Enhanced Anaerobic Fermentation Of Waste Activated Sludge By Alkylpolyglycosides And Fermentative Liquid As A Carbon Source For Enhanced Biological Phosphorus Removal

At present,with the rapid development of China's economy and the increasing population,the total amount of sewage discharge is increasing.Effective removal of pollutants from sewage is an important way to prevent eutrophication.Activated sludge process is widely used in municipal wastewater treatment plants because of its high biological treatment efficiency,easy maintenance,low operating cost and other advantages.However,this strategy has a drawback-the production of a large number of waste activated sludge.The waste activated sludge contains toxic and harmful substances such as heavy metals and pathogens.If the sludge can not be effectively disposed,it will cause secondary pollution to the environment.In addition,waste activated sludge also contains a large number of organic matter,if the sludge is directly burned or landfill will cause a large amount of waste of organic matter.Anaerobic digestion of sludge can realize organic resource recovery and sludge reduction and innocuity.Therefore,sludge anaerobic digestion technology has been identified as a promising disposal strategy for sludge treatment.The technology of biological phosphorus removal?BPR?in urban sewage treatment plant can achieve the removal of phosphate from sewage treatment.The efficiency of BPR is affected by the types and concentrations of carbon sources.However,the serious shortage of carbon sources in the influent of municipal sewage treatment plants,especially in the south of China,leads to the low C/P ratio in the influent,which limits the growth,reproduction and enrichment of phosphorus accumulating organisms?PAO?,and ultimately leads to the low efficiency of BPR.Enhanced biological phosphorus removal technology often uses direct addition of industrial carbon sources?such as sodium acetate,methanol,etc.?,and changes in industrial operation conditions?double sludge process?.However,the direct addition of carbon sources requires a large amount of chemical substances,and changing the process conditions requires an increase in infrastructure costs and complex process operation.The application of sludge fermentation to enhance biological phosphorus removal has attracted the attention of researchers.After nitrogen and phosphorus removal,the sludge fermentation liquid rich in short chain fatty acids?SCFA?can be directly introduced into the urban sewage treatment plant to supplement the carbon source,thereby improving the BPR efficiency.O/EI process was a new biological phosphorus removal process developed by our research group,which had simple operation conditions and high BPR efficiency.However,the study on enhanced aerobic/extended idle?O/EI?biological phosphorus removal by sludge fermentation liquid has not been reported,and the BPR efficiencies of new O/EI process and traditional A/O process using sludge fermentation liquid as carbon source were not compared,and the change of polymers were not clear.Firstly,the effects of alkyl polyglycosides?APG?on the anaerobic hydrolysis and acidification of waste activated sludge were investigated in a sequencing batch reactor at medium temperature.The results showed that APG could promote the anaerobic hydrolysis and acidification of sludge.When the dosage of APG increased from 0 to0.2 g/g,the maximum soluble chemical oxygen demand?SCOD?content increased from 612 mg/L to 4561 mg/L,the soluble protein content increased from 305 mg/L to2410 mg/L,and the soluble polysaccharide content increased from 171 mg/L to 1368mg/L.When the dosage of APG further increased to 0.3 g/g,the content of dissolved organic matter did not increase significantly,so the optimum dosage of APG was 0.2g/g.In addition,APG could promote the accumulation of SCFA,and when the dosage of APG was 0.2 g/g,the maximum yield of SCFA was 125.3 mg/g,which was 1.5 times that of the blank group,and the optimal fermentation time was 6 d,significantly less than that in the blank group.Acetic acid and propionic acid accounted for the largest proportion of SCFA components.Further study showed that APG self-degradation contributed little to SCFA,and APG could reduce the surface tension of sludge.When APG dosage was 0.2 g/g,the surface tension of sludge decreased by 42.3 mN/m,which was significantly higher than that of low concentration APG dosage group.Furthermore,the yield of SCFA produced by APG-enhanced sludge anaerobic fermentation still has the possibility of increasing.The researchers explored the synergistic effect of free nitrite?FNA?and APG-enhanced sludge anaerobic fermentation.When FNA combined with APG,SCFA production increased sharply,and SCFA production was closely related to FNA concentration.When FNA concentration was 0.51 mg/L,the maximum yield of SCFA was 248.4 mg/g,and when FNA concentration further increased to 1.54 mg/L,the maximum yield of SCFA was 354.9mg/g.However,further increasing the concentration of FNA to 2.13mg/L,the SCFA concentration dropped to 298.4 mg/g.When FNA was combined with APG,the SCOD/TCOD in sludge decomposition increased sharply.When the FNA concentration was 0.51mg/L,the SCOD/TCOD maximum value was 0.31,the FNA concentration was further increased to 1.54 and 2.31 mg/L,and the SCOD/TCOD ratio continued to increase to 0.37 and 0.39.The ratio of SCOD/TCOD increased with the increase of FNA concentration.FNA combined with APG had synergistic effect on sludge hydrolysis and acidification.When FNA combined with APG,the degradation rate of BSA increased to 68.9%on 3 d,which was significantly higher than that of FNA and APG alone.When FNA was combined with APG,the degradation efficiencies of glucan,L-alanine and glucose were also higher than those of single experiment group.The combined application of FNA and APG had significantly higher effects on protease and alpha-glucosidase,AK and BK metabolic activities than FNA and APG alone.However,the activities of F420 key enzymes in the combined group were significantly lower than those in FNA and APG alone.Finally,the feasibility of APG-enhanced waste activated sludge anaerobic fermentation liquid as carbon source to enhance phosphorus removal performance of the new aerobic/extended idle?O/EI?biological phosphorus removal process was explored,and the phosphorus removal efficiency of SCFA-rich sludge fermentation liquid a carbon source for the new O/EI and traditional anaerobic/aerobic?A/O?processes were compared.The results showed that when APG-enhanced sludge fermentation liquid was used as carbon source,the COD and phosphate contents in the effluent of O/EI process were 23 mg/L and 0.89 mg/L,respectively,and the corresponding removal efficiencies were 94.1%and 91%,indicating that APG-enhanced residual sludge anaerobic fermentation liquid could be used as carbon source for biological phosphorus removal.In addition,when the sludge fermentation liquid was used as carbon source,the phosphorus removal efficiency of O/EI biological phosphorus removal process was higher than that of traditional A/O process.The mechanism study showed that when the sludge fermentation liquid was used as carbon source,the relative abundance of PAO was about 38.2%.The maximum content of NO₂^--N in unit cycle of O/EI process was 4.12 mg/L,which was lower than that of A/O process.Enzyme activity analysis showed that the activities of PPK and ACS in O/EI process were higher than that in traditional A/O process.