well established and has proven to be effective and economical. The use of membranes has also made it possible to meet ever increasing stringent discharge requirements and made it possible for totally closed loop industrial plants. Membrane technology has also been used to make extremely pure water for high-pressure boilers and for electronics grade water for semiconductor manufacturing. Unlike other treatment technologies that may be targeted to certain contaminants like Nitrogen or Phosphorous, membrane do not discriminate and act as a molecular sieve and will reject all ions dissolved in water. The only variation is the extent of rejection of each ion. Multivalent ions are rejected better than monovalent ions for example. However, because reverse osmosis membranes can be used in series, it is technically feasible to reach any water quality no matter how pure by multiple passes of filtration.

Membrane Filtration of Drinking Water

There has been a trend in recent years towards the use of polymer membranes for treatment of potable water for domestic and industrial use. There have been significant advances in polymer chemistry within the last 20 years, and the use of membranes is becoming more widely accepted. In addition to the membrane itself, significant advances have occurred with respect to the delivery system. New technologies are appearing all the time and membrane systems now offer an effective competitive treatment method option.

Membranes were first developed primarily for desalination treatment to make drinking water. However, now membranes are also used to treat brackish water and even fresh waters for the purpose of drinking water production. One of the factors driving this has been the occurrence of contamination by certain bacteria including Giardia and Cryptosporidium, which are not removed when using conventional water treatment and disinfection methods.

Membrane Technology for Reclaimed Water

Since membranes have been used for the past two decades to treat wastewater effluent that is discharge into water bodies that become drinking water sources, the use of membranes for unplanned indirect water reuse is well established. In all of the cases shown above, membranes are being considered for planned reclaimed water reuse. In fact, the creation of membranes has made it possible to even consider reusing treated effluent as drinking water. No other treatment method except for evaporation and distillation could accomplish such a complete separation. Even an incredibly complex treatment process of many dissimilar treatment technologies could not compare to the purity and efficiency of membrane filtration.

Because membrane technology is fairly new, it’s possible uses are only now becoming clear. These uses and the subsequent guidelines for use will need to develop and advance in the same way that membrane technology has advanced. The use of membranes to treat wastewater effluent for the purpose of making potable water is one of many examples of new possibilities created by membranes.

Reusing water by membrane filtration is quite common. The scope of this water reuse is expanding each year. Membranes have been used to treat wastewater that is discharged into Class 1 surface waters that become drinking water supplies. Membranes have been used to recycle industrial plant water so it can be reused an unlimited number of times. Membranes are used to recycle cooling tower water from power plants. All of these are examples of reclaimed water reuse.

Until recently, the planned reuse of treated effluent, whether indirectly or directly augmenting water supplies has been limited to membrane polishing of treated municipal sewage. After two stages of treatment, membrane separation of municipal effluent represents a tertiary treatment process of pretty clean water, and the membrane use is limited to polishing prior to discharge. Recent advances in membrane delivery system technologies have made it possible to now treat almost any wastewater source without any previous stages of pre-treatment. Even in the case where membranes are used as tertiary treatment, Microfiltration followed by reverse osmosis filtration has been used.

Because of a new membrane device where the membrane surface is vibrated, treatment of just about any wastewater using direct reverse osmosis without any additional equipment for pre-treatment is now possible. This new device known as VSEP was developed by New Logic Research in Emeryville California. Because of this advance, any source of wastewater can be considered for treatment and ultimate reuse of reclaimed water as drinking water.

VSEP Advantages

VSEP employs torsional vibration of the membrane surface, which creates high shear energy at the surface of the membrane. The result is that colloidal fouling and polarization of the membrane due to concentration of rejected materials are greatly reduced. Since colloidal fouling is avoided due to vibration, the use of prefilters is not required. In addition, the throughput rates of VSEP are 5-15 times higher in terms of GFD (gallons per square foot per day) when compared to other types of membrane systems. [5] The sinusoidal shear waves propagating from the membrane surface act to hold suspended particles above the membrane surface allowing free transport of the liquid media through the membrane.

The VSEP membrane system is a vertical plate and frame type of construction where membrane leaves are stacked by the hundreds on top of each other. The result of this is that the horizontal footprint of the unit is very small. As much as 2000 square feet (185 m2) of membrane is contained in one VSEP module with a footprint of only 4′ x 4′.

VSEP employs torsional oscillation at a rate of 50 Hz at the membrane surface to inhibit diffusion polarization of suspended colloids. This is a very effective method of colloid repulsion as sinusoidal shear waves from the membrane surface help to repel oncoming particles. The result is that suspended solids are held in suspension hovering above the membrane as a parallel layer where they can be washed away by gentle tangential crossflow. This washing away process occurs at equilibrium. Pressure and filtration rate will determine the thickness and mass of the suspended layer. Particles of suspended colloids will be washed away by crossflow and at the same time new particles will arrive. The removal and arrival rate will be different at first until parody is reached and the system is at a state of equilibrium with respect to the diffusion layer. (Also known as a boundary layer) This layer is permeable and is not attached to the membrane but is actually suspended above it. In VSEP, this layer acts as a nucleation site for mineral scaling. Beneath the hovering suspended solids, water has clear access to the membrane surface.

