Study On Treatment Of Rural Toilet Wastewater By MBBR Process Under Low Temperature

The problem of toilets has become a key factor restricting the development of rural economy and environment.The lack of collection and anti-seepage measures of traditional toilets in rural areas leads to the spread of a large number of bacteria and eggs,and serious pollution of groundwater.About 50%of rural water sources are polluted by toilet waste water.Rural water latrines are the development trend and the main direction of the toilet revolution.Because most rural areas are relatively backward in development and lack of underground pipe sewage collection and discharge facilities,centralized treatment is difficult.Moving Bed Biofilm Reactor（MBBR）,as a new kind of Biofilm Reactor,has been widely paid attention by researchers in recent years,MBBR process combines traditional microbial water treatment technology with activated sludge process,and has the characteristics of less residual sludge,strong impact resistance load,and a wide variety of microorganisms,it mainly depends on the density of suspended filler close to water for hanging film,through the biofilm and fluidized bed to realize the efficient attachment and dynamic renewal of microorganisms,the use of all kinds of microbial metabolism activities to ensure a good effect on the removal of pollutants,so as to achieve the purpose of wastewater purification.This experiment was carried out on the basis of the low efficiency of MBBR process in practical application due to the cold winter climate in the rural areas of northern China.The test water is a mixture of pig manure and tap water to simulate toilet wastewater,and the microbial film is coated by the rapid sludge method.The effects of temperature,hydraulic retention time and aeration rate on the removal efficiency of TP,NH₄⁺-N,COD and TN were investigated.Explore and calculate how to take heat preservation or heating measures to make rural water closets operate efficiently and normally at the lowest temperature.The results show that the rapid sludge discharge method is adopted to hang the film,the filling rate is 40%,the temperature is about 22℃,the hydraulic retention time is 12 h,and the aeration rate is gradually increased from 0.6 L/min to 1.5 L/min,at about 24 days,the biofilm was basically in a stable stage,and the yellowish brown flocculent layer appeared on the surface of the suspension filler,and rotifers and clock worms could be observed through microscopic examination,combined with the characteristics of the water quality index of the toilet wastewater and the measurement results,the system can remove 50%,90%,80%and 50%TP,NH₄⁺-N,COD and TN respectively,under the stable state.The film is hung through the rapid mud-discharging method,which not only has a shorter period of film hung,but also has strong adhesion to various microorganisms.Under the conditions of hydraulic retention time of 12 h,aeration rate of 1.5 L/min,filling rate of 40%respectively,the effects of four temperature gradients of 4-6℃,8-10℃,12-14℃and 16-18℃on the removal efficiency of each water quality index were investigated.The results showed that the minimum temperature for MBBR process to maintain biological activity was 8-10℃,and the removal rates of TP,NH₄⁺-N,COD and TN were28.76%,59.45%,74.18%and 34.26%respectively.Keeps the same working condition of the above circumstances,hydraulic retention time for 16 h,24 h,8 h,32h four different gradient system of removing the water quality index,the influence of the analysis of test results can be concluded that prolonged HRT to 24 h for MBBR process under the condition of the optimal processing efficiency of operation parameters,the system of TP,NH₄⁺-N,COD and TN removal rate were 38.35%,77.36%,75.31%and 40.88%respectively.Under the condition of the above conditions remain the same,aeration rate is 0.8 L/min,1.6 L/min,2.4 L/min,3.2L/min four different gradient system of removing the water quality index,the influence of the analysis of test results can be concluded that increasing the air to 2.4L/min for MBBR process under the condition of the optimal processing efficiency of operation parameters,the system of TP,NH₄⁺-N,COD and TN removal rate were46.12%,83.43%,82.85%and 47.31%respectively.Above all,the optimal operating parameters are temperature 8-10℃,hydraulic retention time 24 h and aeration rate2.4 L/min,the system of TP,NH₄⁺-N,COD and TN removal rate were 46.12%,83.43%,82.85%and 47.31%respectively,the effluent water quality can reach the standard of farmland irrigation water.At the end of the test,the best combination of the parameters under the low-temperature conditions obtained from the test will be combined with the actual project,and the heating method of converting solar light energy into electric energy is adopted to maintain the water in the purification tank at a minimum temperature of 8-10℃to ensure biological activity,and through calculation,the heat lost in the wastewater in the Johkasou can be compared with the heat produced by solar energy,and the most economical and applicable way can be used to get the number of solar panels installed.This method is also applicable to the Johkasou of sanitary water closets in different regions wastewater treatment.