Effects Of Salinity And Heavy Metals On The Performance And Microbial Community Structure Of Sequencing Batch Bioreactor

The effects of salinity and heavy metals on the performace and microbialcommunity structure of sequencing batch reactor (SBR), sequencing batch biofilmreactor (SBBR) and granular sequencing batch biofilm reactor (GSBR) wereinvestigated.The average removal efficiencies of COD and NH4+-N decreased from98%to33%and from97%to30%in a SBR, respectively, with the increase of salinity from0.5%to6%. With the increase of salinity from0.5%to6%, the specific oxygenutilization rate (SOUR) increased at the beginning, and then it decreased. The specificammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specificnitrate reduction rate (SNRR) decreased77%,88%and58%, respectively, with theincrease of salinity from0.5%to6%. The protein (PN)/polysaccharide (PS) ratios inloosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) decreased from4.8to0.9and from2.9to1.4with the increase of salinity from0.5to6%, respectively. Thefour peaks identified by three-dimensional excitation-emission matrix (3D-EEM)fluorescence spectroscopy in LB-EPS and TB-EPS were attributed to protein-like andhumic acid-like substances. Fourier transform infrared (FTIR) spectra suggested thatthe salinity variation had more distinct effect on the functional groups of PN inLB-EPS and PS in TB-EPS. The sludge volume index (SVI) showed a linearcorrelation with LB-EPS (correlation coefficient, R2=0.9479) and TB-EPS(R2=0.9355), respectively. The microbial diversity increased with the increase ofsalinity from0.5%to3%, subsequently it decreased with the increase of salinity from4%to6%. The increase of salinity had more distanct effect on Nitrosomonas sp. Is32than Denitromonas sp. D12-45.1and Denitromonas sp. D2-1. The predominantmember of microbial community under different salinities in the anoxic-aerobic SBRwas related to α-and β-proteobacteria class.The average removal efficiencies of COD and NH4+-N decreased from96%to 36%and from94%to27%in a SBBR, respectively, with the increase of salinity from0%to8%. With the increase of salinity from0%to8%, SOUR for biofilm andsuspended sludge increased at the beginning, and then it decreased. As salinityincreasef from0%to8%, the SAOR, SNOR and SNRR for biofilm decreased74%,82%and65%, respectively, and these for suspended sludge decreased80%,84%and70%, respectively. As salinity increasef from0%to8%, the PN/PS ratios in LB-EPSand TB-EPS for biofilm decreased from2.4and3.0to1.3and1.8, and these forsuspended sludge decreased from1.6and2.8to0.6and1.2, respectively. The fivepeaks identified by3D-EEM fluorescence spectroscopy in LB-EPS and TB-EPS frombiofilm and suspended sludge were attributed to protein-like and humic acid-likesubstances, and three peaks in LB-EPS and TB-EPS from biofilm were attributed toprotein-like and humic acid-like substances. FTIR spectra indicated that the functionalgroups of PS in LB-EPS and TB-EPS from biofilm and suspended sludge wereaffected by the increase of salinity more easly. The microbial diversity in the biofilmwas always higher than that in the suspended sludge under different salinities. At classlevel, the predominant member of microbial community under different salinities in aSBBR was related to Actinobacteridae class.The average removal efficiencies of COD and NH4+-N decreased from92%to25%and from93%to21%in a GSBR, respectively, with the increase of salinity from0%to8%. With the increase of salinity from0%to8%, SOUR increased at thebeginning, and then it decreased. The SAOR, SNOR and SNRR decreased89%,92%and78%, respectively, with the increase of salinity from0%to8%. The PN/PS ratiosin LB-EPS and TB-EPS decreased from6.2and5.7to1.6and1.1with the increase ofsalinity from0%to8%. The three peaks identified by3D-EEM fluorescencespectroscopy in LB-EPS and TB-EPS were attributed to protein-like and humicacid-like substances. FTIR spectra suggested that the salinity variation had moredistinct effect on the functional groups of PS in LB-EPS and TB-EPS. The SVIshowed a linear correlation with LB-EPS (R2=0.9067) and TB-EPS (R2=0.8913),respectively. The relative hydrophobicity (RH) of granular sludge had a linearcorrelation with PN/PS ratio in LB-EPS (R2=0.9169) and