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Treating the Blues: Low-cost, sustainable nitrate treatment

Advances in biotechnology now mean that low-cost, sustainable nitrate treatment for drinking water and wastewater is possible, Microvi Biotechnologies' Ajay Nair and Dr Fatemeh Shirazi write

Nitrate (NO3-) is one of the most widespread water pollutants in the world and has made numerous headlines over the last few months. While it can occur naturally in groundwater, nitrate levels can rise to unsafe concentrations as a result of fertiliser runoff, industrial activities, and wastewater discharge.

Elevated levels of nitrate can cause methemoglobinemia (“blue baby syndrome”) by competing with oxygen for binding with hemoglobin, effectively starving the body’s cells of oxygen. This can have a significant effect on infants, pregnant mothers, and the elderly.

Nitrate pollution is a growing problem globally, especially in countries with extensive groundwater sources. In California, for example, the U.S. EPA indicates that 10 per cent of groundwater and more than 3,000 drinking water wells are impacted by nitrate. Around the world, hundreds of millions of people rely on water contaminated with nitrate well in excess of the World Health Organization (WHO) guidelines of 50 mg/L. The UK, with a Maximum Concentration Limit (MCL) of 50 mg/l, has areas which currently suffer from seasonal and continuous groundwater nitrate contamination, especially in central and southern regions who rely heavily on groundwater resources. 

Conventional technologies and waste

Nitrate is highly mobile in groundwater and does not adsorb, volatilize, or naturally degrade in the majority of groundwater aquifers. Often, nitrate in groundwater is not treated but rather blended with uncontaminated water from another source, if one is available. While this can be seen to be attractive because of the potentially low initial capital outlay, a higher cost water plus increased transport for local blending may be necessary. The risk profile is also high with this strategy, being wholly reliant on another resource, leaving exposure to cost increases or a loss of water source. In water-stressed areas this may not be a sustainable or viable option.

Alternatively, the treatment of nitrate-contaminated water can be achieved through two different approaches: 1) separation of nitrate from the water or 2) degradation of nitrate into harmless nitrogen gas. The first approach (nitrate separation) can be accomplished using ion exchange or reverse osmosis, and while great strides have been made in increasing their cost-effectiveness such methods can be costly, energy-intensive, and produce concentrated waste streams that require disposal and subsequent treatment. The transport of nitrate laden brine can be expensive depending upon the availability of a suitable discharge point. There can be significant Totex costs associated with providing a sewer connection not to mention the impact on any treatment processes and receiving waters.

The second approach (nitrate degradation) uses biology to reduce nitrate to nitrogen gas, which is safely released to the atmosphere. This would seem an attractive alternative to nitrate separation. However biological technologies historically available for nitrate degradation are characterised by major disadvantages including: (1) long start-up times and long recovery times after system upsets; (2) the production of biological solids requiring (costly) treatment and disposal; and (3) low organism densities necessitating large footprints to achieve sufficient treatment capacity. There is also a reluctance to have bacteria in direct contact with water intended for human consumption.

The disadvantages of conventional nitrate-removal technologies paint a bleak – and costly – picture for the millions of people in need of nitrate treatment.

A disruptive new paradigm for nitrate degradation

For the past several years, Microvi, a global greentech pioneer based in the San Francisco Bay Area, has been working on an innovative approach to overcome the challenges of treating nitrate and other water pollutants. This new approach is called the MicroNiche Engineering (MNE) platform, where materials science is used to control natural organism populations in a way that has never been possible before. As a result, the Denitrovi technology was born: using natural degraders to convert nitrate into harmless nitrogen gas in a matter of a few minutes all without generating a biological waste.

Denitrovi represents a paradigm shift from conventional nitrate degradation. In conventional fixed-film or suspended growth processes, non-specific organisms are repeatedly grown and removed as sludge. Any attempt to artificially favour a particular species of organism requires complex and delicate control systems which can be notoriously unreliable and limits process flexibility. In contrast, Denitrovi uses specially targeted, high performance natural microorganisms that are completely incorporated at very high density within the Denitrovi composites. These natural nitrate-degrading organisms never leave the reactor, as they are protected from washout, overgrowth, toxicity, and abrupt changes in operation.

