Dissolution Characteristics And Acid Production Of Excess Sludge Enhanced By The Pretreatment Of Thermal-alkali With Rhamnolipid

With the development of urban sewage treatment industry,the output of excess sludge is increasing year by year,which has the characteristics of large output and high content of organic matter,so it has great potential as resource recovery.However,due to the poor biodegradability of excess sludge,the added value of resource products is low.Therefore,it is particularly important to effectively treated and disposed sludge and enhanced the utilization value of sludge resources.In order to improve the biodegradability of excess sludge,rhamnolipid combined with thermal alkali was used to enhance the pretreatment of excess sludge.The process conditions and mechanism of thermal alkali rhamnolipid promoting the fermentation of excess sludge to produce acid were explored.The microbial species diversity and community structure characteristics of excess sludge under the condition of thermal alkali rhamnolipid were analyzed,It provides a new method to improve the acid production efficiency of sludge fermentation.The main conclusions and innovations are as follows:(1)Through the experimental study on the rhamnolipid with thermal alkaline synergistic pretreatment of excess sludge,it was found that rhamnolipid,NaOH,temperature of 40 mg/gVS,60 mg/gVS and 80? respectively had the highest cracking rate,and the cracking rate could reach 14.14%,18.55%and 19.23%respectively.The results showed that rhamnolipid promoted the formation of fulvic acids,and the maximum acid production appeared on the 3.5d of fermentation,which was acetic acid type fermentation;From the perspective of cost performance analysis,when NaOH was 20 mg/gVS,the acid production was the largest in the 1.5d,which was acetic acid fermentation,but with the increase of NaOH,the concentration of butyric acid gradually increased,which was acetic acid butyric acid alternating fermentation;When the temperature was 70?,the acid production was the highest on the first day,which was acetic acid fermentation.Comprehensive analysis showed that the optimal pretreatment conditions were 40 mg/gVS of rhamnolipid,20 mg/gVS of alkali and 70?.(2)By the compound design of response surface center,the relationship between variables(rhamnolipid,alkali and temperature)and response(dissolution rate and acid production)was established.The optimal conditions for increasing soluble organic matter of residual sludge and improving fermentation acid production were obtained:28.44 mg/gVS,35 mg/gVS and 80?,The dissolution cracking rate was 19.99%,the acid yield was 1631.27mg/l,and the fitting degree R2 was greater than 0.99.The results showed that the fermentation acid yield is increased significantly,1584.89 mg/L,and the error rate is 2.93%.It showed that the model can simulate the acid production of organic matter dissolution and fermentation.(3)The influence of rhamnolipid with thermal alkaline co-pretreatment on the structure of microbial group and the change characteristics of microbial flora were analyzed.It was found that there were significant differences among the samples,classes and genera under different environmental factors.Pretreatment factors only affect the quantity of microorganisms,but the difference of diversity and uniformity is not significant.However,rhamnolipid and alkali affect the changes of the population structure of fermentation acid producing microorganisms,especially the changes of Firmicutes and bacteria and Proteobacteria.(4)Taking rhamnolipid with thermal alkaline as pretreatment method,the mechanism of rhamnolipid with thermal alkaline synergistic pretreatment promoting acid production from excess sludge was analyzed.The results showed that the properties of hydrophilic and hydrophobic groups in rhamnolipid structure reduce the surface tension of solid-liquid interface,and hydrophobic alkyl groups interact with macromolecules in sludge cell wall and extracellular polymer to form complexes,which accelerate the transformation of organic matter from solid state to dissolved state The dissolution hydrolysis of dissolved carbohydrates and proteins and the transformation of biopolymerized substances to low molecular weight substances promote the dissolution of sludge and improve the efficiency of thermal hydrolysis and alkaline hydrolysis.In addition,rhamnolipid promoted the increase of Proteus phylum and alkali promoted the increase of Firmicutes phylum during anaerobic fermentation,which was conducive to the formation of VFAs.