Screening and Characterization of Facultative Psychrophilic Denitrifiers for Treatment of Nitrate Contaminated Groundwater Using Starch-Based Biodegradable Carriers
Potential starch degrading denitrifying microorganisms that can grow at 4°C were isolated from lake sediments to remove nitrate from groundwater. Initial screening using soluble starch as the sole carbon source confirmed that two out of twenty-five isolates (strain no. 2 and 47) significantly reduced nitrate in the medium and liberated nitrogen gas during culture. In a second screening, several commercially available starch based materials and different kinds of starch were tested. Strain 47 was found to have the best denitrification performance compared with strain 2. Using starch based carrier C (a commercial packing material) as carbon source, strain 47 could completely reduce the nitrate nitrogen in the medium after one week of batch culture even at 10°C. Strain 47 could remove nitrate even without trace element supplementation, and it could perform optimally at 1X (10ml l−1 of trace element solution) level of trace element supplement. The best temperature for denitrification for strain 47 was 15°C and 20°C, but it could also remove nitrate nitrogen at 10°C and 30°C, although at a slower rate. Reactor studies in a simulated treatment well (a cylindrical reciprocating basket reactor) in a repeated fed batch mode showed a good stable denitrification performance as long as substrate limitation is avoided by adequate supply of starch based carrier. Although the similarity score obtained was not enough for phylogenic identification, the results of 16Sr RNA sequences analysis for the strain 47 showed a close relation to Janthinobacterium lividum or Pseudomonas (Janth) mephitica (95.77%).