Optimization of sludge disintegration from IWK-bunus sewage treatment plant for enhanced biogas yield

Abstract

Biogas is a source of renewable energy (fuel) produced through anaerobic digestion of biomass. Sewage sludge is a form of biomass that is found as sediment (slurry) product of waste water treatment plants. This research is aimed at optimizing the yield of the biogas produced from Indah Water Konsortium- Bunus sewage treatment plant (STP) through sewage sludge disintegration processes. By optimizing the yield, the STP can generate its own future heat and power demands that can possibly be exported to the grid. To achieve that, the plant was physically studied on its operations. The current population equivalent (PE) of the plant is 175,000 instead of the installed capacity of 375,000. This constitutes towards low total solids (TS) and volatile solids (VS) of about 1.89 and 1.38% respectively, and a low overall biogas yield of 1500 m3/day (56% VS reduction) instead of recommended 2200 m3/day (80% VS reduction). Thermal, chemical and thermochemical disintegration techniques were employed to investigate their impact on improving the biogas yield during anaerobic digestion. Modeling and Optimization of the disintegration processes were carried out using STATISTICA. The results of ANOVA and multiple regression analysis show that the optimum variables for the thermal disintegration are: 88°C, 227 rpm and 21 min, with actual degree of disintegration (DD) of 55.4%. For chemical disintegration, the optimum variables are 2.85M NaOH, 229 rpm and 21min and a corresponding optimum DD of 52.68%. The optimum DD for thermochemical disintegration is 61.45% at: 88°C, 2.29M NaOH, and 21 min. Biogas yield was improved by 60%, 15% and 36% v/v using the thermal, chemical and thermochemical disintegration techniques respectively. This shows that yield of biogas can be enhanced through disintegration process, and eventual higher cogeneration potential can be exploited.