| Pharmaceutical wastewater is a type of organic wastewater which contains high concentration of pollutants.They often contain bio-inhibitory and biological toxic substances which make them highly toxic and refractory for treatments.Some wastewaters can possess as high chemical oxygen demand(COD)concentration as tens of thousands mg/L,which is generally higher than the bio-inhibitory concentration for biochemical process and have difficult for using direct biochemical treatment.Current industrial wastewater treatment processes in China generally collect the pharmaceutical wastewaters into a unified collection tank.During this process,rainwater,cooling water and river water are often mixed into the unified wastewater and the concentration of pollutants can below the bio-synthesis inhibitory concentration.By using simple wastewater treatment facilities,the effluent can achieve the standard for centralized wastewater treatment plants.Those processes increased the release of pollutants,so that the pressure of removing these pollutants was transmitted to the centralized wastewater treatment plants.In current days,lots of centralized wastewater treatment plants were over loaded with large amount of industrial wastewater influent,which may lead to emission of large amount of pollutants into aquatic system.Consequently,current pharmaceutical wastewater treatment processes not only cause an increase in the total amount of released pollutant but also greatly increase the cost for wastewater treatments.Both industrial plants and environment regulatory departments have responsibility to reduce emission volume and increase efficiency of treatment for pharmaceutical wastewater.In order to solve problems discussed above,present study investigated the efficiency of MBR(membrane bioreactor)+ UV/O3 processes for the treatment of pharmaceutical wastewater.The effluent was reused as water sources for the followed biochemistry treatment.Typically,the performance of MBR system for the treatment of pharmaceutical wastewater was systematically investigated and the efficiency of combined UV/O3 process for removing pollutants in tail-water from MBR treatment.Finally,the economic analysis of MBR-UV/O3 system was performed.1.Treatment of Pharmaceutical Wastewater use MBRPharmaceutical wastewater was treated using membrane bioreactor process(MBR)for biochemical treatment.The removal of organic pollutants in MBR system under different dilution rates at the same sludge volume load(1.1kg COD/m3)was investigated.The change of sludge volume index(SVI)and MBR trans-membrane pressure(TMP)were also studied.The results showed that COD concentration over 11000mg/L will significantly inhibit removal rate of MBR system where the sludge sedimentation became worse under this condition and lead to a rapid rise in trans-membrane pressure.When COD concentration in influent was reduced to 5500mg/L,the highest removal rate achieved and the sludge settling properties and trans-membrane pressure can be less affected.When the COD concentration of influent continuously to be reduced,COD removal rate of MBR system decreased slightly as the low-biodegradable pollutants were not completely degraded due to reduced hydraulic retention time(HRT).2.UV/O3 Combined Advance Treatment of MBR tail-waterEffluent from MBR system was further treated using UV,03 and UV/O3 combined process.The individual UV,O3 and UV/O3 process for COD removal rate of MBR tail-water were also conducted.Three factors including intensity of UV irradiation,ozone flux rate and air flux rate that can affect UV/O3 combined process in MBR tail-water treatment were investigated for achieving optimal conditions.Biodegradability of UV/O3 combined process in treating MBR tail-water in different duration was investigated and the structures of pollutants before and after the treatment were analyzed by UV-vis spectrum and IR spectrum.The results showed:COD removal rate of UV/O3 combined process in treatment of MBR tail-water was higher than the sum of effects for single UV and O3 treatments.Some coordinate effect was found in UV and O3 processes during COD removal and the optimal process conditions were vacuum ultraviolet rays of 35w at a distance of 10cm from liquid surface,ozone flux at 20mg/min,air flux at 1L/min and treatment time at 60min.under optimal conditions,it is shown that 60min of UV/O3 treatment can remove 95%of UV-254 in MBR tail-water where halogenated hydrocarbons,benzene,toluene,ethyl-benzene,xylene(BTEX)are also mostly removed.In addition,pollutants such as phenols in tail-water were oxidized to small-molecular-weight organic acids and the BOD/COD of tail-water increased from 0.08 to 0.33.3.Reuse of UV/O3 combined process for treating MBR tail-waterUV/O3 combined process treated MBR tail-water was used as unification water source.The effect of reuse ratio(50%,60%and 75%)on the COD removal rate of MBR treatment system was investigated.The obstacle which restricted the improvement in reuse ratio was studied and then the economical analysis of wastewater treatment before and after reuse was accomplished.The results showed that:COD removal efficiency of MBR system can achieve 94%at reuse ratio of 50%.When the reuse ratio increased to 60%,COD removal rate of MBR system was not significantly decreased and the quality of discharge water can be stabilized below third discharge standard at BOD/COD of 0.31.This was benefit for the treatment of secondary wastewater treatment plant.At reuse ratio of 75%,COD removal efficiency of MBR system dropped to 82%.The following studies showed that salt concentration in wastewater was the limit for continuously increasing the reuse proportion of MBR tail-water.When desalt MBR tail-water using 20g/L of mixed anion and cation exchange resins,removal rate of MBR system increased to 93%and COD emission can be reduced up to 79.4%.Economic analysis showed that,the cost of MBR-UV/O3 combined processes on pharmaceutical wastewater treatment was 25.072 Yuan per ton.However,due to decreased costs for using city water and wastewater discharge,the total cost for the combined process was 41.72%lower than the previous process. |
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