The efficiency of ozone as a pre- and post-treatment to UASB treatment was investigated, followed by a study into UASB reactor performance with ozonated wastewater as substrate. Combinations of pre- and/or post-ozonation with UASB treatment gave better results than ozonation or UASB alone and COD reductions of 53.0–98.9% were achieved for treatment of canning and winery wastewaters. A UASB reactor was fed with pre-ozonated cannery wastewater for over 70 d. COD removal improved from between 58.8 and 64.4% to between 85.3 and 91.8% after pre-ozonated substrate feed commenced. Subsequent increases in organic loading rate (OLR) from 2.4 to 3.4 kgCOD m−3.d−1 did not affect reactor performance. By including a final post-ozonation treatment to this UASB effluent a total COD reduction of 99.2% was achieved.

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