| Excess sludge is a by-product of wastewater treatment,which is rich in a large number of organic pollutants,heavy metals,nutrients and so on.It has the properties of "pollution" and"resource".Volatile fatty acids(VFA)production from excess sludge by anaerobic fermentation is a common way of carbon source recovery.In order to solve the problems of slow hydrolysis rate and low acid production efficiency in the traditional anaerobic fermentation process of excess sludge,rhamnolipid(RL),low temperature thermal hydrolysis and the combination of the two methods were used to treat excess sludge,and the strengthening effects of various pretreatment methods on sludge cracking,organic matter dissolution characteristics and fermentation acid pro-duction were analyzed.The results are as follows:(1)The results of single factor experiment showed that the cracking effect of sludge in-creased with the increase of hydrolysis temperature.The highest degree of sludge cracking was found at 90℃,with COD concentration of 2743.3mg/L,sludge cracking degree of 7.4%,and dissolved organic carbon of 489.21 mg/L.The soluble carbohydrate(SC)reached 80.38mg/L,and the soluble protein(SP)concentration increased first and then decreased with the increase of hydrolysis temperature,reaching the maximum concentration of 13.6mg/L at 70℃.With the increase of hydrolysis temperature,the protein components of sludge gradually hydrolyzed and the degree of sludge humification decreased.During anaerobic fermentation,the maximum VFA production of 80℃ hot water hydrolyzed sludge reached 2474.41 mg/L,VFA is mainly composed of acetic acid and propionic acid.The increase of hydrolysis temperature can promote the con-version of long chain fatty acids to short chain fatty acids,so 80℃ is the best condition for sludge thermal hydrolysis.(2)RL single factor experiment showed that there was a significant positive correlation be-tween the hydrolysis degree of sludge and RL concentration.In the study range,the best RL dosage was 80 mg/gTS,the dissolution amount of SCOD reached 2971.1 mg/L,DOC reached 731.07 mg/L,and the sludge cracking degree reached 8.07%.The concentrations of SC and SP reached 127.11mg/L and 125.81mg/L respectively.High concentration of RL could promote the hydrolysis of protein like components,reduce the aromaticity of humus and promote the hydrol-ysis of macromolecular substances.RL pretreatment was helpful to the accumulation of VFA produced by anaerobic fermentation.When RL concentration was 80 mg/gTS,VFA production was the highest,which was 2699.39 mg/L.acetic acid and propionic acid were the main VFA produced.The increase of RL concentration significantly increased the concentration of n-butyric acid.Considering the RL dosage of 80 mg/gTS is the best condition for RL pretreatment.(3)The combined pretreatment has a significant synergistic effect on sludge cracking,and the combination of lower temperature and RL dosage can produce a cracking effect far greater than the corresponding single factor optimal conditions.The optimal conditions of combined pretreatment were RL concentration of 60 mg/gTS and 70℃,and the maximum acid production was 3294.96 mg/L.compared with single factor treatment,combined treatment was conducive to VFA accumulation,and the corresponding acid production was greater than single factor treat-ment,which indicated that combined pretreatment could enhance the fermentation acid produc-tion of sludge.Acetic acid and propionic acid were the main components of VFA in all treatment levels,Combined pretreatment can significantly enhance the acid production of excess sludge. |
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