Mineral scale that precipitates will act in just the same way as any other arriving colloid. If too many of the scale colloids are formed, more will be removed to maintain the equilibrium of the diffusion layer. As documented by other studies, VSEP is not limited when it comes to TSS concentrations as conventional membrane systems are. Conventional membrane systems could develop cakes of colloids that would grow large enough to completely blind the conventional membrane. In VSEP, no matter how many colloids arrive at the membrane surface there are an equal number removed as the diffusion layer is limited in size and cannot grow large enough to blind the system. In fact, VSEP is capable of filtration of any liquid solution as long as it remains a liquid. At a certain point, as water or solvent is removed, the solution will reach a gel point. This is the limitation of VSEP.

In the VSEP membrane system, scaling will occur in the bulk liquid and become just another suspended colloid. One other significant advantage is that the vibration and oscillation of the membrane surface itself inhibit crystal formation. Just as a stirred pot won’t boil, lateral displacement of the membrane helps to lower the available surface energy for nucleation. Free energy is available at perturbations and non-uniform features of liquid/solid interfaces. With the movement of the membrane back and forth at a speed of 50 times per second, any valleys, peaks, ridges, or other micro imperfections become more uniform and less prominent. The smoother and more uniform a surface, the less free energy is available for crystallization.

In the absence of any other nucleation sites, this would lead to a super-saturated solution. In actual fact, what happens is that nucleation occurs first and primarily at other nucleation sites not being on the membrane, which presents much more favorable conditions for nucleation.

Crystals and scale also take time to form. The moving target of the membrane surface does not allow sufficient time for proper germination and development. Other stationary features within VSEP present a much more favorable nucleation site. Whereas, with conventional membranes that are static, scale formation on the membrane is possible and has plenty of time to develop and grow. Another feature of VSEP is that filtration occurs at a dramatically higher rate per m2 than with conventional membranes due to the suspension of colloids above the membrane. Studies have shown as much as a 15x improvement in flux per area. The result of this is that only 1/15th of the membrane area is required to do the same job as a conventional crossflow membrane. This is beneficial for many reasons, one of which is to hold up volume of feed waters.

The result is that filtration occurs quickly and the length of travel of feed waters over membrane surfaces is reduced by as much as 15x. This means that there is much less time for scaling and crystal formation within the membrane system. Crystal formation is a function of time, especially with respect to Silica, which is very slow to grow. If scaling is to occur within the system, it will more likely occur at high-energy nucleation points and not on the membrane. In addition to that, the high filtration rate is capable of making a super saturated solution, which may not even have sufficient residence time to react within the membrane system itself and may wait until it has been discharged to complete the equilibrium process.

Since VSEP is not limited by solubility of minerals or by the presence of suspended colloids, it can actually be used as a crystallizer or brine concentrator and is capable of very high recoveries of filtrate. The only limitation faced by VSEP is the osmotic pressure once dissolved ions reach very high levels. Osmotic pressure is what will determine the recovery possible with a VSEP system.

Examples of VSEP Filtration Applications

 VSEP Treats River Water

New Logic installed its Vibratory Shear Enhanced Processing (VSEP) in July 1997 at a major international electronic disk manufacturing facility at Hokkaido Island in Northern Japan. The VSEP system is used for treatment of river water for ultra-pure water production at this facility. The VSEP system uses an ultrafiltration membrane module and is able to treat river water in order to remove or reduce humic substances, color, turbidity, permanganate consumption and total iron to below the required limits. The application of VSEP membrane technology to treat river water for ultra-pure water production at electronic disk fabrication facility was found to be an attractive economic alternative to the conventional sand filter water treatment technology. Concentration of the raw river water ranges from 5 to 10 mg/L of TSS. Permeate from the VSEP has less than 1 mg/L TSS. VSEP also reduced color from 67 color units to

Commercial Drinking Water Case Study

New Logic has installed a nearly 1 million Gallon per day water filtration system for a major bottling company. The filtration from this system is purified and disinfected using an Ultrafiltration membrane and then sent on to the bottling process where it becomes a consumer product for consumption. In this case, aesthetic improvement was the goal due to a large number of taste complaints. Reduction of TOC causing poor taste has been effectively reduced by the use of a 30,000 mwco UF membrane. One other benefit of filtration is the near complete removal of all bacteria and other organisms. Normally, Microfiltration could be used with higher throughput per SF of membrane, but in this case TOC reduction called for the use of a UF membrane. The previous system design consisted of a Multimedia filter feeding a Carbon filter. Normal operation involves frequent recharging or disposal of the Carbon media. In addition, the water quality led to numerous taste complaints. The addition of VSEP to the process improves taste, reduces TOC, and allows the Carbon filters to run trouble free.

