Partial-Nitrification Regulation Of Low C/N Wastwater Under Micro-Oxygen Conditions

With the rapid development of China's economy,the large-scale discharge of high-concentration organic wastewater such as livestock and poultry breeding wastewater and kitchen waste water has made the denitrification treatment of such low C/N wastewater a difficult problem to be solved.The partial-nitrification and anaerobic ammonia oxidation method has become a new type of biological denitrification method that has attracted much attention because it does not require an external carbon source.In this study,in view of the phenomenon of nitrosation instability and low utilization rate of dissolved oxygen in the application process,artificially simulated wastewater was used to regulate DO in the SBR reactor combined with microporous aeration and mechanical agitation.Temperature,pH,free ammonia,free nitrous acid,HRT and other conditions,in order to effectively prevent NOB from further oxidizing nitrite to nitrate,while maintaining effluent nitrite nitrogen and the concentration ratio of ammonia nitrogen is about 1.32,and partial-nitrification and anaerobic ammonium oxidation is stably achieved under the condition of increasing oxygen utilization efficiency.After 94 days of operation,the microbial population and structure were observed and analyzed by electron microscopy and high-throughput sequencing.The main experimental conclusions are as follows:?1?In the cultivation and acclimation stage of nitrifying bacteria,the DO concentration was raised to 2.5 mg/L to increase the growth rate of AOB and NOB.Then,the DO was adjusted to 0.5 mg/L,and the HRT was controlled to be 240 min,and the domestication of nitrifying bacteria under micro-oxygen conditions was realized.After 45 cycles of reaction,the nitrite accumulation rate increased to over80%.At the same time,the ammonia nitrogen load increased from 0.31kg/m³·d to0.56kg/m³·d,which was increased by about 80%.21 mmol NaHCO₃ was added,and no alkalinity was added during the reaction to maintain a constant pH value,so that the effluent pH was 7.4-7.5,the effluent free ammonia concentration was above 0.1mg/L,and the free nitrous acid concentration was above 0.01 mg/L.Both are at the threshold for inhibition of nitrite oxidizing bacteria.?2?Partial-nitrification was achieved under three different concentrations of free ammonia influent and pH.The partial-nitrification was the most stable when the influent free ammonia was 40 mg/L and the influent pH was 8.0.It is suitable for culturing Nitrosomonas,and the nitrite accumulation rate reaches 95%.When FA was higher than 40 mg/L,the growth rate of ammonia oxidizing bacteria is significantly lowered.When the concentration of free ammonia decreases with the reaction,the activity of the nitrite oxidizing bacteria could be effectively inhibited when the concentration of free nitrous acid rised to 0.03 mg/L.After 94 cycles,the proportion of Nitrosomonas increased from 32%to 39%,the ratio of Nitrospira was 0.2%-0.4%,and the concentration of Nitrosamine was 100-200 times of Nitrospira,which ensured the stability of partial-nitrification.?3?Compared with the pH stability control at 7.8,8.0,8.3,the study was carried out by quantitative alkalinity,and at the end of the reaction,the free ammonia and pH were controlled above the threshold of inhibiting nitrite oxidizing bacteria,that is,the pH of the effluent was ensured at 7.4-7.6.The three-stage alkalinity dosage was reduced by an average of 40%.?4?Experiments had shown that the SBR reactor combined with microporous aeration and mechanical agitation could achieve higher oxygen transmission efficiency and power efficiency,the highest oxygen transmission efficiency reached2.0%,higher than the literature 33%,the power efficiency reaches 19.92%,high70.2%in the literature.In the operation stage,the shortest hydraulic retention time of the effluent nitrite nitrogen and ammonia nitrogen concentration ratio stable at 1.32was 180 min,220 min,270 min,respectively,which was shortened by more than50%compared with the nitrosation of the reactor described in the literature.?5?Scanning electron microscopy showed that pH affected microbial morphology.When the pH was 7.4-7.8,rod-shaped and streptococci were observed.When the pH was 7.5-8.3,globular bacteria were dominant.This also indicated that the microbial flora in the reactor has a certain adaptability to the pH value.At the same time,it was found that the inside of the sludge had a micro-oxygen channel with a width of 1-2?m.This structure facilitates the uniform diffusion of DO inside the sludge,thereby improving the oxygen utilization efficiency of the reactor.?6?The simulated wastewater treated by SBR successfully achieved anaerobic ammonium oxidation in the ASBR reactor,and the removal rate of ammonia nitrogen and nitrite nitrogen reached over 90%.