Removal of volatile acids from synthetic landfill leachate by anaerobic biofilms on drainage aggregates: a laboratory study

Populations of anaerobic bacteria derived from gassing landfills were established on various solid media in laboratory-scale models of landfill drains. Solutions of salts and volatile fatty acids (VFAs), simulating landfill leachates, were circulated through the models for periods of 400 to 800 days and the removal of VFAs and the formation of gas were measured. The ability of the colonized aggregate to remove VFAs from the leachates increased to a maximum over periods of time ranging from 50 to 150 days after the initial colonization phase. The highest rates of VFA removal [3500 mg 1^-1 (bed vol.) day ^-1 at a leachate flow rate of 2.59 1 d^-1 with 16 500 mg 1^-1 total VFAs] were found at the tops of the columns, but the lower sections were also colonized by bacteria capable of removing VFAs. The initial adaptation of the bacterial population to propionic acid degradation was slower than the adaptation to acetate and butyrate degradation. Increasing the propionate concentration in the leachate from 2500 to 7500 mg 1 ^-1 caused a 50% reduction in the rate of removal of VFAs by a bacterial population adapted to a mixture of acetate, propionate and butyrate. The bacterial population eventually adapted to the higher concentrations of propionate. Changing from saturated to unsaturated flow conditions in the drainage models reduced the specific rate of removal of VFAs by 50%.