Study On The Nitrification Efficiency Of Hybrid A/O Process At Low Temperature And The Corresponding Microbial Properties Of Flocs And Biofilms

The low temperature and long duration time of winter in northeast China cause serious threat to wastewater biological nitrogen removal. NH4+-N concentration in the effluent is always higher than standard value. In order to improve the nitrification efficiency of wastewater treatment system under low temperature condition, a large number of studies have been made by scholars all over the world. One of the most effective process is the hybrid process relying on microorganisms both in suspended culture and attached to free-floating media which can achieve year-round nitrification even in the winter and gain additional treatment capacity.The experiment studied which is the key parameter that influence the performance of the hybrid system. Research was also made on control parameter optimizing under the condition of 5℃ and 10℃. At last microbial community structure and diversity of the hybrid system were analyzed when it was in a stable and efficient state, hoping to provide theory and technology support for further research of biological nitrogen removal at low temperature.A lab-scale hybrid system in a A/O configuration was used to treat domestic sewage at low temperature in this study, to decide which is the key parameter that influence the performance of the hybrid system. NH4+-N removal efficiency of different SRT and HRT was compared under the condition of 5℃. NH4+-N removal efficiency is 87%, 82% for 24 d, 18 d and is 85%, 59% for 6h, 4.5h respectively. So it was believed that HRT has more effect on the performance of the hybrid system than SRT.The HRT of hybrid system was increased to 7.5h to achieve a good performance. It was found that when HRT and SRT is 7.5h and 24 d, NH4+-N removal efficiency is 90% and the NH4+-N concentration in the effluent is below 8mg/L under the condition of 5℃. NH4+-N volumetric and sludge loading is 0.180Kg/m3·d and 0.037 Kg/Kg·d for 6h; 0.228Kg/m3·d and 0.046 Kg/Kg·d for 4.5h; 0.108Kg/m3·d and 0.022 Kg/Kg·d for 7.5h.Based on the result of 5℃, HRT was optimized under the condition of 10℃. SRT is between 18 to 24 d. NH4+-N removal efficiency is 99%, 97% and 79% for 7.5h, 6h and 4.5h respectively. The NH4+-N concentration in the effluent is below 1mg/L and 8mg/L for 7.5h and 6h respectively. So it was proposed that the HRT should be set to 6h under the condition of 10℃ in consideration of cost.Microbial community structure and diversity of the hybrid system was analyzed when it was in stable state under the condition of 5℃ and 10℃. We identified 13 and 17 phyla for the suspended and attached biomass samples under the condition of 5℃. Under the condition of 10℃, it was 12 and 13 phyla for anaerobic and aerobic suspended biomass samples respectively. We also identified 13 phyla for aerobic attached biomass sample.The difference in the compositions of the bacterial community among these samples is obvious when analyzing at the genus taxonomic level, whereas it is not for phylum level. The relative abundance of nitrospira which contribute most nitrification in attached biomass samples is much higher than that in suspended biomass samples. Biological diversity in attached biomass samples is also higher than that in suspended biomass samples. And the higher the temperature, the higher biodiversity.