Health Risk Assessment Of Trace Organic Pollutants Remained In The Reclaimed Water Of The Mixed Municipal Wastewater

Water reuse is an increasing demand for many countries and regoins at present. One of key factors is the security of the reclaimed water. The treatment ofter used all though the world at present do not remove the poisonous and harmful pollutants thoroughly, especially the organic, which was always effecting the security of water reuse. Therefore, the ecosystem security assessment and the health risk assessment on the organic pollutants of the effluent of wastewater treatment plants have become the key technique that should be solved as soon as possible.Health risk assessment (HRA) is the process by which all kinds of information related public health should be collected, analysed and explained to estimate the possibility and the level of hazards on the public, wildlife or the ecosystem by some dose of hazard factor. HRA can help people to realize the potential health risk and pay more attention to them, and it can alarm the coming risk in time, which assists governments to formulate the environmental protection policies that are conducted to reduce pollution and protect the public health and ecosystem. At present, HRA has been used in many fields in China, but in the field of water reuse, the related research was not too many and the assessing system and the techniques are not complete yet.The mixed municipal wastewater is of different characteristicses from the common domestic sewage, however, few researches and studies about it was reported before, especially the HRA about the mixed wastewater reuse. Hance, the HRA of the reclaimed water should be studied and researched comprehensively and systematically. This study attempted to complete the related theory preliminarily and practise to do the HRA on the trace organic pollutants of the reclaimed water.Objective1. To find out the key craft to removal the trace organic pollutants within the present and new techique by isolating phthalate-degrading strain and studying its phthalate degrading efficency. 2. To find the scientific evidences of the new wastewater treatment technique to demonstrate it’s more advanced than the present by comparing the removal efficiency of trace organic pollutants in the effluents treated by them and assessing the health risk of them.3. To explore the valid toxicological experiment group to evaluate the hazards of trace organic pollutants in the reclaimed water and evaluate the dose-effect relationship.4. To set up the HRA framework of trace organic pollutants in the reclaimed water.Methods1. To isolate the phthalate-degrading strain from the active sludge of WWTP, and determine its16S rDNA sequence which was sent into Genebank to definite which genus it belonged to. Orthogonal experiment was designed to explore the optimistic conditions for the degradation of the bacterium. The phthalate degrading efficency was determined by liquid-liquid-extraction-high-efficiency-liquid-chromatography.2. Extracted from the influent, the secondary effluent and the tertiary effluent treated by the present technique and the effluent by the advance technique collected from one wastewater treatment plant, the organic extracts was analysed by GC-MS. Comparing with the spectrogram kept in NIST, some kinds of trace organic pollutants were recognized. At the same time, the change of peak area of one trace organic pollutant demonstrated the removal efficiency of the treatment techniques.3. The toxicity of trace organic pollutants in the water samples was studied qualitatively and quantitatively by biological group tests.Firstly, Luminescent bacteria acute toxicity test was used to measure the acute toxicity of the organic extracts in four kinds of water samples, and the vibrio qinghaiensis sp. Q67was adopted. The acute toxicities of all water samples could be evaluated by the light-emitting inhibition rates.Secondly, Vicia faba root-tip cells micronucleus test and single cell gel electrophoresis test was used to evaluate they biological hazard. After sprouting, the seeds of Vicia faba were exposed to the extractant of trace organic pollutants, then the root tip was cut down. Observed them by microscope and counted the cell number in which the micronuleus appeared. The single cell gel electrophoresis test was carried out by using human peripheral blood lymphocyte. After exposed, the lymphocytes were mixed in gelose gel and stained by ethidium bromide (EB) to show the result of electrophoresis by the fluorescent microscope. The number of comets was counted and the tail of the comets were measured by image analysis system.The third step was to adopt yeast estrogens screen and immature rat uterine bioassay to test the estrogenic effect of trace organic pollutants. The yeast with h-ER gene could be activated to express β-galactosidase by some trace organic pollutants with estrogenic activity, which could be evaluated by measuring the activity of β-galactosidase. The immature rats were exposed to the trace organic pollutants by peritoneal injection for3consecutive days and sacrificed on the morning of the fourth day. Body weights and uterine wet weights were determined and calculated the ratio of uterine weight to body weight. Then, the uterine tissues were collected and fixed in acid formaldehyde fixative to make paraffin sections, which were stained by HE to observe the morphous characteristics of uterus including the height of endometrium and the number of uterine gland and which were stained by immunocytochemistry to observe the expression and distribution of ERa and measure the mean optical density (MOD) of positive cells by image analysis system.4. The process of HRA, set up by United States Environmental Protection Association (USEPA), was adopted to evaluate the safety of POPs in the effluents of Wulongkou Wastewater Treatment Plant. And compare the risks between the traditional technique and the new. In order to do this work, Phenol was selected as "Common Criteria", and the toxical intensity was transformed into the phenol concentration at which the phenol showed same toxical intensity as the trace organic pollutants mixture.Results1. One phthalate-degrading strain was isolated from the active sludge of a sewage