Effect Of Pumice As Bulking Agent On Aerobic Composting Of Dewatered Sludge

With the improvement of urban sewage treatment rate in China,the output of dewatering sludge has increased dramatically,increasing amounts of dewatering sludge are produced,and the secondary pollution problem caused by this has become increasingly prominent.Aerobic composting has become one of the most widely used biological treatment technologies in recent years,with the killing of pathogenic microorganisms,nutrient recycling and low cost.The currently used active bulk agents such as rice husk,sawdust,and straw have the disadvantages of Fluctuating property,being easily compacted,and limited sources,which cause the unstable operation of the Compost Engineering.Inorganic material pumice was used instead of the traditional active bulk agent to carry out the aerobic composting of sludge under the conditions of different pumice addition ratio,different type of carbon sources,different ambient temperatures and constant temperature heating.The effects of physicochemical properties and degradation of organic matter during the composting process were investigated,the different nitrogen forms during the composting process were explored,and the characteristics of enzyme activity in composting process were analyzed.The results show that:?1?The compost peak temperature of pumice and sludge with wet weight ratio of0.5:1 and 0.6:1were only 26.6?and 24.1?,respectively,did not achieve the purpose of inactivated pathogenic microorganisms.The organic matter degradation rates were15.20%and 11.65%,respectively.After compost 15d,the seed germination index?GI?values were 76.52%and 73.87%,respectively,which did not reach the maturity requirement.The mineralization rates of organic nitrogen and organic phosphorus were slow in two kinds of mixture ratio.The activities of dehydrogenase,urease and protease of ratio 0.5:1 were significantly higher than the ratio of 0.6:1 over the same period?P<0.01?.Therefore,the wet weight ratio of pumice and sludge was determined to be 0.5:1 from the perspective of composting and composting costs.?2?The temperatures of the piles with addition of sucrose and soybean oil reached the maximum for 39.9?and 33.2?,respectively,which increased 13.3?and 6.6?respectively,compared with control treatment without carbon addition?CK?.At the end of compost,the moisture contents were reduced by 5.45%and 3.88%,respectively,the degradation rates of organic matter were 31.31%and 19.12%respectively.The GI value of adding sucrose was over 85%on the 10^thh day,while that ofsoybean oil treatment was 84.11%,which did not reach 85%.Adding sucrose could significantly promote ammoniation and inhibit nitrification?P<0.01?.The order of TP content was CK>soybean oil treatment>sucrose treatment.Both addition of sucrose and soybean oil could significantly improve dehydrogenase and protease activity?P<0.01?,and there was no significant difference between the two types of carbon sources?P>0.05?.And addition of sucrose could also significantly increase urease activity?P<0.01?,but addition of soybean oil had a certain inhibitory effect on urease activity.Therefore,the addition of easily degraded sucrose could obviously promote the degradation of organic matter in sewage sludge.?3?Compared with the ambient temperature of 25?and 20?,the heating rate of compost with ambient temperature of 30?was the fastest and the highest peak temperature.Five days after composting,the degradation rate of the organic matter was the largest,which was 27.85%,the NH₄⁺-N content was significantly increased?P<0.01?,and NO₃^--N content had no obvious change.The content of DTN was similar to that of NH₄⁺-N,with the maximum TP content of 0.580mg/g.Dehydrogenase activity at ambient temperature of 30?decreased significantly at the end of high temperature?P<0.05?,and the activity of urease and protease decreased first and then increased,which indicated that the carbonization and decomposition of organic matter mainly occurred at the raising and high temperature stages,while the decomposition of nitrogen-containing organic matter lagged behind,and the decomposition of nitrogen containing organic matter was not complete at the end of the high temperature.?4?Under the condition of constant temperature of 35?,the temperature of the pile reached the maximum for 53.3?at 2.25^thh day,and the duration of high temperature above 50?for 2 days.At the end of composting,the moisture content of the pile decreased by 13.14%.The pH was stabilized at 7.91,the EC was 983.60us/cm,and the GI value was 88.21%,it has been full maturity.The degradation rate of volatile organic matter was 35.06%.The first 3 days of composting,the activity of nitrifying bacteria was low,and then the activity was enhanced,which promoted the transformation of NH₄⁺-N to NO₃^--N.The TP content showed a tendency of decreasing first and then decreasing.The changes of dehydrogenase,urease and protease activity under constant temperature heating conditions were similar to those at ambient temperature of 30?.