Nitrification Enhancement At Low Temperature Of Vegetation-Activated Sludge Process

In contrary to conventional activated sludge process, Vegetation-Activate Sludge Process(V-ASP) has its own merits, such as effective odor-free, high capability in pollutants removal and possible landscaping benefit to ambient environments, making it to be an attractive technology for decentralized wastewater. However, V-ASP process confronts a similar problem with other biological treatment technology, unstable nitrification efficiency at low temperature(?15?)that affect system treatment performance. In the present work, bacterial community structure within V-ASP system was analyzed to reveal the causations of low nitrification efficiency, and to find the ways for nitrification enhancement at low temperature.A long-term examination on the treatment performance in V-ASP system was carried out, and the results demonstrated that V-ASP had stable removal performance in COD and NH4+-N, and the average removal efficiency of NH 4+-N was 93.5%. Both of NH4+-N and TN removal efficiency showed decreasing trend with decreased temperature, while had rare correlation with circumstance moisture. Microbial community structure analysis by means of high-throughput sequencing revealed that the dominant species in V-SBR and vegetation-contact oxidation system were Proteobacteria and Bacteroidetes. The proportion of Nitrospira, one typical nitrifying bacteria, was more than 2.2%, which was much higher than that in seeding sludge collected from conventional activated sludge plant of 1.07%. This result evidenced that allocation of vegetation into V-ASP favored accumulation of nitrifying bacteria with bulk that would be beneficial to system treatment performance.Series of batch-test operated under varied temperatures displayed th at temperature had significant effect onto system nitrification effectiveness. V-SBR could achieve stably high NH4+-N removal efficiency under 30?, and decreased gradually with the decreased temperature. Notwithstanding, V-ASP could be recovered at shorter time compared with conventional ASP. The activities of nitrification reaction enzymes, AMO and HAO, in the V-SBR system were also showed positive correlation with temperature. With the decreasing of temperature, it was observed that the abundance of NOB a nd AOB in V-ASP was reduced, reflected by that the proportion of Nitrospira at 15? was reduced to 26.9% compared with that at 30?.Addition of nitrifier enriched sludge and nitrification enzyme into V-ASP system was an effective method to enhance its nitrification performance at low temperature. With a dosage of nitrifier enriched sludge of 0.1 g/g MLSS improved nitrification efficiency of about 12.37%, as well as to ammonia oxidation rate and nitrite oxidation rate. With a dosage of nitrification enzyme of 10 m L/g MLSS, V-SBR nitrification efficiency could be improved more than 13.39%. Meanwhile, one-time dosage of nitrifier enriched sludge or enzymes could maintain improved nitrification efficiency more than 15 days. Hence, it was concluded that nitrification enhancement methods at low temperature were effective and stable for V-ASP system, offering useful guideline for V-ASP application and maintenance.