treatment plant. The16S rDNA sequence of the isolate was determined and referred to the Genebank to identify the biological specy. The isolate was belonged to Pseudomonas sp. The results of orthogonal experiment showed the optimistic conditions:pH8.0, temperature23℃.2. Several kinds of trace organic pollutants were confirmed in the mixed municipal wastewater, including styrene, cumene, a-methyl-binyl benzene、3-ehtyl-binyl benzene,4-ehtyl-binyl benzene,1,3-divinyl-benzene, dibutylphthalate and butyl benzyl phthalate. The peak areas of trace organic pollutants were obviously decreased after treated in wastewater treatment plant, especially by the new technique.3. Concentrated100times, the trace organic pollutants of all water samples could disturb the photogen’s luminous emission, the light-emitting inhibition rates of all samples were significantly different from each other, and the same conditions occurred between the three kinds of effluents.With the same concentration as above, the Viciafaba seeds, exposed with DMSO and the trace organic pollutants extracted from the tertiary effluent and the effluent treated by new technique, took roots that were obviously longer than them exposed with the trace organic pollutants from the influent, and their surface were white still, on the other hand, the seeds exposed to the second effluent seemed as to the influent. The micronuclear rates of root-tip cells were of significantly difference between all groups (P<0.001). Compared with each other, the group of DMSO and the group of new technique were not significantly different from the negative control (P>0.05), but the group of secondary effluent and the group of influent were significantly different from the new technique (P<0.05), at last, there was significant difference between the secondary effluent and the influent (P<0.05). The single cell gel electrophoresis showed that the DNA was orange, the nomal was round group, however, the impaired presented as comet and the tail pointed to the positive electrode. After exposed with DMSO and the trace organic pollutants, the length of comet tails and the tailing ratio were obviously different between all groups(F=243.535and148.623correspodingly, P<0.001). Compared with negative control, the length of comet tails and the tailing ratio of the influent group and the secondary effluent group were significantly different(P<0.01). Compared with the influent group, the comet tail length of the secondary effluent group and the tertiary effluent group were both shorter(P<0.01), and the tailing ratio were both smaller(P<0.01). The tailing ratio of the tertiary effluent group was significantly smaller than the secondary effluent group.Yeast estrogens screen demonstrated that the organic extracts in the new technique effluent showed the activity as estrogen after concentrated1000times, because the activity of β-galactosidase produced by yeast began to appear, otherwise, the same phenomenon occurred for the tertiary effluent, the secondary effluent and the influent at concentration of500times. At same concentration times of the POPs, the activity of β-galactosidase of each group could be listed as, the new technique effluent<the tertiarity effluent<the secondary effluent<the influent. The immature rat uterine bioassay showed there was significant difference only between the high dose group of the influent organic extracts and the negative control (P<0.05), but not between other groups, about the ratio of uterine weight to body weight. After the rat uterine slices stained by HE were measured, it was found that the uterine epithelial cell height, exposed to the tertiarity effluent organic extracts group with high dose, the secondary effluent and influent group with high dose and moderate dose, was significantly thicker than the negative control(P<0.05), but the cell height of the new technique was not(p>0.05). At the concentration of4000times, the the trace organic pollutants of the new technique induced significant height increasing compared with the secondary and tertiarity effluent (P<0.05). At the same concentration as above, the uterine gland number of the new technique group was significantly different from other water samples (P<0.05), meanwhile, the secondary effluent group was not different from the influent (P>0.05). When the the trace organic pollutants of the influent was concentrated only250times, the gland number was different from the4000times (P<0.05). The positive cells of ERa immunocytochemistry was measured, the MOD of the negative control was only different from the influent group with high dose (P<0.05). At high dose, there was not difference between the influent and the three kinds of effluent (P>0.05), but there is between the high dose group of the influent and the moderat and low dose groups of the effluents (P<0.05). 4. When reused as landscape water, the lifetime health risk of the the trace organic pollutants in the new technique effluent was3.912×10-12, the annual individual health risk was5.589×10-14, and the tertiarity effluent was1.566×10-10and2.237×10-13respectively. Compared with the maximum acceptable risk10-6/a, both of the health risks of the new technique effluent and the tertiarity effluent could be ignored.Conclusion1. The trace organic pollutants in the mixed municipal wastewater in Zhengzhou was consisted of styrene and its derivates and phthalate acid esters. Both of the present treatmeat and the new technique could remove the trace organic pollutants obviously, especially the last.2. At some concentration, the trace organic pollutants showed the acute toxicity, biology hazards and estrogenic activity, which suggested that the effluent was of potential health risk when they were reused. After the wastewater was treated in wastewater treatment plant, the trace organic pollutants in the secondary and tertiarity effluent was removed significantly, the new technique was more. It could be concluded that the new technique effluent would be of more security when it was reused.3. When reused as landscape water, the tertiarity effluent and the new technique effluent were both of high security. Comparatively, the security of the new technique effluent was higher, which meaned it would be more helpful to protect the ecosystem.