| Hybrid biofilm treatment technology is one of the main technologies to reduce organic matter efficiently in wastewater biological treatment,with both advantages of biofilm and activated sludge.The start-up phase,biomass and physiological ecology characteristics have a huge impact on treatment efficiency.It usually takes a long time to form biofilm during set-up period.What's more,the biofilm is instability and easy to fall off,leading to shock load capacity of system decline.This phenomenon is especially significant at low temperature.When the temperature is lower than 15°C,pollutant removal efficiency is significantly decreased,especially between 8°C and 10°C.Water temperature in most of northern area drops sharply with a long duration in winter.Frozen period lasts 3~6 months.Winter temperature becomes a key factor if hybrid biofilm treatment technology can discharge reaching the standard.In reaction to a long time of start-up phase and biofilm easy to fall off,this study will analyze the role of quorum sensing(QS)on measured treatment system based on sequencing batch biofilm reactor(SBBR)and regulate the formation of biofilm artificially by QS.Moreover,this research tries to study the influence of QS on biofilm formation and on the biological phase of biofilm-sludge(short for two-phase microorganisms)in SBBR,leading to reveal how QS regulate bacterial physiological behavior and to obtain more stable technology in hybrid biofilm process.This work may offer a feasible approach to enhance hybrid biofilm reactor performance at low temperature.On the basis of optimizing the parameters and carriers of SBBR,variation characteristics of acyl-homoserine lactones(AHLs)and the effects of endogenous AHLs on two-phase microorganisms were analyzed in the process of biofilm formation at room temperature(22 ± 1°C)by statistical methods,in order to study the interaction mechanism of QS and biofilm formation,and the correlation of AHLs and community structure.The results showed that AHLs are closely related to the operating status of system,because the system came into stable phase accompanied by AHLs concentrations reaching peak value(98.02 ± 1.03 ng/L),along with biomass at maximum value(biofilm weight 964 ± 52 ?g/g carrier,sludge concentration 3 622 ± 153 mg/L).There was a linear correlation between AHLs concentrations and biofilm weight(R2 > 0.95).The regulatory AHLs were identified as C6-HSL?C8-HSL?3-oxo-C12-HSL and C14-HSL.The amount of extracellular polymeric substances(EPS)and proportion of each component of EPS were closed related to QS.There was a positive correlation between AHLs concentrations and EPS content in the activated phase of biofilm formation.Every component was index-related to AHLs concentrations,except loosely bound EPS(LB-EPS).Community structure changed along with the growth of biofilm.Dominant genera were closely related to AHLs concentrations in the different stages of biofilm formation.It was obvious that the role of adherent microorganisms for QS in the system is powerful.Based on the analysis of QS in SBBR,microbial physiological ecological changes were monitored by molecular biology methods,to investigate the effect of exogenous AHLs on pollutants removal and on the characteristics of two-phase microbes at room temperature(22 ± 1°C).Moreover,the changes of community structure and functional microorganisms were analyzed when different concentrations of AHLs were adding.The effect of adding exogenous AHLs on biofilm formation was investigated thoroughly.The results indicated that the response of the system to exogenous AHLs was not a signal concentration-dependent manner,exhibited high concentration-dependent inhibition effects instead.Introducing of low concentrations(5 nmol/L and 50 nmol/L)of AHLs significantly increased biological activity(> 20%)and biomass(> 11%),which resulted in better pollutant removal performance,whereas high concentrations of exogenous AHLs(500 nmol/L and 1 000 nmol/L)could limit pollutant removal and reduce microbial activity(> 22%)and biomass(> 10%)obviously.Total AHL level was also closely related to the productions of EPS and community structure.Low concentrations of AHLs decreased LB-EPS content,increased tightly bound EPS(TB-EPS)content,and enhanced relative growth of QS-related bacteria,whereas a contrary trend was observed for higher concentrations.Analyzing of nitrifying bacteria revealed that these additional signal molecules affect the ratio of nitrifying to total bacteria.An increase of nitrifying content was observed with the addition of low concentrations of AHLs;however,a decrease ratio was obtained with higher concentrations addition.Finally,the additive concentration(50 nmol/L)was determined for its best performance.We applied the above results to the start-up phase of SBBR at low temperature(11 ± 1°C,no more than 14°C)and proposed the method that adding exogenous AHLs artificially to promote the biofilm formation and maintain stability of the system,as well as to investigate the effect of exogenous AHLs on the pollutants removal efficiency of system.In addition,the changes of characteristics in biofilm and in activated sludge were analyzed in start-up phase at low temperature.We also studied the role of exogenous AHLs on community structure and functional bacteria in the system at low temperature.An increase in the activity of biofilm was observed,yielding a sustained increase of pollutant removal,finally resulting in shortening the start-up phase for 25%.When the load of the system suddenly increased,the addition of AHLs allowed the removal rate of the pollutant to return to normal within two weeks,suggesting the ability to withstand shock load was stronger.The increase in biology activity was significantly higher than biomass because when the activity of biofilm and sludge increased by 36% and 12%,the corresponding biomass increased only about 20% and 3%.The changes of EPS stimulating by AHLs promoted the microorganisms from suspended growth to attached growth,to obtain rapid formation of biofilm and better sludge settleability,resulting in improving the removal efficiency of system during start-up phase at low temperature(approximately 10%).Analysis of the bacterial community by high-throughput sequencing showed a decrease in species diversity and a marked increase in most of the AHL-related microbial community members.The abundance of QS-related bacteria in biofilm than that of in activated sludge,suggesting QS-related bacteria is more suitable to attached growth.Nitration process was more vulnerable to AHLs,thus the nitrifying bacteria abundance increased significantly after AHLs addition.This study may provide a new research approach for regulating nitrifying bacteria by QS. |
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