Removal Of Typical Persistent Organic Pollutants (pops) In Domestic Wastewater And Their Fading In The Secondary Treatment Process

Persistent organic pollutants (POPs) constitute a class of man-made chemicals with pronounced highly toxic, persistence against chemical/biological degradation, tendency for bioaccumulation in human and animal tissues, and significant impacts on human health and the environment. With the wide development of modern petrifaction industry, impacts from POPs were seriously increased because of the incomplete and rubbish combustion of the petrifaction products and mass use for the plastic products. Thus, the domestic wastewater, as a carrier of pollutants discharge in life and production process, gathers much various pollutants including the POPs. So it is a necessary trend that the domestic wastewater would be reused as main supplement water. Further, it is paid more attention that all kinds of possible remained toxic and harmful materials, especially POPs, impact on the water environmental ecology in the reuse of domestic wastewater. And it appears essential to make sure the existence level in the municipal wastewater and the removal and transformed laws in the conventional wastewater treatment for the POPs.The study was part of the National Natural Science Foundation of China (Grant No. 50838005), it chose 4 classes POPs as the studied objects, namely Polycyclic aromatic hydrocarbons (PAHs), phthalic acid esters (PAEs), polychlorinated biphenyls (PCBs), organic chlorinate pesticides (OCPs). For investigating the wastewater treatment plant in Xi'an by an oxidation ditch process, a long-term the effluent detection of the each phase of the WWTP was done. In addition of the experimental study on the removal mechanism, we establish a removal POPs mathematical model for the conventional secondary treatment process on the municipal wastewater on the basis of the analysis of the mechanism and material equilibrium. The model was simulated to get the ideal results by using the experimental data, the operating parameters and the typical POPs characteristic parameters. The studied conclusions deepen the understanding on the removal and transform mechanism of the POPs in the conventional secondary treatment process. Mainly results and discussions included:(1) The detection analysis method of the PAHs, PAEs, PCBs and OCPs was optimized and perfected. The standard samples of 44 typical pollutions in the above 4 classes POPs were qualifier analyzed by using the GC-MS to optimize each GC conditions and MS conditions on the basis of the other references. Moreover, 16 PAHs and 6 PAEs using the GC-FID and 6 PCBs and 16 OCPs using the GC-ECD were quantified following the external standard calibration procedure, respectively to optimize GC and detection conditions of the 22 compounds detected on the GC-FID and GC-ECD, to get their chromatograph spectrum with the better isolation efficiency respectively in 34.47min and 26.62min. In last, through analyzing and comparing all kinds pretreatment methods for the different POPs in water, the SPE was adopted to pre-treat 4 classes POPs, and to optimize the best method condition by perfecting the recover rate in order to ensure more than 70% of the 4 class POPs.(2) The paper detected the occurrence of the 4 classes POPs and the conventional pollution index of the effluent in each processes in the wastewater treatment plant in Xi′an. The results showed that 8 PAHs, 5 PAEs, 5 PCBs and 5 OCPs were found; among them, PAEs changed from 10⁰μg/L to 10²Î¼g/L with highest concentration, then the concentration of PAHs was below 10⁰μg/L, while PCBs and OCPs had the lowest concentration with less than 10¹ng/L. The changes of typical POPs pollutions showed that PAHs,PAEs,PCBs and OCPs were mainly removed in biochemistry unit, but less in primary settler and secondary settle.(3) According to the wastewater level, NAPT, PHEN and PYR in NAPT, DBP and DEHP in PAEs were ensured as the typical POPs pollutions. Adopting lab-scale experiment, the study analyzed the main adsorbed removal mechanism of the typical POPs by inorganic particles quartz sands, kaolin and natural clay and activated sludge. The results indicated that the adsorption on 5 typical POPs from inorganic particles were monolayer adsorption and well followed the Langumuir equation, which was exothermic reaction. But the adsorption on 5 typical POPs from activated sludge was multilayer adsorption and may be simulated by the Freundlich equation, which was endothermic reaction. And the adsorption from activated sludge was bigger the ten orders, which was related to the adsorbents structure and physical and chemistrical features of the adsorbates; while the specific surface area of the adsorbents was one of the aspects to decide the adsorption ability, namely the adsorption would be stronger with the increase of the specific surface area. In addition, logK_ow of the adsorbates were direct contrasted to the adsorption, namely the adsorption would be stronger with the bigger of logK_ow.(4) According to the characteristics of the wastewater secondary treatment process, the paper studied the POPs removal mechanism including volatilization, adsorption and biodegradation, and established the quantify equations of three removal mechanism. The removal of typical POPs by three mechanism was related to the POPs structure and physical and chemistrical features, and the difference level of adsorption was due to the equilibrium partitioning coefficient K_p of POPs, and the K_p values could be obtained from the adsorption equations, and established the typical POPs removal mathematics model based on the three removal mechanism.The model parameters about wastewater treatment process were confirmed --take, for instance, the WWTP of Xi′an. The result showed that the POPs removal by volatilization very small, the removal can be neglected, and difference POPs had difference removal by biodegraded, the NAPT, PHEN, and PHEN removal by biodegraded respectively were 13.7%, 3.5%, and 1.5%, and PYR and DEHP with less than 0.1% removal ratio. So the adsorption became the main removal mechanism. In according to the obvious adsorption, the removal rate calculation model of POPs was established on the basis of the equilibrium partitioning coefficient K_p. Under the condition of activated sludge of the oxidation ditch as the adsorption subject, the reasonable results were obtained. The results presented that the adsorption rate of POPs increased with the K_p, and approached to a definite value at high K_p values.The above study of paper announced the removal and transform mechanism of the typical POPs in domestic wastewater and the conventional secondary treatment process. It is very important for further study.