Acute and sub-lethal toxicity of landfill leachate towards two aquatic macro-invertebrates: demonstrating the remediation potential of aerobic digestion

A specific landfill leachate that contained 1.036 mgl⁻¹of 2-chlorobiphenyl was used in the study (255 mg l⁻¹ COD and 133 mg l⁻¹ BOD₅). Three, 2-l semi-continuous batch reactors (SBRs) were used to simulate the treatment potential of this method on a small scale. Aerobic digestion effectively reduced the leachates COD concentration. Regardless of dilution, the leachates COD reached a <20 mg l⁻¹ equilibrium after 96 h exposure to aerobic digestion, however, increasing the level of dilution accelerated the process. In untreated leachate, the LC₅₀ for Asellus aquaticus was 57% v/v leachate in deionised water and 5% for Gammarus pulex (96 h, static LC₅₀ tests without nutrition and oxygen depleting conditions). After being exposed to aerobic digestion, these values rose to 95% and 40%, respectively. Prolonged exposure to a 1:20 sub-lethal dilution of the aforementioned leachate has been previously shown to affect the breeding colony size of Asellus aquaticus and a 1:66 dilution influenced the fecundity of a Gammarus pulex population. After remediation by aerobic digestion, however, the population dynamics of both test species remained unaltered.