Study On Low C/N Wastewater Treatment And External Carbon Source Optimization By Inverted A~2/O Process

With the soar of development of China, water pollution is getting worse and worse nowadays. Therefore, the improvement of sewage disposal and drainage water quality has become an urgent affair. There is a lack of carbon sources in most of our domestic sewage, which has caused low rates of nitrogen and phosphorus removal in sewage treatment plants. With the stricter standards for emissions in China, TN and TP and other indicators after the treatment are difficult to meet the emission standards. Reversed A²/O process is to invert the anaerobic and anoxic phases on the basis of the traditional A²/O process, forming anaerobicanoxic-aerobic treatment system to solve problems existing in some traditional process of phosphorus and nitrogen removal. However, due to the weakness of the operating conditions and the carbon source, it is difficult to have a better result when treating low C/N wastewater.In this research, we adopted the reversed A²/O process batch reactor to treat low C/N wastewater. It mainly discussed the domestication and cultivation of reversed A²/O process of sludge and observed the removal effect of COD, TP, NH₄⁺-N and TN under various operating conditions through orthogonal test. Reversed A²/O process along the process of pollutant concentration distribution and the balance of pollutant concentration was analyzed to determine the optimal operating conditions.As the effluent water quality indicators cannot meet the level A emission standard according to the "urban sewage treatment plant pollutant discharge standard "?GB18918-2002?, it is necessary to observe the effects of different kinds of external carbon source on the process, and the effects of different dosage ratio of carbon sources in anoxic/anaerobic phase of the nitrogen and phosphorus removal by the static experiment and to explore its mechanism.?1? Sludge acclimation and reactor start-up. By using the intermittent-continuous cultivation and domestication, after 25 d cultivation and 11 d acclimation, it was found the activated sludge could meet the requirements of the following experiment, the whole process does not appear any exception. In the reversed A²/O process batch reactor, the orthogonal experiment was carried out on 3 working conditions of hydraulic retention time, recycle ratio and sludge age. Through the comprehensive analysis, the optimal combination conditions were obtained: hydraulic retention time was 12 h, recycle ratio was 200%, sludge age was 16 d. Continuous operation under the optimal conditions, the effluent COD, TP, NH₄⁺-N, TN concentrations were 13.03 mg/L, 0.68 mg/l, 0.39 mg/l, 17.72mg/L respectively. The average removal rate was 94.2%, 79.6% and 99.4% and 75.1%, of which the concentration of COD and NH₄⁺-N concentration were more than what is required in the "urban sewage treatment plant pollutant discharge standard "?GB18918-2002? standard A, and that of TP and TN could only meet standard B.?2? The comparison of the effects of different carbon sources on the removal rate of the wastewater and the concentration of intracellular substances were made during the static experiments. Three different carbon sources were added: sodium acetate, methanol and glucose, and denitrification process, release phosphorus-absorb phosphorus process and the effluent quality were compared. It was found adding sodium acetate as the carbon source was the best and the methanol was the second, glucose is the least effective source.?3? Using sodium acetate as the additional carbon source with different dosage ratio of carbon sources in anoxic / anaerobic phase during the static experiments, the changes of concentration of each index and the changes of intracellular substances were analyzed. The results showed that 3 kinds of conditions had little effects on the removal of COD and NH₄⁺-N, but had significant effect on the removal of TN and TP. Through the correlation analysis, the changes of TP were closely related to the content of intracellular substance PHB, poly phosphorus and glycogen, and the best effluent effect was under condition II?anaerobic = 70%:30%?. During the operation of adding carbon source in the reversed A²/O process batch reactor, the removal rates were of obvious difference without adding carbon source and under three working conditions. DGGE profiles further indicated that the different dosage ratio effluent removal effects of nitrogen and phosphorus were different, which was related to the microbial community structure and the richness of the system. Under condition II, the overall effluent was the best, with the average concentrations of TN, TP, NH₄⁺-N and COD being 13.90mg/L, 0.80 mg/L, 0.48 mg/L, 13.02 mg/L respectively, which could meet the standard A according to the "urban sewage treatment plant pollutant discharge standard "?GB18918-2002?. Static experiment and batch reactor results showed that proper anoxic / anaerobic dosage ratio could effectively improve the efficiency of the inverted A²/O process in the treatment of low C/N sewage treatment of nitrogen and phosphorus removal.