Alkyl Ethoxy Polyglycoside Increases Volatile Fatty Acids Production For Excess Sludge Anaerobic Fermentation

With the continuous increase of urban sewage treatment plants in China,a large number of excess sludge have been generated.Improper disposal of the excess sludge caused great harm to human health and environmental safety.Therefore,the green and efficient disposal of excess sludge is an important way for sludge reduction,stabilization,harmlessness,and resource utilization.It is an important way for the reduction and resource utilization that the abundant organic matter containing in excess sludge was converted to volatile fatty acids(VFAs)by anaerobic fermentation.In order to increase the VFAs production for excess sludge anaerobic fermentation,many technologies were improved,such as treatment by heat,ultrasound,microwave,acid and alkali,surfactant and enzyme.The surfactants had been attracted great attentions for its remarkable effect and applicability.In particular,biosurfactants become a hot topic due to biodegradable,environment friendly and non-toxic.In this study,Alkyl Ethoxy Polyglycosides(AEG),a new green biosurfactant,was added to improve the excess sludge anaerobic fermentation for the increase of VFAs production,the main achievements and conclusions are as follows:(1)The improvement of excess sludge anaerobic fermentation by AEG was determined.The effects of AEG on VFAs production of excess sludge anaerobic fermentation was promoted by optimizing the key factors,such as AEG dosage,fermentation temperature and initial pH.The concentration of VFAs was 3302.87±45.8 mg COD/L with the initial pH=10 by addition of 0.4 g AEG/g TSS after 3d fermentation under 35?,which was 8.55 times higher than without addition of AEG,and acetic acid and propionic acid was the main components.(2)The effects of AEG on VFAs production of excess sludge anaerobic fermentation was enhanced by thermo-alkali pretreatment.The dissolution of solid organic matter in excess sludge caused the soluble protein and carbohydrate increase significantly after thermo-alkali pretreatment,which is beneficial for the subsequent anaerobic fermentation of excess sludge.After excess sludge pretreatment with thermo-alkali at 70?,pH=8 for 1 h,0.4 g AEG/g TSS was added for anaerobic fermentation at 35?.The concentration of VFAs was 3480.67 ± 55.8 mg COD/L after 3 days,and the main component was acetic acid.The production of VFAs increased by 613.96 mg COD/L compared with unpretreated sample,indicating significantly increase of the VFAs production.(3)The mechanism of AEG to increase VFAs production of excess sludge anaerobic fermentation was studied.Based on the three-stage theory of anaerobic fermentation,the effects of AEG in different stages were analyzed.With the addition of AEG,the degradation of BSA and dextran was enhanced in the hydrolysis stage.The protease and a-glucosidase activities were 1.96 and 2.25 times higher,respectively,and the Zeta potential decreased from 21.4±0.5 mV to 11.15±0.5 mV,indicating that the presence of AEG promotes the hydrolysis of dissolved organics in the fermentation broth.In the acidification stage,the degradation of L-alanine and glucose was enhanced by AEG,too,indicating that AEG could promote the direct utility of small molecule organic substances(such as amino acids and monosaccharides)by microorganisms to increase the VFAs prodution.In the methanation stage,the degradation of sodium acetate was slow with the addition of AEG,indicating that the activity of methanogens was inhibited by AEG.In summary,a large number of VFAs accumulated during the anaerobic fermentation with addition of AEG,because of the hydrolysis of dissolved macromolecule organics(such as proteins and carbohydrates)and the degradation of small molecule organics(amino acids and monosaccharides)was enhanced and the activity of methanogens was inhibited.The changes of dissolved organic components was analyze by three-dimensional fluorescence spectra which were used to illuminate the solubilization of organic matter in excess sludge during fermentation.After the addition of AEG,the fluorescence intensity of dissolved organic matter(especially protein-like and humic acid-like substances)in the fermentation broth was greatly enhanced.The results showed that AEG promoted the dissolution of organic matter in excess sludge during anaerobic fermentation,which was beneficial for the subsequent anaerobic fermentation.Based on high throughput pyrosequencing analysis,microbial community structure changes during fermentation were revealed.After the addition of AEG,the proportion of Megasphaera and Clostridium bacteria associated with acetic acid,propionic acid and butyric acid in the hydrolysis and acidification of carbohydrates and lactic acid increased significantly,while the proportion of the main VFAs consumer of the fermentation process,Proteobacteria,decreased significantly during the anaerobic fermentation process.The results showed that the addition of AEG could significantly increase the activity of acid-producing bacteria and inhibit the activity of methanogens during the anaerobic fermentation of excess sludge.