Effects of Bulking Agent Ratios on Dewatering and Cost during Sewage Sludge Composting

High initial moisture content can decrease porosity of composting material and inhibit aeration during composting.Mature compost materials,accompanied with bulking agents such as saw dust,can adjust the pile to proper moisture and porosity in order to improve aeration during composting.The feasibility of reducing sludge treatment costs through controlling the ratios of bulking agents and increasing the mature compost was studied.The results showed that both moisture content and degradable organic matter were decreased dramatically when the initial moisture content fell to around 60% and the ratio of sludge to mature compost was 1 ∶ 0.32.The moisture content and volatile solid content of composting material were decreased by 15.4% and 10.1% respectively,and the treatment cost was 83.2 yuan/t wet sludge.When the initial moisture content was about 62%,treatments with different ratios of bulking agents showed similar dehydrating effect,but higher ratio of mature compost and lower saw dust consumption could reduce the treatment cost from 90 to 62.8 yuan/t wet sludge.If the initial moisture content was too high(65%),the decreases in moisture content and volatile solid content were reduced to 5.1% and 5.8% respectively.