The study aims to describe and compare the impact of disposable wastewater addition on biodegradation of biological pretreated solid waste in bioreactor landfills. Two pilot-scale lysimeter landfills were constructed and loaded with pretreated waste and highly alkaline disposable wastewater – namely greywater from student hostel kitchen sinks and wastewater from sewer lines – was added into the lysimeters. The pilot-scale lysimeters were operated for 270 days with leachate recirculation, in the typical ambient temperature of New-Delhi, India. The leachate samples were obtained and then monitored for temporal variations of pH, oxidation–reduction potential, total solids, total dissolved solids, total suspended solids, electrical conductivity, chloride, biological oxygen demand (BOD5), chemical oxygen demand (COD), ammonia–nitrogen (NH3–N), total Kjeldahl nitrogen and gas production. The addition of wastewater to pretreated waste was found to facilitate the onset of methanogenesis and an increase in pH. The methanogenesis was observed for about a month later in the lysimeter to which greywater was added, which resulted in reduced gas production compared to that of the lysimeter fed with wastewater. After 270 days of operation, total quantities of leachate contaminants (BOD5, COD, and NH3–N) were found significantly reduced in the wastewater-fed lysimeter compared to the values found in the greywater-fed lysimeter. This comprehensive study suggested that feeding with wastewater has multiple benefits for enhancing the biodegradation processes of pretreated waste in bioreactor landfills.