Treatment of Concentrated Leachate by Coagulation and Fly Ash Absorption

The concentrated leachate of the Chengdu Leachate Treatment Plant was collected as a subject of case study. It was a very dark coloured liquid possessing high COD, very low BOD5 and low ammonia nitrogen concentration. The combination of coagulation and fly ash absorption was used to treat the concentrated leachate in this study. The effects of pH, coagulant dosage and settling time on COD removal in coagulation process were investigated by single-factor and orthogonal experiments. Results showed that the optimum value was approximately pH 5, aluminium sulfate dosage 1.5g and settling time 50min. The influence of operating factors followed the order: coagulant dosage >; pH >; settling time. Fly ash absorption experiments were performed after finishing the surface modification of fly ash in acid condition. The effects of pH, fly ash dosage and stirring time on COD removal were also studied by single factor. Results showed that the optimum value was about pH5, fly ash dosage 2.5g and stirring time 2.5h. After finishing the final step of fly ash absorption, the overall removal rate of COD was above 80%.