Mechanism Of Pyridine Removal By Manganese Ions In SBR Process By Coercive Activated Sludge

The Sequencing Batch Reactor Activated Sludge Process（SBR）has received increasing attention for its advantages of small footprint and high pollutant removal efficiency.Furthermore,the dense and stratified structure of granular sludge allows it to tolerate extreme environmental conditions and toxic compounds,which are limited by the diffusion of substrates.In addition to macronutrients such as potassium and calcium,trace amounts of heavy metals are essential for the life activities of microorganisms.Differences in the composition of the wastewater affect the formation of sludge particles in SBR,and the secretion of Extracellular Polymeric Substances（EPS）,functional enzymes,and other related substances are altered,thus changing the particle characteristics and effluent quality.Among all heavy metals,Mn²⁺is one of the most common ones,and its effect on activated sludge is mainly because Mn²⁺is a component of many enzymes and activators of microorganisms,and a moderate concentration of manganese ions can improve the activity of activated sludge.Highly active sludge has a strong ability to remove organic pollutants from water bodies and slow down the pressure of organic pollutants on the environment.Therefore,this study aimed to investigate the effect of Mn-stressed activated sludge on the removal of heterocyclic aromatic hydrocarbon pollutants in the SBR process.Pyridine is a common ammonia-containing heterocyclic aromatic compound in industrial wastewater and therefore is used as a representative heterocyclic aromatic compound.In this paper,the effect of Mn²⁺on the microscopic morphological structure of activated sludge,sludge activity and the removal efficiency of pyridine by activated sludge after Mn²⁺stress was systematically described by combining scanning electron microscopy（SEM）,Fourier infrared spectroscopy（FTIR）and X-ray diffractometer（XRD）,and the degradation mechanism of pyridine by activated sludge after Mn stress was explored.The results of the study showed that.The positive effect on COD,TN,NH₃-N and TP was observed when the Mn²⁺concentration was from 0 to 5 mg/L;the opposite was true for 7-10 mg/L Mn²⁺;when the Mn²⁺concentration was>5 mg/L,the removal efficiency of TN,NH₃-N and TP all decreased gradually,and when at day 16,the removal efficiency of TN and NH3-N reached the lowest,44.77%and 51.79%,respectively.The changes in particle size during Mn²⁺stress-activated sludge were small,and the particle sizes were uniformly distributed,all above 1μm.the proportion of<10μm decreased and the proportion of100～1000μm increased with the prolongation of the stress time during Mn²⁺stress.The SEM-EDS analysis showed that the most elements present in the activated sludge were C and O.The quantitative analysis of Mn ions on the surface of the activated sludge before and after 18 days of Mn stress showed that the percentages of C and O atoms decreased from 58.25%and 30.20%to 53.50%and 21.46%,respectively,indicating a decrease in the number of bacteria in the activated sludge;while the Mn element increased from the original 0.19%to 0.63%.FTIR analysis of the functional groups of activated sludge at days 0,10 and 18 showed that the main functional groups were N-H,O-H,-CH₂,C=O,C-N,C-O and C-OH;the activated sludge had the same functional groups during Mn stress,indicating that Mn stress did not change the type of activated sludge functional groups.The removal rate of pyridine after Mn-stressed activated sludge was much higher than that of the activated sludge without Mn stress.When the pyridine concentration was 1 mg/L,the removal rates of pyridine by the activated sludge with/without Mn stress were 40.07%and 33.68%,respectively;when the pyridine concentration was increased to 2 mg/L,the removal rates were 84.82%and 13.74%,respectively;at 5mg/L the removal rate of pyridine by the activated sludge with Mn stress reached96.23%,but the removal rate without Mn was only 18.83%.With the increase of pyridine concentration,the removal capacity of Mn-free stressed activated sludge for pyridine was gradually decreased to the extent that only 10.79%was achieved when the pyridine concentration was 10 mg/L.When the activated sludge degraded 5 mg/L pyridine after Mn stress,the phenomenon of sludge death occurred,mainly because the increase of protein enhanced the extracellular adsorption of pyridine by the activated sludge,resulting in a large amount of pyridine being adsorbed on the bacterial surface leading to a large number of deaths of activated sludge.the black foreign matter that appeared in the bottom of the SBR reactor was analyzed by XRD and known to be a mixture of Si O₂and Mg H₂P₂O₇.The main method of pyridine removal by activated sludge was extracellular adsorption,but some of the pyridines were degraded to CO₂,H₂O and NH₃by the microorganisms in the system,and pyridine was degraded by pyridine ring opening,C-N bond breaking,-OH substitution and hydrogenation,etc.The intermediate products detected were glutaraldehyde,glutaric acid,2,3-dihydro-pyridine,2,4-dihydroxy-2H-pyridin-3-one,1-pyridine-3-one,and 1-pyridine-3-one.pyridin-3-one,1-amino-2-hydroxy-1-6-hexanedioic acid and succinic acid were detected.High-throughput sequencing results showed that the abundance and species diversity of microbial communities changed after Mn stress and pyridine removal.The highest phylum of microorganisms in all samples was Proteobacteria and Bacteroidota;the abundance of Proteobacteria decreased gradually after Mn stress and pyridine removal,50.3%,42.0%and 33.6%,respectively;the percentage of Bacteroidota increased relatively,25.3%,30.8%and 37.6%,respectively.and 37.6%,respectively.At the level of microbial genera,the relative abundance of Ellin6067,Candidatus＿Competibacter and Ferruginibacter,the dominant genera enriched in the SBR system,gradually decreased,while the proportion of NS9＿marine＿group and Terrimonas increased.