Sludge management options for energy recovery using intergovernmental panel on climate change guidelines

Abstract

Treatment and disposal of sewage sludge generate considerable amounts of methane gas (CH4) and have the potential to pose environmental challenges to wastewater treatment. In recent years, the level of awareness on climate change issue in Malaysia has been raised. In support of this action, Iskandar Malaysia (IM) is selected as an eco-friendly city. The selection of sludge management strategies is crucial because various combinations of treatment technologies and disposal methods exhibit different emission rates. To achieve sustainable sludge management, this study aims to investigate and compare two different scenarios for mitigation of methane gas (CH4) using 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines. These scenarios involve landfill, incineration, beneficial use, anaerobic digestion and composting. In order to observe the differences in CH4 gas emission and solid reduction, baseline studies were applied within a period of time (2005-2025) with two different scenarios (business as usual, BaU and counter measure, CM). The year 2025 was chosen as the target years based on IM Comprehensive Development Plan 2025. The BaU scenario represents the current sludge management (SM) without mitigation measures. The CM scenario represents SM with mitigation measures, which includes anaerobic digestion, incineration, composting, landfill and its beneficial use. The use of IPCC method assists the quantification process, based on the calculation of emission factor times activity data calculation. The study areas included sewage treatment plants (STP) located in IM. The current SM in IM uses dewatering and landfill as the disposal options, which consists of drying beds (DB), pond desilting, mechanical sludge treatment (belt filter press and centrifuge system), desludging tanker, and Geobag. The results show that both scenarios present a significant reduction of solids. The BaU scenario offers up to 38.5% potential for solid reduction in the sludge. While the CM scenario offers up to 67.3% of the solid reduction in the sludge by 2025. In BaU scenario, a total of 114,582 tons of solids is estimated to be disposed to the landfill by 2025. However, by applying the mitigation option, an estimated 2,292 tons of solids will be disposed to landfill by 2025. This is about 98% reduction of solids sent to the landfill. The current CH4 emission is approximately 32 Gg CH4 under the BaU scenario and estimated to increase to 37 Gg CH4 by 2025. With the CM scenario, the CH4 emission can be decreased to 77% or to 28.4 Gg CH4/year. The anaerobic digestion can serve as the treatment option to generate up to 62 Gg CH4. There is an increase of energy up to 71% from the treatment category, while 64% of energy increases in overall. By 2025, an estimated amount of 8.6 Gg CH4/year is released under the CM scenario. However, under the BaU scenario without any mitigation measures, 37 Gg CH4 /year was estimated to be released into the atmosphere by 2025.