This Biological Process Removes Nitrogen From Wastewater Without Creating a Waste Stream

Denitrovi technology cost-effectively removes nitrate from groundwater in an automated process that releases only harmless nitrogen gas.

This Biological Process Removes Nitrogen From Wastewater Without Creating a Waste Stream

Treatment occurs in a vessel that includes a reactor tank with a mixer and a quiescent zone ensuring that the biocatalysts never leave the reactor.

Nitrate contamination in drinking water can be a health concern, and it’s becoming more widespread in groundwater supplies nationally and around the world.

Traditionally, processes to treat groundwater for nitrate have been relatively capital intensive and costly to operate, in addition to which they produce secondary waste streams that need to be managed responsibly.

Now, an alliance involving WesTech Engineering and Microvi has introduced the Microvi MNE process for groundwater nitrate removal. The process uses biocatalyst technology in which microorganisms actively convert nitrate to nitrogen gas, which is simply released to the atmosphere. The natural process yields no sludge, brine or reject water. 

Biocatalysts are engineered polymer composites that contain a high density of a single species of natural, nonpathogenic and nongenetically modified microorganisms. These organisms are retained within the biocatalyst and do not enter the water being treated. The company says the technology is energy efficient and requires minimal chemical input.

The process uses a simple reactor with few internal components, straightforward control, and no backwashing or regeneration. Fatemeh Shirazi, Ph.D., director and CEO of Microvi, and Bryce Myers, production group manager with WesTech Engineering, talked about the offering in an interview with Treatment Plant Operator.

TPO: How serious and widespread is the problem of nitrate in groundwater?

Myers: Nitrate is a growing issue. Much of the nitrate problem is in heavily agricultural regions and comes from over-fertilization. It’s widespread in California and Arizona, and other states have varying degrees of impact, including Idaho, Montana, and many Midwestern states.

Shirazi: Nitrate in drinking water is a significant problem globally, specifically in Europe where a number of utilities are dealing with it. In California, about 3,000 wells are polluted with nitrate. In the San Gabriel Basin alone, more than 250,000 acre-feet of water needs to be treated every year to meet the U.S. EPA limit of 10 mg/L. The issue is not going away. 

TPO: How have utilities typically dealt with nitrate in groundwater?

Myers: They’ve had three basic choices. One is to install a treatment system that is expensive to install and operate. Another is to purchase and blend in water from other utilities that don’t have a nitrate issue at very high rates. The third alternative is to shut down and cap the well and look for another water source.

TPO: What treatment technologies are traditionally used for nitrate removal?

Myers: The most common processes are ion exchange and reverse osmosis. Both are effective, but they produce residual waste streams that are expensive to dispose of and, if not handled properly, can complicate the problem further. These processes don’t destroy the nitrate; instead, they concentrate it. 

TPO: How was the Microvi MNE process developed?

Shirazi: Microvi became aware of the nitrate issue in 2011. Our first customers were small aboriginal communities and the Department of Housing in Western Australia. They did not have trained operators, and they needed a solution that would not generate a waste stream and would be very robust and easy to use. Those systems are still in operation and are working well. As we continued development of the Microvi MNE technology, we discovered that the nitrate problem was much bigger than we originally thought. And so we invested a lot in research, product development, reactor design, testing and certification.

TPO: What is the nature of the biocatalyst used in this process?

Shirazi: It is specifically designed to create an environment for natural microorganisms that can degrade nitrate and produce nitrogen gas. We created a biocatalyst composite structure containing billions of these organisms. The structure is extremely porous and extremely hydrated. Pollutants in the water come in contact with the organisms. Water constantly flows in and out of the biocatalyst, and because of the high population of organisms, the nitrate is very quickly converted. Very short retention times can be achieved.

TPO: What is the fundamental difference between this and other biological treatment processes?

Shirazi: The current paradigm is that a biological process repeatedly grows and then wastes microorganisms. You are constantly putting a lot of energy into growing organisms. Then because you can’t provide the right environment for them, they are dying constantly and producing a huge waste stream that has to be managed. 

Myers: We are able to treat nitrates in short times without adding any TSS to the water. There is also a significantly lower operating cost, mainly because the Microvi system requires significantly less carbon; it doesn’t have to sustain cellular reproduction since the microbes are not reproducing as in other biological systems.

TPO: Can you describe the steps involved in the treatment process?

Myers: It is a very simple process. Water comes into a reactor tank containing a mixer that keeps the biocatalyst homogenously distributed. The water flows through that reactor coming in contact with the biocatalyst where nitrates are converted to harmless nitrogen gas. The water then flows into a quiescent zone where it can be collected without any of the biocatalyst going out. Instrumentation monitors the effluent water and controls the feed of a small amount of carbon source to sustain the microorganisms.

TPO: What is involved in startup and commissioning of this process?

Myers: Other biological processes can take weeks to populate biology on startup. With the Microvi MNE process, the biocatalyst is already populated, and startup time is a matter of hours — a day or two at most. The microorganisms when first introduced are dormant; it takes a little time to bring them out of that state to become fully functional. Once that’s done, the operators simply do periodic checks to make sure the chemical is flowing and the mixers are working, and do general inspections of the equipment.

TPO: Are there applications for this technology outside of treating groundwater?

Myers: Denitrification in wastewater effluent is another application, and it is a huge need right now. Many municipalities are being required to treat nitrate to lower levels than ever before. The microorganisms in the Microvi MNE process can meet the new and existing needs with minimal redesign and low operating costs.

Shirazi: With the expertise we have developed in material science and biology, we are looking to create systems beyond nitrate removal. We are working on the removal of ammonia, phosphorus, BOD and complex molecules such as dioxane and VOCs.


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