Water & Wastewater Treatment Magazine
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The Knowledge 34 | JUNE 2018 | WWT | www.wwtonline.co.uk Treating the Blues Advances in biotechnology now mean that low-cost, sustainable nitrate treatment for drinking water and wastewater is possible AJAY NAIR GLOBAL DIRECTOR, COMMERCIAL & TECHNICAL STRATEGY MICROVI BIOTECHNOLOGIES N itrate (NO3-) is one of the most widespread water pollutants in the world and has made numer- ous 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 methe- moglobinemia ("blue baby syndrome") by competing with oxygen for binding with hemo- water plus increased trans- port for local blending may be necessary. The risk profile is also high with this strat- egy, 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 treat- ment 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 accom- plished using ion exchange or reverse osmosis, and while great strides have been made in increasing their cost-effec- tiveness 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 avail- ability 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 (ni- trate 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 his- torically available for nitrate degradation are character- ised by major disadvantages including: (1) long start-up times and long recovery times a‰er system upsets; (2) the production of biological solids requiring (costly) treatment and disposal; and (3) low organism densities necessitat- ing large footprints to achieve sufficient treatment capacity. There is also a reluctance to have bacteria in direct contact with water intended for hu- globin, 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 ex- tensive groundwater sources. In California, for example, the U.S. EPA indicates that 10% of groundwater and more than 3,000 drinking water wells are impacted by nitrate. Around the world, hundreds of mil- lions of people rely on water contaminated with nitrate well in excess of the World Health Organization (WHO) guide- lines 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 contami- nation, 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. O‰en, 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