Analysis Of Extracellular Polymeric Substances From Cyanobacteria And Study On The Influence Of Biochar Treatment On Its Dewaterability

As an important part in the treatment and disposal of cyanobacteria,dewatering can greatly reduce the volume of cyanobacteria and costs of transportation and storage.However,the dewatering of the cyanobacteria has many challenges such as practical applications,high compressibility,poor precipitation performance and many extracellular polymeric substances（EPS）.The EPS has the significance impact on the dewatering of the cyanobacteria.Currently,the problems of the EPS in the dewatering of sludge had been extensively studied.However,the problems of the EPS in the dewatering of cyanobacteria need to be researched.Considering the significance differences in the properties of the cyanobacteria and sludge,it has the significance to research the mechanism EPS in the dewatering of the cyanobacteria.Some studies shown that the addition of biochar can greatly improve the dewaterability of the sludge.The cyanobacteria biochar has many advantages such as high carbon content,strong adsorption,large pores,and the dewatered cyanobacteria mud.The cyanobacteria biochar could realize the efficient dewatering and reduction and the resource disposal of cyanobacteria mud.The cyanobacteria biochar has the excellent application and provides the new treatment technology of the cyanobacteria mud.The main contents of the research and results of the study as the follows:（1）The properties of the cyanobacteria were different from different sources,and the characteristics of the extracellular polymeric substances were the key factors affecting their dewaterability.Research has shown that there were significant differences in the characteristics of cyanobacteria at different growth periods and locations,which would affect their performance of dewaterability.In the cyanobacteria of the Taihu Lak,the correlation fitting analysis showed that the correlation coefficients of EPS polysaccharide content with capillary suction time（CST）and specific resistance to filtration（SRF）were 0.80 and 0.83,and P<0.01,respectively.The correlation coefficients of protein content with CST and SRF were 0.86 and 0.85,and P<0.01,respectively.The different structures of EPS,the correlation coefficients of soluble extracellular polymeric substances with CST and SRF were 0.92 and0.93,P<0.01,and the correlation coefficients of loosely-bond extracellular polymeric substances with CST and SRF were 0.94 and 0.87,P<0.01,respectively.However,the tightly-bond extracellular polymeric substances had no significant effects on the dewaterability of the cyanobacteria.Besides,the Zeta potential,particle size and p H of cyanobacteria had no significant effects on the dewaterability of the cyanobacteria.The samples of the aeruginosa microcystic were similar to the samples of the cyanobacterial.Finally,the polysaccharides and proteins in the EPS of the cyanobacteria had significant influences on the dewaterability of cyanobacteria.The structures of the soluble EPS and loosely-bond EPS had the greater influences on the dewaterability of cyanobacteria than tightly-bond EPS.（2）The addition of Fe Cl₃-impregnated biochar could significantly improve the dewaterability of cyanobacteria mud.The temperature of pyrolysis was 400°C,the particle size was 100μm,and the dosage was 0.20g/（g TS）,the iron-containing biochar could reduce the capillary suction time（90.22%）and specific resistance to filtration（94.94%）of the cyanobacteria mud.It increased the zeta potential of the cyanobacteria mud and reduced content of the EPS and the compression coefficient.By comparing different conditioning methods,it could be found that the improvement of the dewaterability of cyanobacteria mud by iron-containing biochar was better than that of direct mixing of biochar+Fe Cl₃ and Ca O+Fe Cl₃.Finally,biochar loading Fe Cl₃ could play a synergistic effect of the two.Fe Cl₃ played a flocculation effect to make cells gather tightly and reduced the dissolution of extracellular polymers.Biochar played the role of carrier and skeleton support and reduced the compressibility of cyanobacteria mud,which significantly improved the dewaterability of cyanobacterial mud.（3）The modified carbon coupling oxidation process could significantly reduce the EPS content of the cyanobacteria mud and improve the dewaterability.The study showed that the samples of microcystic aeruginosa,the modified carbon reaction of 2%g/（g TS）of persulfate（PDS）and 20%g/（g TS）for 15 min improved the dewaterability of microcystic aeruginosa,and reduced the content of extracellular polymer.The polysaccharides and proteins were reduced 64.64%and 80.99%,respectively.The CST and SRF of samples of the cyanobacteria mud（under the conditioning of 10%g/（g TS）PDS and 20%g/（g TS）modified carbon）reduced 82.05%and 88.61%,respectively.Besides,the dewaterability was significantly improved.The EPS analysis of cyanobacteria mud showed that the polysaccharides and proteins were reduced 30.34%and 75.38%,respectively.The results indicated that catalytic oxidation of degradable EPS components destroyed their structural characteristics and made the hard-to-remove binding water flow out,which improved the dewaterability of cyanobacteria mud.According to the catalytic oxidation,the addition of 5%g/（g TS）Fe Cl₃reduced the CST（78.70%）and SRF（74.60%）of cyanobacteria mud.The results showed that Fe Cl₃ played a flocculation and conditioning role.Thus,the cells dispersed due to EPS degradation were re-aggregated,which could improve the sedimentation of the cyanobacteria mud and reduce its compressibility and improved the dewaterability of the cyanobacteria mud.