Study On Mechanism Of Blocking Calcification Of Anaerobic Granular Sludge Based On Phosphate Regulation

As the main raw material for paper production in the paper industry,waste paper is continuously recycled.The promotion of"zero discharge"and"closed cycle"causes the increasing Ca²⁺in waste paper pulping wastewater,which makes it difficult to treat wastewater by anaerobic biological treatment,and the high concentration of Ca²⁺can easily reduce the treatment efficiency of the anaerobic system,which leads to the calcification of granular sludge,thus severely restricting the development of the waste paper and paper-making industry.Therefore,6 UASB reactors are selected in this study.Divided into low acidification group R1,R2,R3 and high acidification group is R4,R5,R6according to different acidification degree.the UASB anaerobic bioreactor was used to treat organic wastewater with high concentration of Ca²⁺in simulated phosphate-controlled waste paper pulping wastewater in this paper.The main results are summarized as follows:（1）With the aid of such means asμ-CT scanning,reconstruction of projection images into cross-sectional images,3D images and particle reconstruction,and the combination of Ostwald maturation theory and Liesegang ring model,a hypothetical mechanism of calcium migration was proposed to study the control strategy of calcium precipitation in the particle-based anaerobic reactor.（2）The study on effect of phosphate-controlled high-calcium wastewater on the UASB anaerobic bioreactor under different acidification degrees.During the53-day start-up and stabilization phase,the volumetric load of the UASB reactor increased from 3.9 kg COD/（m³·d）to 15 kg COD/（m³·d）,and the COD removal rate remained at 96～99%after stable operation.The reactor started successfully.In the 47-day phosphate-controlled high-calcium wastewater stage,the COD removal rate of the control group R1 and R4 was 96.5%on average,while the R2and R3 in the influent of 1000 mg/L Ca²⁺were reduced to 94.3%,and R5 and R6were reduced to 95.6%;In R2 and R3 in the low acidification,the phosphate slowed down the nucleation and crystallization rate of Ca CO₃,and the retention rate of Ca²⁺was relatively low.In the high acidification,R5 and R6 can produce greater alkalinity,which accelerated the nucleation and crystallization rate of calcium carbonate,and the retention rate of Ca²⁺was relatively high.However,the phosphate of high concentration slowed down the nucleation and crystallization rate of Ca CO₃in R6,making the retention rate of Ca²⁺of R6 be less than R5’s.（3）The study on the physical and chemical properties and microbial diversity of anaerobic granular sludge in the treatment of high calcium wastewater by phosphate regulation under different acidification degrees.After the operation of UASB,the physical and chemical properties of R1-R6 granular sludge were analyzed.The VSS/TSS of R1 to R4 was maintained between 0.67～0.77.However,the VSS/TSS of R5 and R6 are only 0.27 and 0.33,respectively.The ash,density and sedimentation rate were much higher than other reactors.In the Archaea genus,R1 and R4 were dominated by Methanosaeta,while R2 and R3had 2/3 of Methanosaeta and 1/3 of Methanobacterium.R5 and R6 were dominated by Methanosaeta,followed by Methanobacterium.Methanobacterium can react to CO₂/H₂,reducing the contribution rate of CO₂to CO₃^2-and the risk of calcification of granular sludge.（4）The mechanism of blocking calcification of anaerobic granular sludge based on phosphate regulation.XRD and FTIR characterization shows that the sediment on granular sludge was mainly calcite-typed Ca CO₃;through SEM-EDS element analysis andμ-CT,it is confirmed that the sediments of R2 and R3 were dispersed in the granular sludge without agglomeration,while the sediments of R5 and R6 were in the surface of granular sludge,affecting the mass transfer and causing cavities in the granular sludge.Therefore,combining the physical and chemical properties of granular sludge andμ-CT,etc.,it can be seen that in the low acidification group,phosphate can block the calcification of granular sludge,but it is invalid for the high acidification group.The granular sludge can still be calcified,but the phosphate of high concentration slows down the calcification process.