Recovering Alginate Like Extracellular Polymers (ALE) From EPS Of Conventional Activated Sludge

Recovery of alginate like extracellular polymers（ALE）from granular activated sludge（AGS）has promoted the sustainable development of resource recovery from wastewater treatment plants（WWTPs）.On the other hand,the amount of excess sludge production from conventional activated sludge（CAS）is huge.Under this circumstance,ALE extracted from CAS with similar characteristics to AGS will largely expand the potentials of high value materials recovery from WWTPs.Therefore,in this study,the efficiency and purification of protocols were evaluated and the suitable extracted method was identified for recovering high value biopolymers instead of the normal protocols for the“complex EPS substances”.i)The potential,purification and characterization of ALE extracting from CAS were detected by the biopolymers from different WWTPs-CAS.ii)SBR experiments were conducted to investigate the decisive factors including influent quality,operating parameters and microbials affecting the ALE formation and its related mechanisms.iii)different types of surfactants were selected to optimize the ALE extraction protocols for the increment of ALE extraction from CAS.The results of ALE extracting from different WWTPs-CAS,showed that the biopolymers extraction from the flocs of CAS（eight wastewater treatment plants,WWTPs）ranged from 90to 190 mg/g VSS,which is comparative to the lower levels reported for production of the ALE extracted from aerobic granular sludge（AGS）.The compositional characteristics of the biopolymers were observed by FT-IR,3D-EEM and UV-Visible spectra,demonstrating some differences in the composition and property of the biopolymers from the different WWTPs.The biopolymers had a similarity of about 60%to a commercial alginate at the aspect of chemical functional groups and the alginate equivalent was>400 mg/g ALE.These results demonstrate that the biopolymers might also have a potential application as a promising substitute for commercial biopolymers.Furthermore,the biopolymers formation limitations such factors as influent substrate,nutrient content and microbial community that affect the ALE formation and the related mechanisms were also clarified.Among them,increasing soluble organics（SCOD）content and low nutrient content（C/N/P）in the influent could promote the biopolymers formation to an extent.Also,different bacteria in BNR processes might have the positive or negative effects on biopolymers formation.Finally,the diversity and abundance of bacteria were identified to be a crucial and decisive factor controlling biopolymers’extraction and composition.SBR experiments were conducted to investigate the factors affecting ALE formation and its mechanisms.The results showed that ALE from flocculent sludge fed with starch as carbon source was higher than sodium acetate and glucose,up to 220.3±8.0 mg/g VSS.Moreover,low temperature（12 ^oC）was more favorable for ALE formation,at the highest ALE extraction of303.3±21.5 mg/g VSS.It is mainly due to these factors changed the abundance and metabolic activities in the system and have the promotion or or inhibition on ALE formation.Other parameters had little influences on the production of ALE（at the range of 125.0-200.0 mg/g VSS）but some influence on the compositional characters such as polysaccharides,proteins,etc.These results implied that the management or control for these parameters may achieve a targeted culturation for specific biopolymers with more practical and economical applications.Experiments of surfactant combined with Na₂CO₃ method for the protocols optimization demonstrated that with sodium dodecyl sulfate（SDS）surfactant added,ALE was 222.8 mg/g VSS（promoted efficiency at 79.5%）and the purity of alginate was 70%;with cetyl trimethyl ammonium bromide（CTAB=0.8 g/L）,the extraction of ALE was 281.9 mg/g VSS（127.2%promoted efficiency and 54%purity）.As for Triton X-100 with 1.25 m L/L,the extraction of ALE was 250.6 mg/g VSS（102.0%promoted efficiency and 63%purity）.All of three surfactants can increase the extraction of ALE from 12%to 25%-28%VSS with the dosage of0.04 g/g TS（Triton X-100）<0.06 g/g TS（CTAB）<0.19 g/g TS（SDS）,respectively.Moreover,surfactant can enhance the purity of alginate in ALE.The results showed that Triton X-100 was the optimal surfactant for optimizing ALE extraction.The mechanisms can be concluded as follows:i)the surfactant solubilization promotion leading to the fragmentation and dissolution of flocs into aqueous phase,ii)the similar structures between surfactant and alginate promoting solubilization,and iii)the group binding enhancing ALE solubilization and purification.In conclusion,ALE recovery from CAS has similar potentials to AGS in terms of both production and purity of alginate.thus,biopolymers from CAS should also become the new high value bio-materials.Increments of its extraction potential and protocols optimization should be further studied in the future.