| The wastewater that the water treatment plants drain off directly not onlyseriously pollute the water environment, but also waste a great deal of water. Therefore,it has aroused wide public concern how to treat the wastewater discharged out of thewater treatment plants effectively and reuse it. Because the wastewater includes plentyof pollutants coming from the raw water and chemical agents added into the watertreatment process, part of water quality indexes’ values are scores or hundreds of timeshigh than those of the raw water and there maybe exist some risk in the reuse ofwastewater after treatment. As a result, it has profound significance to analyze andevaluate the safety of the reusing wastewater in the water treatment plants and thencontrol the pollutants.In the paper, the relative water quality indexes of turbidity, ammonia nitrogen,permanganate index, aluminium and acrylamide in the produced water were testedafter the reuse of the treated wastewater in two surface water treatment plants of acertain city in northwest China. Based on it, the security probability and health riskvalue of the produced water quality were analyzed and evaluated. What’s more, inview of the water quality indexes which had high security probability values, they wereoptimized and controlled using model experiments, in order to provide the technicalbases for practical production. The main research results and conclusions are asfollows:（1） In both water treatment plant A and B, the relative water quality indexes in theproduced water after the reuse of the treated wastewater were under long-term test. Theresults showed that the contents of turbidity, ammonia nitrogen, permanganate indexand aluminium in the produced water of the two water treatment plants could meet theStandards for Drinking Water Quality. However, acrylamide in the produced wateroccasionally exceeded the Standards for Drinking Water Quality. In August and October,2010, acrylamide in the produced water of water treatment plant A exceededthe Standards for Drinking Water Quality by3.85%and12%, repectively, which ofwater treatment plant B was beyond the Standards for Drinking Water Quality by14%.（2） On the basis of long-term test on the produced water quality, using Q-Qfigures and K-S non-reference test method, the distribution functions of each producedwater quality were determined. According to the distribution functions, the securityprobabilities of each produced water quality were analyzed. The results showed thatthe turbidity, permanganate index, aluminium and acrylamide of the produced water inboth water treatment plant A and B obeyed logarithmic normal distribution after test. Inwater treatment plant A, the security probabilities of turbidity, permanganate index andaluminium in the produced water were all100%, while the security probabilityacrylamide was only94.44%. In water treatment plant B, the security probability ofturbidity in the produced water was100%, while permanganate index, aluminium andacrylamide were99.33%,93.50%and96.36%, repectively.（3） Using the Health Risk Assessment Four-step Method promulgated by NationalAcademy of Sciences, the low security probabilities of aluminium and acrylamide inthe produced water of both water treatment plant A and B were under health riskassessment. The results showed that the maximum personal lifetime health and safetyrisk values of aluminium in both water treatment plant A and B were6.69×10-6and2.90×10-5, repectively, which were all under the maximum lifetime acceptable riskvalue of7.0×10-5. However, there were11.05%of risk value and the maximumlifetime acceptable risk value at the same order of magnitude in water treatment plantB. At present, the content of aluminium in the produced water of both water treatmentplant A and B had no effect on public health, but it had been paid enough attention inwater treatment plant B. The maximum personal lifetime health and safety risk valuesof acrylamide in both water treatment plant A and B were1.84×10-4and1.32×10-4,repectively,4.48%and2.29%of risk value were beyond the maximum lifetimeacceptable risk value of7.0×10-5, respectively. Therefore, acrylamide had higher riskand control measures must be adopted immediately to prevent the risk.（4） On the overstandard of acrylamide in the reused wastewater and its existinghealth risk problem, a series of relative studies on the optimization and control of PAMwere carried out, using sludge dewatering performance Simulation Experiment, tomake the sludge dewater effectively and minimize the reuse risk. The results showedthat to different concentrations of concentrated sludge, PAM added of both anion andcation could reduce sludge specific resistance and improve the sludge dewatering performance. However, the residual acrylamide in the sludge dewatering separatedwater was lower when anion PAM was used. To meet the purposes of sludgedewatering performance, and make low turbidity and residual acrylamide in the sludgedewatering separated water, anion PAM is a better choice. The optimum PAM dosageswere0.16g/L0.25g/L for water plant A and0.09g/L0.16g/L for water plant B, underwhich the residual acrylamide concentration in the produced water of two watertreatment plants was under0.125μg/L throughout the year and the overstandard risk ofacrylamide concentration in the produced water was decreased effectively. |
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