title: Pilot treatment of olive pomace leachate by vertical-flow constructed wetland and electrochemical oxidation: an efficient hybrid process.
abstract: A hybrid process comprising biological degradation in a vertical-flow constructed wetland (CW) and electrochemical oxidation over boron-doped diamond electrodes to decolorize, mineralize and detoxify a leachate from olive pomace processing (OPL) was investigated. Two alternative treatment schemes were compared: According to the first treatment scheme, OPL was treated by electrochemical oxidation followed by treatment in a constructed wetland pilot unit (CW-A). The second scheme comprised of treatment in a constructed wetland followed by electrochemical treatment (CW-B). The constructed wetlands units were planted with Phragmites australis (reeds) and were fed intermittently at organic loadings between 5 and 15 g COD m(-2) d(-1) and a residence time of 3 d. Electrochemical oxidation (EO) was performed for 360 min at 20 A. Treatment of OPL in the wetland at 15 g COD m(-2) d(-1) led to mean COD and color reduction of 86% and 77%, respectively; the wetland effluent with a COD of about 800 mg L(-1) was polished electrochemically for 360 min after which the overall COD and color removal of the combined process (i.e. CW-B/EO) was around 95%, while the final effluent was not toxic against the marine bacteria Vibrio fischeri. Electrochemical oxidation of the original OPL at COD values between 6250 and 14 100 mg L(-1) led to moderate COD and color reduction (i.e. less than 40%) through zero order kinetics. When this was coupled to constructed wetland post-treatment (i.e. EO/CW-A), the overall COD and color removal was 81% and 58%, respectively. The decreased efficiency may be assigned to the increased toxicity of the electrochemically treated effluent which was only partially removed in the natural treatment system.
authors.affiliation: Department of Environmental Engineering, Technical University of Crete, Chania, Greece.
authors.forename: Petros
authors.initials: P
authors.lastname: Grafias
authors.forename: Nikolaos P
authors.initials: NP
authors.lastname: Xekoukoulotakis
authors.forename: Dionissios
authors.initials: D
authors.lastname: Mantzavinos
authors.forename: Evan
authors.initials: E
authors.lastname: Diamadopoulos
mesh_terms: D001673:Biodegradation, Environmental; D003116:Color; D055664:Electrochemical Techniques; D007220:Industrial Waste / Q000517:prevention & control; D031658:Olea; D010084:Oxidation-Reduction; D010865:Pilot Projects; D006109:Poaceae; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D053833:Wetlands
chemical_list: D007220:Industrial Waste; D014874:Water Pollutants, Chemical