VSEP Treats Liquid Manure to make Livestock Drinking Water

Take the following example of treating virtually any wastewater to create drinking water using reverse osmosis membranes. New Logic installed its VSEP equipment in Canada where the purpose was to treat liquid hog manure and generate a concentrated fertilizer slurry as well as clean water to be used as drinking water for the livestock. In this case, the VSEP RO unit is used with no pretreatment of any kind and raw manure is fed to the VSEP RO system. This concept was developed after years of study on the subject of using RO permeate as drinking water for livestock. The University of Guelph in Ridgewood Ontario conducted several pilot trials to validate this process. During the studies, the University examined the quality of the water, the growth performance of starter pigs drinking the water, and the health status of starter pigs. [21]

The first observation was that the pigs drank VSEP permeate when offered as readily as the regular barn water that had been supplied. In fact, the pigs actually drank more of the VSEP permeate than the barn water. The data also showed that there were no health effects that resulted from consumption. The weight gain of the starter pigs in each control group was about the same for pigs who drank barn water compared to pigs who drank VSEP permeate. Pigs drinking barn water had a starting weight of 12.4 kg and an ending weight of 26.6 kg. The pigs drinking VSEP permeate had a starting weight of 12.6 kg and an ending weight of 26.9 kg. The manure treated was very high Nitrogen, Phosphorous, and Potassium. The following table shows the typical analytical results from this test work.

VSEP Treats Acidic Mining Effluent to meet Class 1 Surface Water Discharge

Non-detect The wet process manufacture of phosphoric acid as practiced requires a large volume of process water. This water is used for many of the operations during the manufacture of Phosphoric Acid from Phosphate Ore. The water is stored in vary large ponds known as phosphogypsum stacks. These ponds can be used as storage areas and also as a heat transfer mechanism for cooling. The largest concentration of Phosphate plants in world exists in Florida. One such plant, located at Piney Point was recently closed and the remaining acidic pond water is currently being treated using reverse osmosis membrane filtration.

The Florida Department of Environmental Protection (DEP) has implemented several emergency orders to deal with the closure. Actions taken have included emergency lime treated discharges to surface waters and most recently a plan for ocean discharge in the Gulf of Mexico of process water. Recently, a reverse osmosis filtration system was installed to dewater the pond for discharge.

New Logic participated in pilot studies in cooperation with the Florida Institute for Phosphate Research (FIPR) to evaluate the use of VSEP RO membrane systems. Initial lab studies have shown that VSEP can produce water at an effective rate that would comply with the special Florida DEP requirements. As mentioned above, the State of Florida has established surface water discharge regulations where the receiving water body is part of the drinking water infrastructure. Since discharge in this case would have been in close proximity to drinking water intake, Class 1 standards would apply to the Pond water effluent that is discharged.

The main objective of the filtration was to make very clean water for discharge and at the same time, try to minimize the reject volume left over. It was determined that three passes through Reverse Osmosis would be required to meet the discharge requirements for Fluoride, Ammonia, and Total Nitrogen since the initial values were so high. Then with each stage of filtration optimized and balanced, the remaining reject streams should be further concentrated as much as possible. The following diagram shows the process flow scheme that was developed to achieve maximum volume reduction while at the same time meeting the discharge requirements.

In the case shown above, the reject from the spiral unit can be sent back to the inlet to the second pass step. The reject from the first two RO passes is collected and sent to a smaller concentrator stage of filtration also using Reverse Osmosis. The end result is that the overall recovery can be as high as 85% of the initial volume. The table below shows the final analytical results of the RO treated effluent as it compares to the discharge requirements.

Not only did the filtrate meet the stated requirements for Class I surface water discharge, it also met all the requirements for primary and secondary drinking water standards. The treatment was very clean when compared to the water in the receiving body that is the source of drinking water. In fact, the dissolved solids concentration was only about 13 mg/L while typical drinking water can have up to 1000 mg/L. Because introduction of such clean treated water to the environment might actually be harmful to aquatic life, blending of the RO permeate with well water is being proposed to make discharge to surface waters more acceptable.

Even though the purpose of this discharge was effluent disposal, it results in an unplanned indirect reuse of reclaimed water by its discharge into the waterways that produce drinking water. Even though it was not intentional or planned for the purpose of water reclamation as drinking water, the net result is the same as if it had been planned. This is an extreme example of the capabilities of reverse osmosis membranes being able to treat highly polluted water that can be reclaimed and reused as an augmentation to drinking water supplies. Certainly, if this very concentrated acidic wastewater can be treated and the water reused, then many less concentrated and less potentially harmful effluents can also be safely reclaimed.

Because of advanced membrane treatment processes, any water quality level can be reached. RO filtration can be used in series as illustrated above to reach any reuse requirement no matter how low the contaminant level requirements are. By using membrane filtration in series and by adding back safety mechanisms like carbon filtration or ion exchange to polish the final effluent, there are multiple layers of redundancy and safety of water supply can be insured. With such redundancy, even direct use of reclaimed water as drinking water is completely safe. Even more safeguards can be employed when the water is inserted indirectly into the water supply.

