Combining chemical coagulation with activated coke adsorption to remove organic matters and retain nitrogen compounds in mature landfill leachate

Mature landfill leachate usually contains high levels of both recalcitrant organic matters and nitrogen compounds, which are hard to be removed simultaneously. In view of the difficulty, this study explored an innovative alternative that treated organic matters and nitrogen compounds separately by combining ferric trichloride (FTC) and polyacrylamide (PAM) coagulation with activated coke adsorption. Our study results have shown that the combination of chemical coagulation (750 mg/L of ferric trichloride and 2.0 mg/L of anionic polyacrylamide at pH = 5) with activated coke adsorption (5 g per 100 mL) was able to remove total organic carbon (TOC), chemical oxygen demand (COD), and colority by 91%, 57%, 100%, respectively. The removal efficiency (R.E.) of humic- and protein-like matters both exceeded 95%. Meanwhile, nitrogen compounds, such as nitrite and ammonia nitrogen, were mostly retained in the effluent. They could either be recovered as value-added products through technologies such as negative pressure steam-stripping or removed through methods such as air stripping and ion exchange. Overall, the proposed coagulation-adsorption process may provide a feasible alternative for tackling the worldwide concern over the secondary pollution caused by mature landfill leachate and its effective disposal.