Study On Subsequent Treatment Of Wastewater After Recovering Municipal Sludge Protein

Recovery of sludge protein became an emerging way of resource utilization of municipal wasted activated sludge?WAS?.It was helpful for the application of protein recovery from municipal WAS and provided useful information for high C/N ratio wastewater containing sulfate from chemical and food industry to study the enhancement of methane production from wastewater of protein recovery.Aimed at the high C/N ratio wastewater containing sulfate from protein recovery of municipal WAS,the enhancement of biogas production by dosing iron and chelating agent was investigated and the type and dosage of agents were optimized in this study.Then,the enhanced mechanism was primarily analyzed through probing the key enzyme activity,COD removal,sulfate reduction and variations in trace metal species during anaerobic process.The main results were as follows.?1?The addition of pyrolytic hydrolysate residue can improve the initial pH of protein residue extracted from acid-base imbalance,thus significantly promote the methanogenesis process of the system,and within a certain concentration range,The cumulative methanogenic rate increases with the increase of the amount of pyrolytic hydrolysate residue.The initial pH is 7.6,the cumulative gas production rate is the highest,the removal rate of 87.6 m L/g COD is the highest,and the removal rate of sulphate radical is 66.16.The removal rate of sulphate radical is the lowest,up to 66.16%.The initial pH is 7.6 and the cumulative gas production rate is the highest?87.6 mL/gCOD?,and the sulfate radical removal rate?66.16%?is the lowest.The addition of 10?mol/L NTA is the most economical and effective,and the cumulative gas production rate is 150.4 m L/gCOD.?2?Fe⁰ significantly promoted the methane production process of protein residues with high nitrogen/carbon ratio and sulfate radical,and the cumulative gas production rate increased with the increase of Fe⁰ concentration within a certain concentration range.When40 mg/L Fe⁰ was added,the cumulative gas production rate was the highest.Up to 177.7mL/gCOD.Fe²⁺can also be used to replenish metal Fe and promote the effect of methanogenesis in the system.In a certain concentration range,the cumulative gas production rate increases with the increase of Fe²⁺concentration.When 20 mg/L Fe²⁺is added,the cumulative gas production rate is the highest.Up to 156.2 m L/g COD.The addition of 10?mol/L NTA is the most economical and effective,and the cumulative gas production rate is150.4 mL/gCOD.?3?On this basis,the methanogenic effect of the system will decrease instead of rising.The results showed that the hormesis effect of Fe ion concentration on methanogenic process was"low promotion and high inhibition".On this basis,the cumulative gas production rate was the highest when 10 mol/L NTA and 40 mg/L Fe⁰ were added together,then the results showed that the cumulative gas production rate was the highest when adding 10?mol/L NTA+40 mg/L Fe⁰.The promoting effect of 195.5 m L/gCOD was the most obvious,and the removal rate of COD was the highest?73.29%?,and the inhibition effect of sulfate reduction was the most obvious,and the removal rate of sulfate was the lowest?19.47%?.?4?In line with the change trend of gas production rate and substrate degradation rate of the system,the addition of Fe and its chelating agent makes methanogenic bacteria related enzymes?-glucosidase,dehydrogenase,pyruvate-Fe redox protein redox reductase,acetate kinase,and so on.The activity of phosphor transferase,hydrogenase and coenzyme F₄₂₀ was significantly increased,and the activity of sulfite reductase related to sulfate-reducing bacteria decreased significantly,but had no significant effect on the activity of aps reductase.When 10mol/L NTA+40 mg/L Fe⁰ was added,the activity of methanogenic bacteria was increased by2.53,0.46,1.62 and 2.10 times,respectively,and the activity of sulfite reductase was decreased by 2.10 times.The addition of Fe and its chelating agent increased the degradation rate of substrate while promoting methane production.When 10?mol/L NTA+40 mg/L Fe⁰was added,the degradation rate of polysaccharide and protein was higher than that of NTA and Fe⁰ alone.The degradation rate of polysaccharide was always higher than that of protein.?5?Fe and its chelating agents can significantly promote the hydrolysis and acidification process of the system.The addition of 10?mol/L NTA+40 mg/L Fe⁰ has the best effect on the hydrolysis and acidification of the system,which is associated with Fe and its chelates on the final protein of the system.The addition of Fe and its chelating agent increased the content of volatile fatty acids significantly on the 6th day of the reaction,which indicated that the acidification process of the system was strengthened,and the concentration of organic acids such as butyric acid and valeric acid decreased significantly.When 10?mol/L NTA+40 mg/L Fe⁰ was added,the concentration of acetic acid was the highest?0.50 g/L?,compared with the control group.In addition,the addition of Fe and its chelate significantly decreased the orp of the system.The addition of 40 mg/L Fe⁰ was the lowest,reaching to-343 MV.The time of peak value of dehydrogenase was advanced to the 4th day,and when 40 mg/L Fe⁰ was added,On 4th day,the activity of dehydrogenase was the highest,reaching 310.88 U/gVSS,which increased 256.22%.The peak of delivery was 6 days earlier,and the NTA group with 40 mg/L Fe⁰ and 10 mol/L NTA+40 mg/L Fe⁰ reached a higher gas production rate on the 4th day,which was 23.1 and 19.3 mL/gCOD,respectively,compared with the control group,increased77.69%and 48.46%.In the anaerobic sludge of the blank control group,Fe mainly exists as exchangeable state,sulphide state and residual state.The addition of Fe and its chelating agent makes trace elements transform from unstable to stable state.