A comparison of bulk inorganic constituents and trace pollutant concentration in leachates by landfill type

Landfill leachate characteristics vary depending on the type of waste facilities accept, such as municipal solid waste (MSW), construction and demolition debris (CDD) and MSW incineration (MSWI) ash. Optimizing disposal and treatment practices requires a thorough understanding of the behaviour of leachates from different classifications of refuse. This study provides a critical analysis of variation in leachate quality among over 80 sites based on landfill category: MSW, bulky debris, MSWI ash and MSW-MSWI ash co-disposal. Alkalinity was highest in leachates from facilities accepting MSW (average 2,810 mg L^-1), and the average pH from sites disposing of only ash (7.04) was lower than anticipated. As expected, all leachates were observed to have much greater concentrations of chemical oxygen demand compared to biochemical oxygen demand and require advanced secondary treatment to remove this recalcitrant organic matter. Unsurprisingly, leachates from facilities accepting only ash had elevated concentrations of salts (32,400 mg L^-1 TDS), and those from MSW disposing sites reported high ammonia-nitrogen (381 mg L^-1); co-disposal of MSW with ash resulted in elevated concentrations of both TDS and ammonia-nitrogen (19,400 mg L^-1 TDS, 543 mg L^-1 NH₃-N). Metal concentrations among all leachate types were similar, though arsenic was elevated in landfills accepting only CDD. Trace organic chemicals like benzene were much higher in leachates from sites disposing of unburned residuals compared to those only accepting ash. Variation among landfill types were attributed to leachate flow characteristics, pH, degradation, waste composition and other biogeochemical interactions. The results demonstrate co-disposal practices can potentially require more leachate treatment than separate disposal scenarios.