Enhanced Removal Of Nitrogen And Phosphorus By Step-Feed A/O System With Distribution Of Carbon Source From Anaerobic Zone

According to the researches on Chaohu Lake water pollution, whose eutrophication is mainly rooted in excessive concentration of nitrogen and phosphorus in the lake. Nutrient elements in sewage disposals from sewage treatment plants have more profound and lasting influences on that from non-point source, which results in the consciousness of urbanized sewage treatment plants on removing nitrogen and phosphorus in water, in both designing and remolding respects. Water quality in southern China are characterized by low carbon source and high nitrogen, phosphorus concentration, while traditional methods bring little effect due to defects in low carbon source and ineffective result of the removal about the nitrogen and phosphorus. Thus, research on this topic presents a method of step-feed A/O system with distribution of carbon source from anaerobic zone, in order to provide theoretical and practical basis for upgrading of sewage treatment plants.Through the previous researches on experimentations of A~2/O system operational periods, we found that A~2/O system is not suitable for removing nitrogen and phosphorus. During second half in aerobic zone, A~2/O system was useless to remove the pollutant in the water. What's worse, COD was unnecessarily consumed in aerobic zone due to aeration. Besides, carbon source was not utilized and optimized reasonably. Hence, we need to upgrade the composition and structure of A~2/O system, improve the efficient use of carbon source and make full use of any resources in the experimentation.After upgrading A~2/O system, we adopted step-feed A/O system with distribution of carbon source from anaerobic zone to study the effects of some elements on sewage treatment. These elements are flow distribution ratios, internal reflux positions, sludge loads, C/N ratios, C/P ratios and SRT. We obtained a group of statistic. The optimal flow distribution ratio obtained was 75%:25% from anaerobic zone, and the values of COD, ammonia nitrogen, total nitrogen, total phosphorus in effluent were 20.8 mg/L, 0.64 mg/L, 14.2 mg/L, 0.89 mg/, respectively. The values of COD, ammonia nitrogen and the total nitrogen were almost up to Grade A discharging standard of pollutants for municipal wastewater treatment plant(GB 18918-2002). Flow distribution ratio had a little influence on COD and ammonia nitrogen removal, while had greater influence on total nitrogen and total phosphorus. The internal reflux position in eliminate oxygen zone had better treatment effect. Through the research of load, COD and ammonia nitrogen removal had much room to improve; while the total nitrogen load was controlled on 0.04 kgTN/(KgMLSS?d), better total nitrogen removal could be get. As the ratio of C/N and C/P was increasing, the concentration of total nitrogen and total phosphorus accordingly decreased. Shorten SRT had little help with the removal of COD and total nitrogen, while was beneficial to improve the effect about removaling the total phosphorus.Through studying on kinetics of the activated sludge, we found that added carbon source has exerted a great impact on the denitrification rates of activated sludge whereas the influence of the blowing N2 could be nearly neglected, and the consumption of COD in the experiment turns out to be greater than the original theoretical value on NO3--N reduction. Duration of carbon source, SRT and the retention time in aerobic zone take charge of the results of phosphorus removal. Activated sludge cultivated in this way is capable of denitrifying phosphorus removal, so we can improve the effect on phosphorus removal through further researches.Through RT-QPCR on activated sludge in different testing stages, we found that, the branch C takes the most place in Candidatus Accumulibacter TYPE II, which is the dominant bacteria for activated sludge biota to remove phosphorus. We can do more researches on it in order to improve the effects on phosphorus removal. AOB in active sludge shares similar order of magnitude about the abundance with Nitrospira. With the AOB going up, the ammonia concentration will go up accordingly. Nitrospira can beneficially contribute to removal of total nitrogen.