Experimental Research On Magnetic Flocculation To Strengthen The Urban Wastewater Treatment

With the development of economic, the number of urban population of China is growing, and the living conditions of residents is increasing. Urban sewage is moving towards the trend of large emissions and concentrations."The Emission Standard GB18919-2002for Urban Sewage Treatment Plant" implemented by China on July1st,2003, has proposed more stringent standards for the emissions targets of sewage treatment plant. At present, most of China’s urban sewage treatment plants using conventional activated sludge process, of which secondary treatment effluent is hardly to achieve the current A standard. Therefore, it is necessary to find a way to improve the treatment effect of the conventional activated sludge process. This contents of the research consists of two parts.The first part is the deep treatment of urban sewage by magnetic flocculation,and the second part is the treatment of primary sedimentation tank effluent by the magnetic activated sludge process under the SBR process.In the first part of this test, the effect of deep treatment in urban sewage is compared with three kinds of flocculation by static beaker study, which is Al2(SO4)3, FeCl3and polymerized Fe2(SO4)3. And then the magnetic flocculation test is going on by selecting the best effect of flocculating agent (polymerized Fe2(SO4)3). This test also discusses the effect of flocculation on different dosing quantity of magnetic powder and coagulants, and confirms the optimum process of mixing way and dosing sequence of agents. From the experiment we can draw the conclusion that:the best pH range (7-9) can be got when the magnetic powder50mg/L is dispersed in the water evenly in fast mixing (300r/min) firstly, after that adding the coagulants (polymerized Fe2(SO4)3) into sewage and stirring it2min quickly, and at last adding the coagulants (polyacrylamide)1.0mg/L into sewage and mixing it slowly (60r/min) for8min.In the second part of this test, the ordinary SBR technology is compared with magnetic powder SBR technology on the removal efficiency of COD.The magnetic powder dosage of the magnetic SBR technology is700mg/L, and each cycle supplement magnetic powder for50mg/L. The main content involves different removal rate of COD, TP and ammonia nitrogen between conventional activated sludge and magnetic activated sludge on continuous aeration and intermittent aeration, it can be briefly described for the following four aspects:(1) on the condition of continuous aeration60min and precipitation120min, the residual COD concentration of conventional activated sludge is108.3mg/L, the removal rate is72.9%, and the concentration of TP is6.9mg/L, the removal rate is11.5%, and residual concentration of ammonia nitrogen is27.1mg/L, the removal rate is21.9%.(2) on the condition of continuous aeration60min and precipitation120min, the residual COD concentration of magnetic activated sludge is76.3mg/L, the removal rate is80.9%, and the concentration of TP is4.7mg/L, the removal rate is39.7%, and residual concentration of ammonia nitrogen is16.5mg/L, the removal rate is52.4%.(3) on the condition of intermittent aeration (non-aeration30min and aeration60min), the residual COD concentration of conventional activated sludge is98.1mg/L, the removal rate is75.5%, and the concentration of TP is5.2mg/L, the removal rate is33.3%, and residual concentration of ammonia nitrogen is15.2mg/L, the removal rate is56.2%.(4) on the condition of intermittent aeration (non-aeration30min and aeration60min), the residual COD concentration of magnetic activated sludge is54.3mg/L, the removal rate is86.4%, and the concentration of TP is2.9mg/L, the removal rate is62.8%, and residual concentration of ammonia nitrogen is7.3mg/L, the removal rate is79.0%. from the experiment we can see the result that, the COD, TP and ammonia nitrogen removal efficiency of magnetic activated sludge are increased by10.9%,29.5%,12.8in turn than conventional activated sludge.According to the test results the conclusion is that:the way of magnetic flocculation has a certain effect on the removal rate of COD, TP and ammonia nitrogen, and it can improve the sedimentation performance of flocculation. Compared with the conventional activated sludge, the removal rate of COD, TP and ammonia nitrogen of magnetic activated sludge have a significant improvement, and the sedimentation performance of magnetic activated sludge is better. At the same time, the magnetic separation technology can improve the effect of spate separation and shorten the sedimentation time, it does makes a lot of sense for reduce the land occupied.