Identification Of Pollutants With Toxicity To Biological Treatment In Acrylic-acid Wastewater

Acrylic-acid wastewater has a complex composition and high concentrations of toxic organic pollutants, exerting hazardous risks to human health and ecological safty. With the rising industrial demand for acrylic-acid and the expanding of its production scale, acrylic-acid wastewater has become an important source of petrochemical wastewater toxicity to biological treatment, and causes serious impact on the operation of the wastewater treatment plant.In this study, the toxicity to biological treatment of acrylic-acid wastewater was evaluated by various methods including inhibition test of activated sludge oxygen uptake rate(OUR), inhibition test of dehydrogenase activity, acute toxicity test of luminescent bacteria and inhibition test of microbial biomass of activated sludge. In the OUR test, it was found that the EC50 of total oxygen uptake rate was about 2.19%, while the ones of heterotrophic bacteria and nitrifying bacteria were 2.58% and 0.86%, respectively. Considering the requirement of this study, the OUR inhibition test was more suitable than the other methods, with its relatively moderate sensitivity and simple operations.Deletion test was used to identify the toxic substances among all the organic chemicals determined in acrylic-acid wastewater by physical and chemical analysis in previous study. The results turned out that 11 of them had distinct toxicity effects to biological treatment: Acrylic-acid, Formaldehyde, Acrolein, 2,3-Dihydrofuran, Indigo, Styrene, Methyl acrylate, Ethyl Acrylate, Butyl alcohol, Methylbenzene and n-Butyl acetate. It was also found that all of these organics had particularly severe toxicity on the nitrifying bacteria in activated sludge, suggesting that pretreatment would be very necessary for the protection of wastewater treatment plant with nitrogen removal process.Furthermore, the toxicity contributions of the identified 11 toxic chemicals in acrylic-acid wastewater were compared according to their Toxic Unit and the toxic contribution index. It was found that formaldehyde and acrylic-acid had a combined contribution up to over 86% in all of the toxic chemicals, making them the most prominent toxic chemicals in acrylic-acid wastewater.Based on the determination of the key toxic chemicals, the joint toxicity effect between formaldehyde and acrylic-acid was evaluated by methods inclusive of Toxic Unit, Additional Index, Mixture Toxic Index and ?, and the result turned out to be synergism. The test of luminous bacteria acute toxicity detection showed the same results as the inhibition test of OUR. Research findings in this study provided important directions for the pretreatment of acrylic-acid wastewater.