Research On Anaerobic Acidification And Methanation Of Fe-carbon-rich Sludge Based On Carbon Capture From Wastewater

Municipal wastewater contains lots of organic chemical energy,while the traditional sewage treatment process uses the metabolism of microorganisms to mineralize the organic carbon in sewage,which not only requires a considerable amount of electricity for aeration,but also fails to effectively recover energy from sewage.In the future,wastewater treatment plants?WWTPs?needs to realize the resource and energy recovery from sewage on the basis of removing pollutants.Based on the concept of"carbon capture-anaerobic fermentation",this study combined sludge adsorption with chemical flocculation to achieve the maximum capture of organics from sewage,and investigated the anaerobic acidification and methanation efficiency of the generated Fe-based carbon-rich sludge,and verify whether vivianite was produced in digested sludge;The internal mechanism was also analyzed by metagenomics sequencing.This study investigated the effect of"Sludge adsorption"and"Sludge adsorption-Fe-coagulation"on the capture of organics from sewage.Results of sludge adsorption experiments showed that,the optimal dosage of sludge is 1500mg/L,which can absorb 47.9%COD from sewage;The"sludge adsorption-Fe-coagulation"process enhanced organics capture effect.On the basis of adding1500mg/L of sludge,when Fe³⁺dosed at 30 mg/L,the COD capture rate reached the maximum of 74.2%,and the capture rates of NH₃-N and TP were 35.6%and 90.8%respectively.Taking the sludge generated at Fe³⁺dosage of 18,24,30 and 36 mg/L as experiment group?Fe-sludge?,the properties of the sewage sludge?R0?and Fe-sludge?R1^R4?were compared.And results indicated that the organics content of Fe-sludge increased by 30%than that of sewage sludge,meanwhile,the excessive Fe³⁺in Fe-sludge inhibited EPS secretion of sludge microorganisms,decreased sludge particle size and surface charge,while improved surface site density.To investigate the acidification characteristics of Fe-sludge,Fe-sludge?R1^R4?and sewage sludge?R0?were used for conducting anaerobic fermentation experiment.Results showed that Fe-sludge have favorable hydrolysis and acidification efficiency,and R1 showed the optimal hydrolysis and acidification effect.After fermentation for 7 days,SCOD in R1 was 261.4mg/gVS,and VFAs yield was 215.41 mg/gVS,which were 3.00 and 3.02 times of R0,respectively.Mechanism analysis indicates that during anaerobic fermentation process,Fe?III?in Fe-sludge was rapidly reduced to Fe?II?,the colloidal structure bridged by Fe?III?was rapidly decomposed,and large amounts of organics in Fe-sludge was released,providing sufficient substrates for microorganisms,enabling fermentation bacteria such as Firmicutes to grow rapidly,and further promoting the generation and accumulation of VFAs.To investigate the methanation characteristics of Fe-sludge,Fe-sludge?R1^R4?and sewage sludge?R0?were used for conducting anaerobic digestion experiment.Results showed that total biogas production and methane production of Fe-sludge were both better than sewage sludge,and R2 had the optimal methane production rate of 181.38 ml/gVS,which was 1.94 times of sewage sludge?R0?.However,excessive Fe?III?in Fe-sludge decreased pH and increased ORP value,caused inhibitory effect on anaerobic digestion.Results of microbial community analysis showed that the abundance of hydrolysis and acidogenesis bacteria in Fe-sludge increased significantly while the abundance of methanogen decreased.Further analysis of XRD indicated that vivianite formed in both experimental group and control group,while vivianite content in experimental group increased by 100%because of the higher contents of Fe?III?.