This study investigated the practical application of combined advanced oxidation processes (AOPs), such as homogeneous TiO 2 photocatalysis and heterogeneous photo-Fenton, for the treatment of tannery wastewaters. An optimization study was conducted on the photocatalytic degradation of The combined advanced oxidation process proved to be an efficient and appropriate technique for the effective removal of complex organic compounds in industrial wastewater.

Chromium(III) used in tanning process is not consumed fully and around 30-40% of Chromium(III) is washed away to the environment causing severe environmental problem especially to the aquatic system. To remove Chromium(III) from wastewater, many different treatment techniques have been developed. This study deals with the ability of electrochemical peroxidation process for the removal of Chromium(III) from tannery wastewater in a batch stirred tank bench scale reactor with hopper bottom of 5 L working volume equipped with two iron electrodes which were investigated. The removal percentage of chromium was determined by varying operating parameters such as pH = 2-8, Fe 2+ = 2-5 mg/L, H 2 O 2 = 5-20 mg/L and current density = 10-40 mA/cm 2 were studied. The results showed that the Chromium(III) removal efficiency of 87% was achieved under optimum condition such as pH = 2, Fe 2+ = 2 mg/L H 2 O 2 = 15 mg/L, current density = 30 mA/cm 2 and contact time was 120 min with an electrical energy consumption of 0.073 kWh/L. The operating costs for the removal of Chromium(III) was found to be 0.4 $/m 3 for treated tannery wastewater. The electrochemical peroxidation process proved to be an efficient and appropriate technique for the removal of Chromium(III) from tannery wastewater.

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Combined discharge of domestic and tannery waste waters into streams or surface bodies has been witnessed in Vellore district in Tamil Nadu, India where the tannery processes are carried out at small-scale units. In the present study, an attempt has been made to evaluate the treatability of combined domestic and tannery waste waters using lab-scale activated sludge reactor under extended aeration. Studies on the efficiency of the activated sludge reactors were carried out by varying the solids retention time of 8, 12 and 16 days with a various hydraulic retention time of 15, 20, 25 and 30 h with an organic loading rate varying from 1.61 to 3.32 kg COD/ m 3 / day . The results showed that at the end of 30 h HRT at 16 days SRT with a lower F/M ratio of 0.08 kg BOD/kg MLSS, the maximum reduction of COD was observed to be from 2020 to 175 mg/L. From the bio-kinetic parameters estimation studies, the values of kinetic coefficients are obtained such as the half velocity substrate concentration (K s ), maximum specific growth rate (µ max ), yield coefficient (Y) , maximum substrate utilization rate (k) and decay coefficient (K d ) as 122 mg/L, 0.224 day -1 , 0.539 mg MLSS/mg COD, 0.416 day -1 and 0.088 day -1 . The study reveals that the combined domestic and tannery waste water is amenable for treatment using ASP, with treatment efficiency as high as 91% and the bio-kinetics arrived at better stability of the system and enhanced microbial activities at longer HRT and SRT. Also the design values suggest that the extended aeration system is the appropriate activated sludge treatment process for combined domestic and tannery waste water treatment.