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A combined technological scheme for purification of undiluted high-strength wastewater produced in the shale oil industry was proposed. The initial values of chemical oxygen demand (COD), biological oxygen demand (BOD 7) and phenols in the studied pyrogenic wastewater samples were up to 45, 35 and 1 g/L, respectively. Furthermore, the wastewater had a high toxicity to indicator organism Daphnia Magna (EC 50 = 0.34%) and caused inhibition of oxygen uptake rate (IC 50 = 3.4%) and nitrification rate (IC 50 = 0.7%) in activated sludge treatment. The combination of air stripping, coagulation-flocculation, batch distillation, activated sludge and the Fenton oxidation processes reduced all measured parameters more than 95%. Consequently, a treatment scheme applicable to pyrogenic wastewater was developed.

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In this research, various combinations of physicochemical (coagulation, Fenton process and ozonation) and biological (aerobic oxidation) treatment methods were used to purify wastewater originating from wood soaking basins in plywood production industry. Although the wastewater has good biodegradability (92 %), there is a high fraction of organic material expressed as recalcitrant chemical oxygen demand (COD) of approximately 360 mg L -1 . High fraction of organics is caused by woodoriginating water-soluble material, i.e. extractives, including lignin and tannins. It was found that optimal treatment method for hardwood soaking basin wastewater is the combination of biological pre-treatment, chemical treatment with Fenton reagent and biological post-treatment. Under optimal conditions of combined process performance, up to 99 % removal of the organic loads, nitrogen and phenols was achieved. Besides achieving target discharge limits stated for industrial wastewater, the effluent met the requirements set for municipal wastewater treatment plants, making the treated water acceptable for subsequent discharge into natural water bodies: treated water COD = 90 ± 3 mg L -1 ; BOD 7 = 10 ± 1 mg L -1 . The main result of the present work was the establishment of sustainable, efficient and economically feasible process to treat the wastewater with minimised chemicals consumption. This differs considerably from approaches such as coagulation or wet oxidation, used to treat similar water types according to the literature, and is readily applicable for the production facilities of various scales, including small and medium enterprises, without the need to make changes in existing technological schemes.

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BACKGROUND Among anthropogenic wastewaters, landfill leachate is known to contain numerous persistent organic pollutants, heavy metals, noxious microorganisms, etc., which makes the establishment of an efficient treatment procedure for leachate a matter of great importance. In this work, municipal waste landfill leachate was subjected to various types of chemical (CHEM) and biological (BIO) treatment with the final aim of establishing an optimal treatment scheme combining of individual physico‐chemical and biological processes. RESULTS Three different treatment strategies (CHEM‐BIO, BIO‐CHEM and BIO‐CHEM‐BIO) were compared based on biodegradability and removal efficiencies achieved. Due to high initial biodegradability of raw leachate, the most efficient combined process was aerobic biological pre‐treatment followed by Fenton treatment and subsequently biological post‐treatment. The efficiency of combined treatment processes was investigated at laboratory scale, with over 90% COD and BOD7 removal. Finally, in order to evaluate the economic efficiency of the processes, consumption of Fenton's reagent was compared for CHEM‐BIO and BIO‐CHEM setups, with the latter achieving three times lower reagent consumption, at the same time providing similar treatment efficiency. CONCLUSIONS A readily‐applicable efficient and economically feasible technological solution is provided for the treatment of typical municipal landfill leachate. © 2014 Society of Chemical Industry

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