Study On Denitrification And Character Of Denitrifying Bacteria

In recent years ,with the rapid growth of economy in China, ,a large number of nitrogen and phosphorus discharged into the water,which have caused serious eutrophication, resulting in the quality of water depravation or the lake degenerate, seriously the water was black and olid. Probably 25% of the lakes are influenced by eutrophication in various degrees in our country. So, developing high efficiency biofilm Nitrogen-removal method is the hot issues of research.The compound inoculation and startup were investigated, and the influences of nitrogen-removal (such as dissolved oxygen, COD/N ratio, pH, temperature, and so on) in biological aerated filter were tested in details while treating nitrate wastewater from an iron factory. The results showed that the nitrogen removal rate was more than 90% after 16 days'cultivation using enrichment containing, which included denitrifying bacteria. the efficiency of denitrification was improved, when the concentration of dissolved oxygen was increased from 1.5 to 4.2 mg/L .When dissolved oxygen value was 3.5 mg/L, the efficiency was the best, it was 95.4%; but the result was opposite when it were increased. Even through dissolved oxygen value was 8.0 mg/L; the efficiency was still 44.8%.it can be inferred that there were aerobic denitrifer, nitrate and oxygen were the electron accepter during denitrification. The efficiency of aerobic denitrification was improved. When COD /N were 6-7, it can meet the requirement for carbon source during aerobic denitrification, the removal rate of nitrate nitrogen and COD were up to 3%, 85% respectively. Almost no nitrite nitrogen accumulated. Different carbon resource had different effect on denitrification. The nitrogen removal rate were 92.9%,95.8% respectively when using grape sugar and ethanol as carbon resource, there was no nitrite nearly.The accumulation of nitrite was obviously up to 5.79 mg/L(the accumulation rate of nitrite was 0.96%) when using sodium acetate as carbon resource. No accumulation of nitrite was measured when other carbon sources were used. There was low nitrogen removal rate (18.8%) by endogenous respiration without carbon sources added. There was a good denitrification, when temperature was 22.5℃~33.1℃, pH value was7.0~8.0.During experiment, we found that pH increased till denitrification stopped, then decreased, showing a turning point. ORP decreased quickly and then slowly, when denitrification stopped, ORP value was steady. The results showed that initial pH and nitrate concentration were changed; there was no change in the variations of pH and ORP, and the feature points still appeared, and time was also close. So we could judge the end of denitrification by changes of pH and ORP.A special method emphasized on nitrogen removal for cultivating denitrifying bacteria was employed. The strain X1 was gram positive and spherical. The strain X1 was identified as Pseudomonas putida based on its biochemical and morphological characters and phylogenetic analysis of 16S rDNA sequences (genbank accession NO.DQ836052.1).