Degradation of micropollutants in flow-through VUV/UV reactors: Impact of internal diameter and baffle allocation

Application of VUV/UV process for micropollutants removal in decentralized water supply systems (e.g., rural drinking water treatment) is promising while few researches by far paid attention to the performance of practical flow-through reactors. This study investigated the degradation of atrazine (ATZ), sulfamethoxazole (SMX) and metoprolol (MET) under different hydrodynamic conditions in reactors with varied internal diameters and baffle allocations. Results showed that the target micropollutants could be degraded efficiently in the flow-through VUV/UV reactors following basically the pseudo-first order kinetics (R2 ≥ 0.97). The largest degradation rate constants were found in the D35 reactor and incorporation of baffles in the D50 and D80 reactors accelerated obviously the micrpollutants degradation. The improved performances of the baffled reactors were due mainly to the elevated utilization of HO•, and a new parameter named UEHO (HO• utilization efficiency) was proposed accordingly. The calculated UEHO values of the reactors ranged between 30.2% and 69.2% with the largest found in the D50-5 reactor. This testified the usually insufficient utilization of radicals in flow-through reactors and the effectiveness of baffle implementation. Electrical energy per order (EEO) values of micropollutants degradation in the reactors were in the range of 0.104-0.263 kWh m-3 order-1. The degradation was inhibited significantly by high-concentration nitrate yet the formed nitrite concentration stayed consistently below the drinking water limitation. The acute toxicity of the micropollutant solutions increased first and leveled off afterwards during the VUV/UV treatment, as indicated by the inhibition ratios of luminescence intensity of Vibrio fischeri.