Study On Aerobic Composting Of Sludge And Rice Straw From Urban Sewage Treatment Plant

China’s urban sewage treatment plant sewage treatment capacity has increased significantly,resulting in a large amount of sludge produced in urban sewage treatment plants.Sludge contains a large amount of nitrogen,phosphorus,potassium and other nutritional elements and organic matter,which can be made into organic fertilizer to meet the huge demand for organic fertilizer in China.China is rich in crop straw resources,but the utilization efficiency of straw resources is low.Using straw as a conditioner and mixing sludge with aerobic composting is one of the ways of sludge treatment and disposal.After mixing sludge and rice straw with aerobic composting,fertilizer is made and put into land use,which can achieve the purpose of sludge reduction,stabilization,harmless and recycling,and also solve the problems of low straw utilization rate and decline of land fertility in China.This thesis uses rice straw as conditioner and aerobic comfertilizer mixed with sludge.Analysis of the monitoring parameters of sludge-straw aerobic composting system treatment(temperature,moisture content,pH value,organic matter content,dissolved nitrogen content,dissolved ammonia nitrogen content,soluble nitrate nitrogen content,seed germination index),studied the different size of rice straw and different C/N ratio of sludge-straw aerobic composting system treatment effect.By constructing a random forest model,the monitoring indicators affecting the dissolved total nitrogen content were selected as predictors,and the factors with the greatest influence on the dissolved total nitrogen content were finally selected.The following conclusions are mainly drawn:(1)This thesis studied the influence of rice straw on the treatment effect of sludge-straw aerobic composting system.Three comparison groups were set up:Group A(1mm size),B(0.5cm size)and C(1cm size).Analyze the changes of the monitoring parameters in the treatment process of sludge-straw aerobic composting system,and compare the treatment effect of three groups of sludge-straw aerobic composting system.The experimental results show that the temperature of Group A(1mm size)is 62℃and 50℃for 7d;after 31d aerobic composting,the decrease of Group A(1mm size)is 28.2%,at the end of Group A(1mm size)3.11g/kg,Group A(1mm size)8.8%;Group A(1mm size)has the highest seed germination index(GI),90%.Therefore,the authors believe that the aerobic composting is the best at1mm.(2)In this thesis,the influence of different C/N ratios on the treatment effect of sludge-straw aerobic composting system is studied.There are three comparison groups,namely Group A(C/N ratio=20),Group B(C/N ratio=30)and Group C(C/N ratio=40).The experimental results show that the temperature of Group C(C/N ratio=40)is 63℃and above 50℃for 8d.After 31d aerobic composting,the water content of Group C(C/N ratio=40)was 29.6%and the Group C(C/N ratio=40)was 5.02%.At the end of compost,the dissolved total nitrogen content was highest in Group B(C/N ratio=30),and the Group B(C/N ratio=30)had the highest seed germination index(GI)of 92%.Therefore,the authors suggest that the optimal C/N ratio during the aerobic composting process was 30.(3)In this thesis,the Random Forests(RF)model was constructed.Implement the analysis of the model using the"Random Forest"software package in the R language(version3.4.4).The reactor temperature,water content,pH value,organic matter content,dissolved ammonia nitrogen content,dissolved total nitrate nitrogen content were selected as predictors to analyze the influence of these predictors on the total dissolved nitrogen.Using the percentage of increased MSE(mean square error)of the variable,the higher the MSE%value of the variable,the more important the variable is.Significance of each predictor was assessed by the"rf Permute"package in the R language(version 3.4.4).The random forest model results showed that the organic matter content,the pH value and the reactor temperature were more significant than the total dissolved nitrogen content in the reactor.The variant interpretation of the model was 52.5%.The total dissolved nitrogen content in the stack was correlated with the organic matter content and was statistically significant(P<0.05).(4)In this thesis,seven factors(days affecting the total dissolved nitrogen content of composting,reactor temperature,water content,pH value,organic matter content,dissolved ammonia nitrogen content and dissolved nitrate nitrogen content)were selected as the explanatory variables,and the total dissolved nitrogen content was taken as the explanatory variables.Using the variance inflation factor(variance inflation factor,VIF),the three influencing factors of compost days,pH value and reactor temperature were finally selected as the explanatory variables to predict the dissolved total nitrogen content,and a multiple linear regression(Multiple Linear Regression,MLR)model was established to predict the change of the dissolved total nitrogen content in the reactor during aerobic composting.The model results showed that all regression coefficients passed the test,and the model was fitted with an R~2of 0.7533 and a modified R~2of 0.7386,indicating.