Decomposition of aromatic sulphonic acid syntan in aqueous solution using ozone

Introduction Effluents from leather industries contain high organic and inorganic loadings, and dissolved and suspended solids1,2. Apart from chemicals used in tanning process, other chemicals released from skin and hide contribute chemical oxygen demand (COD, 1000-4000 mg/l), biological oxygen demand (BOD, 300-800 mg/l) and total organic carbon (TOC, 350-1500 mg/l) of wastewater. Syntans (synthetic tanning materials including phenol, formaldehyde and tannin) are organic compounds (high mol wt), which are capable of transforming hides and skins into leather. Syntans, which are not completely absorbed by skins, remain in the effluent of tannery wastewater and are toxic to aquatic life3. Biodegradability of organic tanning agent (sulphonated polyphenols and melamine-based syntan) may vary greatly with their chemical composition and molecular structure, and some of them are toxic to microorganisms present in activated sludge process4-6. In biological treatment process of tannin containing wastewater, alternative methods involving advanced oxidation processes (AOPs: O3, UV and UV/TiO2) or in combination with biotreatment appears to be a feasible option. Ozonation of refractory organic compounds (polyphenols, naphthalene sulfonic acids tannin and lignin) in wastewater usually produces low-molecular weight, biodegradable 7-15 organic compounds (aldehydes, keto acids, and carboxylic acids). This study optimised process conditions for degradability of syntan using ozone (O3) to develop an appropriate biological treatment process.