Effects Of Ca²⁺ And Fe³⁺ On The Performance And EPS Of Anaerobic Sequencing Batch Reactor For Landfill Leachate

Anaerobic sequencing batch reactor（ASBR）is widely used in landfill leachate biologi cal treatment industry due to its simple structure,flexible use and many other advantages.C a²⁺and Fe³⁺are important growth factors of microorganisms,which are ubiquitous and hig h in leachate.Different concentrations of Ca²⁺and Fe³⁺have different effects on anaerobic biological treatment.Therefore,it is very important to study the effect of Ca²⁺and Fe³⁺on a naerobic biological treatment of landfill leachate.At present,in the field of landfill leachate treatment,domestic on the effects of Ca²⁺and Fe³⁺on anaerobic biological treatment of lan dfill leachate,and less research on the extracellular polymer of anaerobic activated sludge.In this study,an anaerobic sequencing batch reactor（ASBR）was used as the research devic e,and Ca²⁺,Fe³⁺and their mixtures were used as the research object.The effects of Ca²⁺,Fe³⁺and their mixtures on the treatment effect of anaerobic sequencing batch reactor in differe nt operating cycles were explored.The changes of Zeta potential,protein and polysaccharid e content of microbial EPS were quantitatively analyzed.Combined with three-dimensional fluorescence spectroscopy（3D-EEM）and Fourier transform infrared spectroscopy（FTIR）,the changes of fluorescent substances and functional groups in extracellular polymer（EPS）composition were revealed by Ca²⁺,Fe³⁺and their mixtures with different concentrations.C ombined with the second derivative spectrum,deconvolution and Gaussian fitting date proc essing methods,the effects of Ca²⁺Effects of Fe³⁺on the secondary structure of microbial E PS protein were studied.The main test results are as follows:（1）In this experiment,ASBR reactor was used as the research device.The acclimation period lasted 79 days,and the influent COD load was gradually increased from2052 mg/L to 20000 mg/L.The monitoring results of COD,p H,alkalinity,VFA and ORP in the reactor showed that by the end of domestication,the COD removal rate was stable at more than 90%,the p H was maintained at about 7.55,the alkalinity was stable at 5500.2mg/L,the VFA content was always maintained below 800 mg/L,and the ORP value was always maintained between-502 m V and-379 m V.During domestication,the reactor always maintains a strict anaerobic environment and a good buffer system,and the overall operation effect was stable.（2）ASBR reactor was used to study the effects of single Ca²⁺,Fe³⁺and their mixtures with different concentrations on the treatment effect of the reactor.Studies have shown that the COD concentration promotion and high concentration inhibition.In the same operation cycle,the COD concentration in the effluent of the reactor decreased first and then increased with the increase of the reactor decreased first and then increased with the increase of the concentrations of Ca²⁺,Fe³⁺and their mixtures in the effluent.Under the same concentration point,the COD concentration in the effluent of the reactor gradually increased with the increase of the operation cycle.With the increase of influent Ca²⁺and Fe³⁺dosage,When the dosage is less than the maximum promotion concentration,the inhibition effect on COD removal gradually increased with the increase of Ca²⁺and Fe³⁺dosage.The effluent p H of the reactor showed the same change rule with the increase of influent Ca²⁺,Fe³⁺and their mixture concentrations,which decreased gradually with the increase of concentration and operation cycle.（3）The effects of single Ca²⁺,Fe³⁺and their mixtures with different concentrations on the surface characteristics and components of microbial EPS were studied by Zeta potential and the contents of protein（PN）and polysaccharide（PS）.The results showed that microbial EPS at different concentrations was electronegative,and Zeta potential increased gradually under the action of single Ca²⁺,while Zeta potential increased first and then stabilized under the action of Fe³⁺and its three mixture ratios.Under the influent Ca²⁺,Fe³⁺and their three proportion mixture ratios,the total amount of microbial EPS increases first and then decreased with the increase of ion concentration.and the PN content was higher than that of PS content.PN was the core component that determined the EPS content.（4）The effects of single Ca²⁺,Fe³⁺and their mixtures with different concentrations on the fluorescent substances of microbial EPS fluorescent substances were studied by three-dimensional fluorescence spectroscopy（3D-EEM）.Microbial EPS mainly had five fluorescence characteristic peaks,the fluorescence peak of aromatic-like proteins,the fluorescence peak of soluble microbial metabolites,the fluorescence peak of methanogenic bacteria-specific coenzyme F₄₂₀,the fluorescence peak of fulvic-like acid in ultraviolet region,and the fluorescence peak of hemic-like acid.The fluorescence intensity of EPS was affected by the influent metal ion concentration,but the EPS composition did not change fundamentally.（5）The effects of single Ca²⁺,Fe³⁺and their mixtures with different concentrations on the main functional groups of EPS in anaerobic activated sludge were studied by Fourier transform infrared spectroscopy（FTIR）.The change of Ca²⁺concentration in influent had significant effect on the functional groups of protein and polysaccharide in microbial EPS.Influent Fe³⁺in influent affected the functional group characteristics in anaerobic activated sludge,especially for the-CONH-group in proteins and the C-O group in polysaccharides.When the concentration of Ca²⁺and Fe³⁺in the influent changed,the main groups in EPS did not change significantly,and the main groups were hydroxyl,amino,amide I,polysaccharide and unsaturated bond.（6）Through the infrared spectrum of amide I region(1600-1700cm^-1),combined with the data processing methods of second-order derivative spectrum,deconvolution and Gaussian fitting,the effects of different concentrations of Ca²⁺and Fe³⁺on the secondary structure of microbial EPS protein were studied.The results showed that the microbial EPS contained five secondary structures,namely,Aggregated strands,α-Helix,β-Sheet,3-Turn helix and Antiparallelβ-sheet/aggregated strands,while the random coil structure did not appear.With the increase of influent Ca²⁺concentration,the 3-Turn helix showed an obvious trend of first increase and then then decrease,and Antiparallelβ-sheet/aggregated strands showed a significant downward trend.The addition of Fe³⁺had a certain inhibitory effect on the relative content ofα-Helix;The relative content of 3-Turn helix showed an obvious trend of first increase and then decrease.In this experiment,the influence of Ca²⁺and Fe³⁺in landfill leachate on the treatment effect of anaerobic sequencing batch reactor was studied,and the influence characteristics of microbial EPS were revealed,which provided a theoretical basis and scientific basis for the continuous development of landfill leachate anaerobic biological treatment industry.Figure[34]Table[6]Reference[128]...