Water Standards

Drinking water is monitored to conform to acceptable levels of many harmful chemicals and organisms. Setting standards is a continual process as more is learned about the potential harmful effects of various constituents. In addition to monitoring health risks, water quality is controlled for aesthetic and operational purposes. For example, water high in sulfate levels while not toxic can have a laxative effect. Water high in iron can lead to hardness and staining in laundering. Water high in organics can have a foul taste. Recent fatalities involving toxic microorganisms have renewed standards review when it comes to monitoring and treatment to prevent harmful bacteria from entering the distribution network. The following list summarizes some of the targeted undesirable ingredients to drinking water.

Arsenic

Arsenic is present at very low levels in all surface waters. It is a naturally occurring chemical found in mineral deposits and will go through a natural dissolution process bleeding it into waterways. Arsenic is a carcinogen and must be controlled in drinking water sources.

Chromium

Trivalent Chromium is the naturally occurring state of Chromium and is not considered toxic. However, naturally occurring Chromium can be oxidized in raw water to form the more toxic Hexavalent Chromium. Other sources of Hexavalent Chromium are from paint and plating wastewater contamination of waterways.

Cyanide

The human body detoxifies small amounts of Cyanide. Lethal toxic effects can occur if the levels are above certain limits and the detoxification mechanism is overwhelmed. Chlorination is normally sufficient to oxidize Cyanide and reduce it to low levels.

Selenium

Selenium is an essential trace element for human consumption. The exact toxic effects of it are not known and its interaction in the human body is very complex. In order to provide safety factors, levels of Selenium are controlled in drinking water so that over exposure to Selenium does not occur.

Uranium

The naturally occurring form of Uranium is as the Uranyl Ion UO2 ++. Uranium, while it may be radioactive, is actually more serious as a toxin to the kidney. At high enough levels, it can cause permanent kidney damage.

Treatment of Oilfield Produced Water

Oilfield produced water is a by-product of oil production and is generated when oil is extracted from the ground. Because of the poor water quality, reinjection has often been the most cost-effective disposal option. However, some produced water is treated to be reused as cooling water, boiler feed water for steam generation, or for surface water discharge. Most produced water generated offshore is treated and then discharged overboard as long as the oil content is less than 30 mg/L.

Injection wells are used for several reasons including steam flooding, cyclical steam injection, water flooding, and disposal of water. The typical depth of injection wells is about 5000 ft and is kept well below shallower drinking water aquifers and is separated by layers of clay and shale that act to cap the injection fluids. The zone into which produced water is injected is porous and permeable to accept large volumes of injected water. In California, there are about 25,000 Class II injection wells where produced water is injected. In oil producing wells, 60% of California’s oil is produced by water flooding to push the oil up to the surface. [18]

Since many injection wells are deep wells and can pass through underground drinking water aquifers, the well casing is lined using cement to prevent leaching of untreated produced water into the drinking water supply. Studies have been conducted in areas with a large number of injection wells in close proximity to drinking water supplies and the results have shown that current best practices are effective and no health effects from commingling have resulted. [17]

Sometimes reinjection of produced water is needed to waterflood a reservoir and to increase the reservoir pressure to force oil to the surface. Other times steam is injected for a similar purpose. However, many times reinjection is only done as a method of disposal. An injection well must be carefully located if its purpose is disposal. It must have the necessary protection to prevent seepage into drinking water sources. It must also be located and sunk into geology that is porous and can accept large volumes of effluent that is loaded with scale forming minerals and salts. Very often an injection well may be located many miles away from the oil drilling site. In these cases, the water must be piped and pumped or hauled by truck, which can be very expensive. [9]

Huge amounts of produced water are generated during oil production. When oil comes out of the ground, water comes with it. The ratio between oil and water can vary quite a bit. In December 2004, the California Department of Conservation estimated that the state produced 723,400 barrels per day of crude oil while at the same time producing about 6,670,613 barrels per day of produced water. This is equivalent to 280 MGD (1,061,000 m3/day) of effluent generation. [16]

This amount is also equivalent to 859 acre/feet of water each day. This is the same amount of water consumed by about 1,000,000 families. Since 1948, the volume of water in Mono Lake has decreased from about 4.3 million acre-feet to the present 2.1 million acre-feet. At the rate of 859 acre-feet per day, treated produced water could replenish and fill Mono Lake in California to its original levels in just over 7 years.

The amount of water in relation to oil varies from well to well. The average ratio presented by the California Department of Conservation for the period of December 2004 was about 90% water and 10% oil statewide. [16] Newer wells have lower water content, and it is not unusual for wells to produce only oil. When water is produced, there are techniques that can be used to minimize the amount of water. In any event, produced water created from worldwide oil drilling operations represents a very large source of raw water that if treated could provide significant quantities of water for direct or indirect supplementation to drinking water supplies. This would be especially valuable in areas like the Southwestern United State where there is a lot of oil drilling activity in very arid regions with limited water supplies.

