The Study Of Nitrate As A Sole Nitrogen Source For The Growth Of Heterotrophic Denitrifying Bacteria In Activated Sludge

Nitrate in the wastewater would lead to eutrophication when it enters into thereceiving waterbody, which has great harm to aquatic environment and human health.Heterotrophic denitrification, which is the most popular method for nitrogen removalfrom wastewater, can reduce nitrate to nitrogen gas. Plants and algae could use nitratefor growth by the way of NA; Recent researchs showed that some bacteria in the soil,shallow and marine sediment also could use nitrate as nitrogen source for growth bythe way of DNRA. This research is to explore the growth characteristics ofheterotrophic microorganisms in the activated sludge with nitrate as the sole nitrogensource, and to provide theoretical support for the biological treatment of industrialwastewater containing nitrate and organic matter. Two parallel SBRs, which wereseeded with activated sludge from WWTP and with nitrate as the sole nitrogen source,were run by anoxic/aerobic (R1) and anoxic (R2), respectively. The results are asfollows.When the reactors were fed with1400mg/L of COD and280mg/L of nitrate, theremoval efficiencies of COD and nitrate were97%and99%, respectively. The systemsperform well and the sludge have good settleability. Nitrogen contents in activatedsludge from both reactors were close to the sludge with ammonium as nitrogen source.The yield coefficients of activated sludge in SBR1and SBR2were0.3536gVSS/g△COD and0.3035gVSS/g△COD respectively, which were lower than that ofsludge cultivated with ammonium as nitrogen source. The maximum denitrificationrates of activated sludge in SBR1and SBR2were0.019mgNO3--N/(mgVSS·h) and0.016mg NO3--N/(mgVSS·h) respectively, which were as high as the activated sludge from WWTP. Compared with the conventional activated sludge system, protein contentin EPS was lower and sugar content in SMP was higher in systems with nitrate as thesole nitrogen source.It was proved from the batch tests that organic nitrogen in cells was synthesizedby the process of DNRA，which reduce nitrate to ammonia and use ammonia tosynthesize organic nitrogen. It is of great significance for the biological treatment ofwastewater containing nitrate and organic matter that denitrifying bacteria could usenitrate as nitrogen source for cell growth. On the one hand, it could save economic costfor the biological wastewater treatment without adding the ammonia nitrogen. On theother hand, sludge yields were much smaller than other studies, which is in favor ofreducing cost from subsequent sludge handling and disposal costs. In addition, forwastewater containing nitrate and organic matter, the anoxic process would be prior toanoxic/aerobic process, thich could save the cost of aeration and has a betterperformance in removal of nitrate and COD.