| Conventional anaerobic digestion is a common process for sewage sludge stabilization.However,the hydrolysis process of sludge solid is very difficult in the anaerobic digestion,which results in the large volume and low rate of gas production.Various kinds of pretreatment technologies and new anaerobic digestion process have been studied in order to improve the performance of anaerobic sludge digestion.Thermal hydrolysis pretreatment(THP)is one of the most common pretreatment methods,which can improve the performance of anaerobic digestion of sludge effectively.However,it has many defects such as large energy consumption,high equipment requirements and operation risk.Address the above problems,our research includes the characteristics of thermophilic anaerobic co-digestion of sewage sludge and food waste,the influence of sludge concentration on its thermophilic anaerobic digestion performance based on low temperature THP,the influence of chemical conditioning on high concentration sluge after low temperature THP and the performance of post THP of sludge anaerobic digestion.The mechanism of different methods on thermophilic anaerobic digestion of sewage sludge are studied and energy budget of the different processes are compared.The main conclusions are as follows:(1)The performance of co-digestion of sludge and food waste is better than single digestion of sludge.The hydrolysis acidification process is very fast in the anaerobic digestion of food waste,which provide much VFA beneficial to the hydrolysis acidification and biogas production of anaerobic digestion of sludge.In co-digestion of sludge and food waste,the production of biogas and methane increased with the increase of organic loading rate.The methane production rate increased with the increase of organic loading rate firstly and then decreased.The operating condition can be set as follow:feed consists of sludge(TS:6%)and food waste in the ratio of 9:1,HRT is 16.7d and organic loading rate is 2.64 kg-VS/(m3·d).The methane production rate is 132.4 mL/g-VS and the reduce efficiency of organic matter is 47%.(2)THP has a significant effect on improving sludge anaerobic digestion performance.The gas production rate had greatly improved while the gas production had a certain growth.After THP the gas production rate of sludge with TS of 6%increased 45.8%while the gas production only increased 11.3%.The increase of the concentration of sludge had great contribution to gas production growth.However,the gas production rate decreased wirh the increase of the concentration of sludge.There was a plunge of the gas production rate between the sludge with TS of 9%and 12%,from 0.0068 h-1 to 0.0040 h-1.(3)The influence of different chemical conditioning on sludge pretreated by thermal hydrolysis varied widely.The order of gas production of each run was as follow:Acetic Acid>pH 3>pH 4.5>THP>pH 9>Hydrogen Peroxide>Un-pretreated>pH 8>Sodium Hypochlorite.Using acetic acid conditioning sludge after THP was more effective and its gas production was 323.7 mL/g-VS which was 22.9%more than Un-pretreated.Acid pretreatment is an ideal chemical conditioning on sludge after THP for anaerobic digestion,with high gas yield and relatively higher VS removal efficiency,without significant inhibition.However,the VS removal efficiency of the sludge conditioned by Acetic Acid is only 36.0%.On the contrary,using oxidant condition sludge after THP had low gas production but high VS removal efficiency.The VS removal efficiency of Hydrogen Peroxide and Sodium Hypochlorite were 54.9%and 47.1%.It will do positive effects to improve the performance of anaerobic digestion of sludge by combining the advantage of different chemicals to develop new kinds of composite chemicals.(4)The sludge characteristics of front THP and post THP is different.Most of readily biodegradable matter in sludge was degraded in anaerobic digestion process and the environment in sludge was changed.So the sludge after digestion had a certain buttering capacity and the remaining COD and carbohydrates were difficult to degrade.The un-pretreated sludge which stopped gas production in BMP can still yield gas with THP and the performance of its anaerobic digestion can be promoted by chemical conditioning.In BMP,the order of gas production of each run was as follow:Post THP+HCl>Post THP>Post THP+NaOH.Using hydrochloric acid conditioning sludge after post THP had better results.The gas production of Post THP+HCl was 113.0 mL/g-VS which was 19.2%higher than Post THP.(5)Among the five designed processes,only two post THP processes could output energy and the process of Post THP+HCl did the best,in which the average annual earnings of heat was 526610 kcal/d.Besides,the VS removal efficiencies in post THP were over 40%,Chemical conditioning had a significant effect on improving the benefits of the process.In a simulation of treating 50 tons of sludge in front THP process,using acetic acid conditioning pH to 4.5(THP+Hac)not only had a low cost of Y2.00 per ton of sludge,but also could reduce external energy supply 1,031,993 kcal/d.THP+Hac output 525KWh more electricity and increased VS removal efficiency by nearly 8 percentage points.Similarly,using hydrochloric acid improved energy outout 308,807 kcal/d with quite low cost in post THP processes. |
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