Catalytic ozonation of bio-treated coking wastewater in continuous pilot- and full-scale system: Efficiency, catalyst deactivation and in-situ regeneration

In this study, the performance of catalytic ozonation in the treatment of bio-treated coking wastewater (BCW) using pilot- and full-scale systems was investigated. Additionally, the removal efficiency of organic pollutants from BCW, the deactivation mechanism of MnxCe1-xO2/gamma-Al2O3, and backflushing optimization for in-situ catalyst regeneration, which have not been previously investigated, were analysed. Results of the 12-month pilot scale experiments showed that catalytic ozonation resulted in the effective removal of organic pollutants when backflushing was applied as an in-situ catalyst regeneration strategy. The effluent chemical oxygen demand (COD) content decreased from 150 to 78 mg L-1, and remained below a discharge limitation of 80 mg L-1, and the stable COD removal efficiencies (from 56.0% to 47.9%) indicated that catalyst deactivation, which primarily resulted from the deposition of inorganic salts on the surface of the catalyst that limited interaction between ozone and active sites and/or prevented electrons transfer, was primarily inhibited by backflushing. The catalyst regeneration via in-situ air- and water-backflushing was attributed to the scrubbing, collision, and/or the loosing effect. Additionally, in the full-scale experiment, the catalytic ozonation process with in-situ alternative backflushing exhibited a stable COD removal efficiency (above 45.6%) for 885 days when water- and air-flushing strengths of 10 L m(-2) s(-1) and 15 L m(-2) s(-1), respectively, were applied with a 7-day regeneration interval. Therefore, the results of this study provide new insights into catalytic ozonation and support its engineering application in BCW treatment. (C) 2020 Elsevier Ltd. All rights reserved.