Beneficial Uses of Produced Water

Produced water is generally high is Silica, Boron, Ammonia, and dissolved organics. While the total dissolved solids can vary a great deal, much of the produced water generated is lower in dissolved solids and salinity than seawater. Seawater desalination is also limited to production sites that are near to the seashore. Produced water would represent a raw water source that can be further inland. Produced water would be comparable to brackish water with regard to salinity and dissolved solids content. It presents a few other challenges when it comes to treatment but is nonetheless a viable resource of water. Produced water has generally been seen as a vehicle to water flood and oil well or as a waste product that must be disposed of.

In keeping with good water practices, and in light of tightening water supplies in arid regions, it makes a lot of sense to treat produced water for some kind of reuse that will alleviate the overall water demand. Even though it has vast water sources, it has been estimated by some that California will outrun its water supply by the year 2020. Specific regions such as Orange County have already come up against the water shortage problem firsthand. Other areas will follow. [11]

There has been a great deal of study done to find beneficial uses for produced water. Many reuse projects have been done for some time. These would mostly involve planned non-potable water reuse for agriculture. In an area near the Kern River in Central California, Chevron is providing about 20 MGD of treated produced water for irrigation to local grape, citrus, and almond farms. The salinity of this produced water is relatively low compared to other produced waters, so crop damage from salinity was not a concern. The operation has been approved and regulated by the Regional Water Quality Control Board. In 1996, Texaco, (Chevron’s predecessor) received an award for Distinguished Service in Environmental planning from the State Water Resources Council. Since irrigation water is one of the recharge sources for underground aquifers, this process is in a sense an unplanned indirect reuse of reclaimed wastewater effluent. The intent was not for water supply recharge, but the result is the same. [14] Some of the non-potable beneficial uses of treated produced water include: [15]

1. Creation of wetlands habitat.
2. Irrigation of croplands.
3. Livestock Drinking Water.
4. Industrial Cooling Water for Power Plants.
5. Boiler Feed to make Steam.

In addition to these non-potable uses, there are many ways that treated produced water can be used for potable purposes. In the Chevron case described above, the activity was basically helping to replenish underground drinking water aquifers. Oil companies have been treating produced water for many years to make feed water for steam boilers. Because of the possibility of corrosion and possible catastrophic failure of steam pressure vessels, the water quality fed to steam boilers must be incredibly pure. Treatment of produced water to make boiler feed water is no more difficult than making drinking water. Since this has been done for many years, it would not require a stretch in imagination to make drinking water from this effluent rather than just disposing of it underground.

Hurdles for Beneficial Uses of Produced Water

Produced water can easily be treated to be safe for human consumption using reverse osmosis membranes. This task is technically quite feasible, and engineering already exists for this work. Rather than not being technically feasible yet, conversion of produced water to drinking water is faced with other barriers including lack of regulation guidelines, public perception, and no motivation or incentive to complete this work. There are many ways to mitigate the perceptions about treating produced water to make drinking water. First multiple stages of membrane filtration and even subsequent stages of redundant other polishing technologies such as ion exchange and carbon filtration can provide huge amounts of redundancy in the design of the treatment plant. While an upset in a membrane water treatment process can lead to hazards for humans, so can upsets in membrane treatment of boiler feed water. If improper water is fed to steam boilers, they can explode and cause fatalities. Safeguards have been engineered and have been in place for many years to mitigate process risk.

In addition to this, produced water that is treated can be indirectly introduced into drinking water supplies. By doing this further “cleansing” by natural means can be accomplished. Water that is percolated or stored in water supply reservoirs may undergo “conditioning” so that it becomes more similar to natural water. Filtration through porous ground structure can aid by having contaminants adsorb onto hydrophobic surfaces. This is a form of filtration. Also, nature has created a very efficient biological system where many organic contaminants are eaten by certain helpful bacteria. This can also help to purify the water. While all this may help to alleviate perceptions about treated effluent, there is also risk that the treated water could become more polluted in other ways. For example, treated produced water would be virtually free from pesticides, heavy metals and Arsenic. As the treated water is introduced into the natural watershed, it would be subject to absorbing these pollutants just as natural water is. In many ways the treated water is cleaner than the receiving body, however, perceptions about that may require blending and even indirect blending well upstream of the outfall for drinking water.

First Example of Reclaimed Produced Water

The San Ardo oilfield is located immediately east of Highway 101 about 30 miles north of Paso Robles, in Monterey County, California. This heavy oil field, discovered in 1948, lies on the gently sloping, eastern margin of the Salinas Basin. The present production comes from steam flooding of the permeable Aurignac shelf sands of the Monterey formation, which are draped over a shallow impermeable basement at ~2500 ft. In addition, the Lombardi sands (0-200 ft thick) conformably overlie the Aurignac at a depth of 1800 ft and provide another reservoir with additional steam flood potential. The western edge of the field is bounded by the complex Los Lobos thrust system, which may have additional reserve potential in these Monterey interval sands.

