| With the rapid development of nanotechnology, nanometer ZnO made by mineral materials is widely used in many fileds for its nano feature. A large of industrial products and daily necessities which contain nanometer ZnO with industrial wastewater and sewage will discharge into the sewage treatment plant, This will inevitably cause serious impact to the original wastewater biological treatment system.The experiments conducted in Integrated side-ditch OCO process and optimized the process under optimum conditions. The effects of different dosages of ZnO NPs on biological nitrogen, phosphorus removal and activitied sludge were studied. It is do good to establish and improve the provide a reference basis of nanometer oxide emissions limits; also provide a reference for perfecting the biological toxicity of nanometer ZnO data.1. The integrated side-ditch OCO process operation key parameters: dissolved oxygen(DO)、 hydraulic retention time(HRT) and pH were optimized and compared and integrated denitrification and phosphorous removal efficiency of the process.Then established the optimums conditions. The optimal operating parameters were listed as follows: Controlling other factors unchanged, control pH about 7.6~8.0, HRT was keep about 12 h(influent flow rate of 20 L/h), DO concentration in aerobic maintained about 2.0 mg/L, The Integrated side-ditch OCO process achieved the optimal effect on wastewater reatment: the removal rate of effluent COD, TP, NH4+-N and TN were 99%, 95%, 99% and 81%, respectively.2. Under the optimum process conditions,experiment was carried out by t aking 0 mg/L、0.25 mg/L、0.8 mg/L、1.5 mg/L、4.0 mg/L of nano-ZnO to th e activated sludge respectively. In each group concentration within 20 days, the influence of nitrogen and phosphorus was examined under different concentrati ons of nanometer zno within the activated sludge. The adsorption of nanometer ZnO particles in activated sludge and the content of zinc in water is analyzed,to learn the inhibition mechanism of nanometer ZnO in the bacteria which ha s a important role in denitrification and phosphorus removel. Learned from theeffects of nitrogen and phosphorus, at low concentration of nanometer ZnO(0.25 mg/L, 0.8 mg/L), the denitrification and phosphorus removal efficiency is e nhanced or not be affected. But at high concentration(1.5 mg/L, 4.0 mg/L), th e efficiency of denitrification and phosphorus removal have been inhibitated. T his made the rate of nitrogen and phosphorus removal rate lower.The migration of nano ZnO when it be released into the sewage system, by monitoring the content of Zn in activated sludge and in effluent, the activated sludge can adsorb nano ZnO, The removal of nano ZnO by sludge activity and nano ZnO concentration. At low concentration, the activated sludge has a high activity, this make the removal rate of nano ZnO increase, at high concentration, the activated sludge has a low activity, this make the removal rate of nano ZnO decrease. The content Zn and nano ZnO effluent concentration was positively correlated with investment.3. Based on the study of exposing different concentrations of nanometer ZnO(0.25, 0.25, 0.8, 0.25 mg/L) to activated sludge, the influence of activated sludge on the subsidence property(SV), activated sludge biomass(MLVSS/MLSS), lactate dehydrogenase release quantity(LDH) and bacteria morphology were studied. By analysising the sludge settle ability, biomass and changes of biological toxicity. The low concentration of nanometer ZnO virtually no activity of activated sludge, the sludge settleability, biomass, lactate dehydrogenase release quantity were no indifference with the without adding ZnO. While adding the relatively high concentrations of nano ZnO(1.5, 4.0 mg/L), sludge settle ability, biomass were decreased, lactate dehydrogenase release was increased, the two concentrations have toxic effects on activated sludge. Under the electronic scanning electron microscope(SEM), the activated sludge shows that configuration of surface, from low concentration to high concentration of sludge surface feature clear gradually blurred,sludge is loose, and cotton wool shaped.4. Through the PCR-DGGE technique, the change of population of activated sludge was studied at different concentrations of nanometer ZnO(0.25, 0.8, 1.4, 0.25mg/L). The results showed that: at low concentrations of nano ZnO, nano ZnO had accelerated the growth of some resistant bacteria, such denitrifying bacteria; and at high concentrations, nanometer ZnO had accelerated the growth of some pathogenic bacteria, which accelerate the sludge aging death... |
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