Study On Dynamic Change Of Nitrogen Fractions During Composting Process Of Digested Sludge

Municipal sludge is rich in plant nutrients and organic matters,providing the condition to be a potential organic fertilizer.Composting offers several benefits such as enhanced soil fertility and soil health – thereby increased agricultural productivity,improved soil biodiversity.Some nitrogen was lost during the composting process with the degradation and transformation of organic matter.The transformation characteristics of nitrogen during the composting process were realized,which is important to control composting conditions and provide the basis for improving the quality of compost.The properties of excess sludge,digested sludge,dry sludge and compost were analyzed in this paper.The different kinds of sewage sludge were collected from different waste water treatment plants in Japan.The change of sludge properties during the digestion and composting process were studied based on the analysis of indexes.The indexes include water content,volatile solid content,EC,p H value,ammonia nitrogen,nitrite nitrogen,nitrate nitrogen,total carbon,total nitrogen and organic nitrogen fractions of sludge.The effects of the design and operation of the digestion and composting process on the organic nitrogen fractions were explored.Some different types of sludge compost were selected as fertilizer and the effect of fertilizers on crop growth was studied by cultivation experiment.The results were as following:(1)Two kinds of high temperature anaerobic digested sludge(55 ?)(HRT5d and HRT10d)were collected from a company in Japan.They were treated with air drying and oven drying to reduce the water content to about 10%.The dry sludge was without debris.After oven drying,the coliform and Salmonella were not detected.The pH value was in the range of 6 to 9.The TC and TKN content were above 360 g C/ kg-TS and 48 g N/ kg-TS,respectively.The germination index of oven drying samples was more than 70%.The digested sludge with oven drying can fulfill the requirements of agricultural application.(2)Different types of sewage sludge including excess sludge,digested sludge and dried sludge were collected from A,B,C municipal waste water treatment plant in Japan to analyze the effect of digestion process on sludge properties.The digested sludge was neutral and weakly alkaline with higher EC.The TN and NH4+-N content increased after digestion process,while C/N decreased.Total Kjeldahl nitrogen content in digested sludge was higher than that in the others.The content of easily degradable organic nitrogen(soluble protein and non-protein nitrogenous substances)in each sludge was in the following order,raw sludge > dried sludge > digested sludge.Digested sludge contained higher membrane-associated protein and cell wall-associated protein than the others,indicating the effect of slow release fertilizer.These results indicate that digestion of sewage sludge increased the fractions of slowly degradable nitrogen.(3)The changes of temperature,NH4+-N,NO2--N,NO3--N,TC,TN,organic nitrogen fractions and germination index with time during high temperature aerobic composting process(A-WWTP)and YM bacteria ultra-high temperature aerobic composting process(B-WWTP)were investigated.The water content and pH decreased during composting processes of A-WWTP and B-WWTP.The pH value changed in the range of 6 to 9.The GI% increased during composing processes of A-WWTP and B-WWTP.During the A-WWTP composting process,the variation of NH4+-N content was shown in coincidence with the change of pH.At the beginning NO3--N content was very low,while NO3--N content showed a rising trend during the composting process.NO2--N content was in low level constantly.The content of easily degradable organic nitrogen(A+B)% had a big random fluctuation.During the B-WWTP composting process,the temperature maintained above 70? and NH4+-N content showed a rising trend.But NO2--N and NO3--N content were in low level because of high temperature.The(A+B)% content increased slowly with time.(4)B-compost-product,C-farmer's compost and commercially available sludge fertilizer were chosen to study the effect of fertilizers on growth of Komatsuna by cultivation experiment.The results showed that when the application amount of the fertilizers were 10gN/m2?20gN/m2 and 30gN/m2,Komatsuna average fresh weight had a certain growth compared with the control group and chemical fertilizer group.There was no significant difference for SPAD value compared with the control group.