RO Reject / Brine Minimization

As water scarcity problems grow, so does the need to create drinking and process water from marginal sources. And while seawater desalination plants have ready access to convenient disposal sites, inland users aren’t so lucky.

In order to receive a permit for a desalination facility, one needs to develop a brine management plan. In some cases, the facility may be allowed to discharge their RO concentrate to the sanitary sewer, but increasingly this is not allowed as POTWs struggle with their own TDS limits. What then is the inland facility to do with their brine?

When it comes to getting rid of salt, there are not many options. Evaporation ponds seem like the easy choice, but they require the right climate to succeed, can be expensive to construct, and are difficult to permit because of the threat they pose to wildlife.

Thermal evaporation is another option, and represents the ultimate in no-brainer fuctionality, but it is not without challenges. High energy costs and the chloride-driven construction requirement of exotic materials makes this a costly choice on both ends of the transaction.

Hauling brine is ultimately the easiest solution, but it is also the most expensive. The costs of hauling brine can fluctuate wildly with the price of fuel, and then there’s the cost of disposal on the other end. A lose-lose with a big carbon footprint.

In contrast to evaporative methods are novel approaches involving membranes. One such method (HERO) achieves higher-than-normal recovery by significantly altering the pH of the feed to keep salts from precipitating. But even with expensive chemical alteration of the feed, HERO recovery can be unimpressive. With HERO, precipitation is the ultimate limiting factor, because should salts drop out of solution inside the HERO membrane module, the membranes could become irreversably fouled.

And then there’s VSEP: the energy-efficient, open channel, vibrating membrane separation system. VSEP picks up where standard RO systems leave off, taking RO brine and concentrating it by as much as 10X in a single pass. VSEP is limited not by precipitation, but by osmotic pressure. For this reason, precipitation of salts within the VSEP filter pack is actually desirable because these newly suspended solids no longer contribute to the osmotic pressure of the feed. And because of VSEP’s open channel flow path, there are no tight spaces in which precipitates can become lodged–VSEP’s vibratory shear simply sweeps them safely out of the system.

If you have RO reject or brine minimization challenges, consider VSEP.

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