A Study On Continuous Batch Feeding For Aerobic Composting Of Excess Activated Sludge Using A Pear-shaped Rotating Drum Reactor

Sewage sludge with high production and nutrient content,existed some problems,such as dehydration hardly and secondary pollution.Current disposal methods,such as landfill and incineration,were not better to meet the requirements of resources and more efficient utilization of sewage sludge.Land application of sewage sludge after aerobic composting is a very promising way of disposal because the sludge contains plants needed nutrients such as nitrogen,phosphorus potassium and so on.However,there are some problems on aerobic composting of sewage sludge,mainly including susceptible to the environment for non-reactor composting system,low efficiency of treating sludge and high energy consumption for the ordinary composting reactor hard to maintain high temperature because of low organic content,serious nitrogen loss and so on.Based on these problems,Some studies on co-composting of sewage sludge using pear-shaped rotating drum reactor were carried out,for investigating characteristics of temperature,nitrogen loss,the efficiency of treating sewage sludge and energy consumption of reactor,using pear-shaped rotating drum reactor.The results are shown as follows.1.Under the conditions of 0.1 m3/(min?m3)of the ventilation rate,the intermittent aerobic co-composting of sewage sludge after centrifugal dewatering and sawdust,lasting 21 days,using pear-shaped rotating drum reactor were carried out.The results showed that it was hard to maintain high temperature during the intermittent aerobic composting.During the whole composting process,the compost temperature above 50 ? only maintained 0.5 days,while the compost temperature above 40 ? also only maintained 1.5days;The GI of the pile was up to 95% after the 18 days composting reaction.,reached maturity requirements.the nitrogen loss of the pile was 15.16% and the treatment efficiency was 8.73g/(L?d)during the whole composting process.And the energy consumption of the reactor was 9.67(kw ?h)/kg.2.Under the conditions of 5.5% of the batch feeding ratio and three kinds of ventilation(0.1 m3/(min?m3),0.122 m3/(min?m3),0.167 m3/(min?m3)),the continuous batch feeding aerobic composting that lasted 30 days were carried out,respectively.The experimental results showed that the optimum ventilation of continuous batch feeding aerobic composting was 0.122 m3/(min?m3).The continuous batch feeding aerobic compost,under the three kinds of ventilation,reached the highest temperature on the 0.75 day,1.25 days,first day,respectively,and the highest temperature were 55.1 ?,56.8 ?,55.6 ? respectively.During the composting process,the pile temperature above 50 ? maintained 1.75 days,2 days,1.25 days,respectively and the pile temperature basically maintained at 45 ? above.The initial moisture contents of the pile were all 60%,and after 30 d composting,the moisture contents desreased to 43.74%,42.56%,43.25%,respectively.The nitrogen loss was 36.27%,36.57%,37.54% respectively after the aerobic composting finshed.During the whole composting process,the compost efficiency was 10.2g/(L?d),which was 1.168 times of the efficiency on the intermittent aerobic composting,while the energy consumption of the reactor was 7.745(kw?h)/kg,which had decreased by 19.91%,compared with the intermittent aerobic composting.3.Under the conditions of 0.122 m3/(min?m3)of the ventilation rate and three kinds of the batch feeding ratio(10%,15%,20%),the continuous batch feeding aerobic composting that lasted 30 days were carried out,respectively.The experimental results showed that the optimum batch feeding rate of the aerobic composting was 10%.The pile temperature above 50? maintained 6days,3days,2days,respectively,which has been extended markedly,compared with the 5.5% of the batch feeding ratio..Under the conditions of 15% and 20% of the batch feeding ratio,the mixture efficiency of the heap decreased markedly after 20 days composting reaction,which leaded to moisture contents rising,pH and GI descending in the late stage of composting,and affected the compost quality.The nitrogen loss were 34.19%,32.25% and 30.15%,respectively after the aerobic composting finshed,which indicated that the higher the ratio of batch feeding,the less the loss of nitrogen.Under the conditions of 10% of the batch feeding ratio,the treatment efficiency was further improved and was 18.33g/(L?d),which was 2.1 times of the efficiency on the intermittent aerobic composting,while the energy consumption of the reactor was reduced to 4.606(kw?h)/kg furtherly.4.The pear-shaped rotating drum reactor had a good effect for the treatment of excess activated sludge.During the continuous batch feeding aerobic composting,the optimum ventilation was 0.122 m3/(min?m3)and the optimum batch feeding rate was 10%.Under the best running condition,this composting reactor can improve the efficiency of the treatment of excess activated sludge and reduce the energy consumption,significantly.Therefore,this new composting reactor had the higher promotion and the better market application prospect.