|
|
 |
| |
| |
Landfill
Leachate Treatment: VSEP Offers a Revolutionary
Solution
February
1, 2001
by Michele Monroe
INTRODUCTION
One of the most important problems with designing and maintaining a landfill
is managing the leachate that is generated when water passes through the waste.
The leachate consists of many different organic and inorganic compounds that
may be either dissolved or suspended. Regardless of the nature of the compounds,
they pose a potential pollution problem for local ground and surface waters.
Many factors influence the production and composition of leachate. One major
factor is the climate of the landfill. For example, where the climate is prone
to higher levels of precipitation there will be more water entering the landfill
and therefore more leachate generated. Another factor is the site topography
of the landfill that influences the runoff patterns and again the water balance
within the site.
VSEP and Landfill Leachate
Current leachate treatment options include recycling and re-injection, on-site
treatment, discharge to a municipal water treatment facility or a combination.
However, with stricter regulations regarding ground and surface water contamination,
landfills are having to find new treatment alternatives. One treatment approach
is to use VSEPTM (Vibratory Shear Enhanced Processing). Developed by New Logic
International, Inc. of Emeryville, California, this advanced membrane technology
has made it possible to filter streams containing a variety of components without
the fouling problems exhibited by conventional membrane systems. This new system
does not only filter the suspended solids but also reduces or eliminates dissolved
organics and inorganics. The result is a crystal-clear water stream and a concentrated
sludge.
The main difference between VSEP and traditional crossflow membrane filtration
is the mechanism by which the foulants are prevented from accumulating on the
membrane surface. A traditional crossflow system relies on the fluid velocity
of the feed material to reduce fouling. The high feed velocity creates shear
forces in the liquid which help maintain the motion of the solids and slow their
deposition onto the membrane surface. However, a thin, stagnant boundary layer
remains on the surface of the membrane that allows the solids to accumulate and
eventually deteriorate the throughput rate. On the other hand, a VSEP system
utilizes a patented vibratory drive mechanism that creates a high shear force
on the surface of the membrane in order to repel foulants. This mechanism enables
the filter to maintain higher, sustained throughput rates and process larger
volumes of material economically without the pretreatment costs of conventional
crossflow systems.
CASE STUDY
Western Landfill Using VSEP for Nickel Reduction
Many tests have been performed on VSEP laboratory and pilot units with leachate
from various landfills. Depending on the location of the landfill, the chemistry
of the leachate and the discharge specifications have differed. The most extensive
test work has been completed on leachate from a landfill located in the Western
U.S. The discharge specification at that location requires the reduction of chelated
nickel.
Membrane Selection and Testing
The initial testing was completed on a small laboratory VSEP unit and was used
primarily to identify a membrane that would meet the discharge specifications.
A thin-film nanofiltration membrane with a 50% sodium chloride rejection was
selected. This membrane was used to construct a 1.393 m2 (15 ft2) filter pack
for pilot test work on a slightly larger VSEP unit. The pilot testing confirmed
the information that was collected during the laboratory test work, including
nickel rejections and flux data (see Figure 2).
Figure 2. Pilot test data showing the relationship between flux and amount of
filtrate which was recovered from the feed stream.
System Design and Processing
After both the preliminary test study and additional pilot testing, VSEP was
selected as the appropriate treatment system for the leachate. The single VSEP
unit will be filtering 113.6 l/m (30 gpm) of the leachate in order to reduce
the nickel by 85-90%. The clean effluent stream from the VSEP will be discarded
to the local POTW. The concentrated stream or sludge will remain on-site for
further treatment, including volume reduction by evaporation and some chemical
treatment. The site hopes to evaluate the possibility of reusing the clean water
but at this time the goal was to meet the local discharge specifications.
VSEP offered many advantages compared to alternative treatment systems that included
large amounts of chemical addition or required extensive space for installation.
The vibrating membrane units are compact, cost effective and easy to maintain.
VSEP units are flexible in that they can be manufactured with almost any membrane
media. This feature enables the systems to be customized to fit the processing
requirements for different leachates given the chemical composition of the stream.
The membrane filter packs are modular and can be replaced to meet changing processing
requirements.
CONCLUSIONS
Though membranes have experienced great advances in the past twenty years, their
use in leachate treatment has only been explored recently. With more stringent
regulations placing greater emphasis on leachate treatment, the industry is seeking
new technologies to solve the problem. Offering economic and operating advantages,
VSEP is a leading technology for treating landfill leachate and will continue
to revolutionize the use of membranes in the industry.
References
1. Diaz, L. F., G. M. Savage and C. G. Gouleke. "Resource Recovery from Municipal
Solid Wastes", Volume II, Final Processing, CRC Press, Inc., 1982
2. Farquhar, G. J., "Leachate Production and Characterization in Civil Engineering",
pp. 317-325 (1989)
3. "Procedures Manual for Ground Water Monitoring at Solid Waste Disposal Facilities" "A
Current Report on Solid Waste Management", United States Environmental Protection
Agency, EPA/530/SW-611, August 1977
|
| |
|
