Effect of powdered activated carbon addition on sludge dewaterability and substrate removal in landfill leachate treatment

The effect of powdered activated carbon (PAC) addition on substrate removal and sludge dewaterability was investigated in the co-treatment of leachate and domestic wastewater in an activated sludge system. The ratio of leachate in the total wastewater varied from 5 to 25% on a volumetric basis. The inert COD in the leachate could be decreased to very low levels by PAC addition. The specific resistance to filtration (SRF) of the activated sludge peaked during the removal of readily biodegradable COD and then declined when mainly non-biodegradable matter was left over. In the co-treatment case, the SRF of the sludge was shown to increase with an increase in leachate ratio, indicating that the sludge dewaterability (filterability) was negatively affected by the presence of leachate. When leachate was treated alone, the SRF of the sludge was much higher than the SRF of the sludges from domestic wastewater treatment or co-treatment. In any case, the addition of PAC to activated sludge could decrease the residual COD and suppress the peak SRF values. Overall, the results implied that in practice the addition of PAC addition to activated sludge will have a positive impact on substrate removal and sludge dewaterability. This effect will be most obvious at high leachate inputs.