Chemibiological treatment of difficult wastewaters: case study on tanning wastewater

摘要

Chemibiological treatment with H_2O_2 cracking was studied using several difficult wastewaters; that on tanning wastewater is reported here. The H_2O_2 oxidation was aided by ferrous sulphate, also known as the Fenton process; the effluent was then further treated in a biological sequencing batch reactor (SBR). Experiments were carried out to study the effects of and to obtain the optimum values for three parameters: concentrations of Fe~(2+), H_2O_2 and OH~-, on COD and colour reductions. The chemical treatment was found very effective in reducing colour, but only moderately effective on COD reduction; however it had rendered the organics more amenable to biological treatment. The optimal pH for H_2O_2 cracking was found to be at pH 2.9-3.9; the optimum FeSO_4 concentration was about 200 mg/L, resulting in about 60% COD and 90% colour reductions, with the Fe~(2+) regenerated and partially complexed or precipitated. the lab scale biological SBR had reduced the residual COD after chemical cracking of 300-500 mg/L to below 60 mg/L; while colour was reduced from about 300 PtCo to below 30 PtCo. This study has shown that a simple process feasible for small operators is able to treat a difficult wastewater to a level accepted as safe for discharge to surface waters.