Development of Advanced Wastewater Treatment System for Efficient and Complete Degradation of Refractory Chemicals by Combination of Biological Treatment and Ultraviolet Irradiation

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The feasibility of complete degradation of refractory chemicals in wastewater by combination of biological treatment and ultraviolet irradiation with TiO_2 as a catalyst was investigated. Nonylphenolethoxylate (NPE) was selected as a model chemical and its biodegradation by a isolated bacterial strain Pseudomonas sp.TR01 was investigated first. Although the polyoxyethylene part of NPE was efficiently degraded by strain TR01, dead-end products were accumulated in the culture medium. The metabolite was identified as NPE with short ethoxy-chain (NP2EO,NP3EO) and their carboxylated derivattives (NP2EC,NP3EC). These refractory dead-end metabolites could be degraded by ultraviolet irradiation with TiO_2 being suspended in the reaction mixture without occurence of detectable by-products by HPLC,GC,and GC-MS assays, suggesting complete degradation. The degradation efficiency increased with increase of temperature, but was not affected by pH.Soluble and suspended materials in the reaction mixture lowered the efficiency. These factors should be taken into consideration for constructing real treatment systems.