In this sense, Microvi have overcome the intrinsic issues with conventional biological treatment, and not just for nitrate removal but for any biological system.

A key motivation behind the Denitrovi technology was to meet the urgent need of communities around the world who require a simple, effective and waste-free solution for high nitrate. The first installation of this new technology took place in Aboriginal communities in Western Australia in 2012. The installation is continuing to remove nitrate from groundwater in the last five years with the same biocatalysts. The biocatalysts are still very effective with no signs of deterioration in performance over five years. In this case, with such a remote site, no conventional technology could have been simple enough to be effective.

In January 2017, the first full-scale installation of the Denitrovi technology began operation at the Sunny Slope Water Company in Pasadena, California. In the preceding years, the Denitrovi technology was evaluated according to strict standards and protocols set by the California Division of Drinking Water (DDW). This included the evaluation of a number of parameters, including dissolved oxygen, nitrate, turbidity, total coliform, and specific microbiological tests. During this project, steady state nitrate removal was achieved in a short period of time, days as opposed to the weeks that are often required for conventional biological technologies. The short start-up period was an indicator of the high biocatalytic density available for nitrate degradation from the first day of operation. 

Advantages of the new approach

This new nitrate removal system is extraordinarily efficient. Less water is lost or needs costly recovery processing, with a water recovery of over 98 per cent. It is also flexible. The system can be retrofitted into existing tanks or installed simply into new systems. The start-up and recovery time is quick, providing a good solution for both continuous and intermittent use.

Microvi’s nitrate removal technology can offer cost saving compared to a traditional nitrate removal system. It has lower energy and chemicals requirements and requires no reactor backwashing. Economic analysis performed by a third-party engineering firm found that the Denitrovi nitrate removal system offers whole of life cost savings on the order of 35 per cent as compared to ion exchange systems for a specific application.

For the plant designer and owner, removing the need to find, secure and then maintain a disposal route for the undesirable concentrated brine waste is hugely significant. The minor mass and volume of waste generated along with its inert nature make it much easier to dispose reducing the requirement for costly treatment. The end user can be assured that they are not reliant on a third party or changing legislation to accept their waste and therefore have total control of long term commercial and operating costs.

For the plant operator, this new process is easier and faster than traditional biological treatment. With treatment rates of just minutes, there can be smaller tanks where the biocatalytic composites convert nitrate more efficiently. Short treatment times reduce the plant’s footprint and allows for modular/standard systems built and tested off site. The simple reactor has minimal internal components, straightforward control, and no complex backwashing. A carbon source is required to provide the biology with the necessary conditions to deliver nitrate removal.

With simpler operation, the system is more reliable, and there is less opportunity for mechanical equipment to fail. When the biocatalysts are subjected to upset conditions or dramatic variations in influent quality, their performance is nearly unchanged, and at worst performance recovery is very quick minimising any downtime or run to waste.

For the conscientious customer, Microvi MNE provides safe drinking water at an affordable cost using a sustainable technology.

Conclusion

With its straightforward operation, simple maintenance and low energy needs, Microvi’s nitrate removal technology is disrupting the industry’s approach to nitrate treatment. From installations in Australia and California, demonstrations in Arizona and Alabama, and overwhelming interest from water companies globaly, this innovative technology is poised to dramatically impact the quality of drinking water around the world.

Whilst addressing nitrate pollution has been a primary focal point, the Microvi MNE technology is also able to address other pollutants such as perchlorate, NDMA, Dioxane, VOCs and DOC to name just a few in drinking water, but can address wastewater treatment requirements equally as effectively. This highly versatile technology may just well hold a key to the future of biological water treatment across a wide range of applications.

This article originally appeared in the June issue of WWT

Topic: Innovation , Treatment
Tags: nitrate pollution , wastewater , drinking water , water pollutants , groundwater , water treatment , treatment

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