Studies on the effect of pre-treatment of vegetable tanning process wastewater prior to biological treatment

Vegetable tanning process is carried out by the tanning industry for making of thick leathers used in shoes, suitcases and wallets. The vegetable tanning process wastewater (VTW) contains tannins which are polyphenolic and recalcitrant. The present study was focused on Fenton's oxidation (FO), ozonation (OZ) and Fenton's oxidation followed by ozonation (FO + OZ) processes as pre-treatment for VTW. The optimized H2O2/COD ratio for FO was found to be 1.25 and the ozonation contact time was optimized as 30 min. The maximum removal of tannins observed for each pre-treatment was found to be 49.5 %, 27 % and 74.6 % for FO, OZ and FO + OZ, respectively. Fourier Transform - Infra Red (FT-IR) Spectroscopy and Electro Spray Ionization - Mass spectroscopy (ESI-MS) analysis were performed to confirm the breakdown of tannins after each pre-treatment. After pretreatment, the samples were subjected to aerobic treatment and the process efficiency was evaluated in terms of Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD5) removal. The effect of pre-treatment prior to biological treatment was assessed with the help of Monod kinetics. The kinetic parameters and the cost estimates for each pre-treatment were explained in detail in the manuscript.