Potential of Catalytic Ozonation as Advanced Treatment of Reverse Osmosis Concentrate from Coking Wastewater Reuse

Catalytic ozonation was adopted for treating the brine derived from a two-stage reverse osmosis (RO) treatment in bio-treated coking wastewater reclamation. The preparation parameters of Mn/γ-Al2O3 and Mn-Ce/γ-Al2O3 catalysts were optimized. The effects of operating conditions on the ozonation alone, Mn/γ-Al2O3 and Mn-Ce/γ-Al2O3 catalytic ozonation were systematically compared based on the indicators such as COD, color, A254 and pH. The optimal parameters for both Mn/γ-Al2O3 and Mn-Ce/γ-Al2O3 catalysts are Mn and/or Ce loading of 1.0 wt% and pyrolysis temperature of 673 K. The COD removal is 15.7%, 27.6% and 38.9% after 30 min for ozonation alone, Mn/γ-Al2O3 and Mn-Ce/γ-Al2O3 catalytic ozonation, respectively. It indicates that the introduction of Ce into the Mn/γ-Al2O3 catalyst can significantly improve the COD removal, which is beneficial to the subsequent evaporation and crystallization processes. During catalytic ozonation, ozone dose, reaction temperature and catalyst dose have positive effect on the COD removal, and increasing the initial pH from 5.0 to 7.3 significantly improves COD removal, while further increasing pH has slightly positive effect on COD removal. According to the results of apparent molecular weight distribution and GC/MS, Mn-Ce/γ-Al2O3 catalytic ozonation is the most efficient for the removal of macromolecular effluent organic matter (molecular weight > 5 k Da) and also for the degradation of refractory pollutants in the ROC among the three oxidation processes. Under the same reaction conditions, the presence of Mn/γ-Al2O3 catalyst can reduce ΔO3/ΔCOD by at least 34% compared to ozonation alone. Furthermore, Mn-Ce/γ-Al2O3 catalytic ozonation can reduce the ΔO3/ΔCOD from 2.6 of Mn/γ-Al2O3 catalytic ozonation to 0.9 in the case of achieving similar COD removal. Catalytic ozonation has the potential to treat ROC derived from bio-treated coking wastewater reclamation