Development of a treatment train for the remediation of a hazardous industrial waste landfill leachate: A big challenge.

This study focuses on the development of a treatment train for a leachate from a hazardous industrial waste landfill (HIWL) previously treated by: (i) catalytic oxidation with hydrogen peroxide (H2O2) for sulphide and sulphite conversion into oxidized sulphur species, including sulphate, and (ii) chemical precipitation of sulphate as barite. The complete treatment line counted on four more stages: (iii) 1st biological oxidation for removal of biodegradable organic compounds and nitrogen species, (iv) coagulation with ferric chloride (coagulant dose of 100 mg Fe L-1, pH 2.8) for removal of a fraction of recalcitrant organics and suspended solids, (v) photo-Fenton oxidation using ultraviolet A (UVA) radiation (PF-UVA) (pH 2.8, initial total dissolved iron content of 140 mg L-1, treatment time of ~4 h) for recalcitrant organics degradation and biodegradability improvement, and (vi) 2nd biological oxidation for removal of the biodegradable organic matter resulting from the PF-UVA process. The use of anodic oxidation or photoelectro-Fenton processes in stage (v) demonstrated to be unfeasible. A chemical oxygen demand (COD) below 1000 mg O2 L-1, a common limit imposed by municipal wastewater treatment plants (MWWTPs) to effluents discharged into the municipal sewer, was achieved after a feasible treatment time (~4 h) using the multistep approach. The remediation of the HIWL leachate proved to be a big challenge.

Development of an integrated treatment strategy for a leather tannery landfill leachate.

This study aimed at developing an efficient multistage treatment strategy for a complex industrial landfill leachate: a leather tannery landfill leachate. Based on the leachate physicochemical characteristics, the following treatment train was delineated and tested: (i) initial biological process for removal of biodegradable organics, ammonium and alkalinity, (ii) coagulation/flocculation process for total removal of chromium and partial removal of recalcitrant organics and suspended solids, (iii) advanced oxidation process (AOP) or electrochemical AOP (EAOP) for degradation of recalcitrant organics and biodegradability enhancement, and (iv) final biological polishing step. Two initial biological treatment configurations were applied: one comprising nitrification and the other nitrification-denitrification. Coagulation/flocculation was optimized in terms of pH, coagulant dosage (iron(III) chloride) and flocculant nature and dosage. The following AOPs/EAOPs were tested: Fenton, photo-Fenton with UVA or UVC radiation (PF-UVA or PF-UVC), anodic oxidation (AO), electro-Fenton (EF) and photoelectro-Fenton with UVA radiation (PEF-UVA). The biological nitrification-denitrification was beneficial not only because it avoided the need for alkalinity addition during nitrification and decreased the amount of substrate added during denitrification, as expected. Over and above that, it reduced the acid consumption in the coagulation/flocculation, avoided the application of an additional stage comprising nitrites oxidation to nitrates prior to the AOP/EAOP, and improved the efficiency of Fenton's reaction based processes. Following nitrification-denitrification, the coagulation/flocculation was maximized at pH 3.0 and 400 mg Fe L-1 with no flocculant addition. The PEF-UVA process was the best AOP/EAOP. The final leachate fulfilled the discharge limits into waterbodies.