| There are abundant carbon sources in domestic sewage,recycling it is of great significance for achieving energy balance in sewage treatment plants.HRAS is currently the mainstream process for carbon source biological recovery,which has good recovery efficiency for particulate and colloidal carbon sources,but low recovery rate for dissolved carbon sources,limiting the improvement of process carbon source recovery rate.The efficiency of activated sludge in adsorbing dissolved carbon sources needs further research.In addition,in the study of the mechanism of activated sludge adsorption of dissolved carbon sources,the contributions of different adsorption pathways,the main controlling forces of the adsorption process,and the effects of sludge properties and microorganisms on adsorption efficiency and pathways are still unclear.DO is an important parameter of the HRAS process,which is not only closely related to the energy consumption of the process operation,but also has a significant impact on the adsorption of dissolved carbon sources by sludge by affecting its properties and microbial communityIn response to the above issues,this study selected Bovine Serum Albumin,glucose,and humic acid as typical dissolved carbon sources,and conducted sludge cultivation under DO conditions of 0.5,1.0,and 1.5 mg/L.The sludge properties and microbial community structure were measured;The adsorption equilibrium time and equilibrium adsorption rate of activated sludge on dissolved carbon sources were studied.The functional groups involved in the sludge adsorption process were analyzed through FTIR,and the contributions of cell proliferation,extracellular adsorption,EPS conversion,and cell storage pathways to the adsorption of dissolved carbon sources by sludge were analyzed.The xDLVO theory was used to analyze the main controlling forces in the process of sludge adsorption,Analyzed the effects of sludge properties and microorganisms on the efficiency and pathway of sludge adsorption of dissolved carbon sources.Deeply analyzed the mechanism of sludge adsorption of dissolved carbon sources.The main conclusions obtained are as follows:(1)Analysis of sludge properties found that as DO increased,sludge SVI increased,sludge particle size decreased,and sludge specific surface area increased,which is related to the increase in shear force generated with the increase of aeration rate;The Zeta potential and relative hydrophobicity gradually decrease;The EPS content of sludge shows a trend of first increasing and then decreasing,and the protein/polysaccharide value of sludge decreases,which may lead to a decrease in hydrophobicity;The PHA content shows a trend of first increasing and then decreasing,which is attributed to the moderate energy supply when DO is 1.0 mg/L,which is beneficial for sludge to store carbon sources as PHA.As DO increases,the species richness and diversity of sludge increase.The relative abundance of carbon storage bacteria and EPS producing bacteria showed a trend of sludge 2(DO=1.0 mg/L)>sludge 3(DO=1.5 mg/L)>sludge 1(DO=0.5 mg/L),which was consistent with the change trend of sludge EPS content and PHA content.(2)The experimental results of sludge adsorption of BSA showed that the adsorption of BSA reached equilibrium within 120 minutes,with an adsorption efficiency of sludge 2(65.16%)>sludge 3(60.03%)>sludge 1(53.37%);Sludge adsorption of BSA is a spontaneous endothermic process,and the fitting effect with Freundlich adsorption isotherm,inter particle diffusion model and pseudo second order adsorption kinetic model is better,indicating that sludge adsorption of BSA is a multi-layer adsorption process,and the diffusion process of BSA in the sludge floc gap and its binding process on the sludge surface adsorption sites are the main speed limiting stage.FTIR analysis also showed that the process of sludge adsorption of BSA involves chemical adsorption,with functional groups such as C-H,C=O,N-H,C-N,C-OH,OH participating in the adsorption,and hydrogen bonding forces present.The analysis of adsorption pathways shows that the dominant pathways for BSA adsorption in sludge 1(DO=0.5 mg/L)are extracellular adsorption and cellular storage,while the dominant pathways for BSA adsorption in sludge 2(DO=1.0 mg/L)and sludge 3(DO=1.5 mg/L)are cellular storage,which is related to the higher abundance of carbon storage bacteria in sludge 2 and sludge 3.XDLVO analysis shows that there is an attractive interaction between sludge and BSA,and the polar force is the dominant force.The correlation analysis showed that the relative abundance of EPS content,PHA content,Flavobacterium,Plasticumulans and Zoogloea had a strong positive correlation with the BSA adsorption efficiency.The increase of the abundance of carbon storage bacteria and EPS bacteria was conducive to the adsorption of protein substances.(3)The experimental results of glucose adsorption on sludge showed that the adsorption of glucose reached equilibrium within 90 minutes,with an adsorption efficiency of sludge 2(69.04%)>sludge 3(66.81%)>sludge 1(59.27%);Glucose adsorption by sludge is a spontaneous endothermic process,which is better matched with Freundlich adsorption isotherm,interparticle diffusion model and pseudo second-order adsorption kinetic model.FTIR infrared analysis also showed that chemical adsorption occurred during the glucose adsorption process of sludge,with functional groups such as C-H,C=O,N-H,C-N,C-OH,O-H participating in the adsorption process,and hydrogen bonding forces were present.Under different DO conditions,the dominant pathway for sludge to adsorb glucose is cell storage,which may be related to the carbon source of sludge culture being glucose.XDLVO analysis shows that there is an attractive interaction between activated sludge and glucose,and the polar force is the dominant force.The correlation analysis showed that the relative abundance of EPS content,PHA content,Flavobacterium,Plasticicumulans and Zoogloea had a strong positive correlation with the efficiency of glucose adsorption,the relative abundance of carbon storage bacteria and EPS bacteria was conducive to the adsorption of sugars.(4)The experiment of sludge adsorption of humic acid showed that the adsorption of humic acid reached equilibrium within 120 minutes,and the adsorption efficiency was sludge 1(47.77%)>sludge 2(42.59%)>sludge 3(39.93%);The adsorption of humic acid by sludge is a spontaneous endothermic process,and the fitting effect with Freundlich adsorption isotherm,inter particle diffusion model and pseudo second order adsorption kinetic model is better.FTIR infrared analysis also showed that chemical adsorption occurred during the process of sludge adsorption of humic acid,with functional groups such as C-H,C=O,N-H,C-C,C-N,C-OH,O-H participating in the process,and hydrogen bonding forces existed.Under different DO conditions,the dominant pathway for sludge to adsorb humic acid is extracellular adsorption.xDLVO analysis shows that there is an attractive interaction between sludge and humic acid,and the polar force is the main controlling force for adsorbing humic acid.Correlation analysis shows that the SVI,particle size,surface area,Zeta potential,and relative hydrophobicity of sludge are highly correlated with the adsorption of humic acid.The smaller the SVI,the larger the particle size,the higher the Zeta potential,and the stronger the relative hydrophobicity,the higher the adsorption efficiency of humic acid. |
