Incorporation of electrochemical advanced oxidation processes in a multistage treatment system for sanitary landfill leachate

The current study has proved the technical feasibility of including electrochemical advanced oxidation processes (EAOPs) in a multistage strategy for the remediation of a sanitary landfill leachate that embraced: (i) first biological treatment to remove the biodegradable organic fraction, oxidize ammonium and reduce alkalinity, (ii) coagulation of the bio-treated leachate to precipitate humic acids and particles, followed by separation of the clarified effluent, and (iii) oxidation of the resulting effluent by an EAOP to degrade the recalcitrant organic matter and increase its biodegradability so that a second biological process for removal of biodegradable organics and nitrogen content could be applied. The influence of current density on an UVA photoelectro-Fenton (PEF) process was firstly assessed. The oxidation ability of various EAOPs such as electro-Fenton (EF) with two distinct initial total dissolved iron concentrations ([TDI]0), PEF and solar PEF (SPEF) was further evaluated and these processes were compared with their analogous chemical ones. A detailed assessment of the two first treatment stages was made and the biodegradability enhancement during the SPEF process was determined by a Zahn–Wellens test to define the ideal organics oxidation state to stop the EAOP and apply the second biological treatment. The best current density was 200 mA cm−2 for a PEF process using a BDD anode, [TDI]0 of 60 mg L−1, pH 2.8 and 20 °C. The relative oxidation ability of EAOPs increased in the order EF with 12 mg [TDI]0 L−1 < EF with 60 mg [TDI]0 L−1 < PEF with 60 mg [TDI]0 L−1 ≤ SPEF with 60 mg [TDI]0 L−1, using the abovementioned conditions. While EF process was much superior to the Fenton one, the superiority of PEF over photo-Fenton was less evident and SPEF attained similar degradation to solar photo-Fenton. To provide a final dissolved organic carbon (DOC) of 163 mg L−1 to fulfill the discharge limits into the environment after a second biological process, 6.2 kJ L−1 UV energy and 36 kWh m−3 electrical energy were consumed using SPEF with a BDD anode at 200 mA cm−2, 60 mg [TDI]0 L−1, pH 2.8 and 20 °C.