Effects Of Multiple Chemical Uncouplers On Sludge Reduction In The A~2/O Process

The activated sludge proeess is the world's most popular use bio-treatment technology for the urban sewage treatment plant, but the process has a flaw, that generates a considerable number of exeess sludge daily as a byproduct, sludge treatment and disposal have been a serious problem for the urban sewage treatment plant. Common sludge reduction technologies, such as cryptic growth, micro-predation, high dissolved oxygen, membrane bioreactor technology and so on, most of them have flaws, such as high energy consumption, difficult to control the reaction conditions, high operating costs, etc. , and in fact they all belongs to sludge treatment, not sludge reduction. Compared to the above methods, adding uncouplers into the activated sludge process, can inhibit the synthesis of biological metabolism, reduce the amount of excess sludge production in the sewage treatment system, this method can reduce sludge production fundamentally and in essence. First of all, the effectiveness of four chemical uncouplers in reducing sludge production from A2/O porcess was compared to screen effective, cheap and non-toxic available chemical uncoupler and determined the optimal concentrations; then on this basis, the 2,4,5-trichlorophenol (TCP) in different dosing methods on the effect of sludge reduction, and the substrate removal and microbial activity effects. The main conclusions of this paper are as follows:①The effects of four chemicals, including 2,4-dinitrophenol (DNP) , m-chlorophenol (mCP) , 2,4,5-trichlovophenol (TCP) and 3,3',4',5-tetrachloro salicylanicide (TCS) , on A2/O process sludge yields were compared. It was found that these four chemicals are good uncouples which can effectively reduce sludge yield. TCP was the most effective chemical uncouplers in reducing sludge production rate, and had less effect on the process performance.②The chemical uncouplers with a lower pKa value have a greater dissipation of energy and a higher potential to reduce sludge production. However, the experiment found that, TCP, mCP, DNP comply with the above rules, TCS does not comply with this law.③It appears that selection of chemical uncouplers and optimization of its dosage should be based on a compromise of the desired sludge reduction, substrate removal and sludge settling characteristics. TCP was determined as a good chemical uncoupler, 53.07% of sludge reduction was achieved at a TCP concentration of 4mg/L, while the COD removal efficiency was lowered only by 3.88% as compared.④2,4,5-trichlovophenol(TCP), selected as a relatively good chemaicl uncoupler based on the above step, was added to the A2/O process, and was studied in different dosage mode. The results showed that: while maintaining the total dosage of TCP, large-dosage one-time addition is better than small-dosage split addition. TCP was able to reduce sludge yield by 67.10% when the TCP dosage was 240 mg?(2d)-1, but sludge production was only reduced by 35.90% if TCP was added 120 mg every day.⑤In the different dosage mode experiment, the COD removal capability was decreased by 26.80% when dosed 240 mg TCP every other day, but effluent nitrogen concentration was not affected adversely by the presence of TCP regardless of any dosage mode, the removal efficiency of phosphorus was slightly decreased, SVI of sludge were slightly increased by addition of TCP, but did not seriously affect the sludge settling characteristics.⑥Microbial reduction of population structure changed in the TCP sludge reduction system with different dosage mode, such as protozoa and metazoa instructions in the type and number of microorganisms on a certain level of reduction, sludge flocs were also becoming looser. After adding TCP, the Sludge Oxygen Uptake Rate (SOUR) values increased, indicating TCP can improve the microbial respiration rate. From the economic benefit accounting of comparison system and TCP sludge reduction system, the operation cost of wastewater (including sludge treatment) could reduce 0.004 yuan/m3; it showed that applying TCP to reduce excess sludge production in A2/O process is not only technically feasible but also economically feasible.