The Comparative Study Of The Sewage Recycle Treatment Process Based On Zebrafish Toxic Effects

On the water safety issues of the recycling process, this paper applied zebrafish embryos as a model organism for biological testing materialson and zebrafish embryos exposing biological toxicity testing and detection technology, to study the difference between two typical sewage treatment process which are Activated Sludge at high load (A) and modified Anaerobic-Anoxic-Oxic process(B) from the sewage treatment plant from a coastal city in the south of China. Then provided experimental evidence to the optimization of the sewage treatment process and reduced the ecological risks of reclaimed water.The major results and conclusions are summarized below:(1)The effluent from the sewage treatment plant which was disinfected by sodium hypochlorite had a significant lethal toxic effects on zebrafish embryos, also made zebrafish embryos produced semi-lethal toxic effects in different toxicological endpoints, such as pigmentation reduction, delay hatching, heart rate decrease, abnormal yolk sac and capuchin.The result showed that, the biological detection methods applied in this study had a high sensitivity, so established a evaluation system of recycled water ecological risk through the recycled water after disinfection by sodium hypochlorite exposure and the toxicity of zebrafish embryos.Using the toxicity of zebrafish embryos to study the difference in sewage treatment process was more simple, fast, direct, and reliable than chemical analysis methods by large instruments.(2)The research applied the Ecological Risk Assessment Index of recycled water by toxicity of zebrafish embryos, compared two typical craft section of A and B, studied the toxic effects and differences of the disinfectant water (into the pool, aerobic aeration tank, and secondary sedimentation tank). The results showed that, both aeration-disinfectant had a higher lethal toxicity on zebrafish embryos than influent-disinfection, B aeration process-disinfectant had a significantly72h lethal toxicity on zebrafish embryos, and higher than A aeration-disinfectant. The two typical process of sewage treatment effluent after disinfection both made the zebrafish embryos with varying degrees of semi-lethal toxic effects:heart rate decreased, pigmentation reduction, abnormal yolk sac, capuchin and hatching delay. A process aeration tank segment made zebrafish embryos larger for pigmentation reduction, B craft segment aeration tank made zebrafish embryos larger for hatching and heart rate, both sewage treatment process of capuchin toxicity effect reduced. Overall, B craft segment aeration tank is higher than A in lethal toxic effects and semi-lethal toxic effects.(3)To further research the reasons that A, B two typical sewage treatment process had different toxic effects on zebrafish embryos, comparated the zebrafish embryo toxicity differences between the two typical sewage treatment process water which disinfected by sodium hypochlorite. The results showed that, the aeration process of A had brought greater lethal toxicity, then the lethal toxicity decreased after the secondary settling tank. The lethal toxicity differences in each unit of B process was more obvious, and A2/O process water samples had higher varying degrees segment lethal toxic effects on zebrafish embryo, modified Anaerobic-Anoxic-Oxic process all increased the lethal toxic effects to zebrafish embryo. In the process of A, zebrafish embryos showed for different lethal toxicity effect, both yolk sac abnormality rate and pigmentation reduction increased step by step, then the toxicity decreased after the secondary settling tank. In A2/O process of B, zebrafish embryos appeared significant toxic effects which was capuchin, pigmentation reduction, heart rate decreased, pigmentation reduction and other toxic effects, reducing the secondary clarifier section at varying degrees of toxicity, then the toxicity decreased after the secondary settling tank in different degrees. The process of aerobic tank and ultraviolet disinfection tank had higher hatching toxic effects on zebrafish embryos.The lethal toxic and semi-lethal toxic effects showed that,the sewage treatment process water in each tank had a greater lethal effects on zebrafish embryos. Different treatment process could lead different semi-lethal toxicity on zebrafish embryos. The complex biochemical processes of sewage treatment brought higher lethal toxicity after disinfection.(4) In order to research the reasons that A, B two typical sewage treatment process had different toxic effects on zebrafish embryos, Studied the relationship between humic acid regularity in the process of sewage treatment and the lethal toxicity on zebrafish embryos. The results showed that, the lethal toxicity on zebrafish embryos was consistent with the various of humic acid in the sewage treatment process. Experimental results showed that, the sewage treatment process was more complex, the higher of the dissolved humic acid generated by microbes, and the lethal toxic effects on zebrafish embryo was higher, it showed that the relationship between microbial biochemical processes and zebrafish toxic effects was close.