•The co-gasification of food waste was compared with that of sewage sludge.•Food wastes are more favorable than sewage sludge for residue and energy output.•Two decentralized gasification-based disposal schemes were proposed for Singapore.•Monte Carlo simulation-based cost-benefit analysis was conducted.•The proposed schemes are financially superior to the incineration-based scheme. The compositions of food wastes and their co-gasification producer gas were compared with the existing data of sewage sludge. Results showed that food wastes are more favorable than sewage sludge for co-gasification based on residue generation and energy output. Two decentralized gasification-based schemes were proposed to dispose of the sewage sludge and food wastes in Singapore. Monte Carlo simulation-based cost-benefit analysis was conducted to compare the proposed schemes with the existing incineration-based scheme. It was found that the gasification-based schemes are financially superior to the incineration-based scheme based on the data of net present value (NPV), benefit-cost ratio (BCR), and internal rate of return (IRR). Sensitivity analysis was conducted to suggest effective measures to improve the economics of the schemes.