Isolation of Pseudomonas strain EM5 with and efficient nitrate-degrading activity and the Optimum conditions for nitrate biodegradation using immobilized cells

Abstract

ABSTRACT          Thailand is an agricultural country like so many other countries in the world. However, the excessive use of chemical fertilizers is causing groundwater pollution due to the effects of synthetic nitrogen fertilizer. Consequently, we initiated a study series to find a microorganism having good nitrate (NO3) degrading ability, and to find the optimum condition for nitrate biodegradation. Several bacterial cultures were examined for their ability to utilize and convert nitrate into ammonia (NH3), nitrogen dioxide (NO2) and nitrogen (N2) gas. We found only six isolates were capable of completely reducing NO3 to molecular nitrogen, especially the isolate EM5. The isolate EM5 was identified as Pseudomonas sp. Several important parameters in the biological treatment process were tested in parallel with the controls, i.e., controlled pH conditions, selected amount of cell mass, and initial nitrate concentrations. The results showed that the denitrification property was significantly improved using immobilized cells compared to that of free cells, where one g of immobilized cell could totally remove 200 ml/L nitrate within two hours and was able to degrade up to 1,000 ml/L nitrate within four hours. It is expected to use the isolate EM5 in many applications to reduce the amount of nitrate in solution, such as immobilized cell reactor to reduce the amount of nitrate in drinking water.