Treatment Of Refractory Pollutants Contained In Dyeing Wastewater By Using Ionizing Radiation And Its Coupling With Biological Technology

Dyeing wastewaters are extremely complicated. However, most of the wastewatersare organic wastewater, whose core treatment process is based on generally biologicaltechnology. As typical refractory organic pollutants in dyeing wastewater, polyvinylalcohol (PVA) and azo dyes have made a serious problem on biological process. Thepurpose of this study is to enhance biodegradability of refractory organic dyeingwastewaters and to remove refractory organic pollutants in these wastewaters by usingionzing radiation (IR) as a pretreatment, then to explore the possibility of refractoryorganic dyeing wastewater treatment by using IR coupling with biological process.Ionizing radiation-induced removal of PVA was investigated in aqueoussolution under γ-irradiation using a60Cobalt source. The results showed that thebiodegradability of PVA-containing wastewater with low initial concentration(e.g.,330mg/L) could be improved greatly with increasing irradiation dose.Specific oxygen uptake rate (SOUR, mg O2· g MLVSS-1· h-1) of activatedsludge using the9kGy irradiated PVA solutions was enhanced34%at0.5h.Under γ-irradiation, PVA removal pathway was found to be affected bydecomposition and polymerization. The decomposition effect dominated thePVA removal process at low PVA concentration, i.e.,330mg/L under neutralcondition. Hydroxyl radicals (OH) and hydrogen atoms were found to be thekey radicals in PVA decomposition. Oppositely, the polymerization/crosslinkingeffect dominated the PVA removal process at high PVA concentration, i.e.,3000mg/L under neutral condition. Also, OH radicals were found to be the keyradicals in PVA polymerization/crosslinking. Furthermore, acidic condition wasmore benefit for PVA polymerization under γ-irradiation.Ionizing radiation-induced degradation of an azo dye-Alizarin yellow-GG(AY-GG) was investigated in aqueous solution under γ-irradiation. The results showedthat IR had a good performance on biodegradability enhancement and acute toxitiydelimination of the azo dye wastewater. However, the SOUR curve appeared todecrease at early stage of irradiation (<1kGy), indicated that a partial toxicintermediates could generate that inhabited the activities of aerobic microbes. Fortunately, the inhibition was eliminated by further irradiation. The SOUR curvesincreased step by step. Furthermore, the acute toxicity of the solution decreasedobviously at9kGy. In addition, the similar law of biodegradability enhancement andacute toxitiy delimination of a simulated dyeing wastewater containing PVA and AY-GGwere found during γ-irradiation.Ionizing radiation of actual dyeing wastewaters was investigated byelectron beam (EB) irradiation using an electron accelerator. The results showedthat dyeing wastewaters with poor biodegdability (BOD5/COD <0.3) were suitfor IR-biological treatment. Thus, PVA contained dyeing wastewater(BOD5/COD <0.1) was studied by using IR-membrane bioreactor (MBR)coupling treatment. The results indicated that IR pretreatment slowed down themembrane (0.02μm) fouling by PVA (Mw:74800~79200). Finally, the researchachived the goal that using IR-MBR coupling process as the PVA containeddyeing wastewater treatment.In addition, synergistic effect was found during the treatment of PVA orAY-GG aqueous solutions between IR and ozone (O3) oxidation. Importantly,the synergistic effect not only appeared to enhance OH yeild during the IR andO3oxidation at the same time, but also appeared to remove the total organiccarbon of wastewaters by the sequential order of O3oxidation followed by IR.