Chemical denitrification of nitra te from groundwater via sulfamic acid and zinc metal
Nitrate (NO3 -) concentrations in groundwater have increased globally (Kapoor and Viraraghavan 1997). Wastewater, fertilizers, and livestock farming are major sources of nitrate in groundwater supplies. Groundwater in many locations is used as a supply for drinking water, and high nitrate concentrations present a potential risk to public health, particular to infants (Gangolli et al., 1994). In the United States, the Environmental Protection Agency has set a maximum contaminant level (MCL) for nitrate in drinking water of 0.71 mM (10 mg of NO3-N L) (Pontius, 1993). There are many methods for nitrate removal from water. Biological denitrification reduces nitrate to a gaseous nitrogen species. The gaseous product is primarily nitrogen gas, but it may also be nitrous oxide or nitric oxide. A broad range of bacteria, including many in the genera Pseudomonas, Micrococus, Archromobacter, Thiobacillus, and Bacillus can reduce nitrate. Natural biological denitrification occurs, although not extensively, in aquifiers in which a sufficient source of reducing organic carbon is present. Water treatment processes stimulate denitrification by injection of nutrients. Such organic compounds as methanol, methane, glucose, and starch or mixtures of these (e.g. a sugary brewery waste) can be used as carbon sources (Soresen and Jorgensen, 1993). The feasibility of biologically removing nitrate from groundwater had tested by using cyanobacterial cultures. Results demonstrated that nitrate contaminated groundwater, when supplemented with phosphate and some trace elements, can be used as growth medium supporting vigorous growth of several strains of cyanobacteria. As cyanobacteria grew, nitrate was removed from the water (Qiang et al., 2001). Nitrate removal by hydrogen coupled denitrification was examined using flow through, packed-bed bioreactors for treating nitrate contaminated drinking-water supplies. Nitrate removal was accomplished using a Rhodocyclus sp., strain HOD 5, isolated from a sole-source drinking-water aquifer (Smith et al., 2005).