TB-EPS (R2=0.9494),respectively. The microbial diversity increased with the increase of salinity from1% to2%, subsequently it decreased with the increase of salinity from3%to8%. At classlevel, the predominant member of microbial community under different salinities in aGSBR was related to γ-proteobacteria class.With the increase of Cu(II) concentration from0mg/L to50mg/L, the averageremoval efficiencies of COD and NH4+-N decreased from93%to58%and from93%to50%in a SBR, respectively, and the average concentration of NO3--N in theeffluent increased from0.10mg/L to0.65mg/L. As the Cu(II) concentrationincreased from0mg/L to50mg/L, SOUR decreased from27.82mg O2/(g MLSS h)to15.37mg O2/(g MLSS h), and SAOR, SNOR and SNRR decreased from58%,54%and51%, respectively. The PN/PS ratios in LB-EPS and TB-EPS increased from2.6and1.8to3.9and2.6with the increase of Cu(II) concentration from0mg/L to50mg/L. The six peaks identified by3D-EEM fluorescence spectroscopy in LB-EPS andTB-EPS were attributed to protein-like, humic acid-like and fulvic acid-likesubstances. FTIR spectra suggested that the increase of Cu(II) concentraton hasdistinct effects on the functional groups of PS and PS in LB-EPS and TB-EPS. TheX-ray photoelectron spectroscopy (XPS) results indicated that Cu(II) existed inLB-EPS and Cu(I) existed in TB-EPS. The microbial diversity decreased with theincrease of Cu(II) concentration from10mg/L to50mg/L. At class level, thepredominant member of microbial community under different Cu(II) concentrations ina SBR was related to Actinobacteridae class.The average removal efficiencies of COD and NH4+-N decreased from96%to62%and from94%to50%in a SBBR, respectively, with the increase of Cd(II)concentration from0mg/L to50mg/L. As the Cd(II) concentration increased from0mg/L to50mg/L, SOUR for biofilm and suspended sludge decreased from35.45mgO2/(g MLSS h) to15.95mg O2/(g MLSS h) and from38.01mg O2/(g MLSS h) to17.28mg O2/(g MLSS h), respectively. As the Cd(II) concentration increased from0mg/L to50mg/L, SAOR, SNOR and SNRR for biofilm decreased74%,61%and51%, respectively, and these for suspended sludge decreased75%,63%and58%,respectively. The PN/PS ratios in LB-EPS and TB-EPS for biofilm increased from2.4and2.9to3.4and3.9with the increase of Cd(II) concentration, respectively, andthose for suspended sludge from2.8and1.8to3.9and3.1, respectively. The five peaks identified by3D-EEM fluorescence spectroscopy in LB-EPS and TB-EPS fromsuspended sludge were attributed to protein-like and humic acid-like substances, andfour peaks in LB-EPS and TB-EPS from biofilm were attributed to protein-like andhumic acid-like substances. FTIR spectra suggested that the Cd(II) concentrationvariation has distinct effects on the functional groups of PN and PS in LB-EPS andTB-EPS from biofilm and suspended sludge. The microbial diversity in the biofilmwas always higher than that in the suspended sludge under different Cd(II)concentrations. At class level, the predominant member of microbial communityunder different salinities in a SBBR was related to Actinobacteridae class.With the increase of Cr(VI) concentration from0mg/L to30mg/L, the averageremoval efficiencies of COD and NH4+-N decreased from95%to24%and from93%to16%in a GSBR, respectively, and the average concentration of NO3--N in theeffluent increased from0.55mg/L to1.88mg/L. As the Cr(VI) concentrationincreased from0mg/L to30mg/L, SOUR decreased from34.86mg O2/(g MLSS h)to12.18mg O2/(g MLSS h), and SAOR, SNOR and SNRR decreased from82%,73%and53%, respectively. The PN/PS ratios in LB-EPS and TB-EPS increased from6.9and6.8to7.7and8.3with the increase of Cr(VI) concentration. The five peaksidentified by3D-EEM fluorescence spectroscopy in LB-EPS and TB-EPS wereattributed to protein-like, humic acid-like and fulvic acid-like substances. FTIRspectra suggested that the salinity variation has distinct effects on the functionalgroups of PS and PN in LB-EPS and TB-EPS. The XPS results indicated that aportion of Cr(VI) was reduced to Cr(III). The RH of the granular sludge exhibited abetter linear correlation with the PN/PS ratio in TB-EPS (R2=0.9782) than that inLB-EPS (R2=0.9172). The abundances of Actinobacteridae in the aerobic granularincreased with the increase of Cr(VI) concentration.