| Thermal power plants consumes a large amount of water during production,which meanwhile produces a large amount of waste water awaiting for treatment.Thermal power plant,which is able to use reclaimed water,has been not allowed to increase water utilization capacity according to requirement of national environmental protection policies and regulations of China since 2015.Thus,thermal power plants have to compete with local facilities for freshwater resource.Increasing lacking of freshwater resource becomes the limiting factor for development of thermal power plants.Therefore,to solving this water limitation problem,it is urgent importance to develop intensive treatment technology for municipal tailwater,and optimize water utilizing strategy in thermal power plant.Ozone oxidation reaction can quickly destroy the structure of macromolecular organic pollutants,which transform refractory organic matter into biochemical small molecular substances.A fresh oxygen atom is produced during ozone oxidation,which benefit to the subsequently aerobic biology treatment.Biological fixed bed has the advantages of high efficiency,stability,easy operation and automatic control.The microbial friendly oyster shell packed biological fixed bed can maximumly maintain biomass in the reactor during treatment of oligotrophic tail water,which ensures stable operation of biological treatment.MBR has a good interception effect on colloidal suspensions(SS,organic matters,microbes and so on.Therefore,this study develops a tail water intensive treatment technology with ozone-oyster shell biological fixed bed reactor-MBR?OOFBR-MBR?process.Tailwater after treatment can be used as industrial water in thermal power plant.With aspect of operational management,the water using strategy of thermal power plant is optimized,the standard for recycling water quality is established,and the model for water recycling is developed based on water mass balance.The main results of this study are listed as followed:Tail water of municipal wastewater treatment plant with discharge standard B was treated by OOFBR-MBR process.Influence of ozone dosage and hydraulic retention time on tailwater treatment was investigated.With the increase of ozone dosage,COD and TP removal efficiency of OOFBR and OOFBR-MBR show the trend of first increasing and then decreasing,the highest removal efficiency of COD achieves 66%and 83%in OOFBR and MBR,respectively.The highest removal efficiency of TP obtains 58%and 65%OOFBR and MBR,respectively.Removal efficiency of NH4--N keep increasing with increase of ozone dosage.With the increase of influent flow,removal efficiency of COD and TP first increase and then decrease.the Highest COD removal efficiency achieves 45%and 73%in OOFBR and OOFBR-MBR,respectively,while the highest TP removal efficiency of obtains 27%and 43%,respectively.However,NH4--N removal efficiency decreases rapidly in OOFBR,which remains an average removal rate of 92%in MBR.The optimized operation condition for OOFBR-MBR process are:ozone dosage 40?70 mg/L,influent flow 3?6L/h(?HRT 25?50h,volumetric load 0.0096?0.019kg COD/?m3·d??,maximum loading rate 0.0192 kg COD/?m3·d?.For tail water meets the first class standard B of pollutant discharge standard of municipal sewage treatment plant.Under the condition of 70mg/L ozone dosage and HRT of 25h?6L/h of influent flow?,the removal efficiencies of COD,NH4--N,TP and turbidity reach 66%,90%,45%and 68%in the OOFBR,respectively,which achieve 41%,87%,15%and 91%in the MBR,respectively.Thus,a total removal efficiencies of COD,NH4--N,TP and turbidity obtain up to 81%,99%,65%and 97%by OOFBR-MBR processes,respectively.p H of MBR effluent is 7.47?7.85,turbidity<0.2 NTU,COD<9 mg/L,NH4--N and TP<0.3 mg/L,which meets the influent water quality required by RO system.Effluent of RO is further used as refilling water for thermal power plant boiler.The results of gas chromatography-mass spectrometry?GC-MS?analysis and nitrogen mass balance indicate high conversion efficiency for carbon,nitrogen and phosphorus in OOFBR-MBR system.Refractory organic matter in the OOFBR is first oxidized by ozone to biodegradable small molecule organic matters,which is further degraded by microorganism on the oyster shell,the residual NH4--N and COD can be further removed in MBR,which intercepts the residual organic matter and colloidal suspension?SS?effectively.Most ammonia?about 90%?were converted to nitrite by aerobic ammonia-oxidizing bacteria in the OOFBR,which were further oxidized to nitrate nitrogen nitrite-oxidizing bacteria.Nitrate is partially?about 15%?reduced to nitrogen gas in OOFBR-MBR through denitrification.TP is enriched by phosphorus accumulating organisms?PAOs?in aerobic sludge,which can be removed through sludge discharging.High-throughput sequencing is used to analyze the microbial community structure characteristics in the OOFBR-MBR based on 16S r RNA gene.The abundance of microflora in sludge of OOFBR and MBR changed significantly before and after addition of ozone.Bacteria community in OOFBR reserved 29.2%of OTU?operation taxonomy units?in inoculum sludge,reduction of total OTU achieves28.5%.Meanwhile,31.3%of OTU retains in MBR after ozone addition,but total OTU maintains stable.These results demonstrate ozone has obvious selective influence on microorganisms in OOFBR-MBR,and the membrane has strongly interceptive effect on microorganisms.Deinococcu-Thermus and Planctomyctes increases significantly in OOFBR,there are 9 species of high abundant bacteria which might play important role in organic pollutants removal.Firmicutes,Actinobacteria and Planctomyctes increased significantly in MBR after ozone addition.Nitrosospira is the mainly aerobic ammonia-oxidizing bacteria,Nitrospira and Nitrobacter is the main nitrite oxidizing bacteria,and the denitrifying bacterium are mainly comsist of Bradyrhizobium and Hyphomicrobium in the OOFBR-MBRFocusing on the residual refractory organic matter,ammonium and TP in wastewater,the optimal control strategies of OOFBR-MBR are as followed:When the influent COD,NH4--N and TP increase,the ozone dosage should be increased accordingly to enhance the conversion of refractory organic matter and increase dissolved oxygen concentration.Prolonging the contact time of microorganisms and wastewater by extending the HRT,which is beneficial to maintaining ozone-resistant microorganisms and biodegradation.When COD,NH4--N and TP in tail water decrease,the ozone dosage is reduced and the HRT is shortened accordingly,to ensure efficient removal of pollutants in OOFBR-MBR reactors.Because of water resources shortage and large water consumption in thermal power plants,the advanced treatment technology of tail water by OOFBR-MBR for recycling is recommended.Based on the characteristics of complex water flow and large difference in water quality requirements,an optimized water balance model is established by analyzing the capacity distribution,consumption and discharge in different section of thermal power plants.With aspect of operational strategy,a water distribution optimization scheme for multi-water sources and multi-users is formulated,and the operation and maintenance strategy of single water source for multi-using,gradient water using and recycling of water in thermal power plants is developed.Besides,technologies for minimizing water using are demonstrated,such as water use and wastewater discharging reduction,and classified treatment of salt-containing waste water for sub-quality reuse.Taking a power plant in Zhanjiang with capacity of 2×600 MW as an example,the tail water of the municipal wastewater treatment plant meets the requirements of industrial water quality,after advanced treatment by OOFBR-MBR system.The total water using capacity can be reduced from 6849 m3/d to 3560 m3/d,and the average water consumption for electricity generation can be reduced from 0.297 m3/?MW·h?to 0.143 m3/?MW·h?,and the terminal waste water discharge is 512 m3/d after applying the optimized water using technology strategy.Engineering investment is76.7261 million yuan,project income is 11.875 million yuan per year,investment payback period is 6.46a. |
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