Combined Advanced Oxidation Processes and Aerobic Biological Treatment for Synthetic Fatliquor Used in Tanneries

The use of synthetic oils, fats, and fatliquors in the leather industry has become popular due to their superiority in terms of high emulsifying power when compared to natural oil based fatliquor. Compared to natural oil based fatliquor, the quantity required is lesser and the leather is not unduly loaded with fats and oils to achieve specific softness. Generally, synthetic fatliquors are prepared from paraffins and are made emulsifiable by sulphochlorination to produce chlorinated paraffin sulphonates. Due to the inherent nature of synthetic fatliquor and its low BOD5/COD ratio of 0.077, it is adsorbed over the microbes and reduces the efficiency of the aerobic treatment unit in the treatment plants. Hence the aim of the present study was to evaluate the environment friendliness of synthetic fatliquors containing chlorinated paraffin sulphonate,;, by undertaking aerobic biodegradation studies at the same operating conditions maintained in the tannery effluent treatment plants, viz., f/m ratio of 0.15 and hydraulic retention time (HRT) of one day. Considering the nature of the compounds present in the synthetic fatliquors, the biodegradability of the fatliquor was sought to be improved by adopting advanced oxidation processes (AOPs) like UV/H2O2 and Fenton's reagent as pretreatment. AOP pretreatment of UV/H2O2 and Fenton's reagent improves the BOD5/COD ratio of synthetic fatliquor from 0.077 to 0.3 and 0.37 and the biodegradable organics are effectively degraded in the aerobic reactor. UV/H2O2 pretreated synthetic fatliquor produced biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) of 45 and 330 mg/L in the aerobic reactor and Fenton's reagent pretreated fatliquor produced BOD5 and COD of 28 and 240 mg/L in the aerobic treated effluent. It was evident from FT-IR analysis that the chlorinated paraffin sulfonates are degraded efficiently in the batch reactor after AOP pretreatment and short chain chlorinated compounds ani carboxylic acids presence are observed in the operating conditions maintained in the batch aerobic reactors.