| In recent years,with the increasing emphasis on environmental protection,the urban wastewater treatment industry has developed rapidly,and the surplus sludge production of wastewater treatment plants has been increasing.At the same time,due to the poor stability,serious pollution hazards,and difficult handling characteristics,more and more environmental problems are caused by the sludge.How to treat the sludge in a scientific and rational way has become more and more important.Aerobic composting with straw or other blends is one of the effective methods to treat municipal sludge.This method can not only achieve the requirements of sludge stabilization,reduction,harmlessness,and resource utilization.Composted finished products can also be converted into organic fertilizers for land use,which can effectively alleviate the problems such as low utilization of straw resources,excessive application of chemical fertilizers,and declining land fertility in China.And the processing method has Low operating costs,simple process and a broad vision of application.However,there are problems such as unreasonable control of process parameters,lack of product risk assessment,and unreasonable product application rate in sludge aerobic composting.Therefore,this paper carried out the experimental study on aerobic compost control parameters,risk assessment and product application amount for sewage sludge Baoding.Firstly,corn straw is selected as the compost blend according to relevant data,Sludge harmless for treatment purposes,and the specific parameters of the C/N,moisture content,and ventilation volume of the material are adjusted for orthogonal comparison test.Afterwards,the results of the orthogonal test were analyzed using spss software and the optimal operating parameter combination of sludge aerobic fermentation was obtained.Then on the basis of the optimal combination of parameters,the aerobic fermentation process was studied.The optimum operating parameters for sludge aerobic composting are:ventilation,0.04m3/m3ˇd-1;C/N,35;moisture content,55%.The changes of indicators such as temperature,volume,moisture content,nutrient elements,heavy metals,and seed germination index during aerobic fermentation were analyzed in detail,and the relevant mechanism of sludge aerobic fermentation process was discussed.Among them,the change mechanisms of temperature,nitrate nitrogen,and total nitrogen accord with y=79.175x-0.211(curve before),y=56.846x-0.199,(curve after);y=11.299x2-55.811x+787.38;y=0.0033x4-0.0911x3+0.833x2-2.4675x+9.5618.In addition,according to the heavy metal content of the test compost products,pollution index assessment method and geoaccumulation index evaluation method were used to analyze the pollution levels.Among them,the comprehensive pollution index was31,and the pollution index of ground accumulation index of zinc(Zn),cadmium(Cd),chromium(Cr),lead(Pb),and copper(Cu)was 2.24,6.54,-0.89,2.70,1.37,respectively.Finally,based on the heavy metal content of compost products and the actual conditions of soil in Hebei Province,with reference to the national agricultural sludge standard,and using relevant calculation formulas,the one-time maximum application amount,safe application amount,and controlled safety application of sludge aerobic compost products were calculated respectively.The application amount of compost products were:the maximum one-time application amount,23.69t/(hm2ˇyear);the safe application amount,3.45t/(hm2ˇyear);the controlled safe application amount,21.32t/(hm2ˇyear).The results show that the compost products meet the relevant requirements of national standards for harmless aerobic compost under the optimal operating parameters;In the early stage of controlling the application amount of compost products,combined with the corresponding monitoring methods,the environmental risks of composted land use can be effectively controlled. |
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