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In this research, the use of laboratory-scale tests to evaluate the effect of various non-hazardous wastes on refuse decomposition is demonstrated. Non-hazardous wastes are receiving increased interest from landfill owners especially with respect to bioreactor operation. These wastes could benefit bioreactors in that they represent sources of liquid, nutrients, and/or substrate. However, landfill operators should exercise caution in accepting these wastes, as some could have detrimental effects on refuse decomposition. Three wastes were evaluated including (1) aerobically digested wastewater treatment plant biosolids which represent a nutrient source, (2) burnt sugar, which is a viscous glucose/lactic acid mixture from an agricultural process and represents a high carbon, acidic substrate, and wastes from the production of fabric softener and detergent. As each waste had unique properties, testing protocols were adapted to address the specific concerns surrounding each material. Biosolids were compatible with refuse decomposition but they did not increase maximum methane production rates and yields or reduce lag times to the onset of methane production. There is some evidence that biosolids increased ammonia and phosphorus, but these were not found to be limiting. Burnt sugar experiments suggested that actively decomposing refuse has the potential to attenuate relatively high loading of a highly degradable and low pH substrate. Detergent experiments demonstrated significant inhibition of refuse decomposition at low waste additions.