pH sequential ozonation of domestic and wine-distillery wastewaters

Domestic and wine-distillery wastewaters were treated by semi-batch and continuous pH sequential ozonations. The process involves a succession of acidic and alkaline wastewater pH conditions. The alkaline periods allow oxidation of organic matter by hydroxyl radical and produce carbonates that eventually would inhibit the oxidation. On the other hand, the acidic periods favour the development of direct ozone reactions and strip off carbonates as carbon dioxide from the wastewater. Experimental results of pH sequential ozonation showed degradation and removal rates of wastewater pollutants higher than those achieved at constant either acidic or basic pH. The most significant improvement of ozone efficiency and pollutants removal were obtained by controlling the number of cycles, pH and time of acidic and alkaline phases. Also, ozonated wastewaters showed high biodegradability as deduced from their BOD/COD ratios. The feasibility of treating domestic and wine-distillery wastewater by an integrated activated sludge (ASP)-pH sequential ozonation system was evaluated. Integrated ASP-ozonation at constant pH processes were also carried out for comparative purposes. In these combined experiments, pH sequential ozonation showed advantages compared to ozonation at constant pH in reducing global parameters such as COD, TOC and TKN, but ozonation at constant pH led to higher removal of polyphenols and UV254 absorbing compounds. (C) 2001 Elsevier Science Ltd. All rights reserved.