There are limited injection zones in this area, and the reservoir is experiencing high pressures from previous injection of produced water. The resulting high pressure degrades the performance of steam flooding. In addition, due to the water and steam reinjection, the water to oil ratio has increased to 95%. It has been decided that dewatering the reservoir would improve utilization of the field for the future.

Aera Energy, jointly owned by Shell and Exxon operates oil drilling operations in San Ardo and produces about 70% of the oil from this region. Recently Bob Liske, of Aera Energy conducted pilot trials to examine dewatering of the reservoir by treating produced water using conventional reverse osmosis membranes. Currently, Aera Energy treats about 40,000 bpd for steam generation and reinjects about 100,000 bpd of produced water disposal. The results of Bob’s study done in conjunction with the Department of Energy (DOE) were presented at the 69th Annual Petroleum Environmental Research Forum (PERF) in Nov. 2005.

The possible beneficial uses of treated produced water were to include irrigation, seawater intrusion prevention for the local aquifer, and reuse by local industry. The proposed process would include a primary clarifier where coagulant is added to precipitate and coagulate hardness and other solids. The water is then cooled since it is hot in process and then sent to a RO pilot plant for filtration of dissolved solids. The goals for treatment are shown in the following table.

The pilot trails were completed successfully and the test work showed that the membrane system, with proper pretreatment, was able to meet the stated goals for treated water. In his paper, Bob talks about the other obstacles to implementing the plan which includes the seasonal demand for water, high cost of treated water transport, and regulatory uncertainties. [10]

Chevron’s Operations in San Ardo

According to a Staff Report issued to the California Regional Water Quality Control Board (CRWQCB), Chevron Exploration and Production Company also operates in the San Ardo oilfield. San Ardo is located in the Southern portion of the Salinas Valley. The valley narrows at the southern end, and this is where the oil fields are located, just south of San Ardo. The San Andreas Fault and one mountain range border the Salinas Valley to the East. The San Marcos Fault and another mountain range border the Valley to the West. The Salinas River travels down the center of the Valley to the outfall to the North into the Pacific Ocean. The Pas Robles Aquifer runs parallel to the Salinas River just below. This aquifer is estimated to be 200-400 feet thick at an initial depth of 10-20 feet below ground. This aquifer runs through the entire valley floor including the oil field areas. [12] Interestingly, this is one of the most active earthquake zones in California.

The Salinas River is the primary recharge for the underground aquifer. Rainfall in this area is only about 10″ per year. Only about 10% of rainfall is able to percolate to the sunken aquifer. The Salinas River is fed by headwaters and releases from the Nacimiento and San Antonio Reservoirs. As mentioned earlier, the volume of water in the Salinas Valley aquifer is declining by about 18,000 acre-feet per year. (5.8 billion gallons/year). [13]

Chevron extracts oil, gas, and produced water from the San Ardo oilfield. Chevron produces about 3,139 bpd of crude oil and about 76,171 bpd of produced water of which about 54,137 bpd is reinjected for disposal (according to California Department of Conservation, December 2004).

With increasing hydraulic pressure in the oil reservoir and with the resulting less efficient steam flooding, Chevron, like Aera Energy, is looking to dewater the oilfield and stop reinjection of produced water. The CRWQCB also recognizes that the natural aquifer levels have been dropping and that seawater intrusions at the Northern boundary of the aquifer are moving inland and are threatening water supplies. Future water shortages could result in the very near future. With both parties’ interest aligned, Chevron petitioned the CRWQCB for a permit to discharge treated produced water into the southern recharge area of the basin.

The permit petition calls for 2.1 MGD of average treated water flow and 6.3 MGD of peak flow for discharge. The proposed water treatment plant is to include oil/solids separation, degasification, warm lime softening, multimedia filtration, ion exchange softening, a double pass RO filtration, sodium adsorption adjustment, neutralization, and constructed wetlands for percolation to the aquifer. This contribution to the aquifer water supply would offset about 1/10th of the draw down in the aquifer from supply/demand problems.

Chevron will construct a 35-acre area that is segmented and surrounded by five-foot tall earthen berms to receive the treated water. These wetlands will provide equalization and also quality assurance opportunities so that upsets can be mitigated. The wetlands will be planted with native plants such as Cattails, and the water will freely flow at a depth of about 6-12″. This portion of the wetlands will be lined with plastic or bentonite soil to prevent initial percolation. During initial treatment, sedimentation, microbial degradation, precipitation, and plant uptake will further purify the treated water. The water will flow through the 35 acre wetland area into two 7.5 acre recharge disposal basins. These will be excavated to a depth of 6 feet and from here the water will be allowed to percolate to the shallow underground aquifer.

During the permitting process, Chevron asked that the project be described as a water reclamation for reuse project rather than an effluent disposal project. The project clearly has benefits to augmentation of the badly depleted Paso Robles aquifer and the obvious intention of Chevron to be a good neighbor and produce an environmentally wise project like this is well warranted. The CRWQCB stated that water reuse was just incidental to the project and refused to refer to the project more as a water reclamation project. Its own staff report refers the volume of reclaimed water that would enter the drinking water supply and what the equivalent number of families’ demand the water supply would equal. The reuse of this water will not only slow the reduction in aquifer volumes but could help to also slow the seawater intrusion at the Northern boundary by increasing aquifer flows.

