| Hydrogen is regarded as the most potential clean energy for development in the 21 st century,but its production has been associated with high-cost and high-energy.In order to seek low-cost,high efficiency and high-purity hydrogen producing method,it will be focusing its attention to biological hydrogen production.Biological hydrogen production is hydrogen producing bacteria according to their physiological metabolism characteristics by decomposing organic matter to produce molecular hydrogen through fermentation process.Surplus sludge is the product of urban sewage and wastewater treatment by activated sludge method,and rich in organic matter,the organic matter into hydrogen by anaerobic fermentation is an effective way to solve the sludge,but also get clean energy.Surplus sludge contains large amounts of organic matter,but these are mainly concentrated in microbial cells,and difficult to be absorbed by microbes.In order to promote the hydrolysis of surplus sludge,in this investigation,researched the technology of papain pretreatment sludge and explore the optimal reaction conditions.Followed,using the pretreated sludge as the matrix to investigate anaerobic fermentation influence on surplus sludge performance and evaluate the significance of papain pretreatment on the hydrogen production from the type of ethanol fermentation.Experimental study shows that:(1)By optimizing the hydrolysis conditions of papain,finally get the best hydrolysis reaction conditions of the surplus sludge is that,enzyme concentration is 7.5mg/L,the reaction temperature is 72.5?,the reaction time is 5min.Under the condition,the surplus sludge SCOD/TCOD value of 59.9%,which increased by 31.8% compared with the original sludge,and COD solubility is 90%.(2)After pretreatment,the performance of surplus sludge is improvement,and the microbial cell wall is dissolve to a certain extent.The pretreated sludge anaerobic digestion system is more stable and has a stronger ability to balance the p H changes.Besides,the gas production rate and hydrogen purity has increased.(3)The relationship between surplus sludge ammonia nitrogen content and the time of papain process is close,the longer the duration of action,the higher the amount of ammonia nitrogen in sludge;The polysaccharide content in sludge increased significantly with the increase of enzyme dosage,but it was caused by the release of polysaccharides from microbial cells;Under suitable concentration of papain,the long chain fatty acids in sludge can be oxidized into short chain fatty acids.(4)During the operation of anaerobic fermentation reactor,the COD removal rate shows slightly decline and then gradually increase,finally stabilize.When the system is running mature the COD removal rate basically stable,the COD removal rate in the experimental group is 31% ~ 34%,and in the control group is 26% ~ 32%.(5)During reactor operation,the system oxidation reduction potential continue to decline,but gradually stable at around-230 mv on 50d;As reactor operation,the rapid increase in VFA content,the experimental group reached maximum at 35 d,about 1913mg/L,and the control group reached the peak value of 1466 mg/L at 50d;During operation,The effluent p H value tended to decrease until it stabilized at around 4.45,which showed the characteristics of ethanol type fermentation.(6)In the initial stage of reactor operation,the gas production rate is very low,and the hydrogen content is almost zero.With the reactor operation,the experimental group gas production rate reached the maximum value of 3405 m L/d at 44 d,while the control group until 50 d to reach the maximum value of 2945 m L/d,and generally lower than the experimental group daily gas production.As the reactor continues to operate,the system gas production rate and hydrogen purity is stable,the experimental group gas production rate is approximately 3300 m L/d,the hydrogen purity is 47%,and the control group gas production rate is 2900 m L/d,the hydrogen purity is 44%. |
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