| Enhanced biological phosphorus removal?EBPR?process has gradually become a hot spot in the treatment of phosphorus pollution and overcoming eutrophication with the advantages of low energy consumption,low cost,less pollution and higher efficiency.However,the traditional EBPR process has many disadvantages such as easy expansion of sludge and poor stability of phosphorus removal.The competition between phosphate accumulating organisms?PAOs?and glycogen accumulating organisms?GAOs?is considered to be an important reason for the decrease of phosphorus removal efficiency.EBPR is achieved by controlling the excessive absorption and release of phosphate by activated sludge in the process of anaerobic and aerobic alternation.Based on the theory of nonequilibrium growth,the dominant colony with the ability of rapid storing and consuming the substrates has a competitive advantage by strengthening the non-equilibrium conditions on the microorganism.Thus,it is beneficial to screen of phosphorus microorganism,and to achieve the purpose of high efficiency biological phosphorus removal.The sludge shift SBR process combines the continuous operating biological selector with the intermittent running SBR to create the substrat concentration gradient non-equilibrium conditions in space and time,and the activated sludge is circulated dynamically in parallel SBR by reflux mode.Continuous dynamic screening of phosphorus accumulating microorganisms was achieved by substrate concentration gradient.In this thesis,sludge-shifting sequencing batch reactor process was used to study the effect of sludge shift on the process performance,to obtain the phosphorus removal approach of the sludge shift process,to investigate the effects of different process conditions on the synthesis and transformation of the storage materials in the cells of phosphorus accumulation microorganism,and to study the effect of extracellular polymeric substance?EPS?on phosphorus removal.Meanwhile,the molecular biological technique was used to study the distribution of microorganism?PAOs and GAOs?and its response mechanism to phosphorus removal.The mechanism of screening and enrichment of PAOs is elucidated to provide ideas and methods for improving the phosphorus removal performance of the existing EPBR process.The main results are as follows:?1?Sludge shift can increase the total amount of activated sludge in the SBR and improve the settling performance of the sludge,besides,it can enhance the water filling ratio and processing capacity of SBR process.With the sludge shifting ratios?R?of 30%,the total amount of sludge in the sludge-shifting sequencing batch reactor was 24.46%higher than that in the traditional SBR process.The average sludge sedimentation index were 208,96 and 94respectively,with the R values of 0,15,30 and 40%.The water filling ratio of the system was39%,45%and 56%respectively,which increased by 30%,50%,and 86%respectively than the traditional SBR process.?2?Sludge shift significantly enhanced the phosphorus removal performance of the traditional SBR process,and the amount of sludge shift significantly affected the phosphorus release in the anaerobic stage.With the R value of 0/15/30/40%,the average removal rates of Tatal Phosphorus?TP?were 48%,81%,92%and 91%respectively.With the R value of 30%,the performance of phosphorus release was the best,and the highest PHB content reached 24.3%of the dry weight of the cell.The anaerobic phosphorus release rate in the selector showed a good positive correlation with the change of the PHB content in the sludge.The results of static phosphorus release experiment showed that,under the condition of 0/15/30/40%sludge shifting ratios,the anaerobic phosphorus were 17.82mg/L,29.85mg/L and 30.35mg/L respectively and the rates of which were 7.00,11.17 and 8.83mgTP/?gMLSS·h?,respectively.The traditional PAOs phosphorus removal mechanism plays a major role in the system,and it existsa denitrifying phosphorus removal process.Under the 30%sludge shifting ratios,the phosphorus removal amount of traditional PAO metabolic mode accounted for 76.81%,the assimilation phosphorus removal rate was 15.43%,and the denitrifying phosphorus removal amount accounted for 7.76%.?3?Sludge shift enhanced the synthesis of PHB and glycogen in EPS and significantly promoted the synthesis of PHB in the anaerobic phase,but the increase of the synthesis of PHB was not obvious under the amount of 40%sludge shifting ratios,however,the synthesis of glycogen showed a significant increase.Under the condition of 30%sludge shifting ratios,the efficiency of phosphorus removal increased from 20%to more than 85%in the early period of acclimatization,though the poly-phosphate in the EPS didn't change obviously,which indicates that the metabolic pathways of the system are not completely consistent with that of traditional EBPR process.?4?The results of FISH and PCR-DGGE showed that with the increase of sludge shifting ratios,the relative number of microbial populations decreased,and the main bacterial colony changed significantly.The sludge shift enhanced the screening and enrichment of PAOs,and inhibited the growth of the GAOs,and the reduction rates of that were 4%,2.8%,5.6%,5.3%respectively,under the condition of 0/15/30/40%sludge shifting ratios.Besides,the sample similarity coefficient under that condition was 54.7%,51.9%,36.8%and 48.4%respectively.Meanwhile the content of PAOs was 35%,42%,46%,45%,respectively.According to the sequencing,the Pseudomonas was the dominant colony of PAOs,while the ciliated genus Leptothrix?a kind of filamentous bacteria?and Sphingomonas?GAOs?were inhibited.?5?Sludge shifting ratios significantly enhanced the ability of the activated sludge to accumulate phosphorus in the system.Under anaerobic conditions,EPS rapidly absorbed the substrates,which effected the phosphorus removal significantly.The concentration of total phosphorus in the sludge at the end of the aerobic stage reached 13.30mg/?g MLSS?and37.71mg/?g MLSS?in the SBR and SS SBR?Under 30%conditions of sludge shift?respectively,which indicates that so that the content of phosphorus in the sludge in SS SBR process is nearly 3 times more than that in traditional SBR process.Phosphorus release and phosphorus uptake in SS SBR process are mainly performed by EPS.The phosphorus content in the EPS at the end of aerobic stage accounts for 63.88%of that in total sludge(TPEPS/TP Sludge),and the rate of phosphorus release is faster.By using activated sludge alternately under high and low substrates load,EPS is used as a carrier to achieve rapid absorption and release of phosphate,which has great application potential for the recovery of phosphorus resources in future urban sewage plant.?6?The application studies of SS SBR process in urban sewage projects show that sludge shift enhances the nitrogen and phosphorus removal performance.The amount of sludge shift has a significant effect on the removal efficiency of the pollutants.When the sludge s hifting ratios reaches to 30%,the average removal efficiency of total nitrogen and phosphorus removal increased from 45%to 46%,65%and 85%respectively,and the concentration of effluent COD,ammonia,TN,and TP reached GB18918-2002 level A standard.Compared with the traditional SBR process,the treatment capacity can be increased by nearly 50%under the condition of 30%sludge shifting ratios. |
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