VSEP Validation Testing

New Logic has pilot tested several projects where the objective was treating produced water for beneficial uses. Much of this work has been done in Alberta Canada where the primary objective is to create clean water to be used as boiler feed water (BFW). New Logic has current projects in the Gulf of Mexico and in Peru and also previous projects in Venezuela where VSEP was used to treat produced water for surface water discharge.

New Logic set up onsite pilot trials near San Ardo to treat produced water to measure compliance with the CRWQCB regulations. New Logic delivered the test equipment and staffed the pilot testing for several months. In this case, the treatment process would only involve some chemical pretreatment to adjust pH for Boron removal and cooling of the water for optimum membrane performance. The system tested consisted of a two pass RO membrane system.

The primary objective is to treat the produced water and possibly miscellaneous wastewater streams in order to create water that is clean enough to be discharged to the local aquifer. Since the feed water may change with time and since other possible wastewaters may be added, the water quality designed for should be well below the limits set. The table below shows the stated limits and the measured water quality during testing.

The proposed process would be comprised of two stages with the first reverse osmosis stage removing the bulk of the clean water for spiral polishing and then sending the reject from this stage to another treatment method or reinjection. The system would be operated in single pass mode using equalization so that the predicted percentage of filtrate is removed from the system with one pass through the module. The illustration below shows the flow scheme developed.

The results with respect to the primary objective of generating permeate of a quality that reaches the goals for recharge to the aquifer were met. The water treated was very high in Chlorides and other chemicals and because of the very low limits for discharge, two stages of RO filtration were required. In this case, VSEP RO was used as a primary stage with the RO filtrate being polished in a 2nd stage using a conventional Spiral RO system. This test illustrates the ability of VSEP to treat water that is very high is TDS and in other scale forming components. In fact, in this case, Silica, Carbonates, and Sulfates were at saturation with respect to solubility.

Treated Produced Water Results

New Logic was given special discharge requirements that were set by the CRWQCB as shown in the table above. All of these parameters were met or exceeded. Primary drinking water pollutants were not tested during this pilot trial since the surrogates shown above were assumed to indicate general water quality. The table below shows the treated produced water after two passes through RO as it relates to the primary pollutants governed by the EPA’s Primary Drinking Water Standard and the CRWQCB.

By using VSEP to treat the produced water using a two-pass RO system, the resulting water is extremely clean. In fact, by the measurements in the above table, it is cleaner than the tap water serving Contra Costa County in California. For example, the CCWD tap water contains an average of about 200 mg/L of TDS and 50 mg/L of Chloride. [26]

Produced Water Treatment Method Comparisons

Deep Well Injection

Deep well injection is used for many difficult to deal with waste streams including produced water. However, the option of Deep Well Injection is limited by the underlying geology. Any deep well discharge must be protected against mixing with drinking water aquifer supplies. The permitting process can also be long and arduous. Usually, deep well injection is a last resort since it is more difficult and time consuming than other methods of disposal.

Costs for disposal wells like the one shown on the right are mostly related to permitting, drilling, and logistics. Very often, disposal well locations are not in the same area as well water supply for drinking water. This means that brine reject would need to be piped and pumped dozens of miles to a suitable location with porous rock formations. One other factor is that in many areas of the United States, oil wells are becoming depleted. Such spent wells are candidates for disposal wells. There are some costs involved in converting the well to a disposal well, but overall, there are cost savings if existing wells can be used for this purpose.

Vibrating Membranes as an Option for Produced Water Reclamation

The invention of membranes is a recent event and has made the reuse of reclaimed water possible. Produced water represents a very significant source of raw water that can be treated by using membranes to make potable water either for direct or indirect reuse. Previously, sources for reclaimed water were limited to those applications that conventional membrane systems could handle. One of the new developments includes the new open channel plate and frame type polymeric membrane filtration systems. There are several types including the VSEP (Vibratory Shear Enhanced Process) made by New Logic Research of Emeryville, California. Now with the advent of these types of membrane systems, almost any wastewater source can be considered for water reclamation.

Competition and scientific advances have greatly reduced the cost of membrane systems. Reverse Osmosis was previously not appropriate due to solubility limits. Now with this limitation removed as in the wide channel flow membrane modules like VSEP, RO membranes offer an excellent alternative to treat difficult high solids wastewater such as acidic phosphate effluent or produced water from oilfields to create reclaimed water. RO VSEP membranes can be used in parallel and in series to handle any flow and produce any water quality needed.

The VSEP filtration system incorporates a modular design, which makes it compact. Because the basic design is vertical rather than horizontal, the needed floor space per unit is inherently less than other types of dewatering systems. The VSEP does require up to 17’ in ceiling clearance. In most industrial applications ceiling clearance is ample; it is floor space which is limited.

