Study On Reuse Of Treated Water From Municipal Wastewater Treatment Plant In Scenery Water

Reclaimed water, as the second water resource of a city, is used in people’s daily lifeincreasingly. One of the most important ways for reclaimed water being used is that to beused in the scenery water. However, there are a lot of problems that should be researched inscientific ways when it is being used in the scenery water, especially the ecological securityproblem which has become a hot issue. From the perspective of the application that thesecondary effluent and the deep treatement effluent from wastewater treatment plant(WWTP)being used to the scenic water body, this paper studied the variation of water quality ofsecondary effluent and deep treatement effluent that being recycled in the model test systemwhich to simulate the water in the scenic water boby, meanwhile using the method ofcomprehensive pollution index and lake eutrophication assessment to evaluate the scenerywater from treated water of WWTP in the test system, then combined with the comprehensivetoxicity test to study the ecological toxicity effect of treated water used for landscape waterbody. The research results showed that:（1） When the treated water from WWTP being used to scenic water body, thechange rules of water quality are different in different hydraulic retention time.Under thesimilar condition, the secondary effluent system with sand in it can let Total nitrogenconcentration of the system outlet decreased by22.81%.The test with sand in it can alsoreduce the concentration of TP, PO43--P and COD. The concentration of TN would beeffected by temperature, low temperature can restrain the growth of algae while thetemperature can accelerate the growth of algae at most of the time.（2） Concentration of Total nitrogen in summer is lower than that in autumn andwinter which was contained in the secondary treated effluent and deep treatement effluentfrom wastewater treatment plant. The variation of TN and NH4+-N concentration in the testsystem under different hydraulic retention time is small. In the secondary effluent and deeptreatement effluent from wastewater treatment plant, the form and content of phosphorusvaried with the season changing. The concentration of TP in winter was lower than that inspring, and the proportion of PO43--P content in winter was lower than that in spring.Change rules of TP and PO43--P content is different with different hydraulic retention timeof test system. （3） Total nitrogen was the main pollution factor in secondary effluent and deeptreatement effluent from wastewater treatment plants. When the hydraulic retention time is3days and5days, the number of fecal coliforms in test system can meet the standards, Whenthe hydraulic retention time is10days, the number of fecal coliforms in test system growsto24000per liter. Turbidity of system will not arouse people’s discomfort. Nutrient indexincluding NH4+-N and TP can meet standard requirements. There’s no organic pollutionmatter, DO and pH of system can meet the requirements of the standard.（4） Comprehensive pollution index evaluation and eutrophication evaluation resultsshowed that the water quality was optimized in the test system when the hydraulic retentiontime is3days and5days, in autumn, when the hydraulic retention time is10days, the waterquality didn’t occur deterioration in secondary effluent system and deep treatment effluentsystem, while in summer, the water quality occured deterioration, when hydraulic retentiontime is28days, in winter, water quality didn’t occur deterioration in testsystem,eutrophication status of system are greatly influenced by the incoming water,eutrophication status of advanced treatment water is moderate. The pollution level of systemcan be optimized when we added quartz sand. In winter, when the tempreture is low, thepollution level of system is better than that in spring.（5） After advanced treatment, Cytotoxicity of secondary effluent can be reduced by24.3%, During NaClO disinfection process, disinfection by-products such as THMS withbiological toxic produced, which can cause the luminescent bacteria inhibition. Thegenotoxicity of deep treatment effluent system is more remarkable than that in secondaryeffluent. TII50decreased by61.16%,66.53%and60.54%when the dosage of ferrictrichloride(FeCl3) respectively are5mg/L,10mg/L,20mg/L, and when the dosage offerric trichloride(FeCl3) was10mg/L, the cytotoxicity of test system water is minimized,FeCl3has inhibition on luminescent bacteria. With FeCl3flocculation precipitation,genetotoxicity effect is more significant than that in Secondary effluent.With the increase ofFeCl3dosing, the genotoxicity of secondary effluent was more significant than that insecondary effluent.（6） The results of freshwater photobacterium comprehensive toxicity evaluation forsecondary effluent and deep treatment effluent was low toxic and nontoxic respectively, andthe cytotoxicity of secondary effluent decreased by FeCl3flocculation precipitation. When theconcentrated time is20, the evaluation result of secondary effluent was high toxic, while theevaluation result of deep treatment effluent was poisoning. When the concentrated time is100, the evaluation result of both secondary effluent and deep treatment effluent was high toxic.The results of pollution index value of PI on secondary effluent and deep treatment effluentwas no pollution and light pollution. The value of PI increased with FeCl3dosing quantityincreased, the inhibition effect of cell mitosis was weakened when the secondary effluentwith advanced treatment, and also the inhibition effect of cell mitosis was weakened when thesecondary effluent was flocculated by FeCl3.