| Objective:To take the input and output of Wulongkou sewage treatment plant in Zhengzhou city as the research subjects, evaluate the effect of the secondary and tertiary treatment processes, and discuss the health risk to the human body arised by the recycled water for landscape water. Through the comprehensive toxicity test, to evaluate the safety of their water quality and express the health hazards caused by water pollution qualitatively and quantitatively.Methods:(1) The distributed rule of chemistry organic matter and heavy metals in secondary and tertiary processed water of the sewage treatment plant were detected. The chemistry organic matter and the heavy metal density, the elimination rate and the water quality guarantee rate of the two kind of processing craft water leakage were compared and analyzed when they were reused for landscape water.(2) Taking heavy metal copper (Cu), cadmium (Cd), lead (Pb), zinc (Zn) as examples, the risk assessment by the carcinogenic and non-carcinogenic health risks on the human body was carried out when secondary and tertiary processed water were reused for landscape water.(3) The comprehensive toxic tests of the inlet and outlet water were carried on. Acute toxicity was detected by luminescent bacteria toxicity test, hereditary toxicity was detected by micronucleus test inVicia faba root tips and comet assay of human blood lymphocytes.(4) Using statistical software SPSS 12.0, statistical analysis referred to Bonfferoni test for multiple comparisons when significant difference were detected by one-way analysis of variance (ANOVA). A difference at P<0.05 was considered statistically significant.Results:(1) The concentration of all pollutants in inlet, secondary and tertiary processed water were analyzed with non-parametric hypothesis testing method and it was found that they fit with lognormal distribution.Using K-S test to do the numerical test, the lognormal distribution was used as the statistical model for the calculation of the guaranteed rate and health risk assessment.(2) The concentration of all pollutants in inlet, secondary and tertiary processed water are significantly different (P<0.05); on the basis of secondary processed water, the elimination rate of ammonia nitrogen (NH3-N) and TP in tertiary processed water is higher; when secondary and tertiary processed water were reused for landscape water, the concentration of NH3-N, TP, TN, Cd in secondary processed was too high to meet the quality for reuse. In tertiary processed water the guarantee rate of TP was significantly increased and other indicators were improved.(3) When secondary and tertiary processed water were reused for landscape water, the carcinogenic annual risk was in the range of 10-8/a to 10-8/a, and less than the acceptable risk level 5×10-5/a which was recommended by International Commission on Radiological Protection (ICRP). The human health hazard risks of non-carcinogenic chemicals was distributed in the range of 10-10/a to 10-13/a which is much lower than the internationally recognized acceptable risk level 10-6/a.(4) Toxicity results:the inhibition rates of luminescent bacteria, micronucleus frequencies of Vicia faba root tip cell,and human blood lymphocytes'comet tail length and tailing rate of the secondary and tertiary processed water were significantly lower than the inlet water (F=12.159, P=0.008;F=56.850,P=0.001; F=18.165, P=0.001; F=167.635,P=0.001). The tailing rate of the tertiary processed water were significantly lower than the secondary processed water(P<0.05).Conclusions:(1) When urban sewage undergoes the secondary biological treatment, the pollution levels decrease significantly; sewage advanced treatment technology plays an important role in urban wastewater reuse, and it is an effective means to protect the quality of reclaimed water achieves the standard.(2) When reclaimed water was reused for landscape water, the carcinogenic and non-carcinogenic health risks on the human body is low and negligible.(3) The toxicity of the treated water decreased significantly, but it still has a certain ecological risks to the environment, and the toxicity evaluation of reclaimed water is essential. |
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