| China’s natural villages are widely distributed,the number of scattered farmers is huge,sewage pipe network is difficult to cover,decentralized sewage has become an important source of rural water pollution.The septic tank is the most traditional sewage collection and treatment facility in the natural village.At present,the three-chamber septic tank is widely used,which is easy to form short flow and dead zone.The treatment efficiency is low and the effluent quality is poor.Direct efflux can cause water pollution.The existing septic tanks for farmers to properly transform,as an effective pre-treatment facilities for the scattered farmers living sewage to create conditions for the use of local resources.This is to improve the rural ecological environment,the construction of beautiful villages,and even promote the construction of new socialist countryside are of great significance.In this study,the latest research results of the anaerobic reactor are used to optimize the design of the traditional three-chamber septic tanks.The new septic tank structure was as follows:the inlet pipe is located in the lower part of the first chamber of the reactor,along the height of the first chamber set the multi-layer orifice plate,the second compartment set the baffle plate,place the ceramic packing in the third chamber,and the fourth chamber collect the effluent for the farmland irrigation or the connection follow-up device for further processing.In this paper,fluent software is used to simulate the flow field distribution of the first chamber of the new reactor.The simulation results are verified by RTD tracing test.Based on this,the pore size,spacing and orifice distance from the inlet and other main parameters;and through the sewage treatment simulation experiment on the new reactor treatment effect was verified.The numerical simulation results show that the aperture of the orifice plate is 20-30mm,the hole opening ratio is 8%-12%,the spacing between the orifice plates is 60-90mm,and the orifice plate is close to the outlet setting for the new reactor used in the experiment When the distance between the orifice plate and the inlet pipe is 180mm,the shear effect of the orifice plate is obvious,the flow field distribution between the orifice plate is more uniform,the flow velocity is increased and the flow state is closer to the mixed flow.The results of RTD tracer show that the aperture of the first chamber in the reactor is 20mm-30mm and the orifice spacing is about 60mm.The dead zone in the first chamber is only about 10%tends to return to the mixed flow,consistent with the results of numerical simulation.The removal rate of COD and BOD reached 72%-84%and 80%-92%respectively after the stable operation of the reactor.Compared with the traditional septic tanks,the COD removal rate increased by 30%-40%,animal and vegetable oil and LAS removal rate of 71%-90%,35%-45%,nitrogen and phosphorus removal similar to the traditional septic tank is about 5%-20%,the biochemical indexes of effluent quality meet the requirements of irrigation water quality.The comparison experiment with different orifice plate setup conditions showed that the pore size and spacing of the orifice are the two factors that have the greatest influence on the effluent treatment.The removal rate is between 30%and 50%.When the pore size is 20mm and the orifice spacing is 60mm,The removal rate of COD and BOD in the first compartment is more than 50%,the best effect.It is shown that the orifice plate setting conditions determined by numerical simulation and RTD tracer experiments can be applied to the optimal design of the reactor. |
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