Nanofiltration retentate treatment from urban wastewater secondary effluent by solar electrochemical oxidation processes

Abstract Comparison of electrochemical processes at pilot plant scale for the elimination of organic microcontaminants in actual urban wastewater treatment plant secondary effluents pre-treated by nanofiltration ([Cl−] = 1100–2000 mg L−1) membranes (for reducing total volume to be treated and increase water salinity), has been addressed. Anodic oxidation (AO), solar-assisted AO, electro Fenton (EF) and solar photoelectro-Fenton (SPEF) processes have been evaluated by using, when required, ethylenediamine-N,N’-disuccinic acid (EDDS) as complexing agent to maintain iron in solution at natural pH. Target water was spiked with a mix solution of microcontaminants: pentachlorophenol, terbutryn, chlorfenvinphos and diclofenac at initial concentrations of 500 and 100 μg L−1, each. AO and EF processes obtained similar degradation rates as added EDDS competed with microcontaminants for oxidant species. SPEF and solar assisted AO showed that high chloride concentrations was a crucial factor since chlorine species generated by solar-assisted AO were enough for efficient microcontaminant removal avoiding the addition of EDDS. Degradation monitoring of microcontaminants contained in actual urban wastewater treatment plant effluents was carried out by liquid chromatography coupled to hybrid quadrupole-linear ion trap-mass spectrometry.