Ecotoxicity Assessment Of Poly(Dimethylaminostyrene)and Its Removal And Degradation In Wastewater

As an important global textile production and consumption country, China has contributed greatly to the whole national economies in terms of textile printing and dyeing industries, and the production and use quantity of poly(dimethylaminostyrene)(PDMAS), as an important textile additive in the textile printing and dyeing industries, accounted for a great proportion in the world. The rapid development of technologies producing PDMAS has greatly promoted the development of overall field of textile chemicals and textile printing and dyeing industry, resulting in the discharge of a large number of PDMAS pollutants, generated in the production and use procedures, into the environment together with the wastewater treatment process effluent, with a potential threat to the environment. Unlike the systematic study of polydimethylsiloxane (PDMS) in the environmental behaviors, the environmental problems of PDMAS, neither in the scientific nor industry community, have not attracted sufficient attention.This thesis systematically studied the environmental behavior and degradation (removal) mechanism of PDMAS in the soil and water from three research perspectives:a) ecological toxicity of PDMAS, b) biodegradability of PDMAS in ASBR anaerobic reactor, and c) PDMAS’s degradation mechanism and pathways in microemulsion by Fenton reagent. The major findings are:1. Three acute toxicities were carried out in this study. They were the luminescence inhibition of luminous bacteria in the PDMAS emulsion, the inhibition of the cabbage seed germination and root elongation, the earthworm survival and weight loss in the soil which were contaminated by the PDMAS, respectively. These acute toxicity tests showed that within the PDMAS microemulsion exposure concentration range of0.05-2.5mg/mL and PDMAS exposure concentration range of0.01～1.0mg/g, they all have significant dose-response relationships at the each test. Relatively higher concentrations of PDMAS samples showed more obvious toxic effects. Meanwhile, the three test methods also showed slightly different toxic effects of ammonia value and viscosity of PDMAS. In the detection concentration range of the PDMAS emulsion, the PDMAS emulsion of higher ammonia values had more significant luminescence inhibition of photobacterium phosphorem (strain T3), because of the proton process of ammonia alkyl side chain of PDMAS. However, the viscosity of PDMAS had no significant effects on luminescence inhibition. The soil samples contaminated by higher viscosity PDMAS have higher weight loss rates and lower survival rates of earthworms (E. foetida), and the ammonia value of PDMAS did not significantly affect the weight loss and survival of earthworms. The soil samples contaminated by different ammonia value and viscosity of PDMAS did not have a significant impact on the inhibition of seed germination and root elongation.2. The long-term biodegradability experiments of PDMAS in a ASBR reactor showed:only less than9.5%of the PDMAS entry into the environment together with the water discharge from the reactor, while most of the PDMAS were lagged or accumulated in the reactor (reactor wall and sludge adsorption), and later discharged into the environment with the sludge. The organic matters’analysis (average molecular weight and functional group) results of the ASBR reaction in the effluent and sludge showed that the higher molecular weight of the PDMAS had more retention or accumulation in the reactor anaerobic, and biological treatment process would had no significant degradation process. Mean the while; the further anaerobic shake flask experiments verified the very low biodegradability of PDMAS in the anaerobic biological treatment process.3. The results of PDMAS’s degradation mechanism and pathways in microemulsion by Fenton reagent showed that Fenton reagent oxidation technology is a suitable choice for physic-chemical pretreatment of PDMAS emulsion wastewater with COD removal efficiency reached about80%. Under the Fenton reaction conditions, PDMAS was removed primarily through flocculation and adsorption, coupling with a key process of oxidation. It was also observed that the molecular weight of the PDMAS was correlated to the COD removal efficiency in some extent, that is, the PDMAS samples in high molecular weight was removed with a slightly higher COD removal efficiency. The degradation pathway of the PDMAS under Fenton reagent oxidation process was as follows:a) firstly, the cyclization reaction of the PDMAS occurs under low pH conditions; b) the subsequent occurrence is side-chain scission due to oxidation of the hydroxyl radical reaction; c)simultaneously, the main chain scission reaction happens randomly. In addition, changes of the concentration of H2O2and Fe2+, and the value of ORP and pH in the Fenton reaction process verified that the molecular weight and ammonia values of the PDMAS affects the consumption of H2O2in the Fenton oxidation process, and intermediates affect the process of the Fenton reaction in the degradation process. These findings and laws further verified the PDMAS removal mechanism and degradation pathways.In summary, relative to the PDMS, PDMAS showed stronger acute toxicity, and presented a potential threat to the environment. We verified that that the PDMAS entry into the environment through the sludge disposal of wastewater treatment process, and only a small amount of the PDMAS entry into the environment through wastewater discharge, and little effective biodegradation was observed in the process of biochemical treatment. The PDMAS can be removed primarily by the flocculation and adsorption in the Fenton process. Oxidation broke the PDMAS structure (all of side-chains scission, main chain scission randomly and smaller molecular weight siloxane polymer generated), which greatly promoted the flocculation effect of the removal efficiency. The results from this study provide a theoretical base and technical support for the safe use and effective removal of PDMAS.