In the case of produced water treatment, the primary benefits are the creation of potable water for reuse and also reduced costs of operation since VSEP treatment is less expensive than injection well disposal.

Conclusion

Arid regions of the United States such as the southwest states of California, Arizona, New Mexico, and Texas are rapidly growing in population. Local Water Utilities are scrambling to come up with economical sources of drinking water. There has been a lot of research on this subject, and this prospect poses a challenge for creative engineers working on the project. Due to competition and scientific advances, membranes are becoming a much more economical method of delivering drinking water from any source including produced water.

New Logic has been contacted by many engineers in the Southwest and is currently working on various research projects to measure the suitability of using VSEP technology to treat brine reject from brackish water desalination plants and many other saline wastewaters with the purpose of making drinking water. The initial results are very promising and warrant further consideration. The VSEP technology has been used for more than a decade in the chemical processing industry. This unique opportunity for treatment produced water comes at a time when the VSEP technology is mature, proven, and very cost effective.

Water companies are currently looking for alternative sources of water including reclaimed sewage and desalinated seawater. Reclaimed sewage even when introduced indirectly will always have a stigma attached to the idea. Seawater desalination is only possible if the plant is located near the coast. Other less saline waters are expensive to operate. Brackish water and produced water treatment using RO membranes are much less expensive to run than seawater desalination due to lower dissolved solids content.

Produced water is already being indirectly reclaimed and reintroduced into the drinking water supply. In the case of irrigation, the aquifer augmentation is not intentional but is inevitable. In the case of Chevron’s aquifer discharge, the intention has dual purposes, to treat effluent and to add to local water supplies. There are probably many more cases of aquifer augmentation using treated produced water. Given the extreme water supply shortages and given the willingness of companies like Chevron to participate, perhaps it is time to plan for and intentionally use membrane treated produced water to supplement dwindling water supplies.

References

1] EPA – Guidelines for Water Reuse – EPA/625/R-04/108/ – September 2004

2] AWWA – Dawn of the Replacement Era – May 2001

3] U.S. Census Bureau – Interim Projections of the Total Population for the United States – April 2005

4] Douglas M Ruthven, Separation Technology, Wiley-Interscience 1997

5] R. Brian, K. Yammamoto, Y. Watanabe, Desalination Publications, ISBN 0-86689-060-2, Oct 2000

6] Jean-Philippe Nicot, et al, Disposal of Brackish Water concentrate into depleted oil & gas fields

7] Robin Foldager, Economics of Desalination Concentrate Disposal Methods – Fall 2003

8] Dan Arthur, Brian Bohm, GWPRF & CBM Beneficial Use Study, All Consulting May 2002

9] David B. Burnett, Potential for Beneficial Use of Oil and Gas Produced Water, Global Petroleum Institute

10] Bob Liske, Recovery of More Oil-in-place at Lower Production Costs while Creating a Beneficial Water Resource, Aera Energy, presented at the 69th Petroleum Environmental Research Forum (PERF) in Nov 2005

11] Raymond Ouellette, et al, Overview of Regulations for Potential Beneficial Use of Oil Field Produced Water in California, Kennedy/Jenks Consultants,

12] State of California, Central Regional Water Quality Control Board, Staff Report for Regular Meeting, December 3, 2004

13] Horacio Ferriz, Groundwater Resources of Northern California: An Overview, HF Geological Engineering, Department of Physics and Geology, California State University, Stanislaus, 2001

14] IPIECA, Water Resource Management in the Petroleum Industry, Feb 2005

15] John A. Veil, et al, A White Paper Describing Produced Water from Production of Crude Oil, Natural Gas, and Coal Bed Methane, Argonne National Laboratory, prepared for Department of Energy

16] California Department of Conservation, Monthly Oil and Gas Production and Injection Report, Dec 2004

17] California Department of Conservation, The Effects of Oilfield Operations on Underground Sources of Drinking Water in Kern County, Publication No. TR 36

18] California Department of Conservation, Application for Primacy in the Regulation of Class II Injection Wells Under Section 1425 of the Safe Drinking Water Act. April 1981

19] Texas Water Development Board, Binational Desalination Conference – Managing Concentrate in the Desert, October 2004

20] Texas Water Resources Institute, tx H2O, Sept 2005

21] Jim Morris, Ron Flemming, Malcolm Alpine, Pigs Accept Drinking Separated Water from Liquid Manure, Ridgetown College, January 2004

22] Singapore Water Reclamation Study – Expert Panel Review and Findings June 2002

23] United Nations Environment Programme, Water and Wastewater Reuse, Nov 2005

24] J. Mallevialle, I.H. Suffet, Influence and Removal of Organics in Drinking Water, Lewis Publishers 1992

25] I. Bremere, M. Kennedy, P Michel, R. Emmerick, G. Witkamp, J. Schippers, Desalinatiuon (1999) 51-62

26] Contra Costa Water District, Your Drinking Water, 2005

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