Denitrification of water in a microbial fuel cell (MFC) using seawater bacteria

The sea contains various microbes which have an ability to reduce and oxidize substances like iron, sulphur, and nitrate. Most of these processes happen in the seawater, but can also be applied for purification of wastewater. In the present work, a consortium of seawater bacteria has been used for the first time in a microbial fuel cell to reduce nitrate in synthetic water samples and produce electricity by oxidizing organic matter. The concentrations of nitrate and nitrite were reduced to well below their permissible limits. Moreover, the growth of the bacterial consortium in cathode causes an increased electricity production in the cell because of the increased bacterial activity. The performance of the cell with a bicarbonate buffered solution in the cathode was superior to that obtained with the commonly used phosphate buffered solution. As bicarbonate is the natural buffering agent found in the sea, the use of bicarbonate buffered solutions is eco-friendly. The same seawater bacterial consortium was used in both the anode and the cathode, confirming their adaptability to different environments. Unfortunately, denitrification was accompanied by the generation of high concentrations of ammonium in the anode and the cathode, probably because of the use of nitrogen gas for sparging the anolyte. This aspect merits further investigation

Defluoridation of reject water from a reverse osmosis unit and synthetic water using adsorption

Many parts of the world have excess fluoride in drinking water. At some locations, nitrate is also in excess. Hence, reverse osmosis (RO) units have been installed M several villages in India. Reverse osmosis is a good technique, but it has the disadvantage of discarding a considerable amount of the inlet water as a reject stream. This is an unsustainable way of using water. Two adsorbents, namely, a hybrid anion exchange resin embedded with zirconium oxide nanoparticles (HAIX-Zr), and activated alumina (AA) were used in column experiments. For water containing only F-, HAIX-Zr had a better capacity than AA. The same trend was observed with synthetic water samples containing other ions in addition to F-.(-) However, for RO reject, the converse was true, and the capacities of AA and HAIX-Zr decreased significantly. For AA, the presence of a small concentration of HCO3- increased the uptake of F- by 100% compared to water containing only F-. For HAIX-Zr, the adsorption capacity decreased as the concentration of co-ions increased. The cost of treated water varied from (sic) 0.1-1.5/L (US $0.002-0.03/L) for AA and (sic) 0.2-11.5/L (US$ 0.004-0.23/L) for HAIX-Zr