Control Strategy Of Anammox Sludge Granulation And Apoptosis Characteristics Under Starvation Stress

Granular sludge process has significant advantages in biological aggregation,activity and pollutant removal rate,and is considered to be an effective means of preserving biomass.However,the cultivation of granular sludge involves the interaction of environment and microorganism,and the starvation stress represented by influent load impact,nutrient concentration reduction and space limitation is a major environmental factor.Therefore,the rapid formation of granular sludge and the maintenance of the stability of mature particles have been the focus of attention.In view of the granulation problem of sludge,the signal molecular hypothesis of rapid granulation based on quorum sensing(QS)effect believes that microorganisms communicate through signal molecules,regulate the expression of related genes through QS effect,promote the production of extracellular polymer substance(EPS),and play an important regulatory role in the formation of granular sludge.Intercellular signaling molecules are also involved in regulating the active apoptosis of the population in response to environmental changes.Therefore,programmed cell death(PCD)of the community under environmental stress has an important relationship with the granulation process dominated by quorum sensing.This study based on the QS effect and mechanism of cell apoptosis,starvation and granulation experiment were set up.The characteristics of sludge,EPS content and apoptosis distribution of cells were determined,which provided a new perspective for the culture mechanism of aerobic granular sludge(AGS)and Anammox granular sludge(An AGS)and the stability and optimization of denitrification process.At the same time,the QS mechanism conducive to sludge granulation was analysted.The main research achievements are as follows:(1)After flocculent sludge was inoculated in a sequencing batch reactor(SBR),An AGS reactor effluent was provided as signal molecule source.The nitrification reaction was successfully started within 15 days by increasing the influent ammonia concentration intermittently and providing high hydraulic shear force by the traditional methods of strong aeration and shortening precipitation time.Through the accumulation of signal molecules,the growth rate of mixed liquor suspended solids(MLSS)was significantly increased,the content of EPS was increased,and the polysaccharide/protein(PS/PN)ratio increased from 3.35 to 5.24.Finally,AGS with good performance and average particle size of 2.3mm was obtained.(2)Starvation conditions were used as environmental stressors to study the decay and cleavage of mature An AGS.Moreover,the effects of starvation on the cell apoptosis process of An AGS were studied by adding EPS as control.The results showed that the PN/PS ratio and mechanical strength of granular sludge decreased after 12 days of starvation treatment.The proportion of early apoptosis of cells in the system increased,and the fragmentation of An AGS and microbial activity were positively correlated with the distribution of PCD.After the addition of EPS,the proportion of normal cells in the system increased.Exogenous addition of EPS can alleviate the cracking degree of granular sludge and reduce the activity attenuation rate of Anammox bacteria,which is conducive to the recovery of Anammox system after starvation.(3)AGS,sludge fragments(removing the remaining part of EPS),EPS,and reactor supernatant were added as signal molecular stimulant(SMS)during Anammox flocculent sludge culture.The stimulation and induction effects of signal molecules in different parts of granular sludge on Anammox granulation were investigated to find out the relationship between cell apoptosis and Anammox granulation.The results showed that the average particle size of sludge increased 240%~340% within 37 days.The maximum size of An AGS was 768.296μm after AGS were added externally.The content of EPS increased significantly,and PN/PS reached the maximum 6.2.The denitrification performance of sludge in the system was excellent,and both Ammonium removal rate(ARR)and Nitrite removal rate(NRR)were significantly improved.After exogenous AGS reactor supernatant,the ARR and NRR of the system were significantly better than those of other groups,reaching 3.011 and 4.915,respectively.There were significant differences in the distribution of PCD during Anammox granulation,and apoptosis could be a new parameter to characterize sludge granulation.The signal molecules provided by supernatant had a smaller impact on the original system and the percentage of early apoptosis was the lowest.(4)QS effect is a complex process.In addition to the influence of cell density,QS-mediated signal transduction is also strongly influenced by environmental factors.Such as temperature,p H,substrate concentration,O2 and boundary environment.In addition,different substrates and extreme conditions such as high salt and high ammonia nitrogen load also had significant effects on QS behavior of communities.AHL-based QS and quorum quenching(QQ)can coexist in wastewater biological treatment system.Exogenous QQ signals could affect the diversity and community composition of in-situ QS and QQ bacteria.