Combined Advanced Oxidation Processes and Aerobic Biological Treatment for Synthetic Fatliquor Used in Tanneries Chitra Kalyanaraman,* ,† Sri Bala Kameswari Kanchinadham, † L. Vidya Devi, † S. Porselvam, † and J. Raghava Rao ‡ † Environmental Technology Division, Council of Scientific and Industrial Research−Central Leather Research Institute, Adyar, Chennai 600 020, India ‡ Chemical Laboratory, Council of Scientific and Industrial Research−Central Leather Research Institute, Adyar, Chennai 600 020, India ABSTRACT: 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 BOD 5 /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 sulphonates, 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/H 2 O 2 and Fenton’s reagent as pretreatment. AOP pretreatment of UV/H 2 O 2 and Fenton’s reagent improves the BOD 5 / 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/H 2 O 2 pretreated synthetic fatliquor produced biochemical oxygen demand (BOD 5 ) and chemical oxygen demand (COD) of 45 and 330 mg/L in the aerobic reactor and Fenton’s reagent pretreated fatliquor produced BOD 5 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 and carboxylic acids presence are observed in the operating conditions maintained in the batch aerobic reactors. ■ INTRODUCTION Fatliquoring is one of the key operations in the manufacturing of leather. Fatliquoring is a process of coating the surface of leather fibers with a thin layer of oil. Proper treatment with oils and fats gives the leather full and soft handling flexibility and additional strength. Fatliquoring improves the tensile strength, stitch-tear resistance, abrasive resistance, water-repellent properties, and resistance toward chemical actions. Fatliquors may be anionic, cationic, or nonionic in nature. Depending upon the source of the oils/fats used, the fatliquors can be classified as vegetable, synthetic, or semi-synthetic. 1 The water- insoluble fatliquoring agents used include natural (animal, vegetable, and fish), synthetic fatty acid esters, and petrochemical products. 2 The use of synthetic oils, fats, and fatliquors in the leather industry has become popular due to their superiority over natural products in many respects such as high emulsifying power. The quantity required is less, as a result of which the leather is not unduly loaded with fats and oils to achieve specific softness. Silicone oil and paraffinic hydro- carbons find use in fatliquoring process as components of synthetic fatliquor due to their lubricating and protective action. 3 Generally, synthetic fatliquors are prepared from paraffins obtained either by Fischer−Tropsch method of paraffin synthesis or from the petroleum industry. Saturated hydro- carbons in paraffins having chain length ranging from C 15 to C 24 are chlorinated by chlorine gas in the presence of catalysts and ultraviolet rays. In chlorinated paraffin, the chlorine atoms are firmly attached to paraffins and are not split off even at 150 °C. Chlorinated paraffin is sulphochlorinated and then saponified with caustic soda to produce chlorinated paraffin sulphonates, which is one of the main ingredients for synthetic fatliquor. 4 Leather treated with only synthetic fatliquor becomes too dry and flat and shows a strawy feel. To overcome these drawbacks, synthetic fatliquors are always used in conjunction with natural oils; such a blending mixture therefore gives better results and produces much a softer type of leather. The main components of fatliquor are water, natural fats (e.g., fish oils), surfactants, and the chlorinated paraffin (CPs). They are used in conjunction with sulphated or sulphonated oils, chlorosulphonated paraffins, natural fats, and oils. Typically, chlorinated paraffins with relatively low chlorine content (e.g., ≤ 40 wt % Cl) are used in leather applications. The CPs account for about 10% by weight of the formulated fatliquor. The amount of fatliquor used in the fatliquoring step Received: July 18, 2012 Revised: November 16, 2012 Accepted: November 16, 2012 Published: November 16, 2012 Article pubs.acs.org/IECR © 2012 American Chemical Society 16171 dx.doi.org/10.1021/ie301904g | Ind. Eng. Chem. Res. 2012, 51, 16171−16181