Extraction And Application Of Alginate-Like Extracellular Polymers(ALE) From Conventional Activated Sludge

The extraction of ALE from aerobic granular sludge（AGS）has become a hot topic.However,the world’s primary sewage treatment process is still the conventional activated sludge,and waste sludge production is extensive.ALE can be extracted from conventional activated sludge（CAS）waste,but its quality and quantity differ from that of AGS.However,basing its large quantity and improving quality may find a high-value application direction for conventional activated sludge,which will have substantial significance for the circular economy.Based on this goal,the research first explores the differences in ALE composition structure between CAS and AGS from the perspective of the blocks.Secondly,three purification methods were used to remove proteins and humic acids in ALE and purify polysaccharides to achieve accurate purification of target products in ALE and achieve directional separation of ALE components.Then,the feasibility of ALE application in CAS was explored,and a new Cu（II）adsorbent was prepared by crosslinking ALE with polyethyleneimine/PEI.Finally,the pollutants in ALE were evaluated,and the transfer potential of antibiotic sulfamethoxazole/SMX to ALE was explored.Compared with natural alginate,ALE can be separated into three compositional blocks:GGL,GML,and MML（like units containing guluronate or mannuronate）.Each block forms its basic constituent unit.ALE was extracted with real WAS from CAS,and three blocks were separated:GGL=54%,GML=42%,and MML=4%in weight.Moreover,the GGL blocks in CAS were lower than AGS,down by 1/3-1/2.Furthermore,the GML and MML blocks in CAS were much higher than AGS by more than 1/2.Different compositional blocks of ALE in AGS and CAS should be the reason for forming different properties in applications.For this reason,a further study will be initiated to dispense/reorganize three blocks of ALE from CAS to expand its potential applications based on the compositional blocks of ALE from AGS.Then,appropriate methods were selected to purify ALE components.The protein and humic acid in ALE were removed.Polysaccharide was purified by three different purification methods to achieve accurate purification of target products in ALE and directional separation of ALE components.The results showed that the three methods had a particular effect on the removal of protein and humic acid and the purity of polysaccharides in ALE.The method with the highest removal efficiency of protein and humic acid and the best purification effect of polysaccharide was Pure 1,namely,the Sevag method.The removal rate of protein in ALE can be up to 10%,the removal rate of humic acid can be up to 5%,and the improvement of polysaccharide purity can be up to 4%.In addition we explored some possible applications of ALE,and a new efficient ALE-based Cu（II）adsorbent was prepared by grafting PEI（polyethyleneimine）.The adsorption capacity of ALE has been improved after PEI modification.SEM and BET analyses revealed the formation of ALE’s complex three-dimensional network cavity structures and an increment in the specific surface area after grafting PEI,which provided more active binding sites for Cu（Ⅱ）adsorption.EDS mapping and FTIR analysis showed that the hydroxy,amino,and carboxyl groups in the ALE-PEI adsorbent participated in complexation with Cu（Ⅱ）.The adsorption mechanism possibly involved electrostatic interactions between the cations and negatively charged functional groups.The adsorption obeyed a pseudo-second-order kinetic model and the Langmuir model.The maximum adsorption capacity of ALEC1-PEI,one of the prepared adsorbents,was 98.01 mg/g according to the Langmuir model,and the adsorption of Cu（Ⅱ）proceeded most efficiently at p H 5.The adsorption–desorption experiments of ALEC1-PEI using EDTA suggested that the adsorbent can be recycled.Finally,the risk of contaminants in ALE（the antibiotic sulfamethoxazole/SMX）was assessed.ALE reacted with excess SMX in the solution and reduced the amount of SMX in the whole solution system.That is,ALE has significant inhibition and solubility-reducing effect on SMX.Meanwhile,the partition coefficient K_ALE of sulfamethoxazole SMX in the aqueous phase and ALE was investigated.The results showed that the value was negative,indicating the amount of sulfamethoxazole SMX dissolved in the solution gradually decreased with the increase of ALE concentration.The content of SMX in ALE was investigated,and it was found that the higher the ALE concentration was,the lower the content of sulfamethoxazole SMX was.Thus,ALE at higher concentrations shows less susceptibility to sulfamethoxazole SMX contamination.The partition coefficient K_ALE in the two phases of SMX in the alkaline environment is significantly higher than in the acidic environment,proving that ALE has a more potent inhibition and solubility-reducing effect on SMX in the alkaline environment.In short,high concentration and alkaline environment can enhance the ability of ALE to resist the antibiotic sulfamethoxazole SMX pollution.