| A large amount of waste activated sludge(WAS)is produced in the biological treatment unit of WWTP,and how to realize the high effcient resource conversion of sludge will be an important breakthrough to solve the sludge pollution and alleviate the resource shortage in our country.The recovery of high value-added volatile fatty acids(VFA)from sludge via anaerobic fermentation process has attracted much attention.The C/N of WAS is low in our country,and adding carbon source in fermentation system can solve the problem of nutrient inbalance of fermentation substrate.As a kind of carbon-rich substance,waste cooking oils(WCOs)is a good carbon source for adjusting the nature of WAS.In this paper,WCOs was used as carbon source in laboratory scale expriment.Based on the WAS adjusted with WCOs,the effects of different process conditions on the production of VFA was tested,and the upgrade strategy of acidification efficiency was preliminarily explored.The main results are as follows:(1)The acidification efficiency of conditining sludge was investigated under p H controlled at 5,6,7,9 and 10.During anaerobic fermentation of conditining sludge,Controlling p H can significantly change the degradation behavior of the substrate.Under alkaline conditions,WAS releasd more carbohydrate and protein into the liquid phase but the degradtion of both was not improved.p H10 was considered as the better fermentation p H.In p H10,The maximum yield was 248 mg COD/L and the fermentation broth did not appear the phenomenon of sludge flotation.In the components of VFA in R-p H10,more acetic acid was synthesized and the proportion of acetic acid was approximately 57%.There was a large amount of LCFA not degraded,and the acidification efficiency needed to be improved.The higher proportion of acetic acid in p H10 was due to the presence of more Acetoanaerobium,while the more propionic acid in p H6 was related to Propionispira.(2)The effect of the proportion and feeding mode of WCOs on the fermentation were studied.When the proportion of WCOs was 0.57g/g TS,the accumulation of VFA was superior to others,and the maximum concentration of TVFA was 3550.80 mg COD/L,higher than that of Control group by 1205.77 mg COD/L.The relative abundance of Proteiniclasticum,Preoteinivorax and Alkaliphilus in the reactors with WCOs were significantly higher than that without WCOs.In the experiment of changing the feeding mode of WCOs under the same load,the pulse feeding had a slight advantage in long-term fermentation.If the fermentation cycle was shortened,the initial one-time feeding produce the fastest rate of VFA.The timing and manner of WCOs had little effect on the composition of volatile fatty acids.(3)The accumulation of LCFA is the key factor that limits the futher promotion of acidification efficiency under alkaline condition.In order to solve this problem,the effect of sulfate radical and sulfate radical copuling granular activate carbon(GAC)on fermentation was studied.At low dosage(<1200mg S/L),the promotion effect was not obvious.When the dosage reached 1200 mg S/L,the accumulation of VFA increased significantly,more than 4 times as that of the control group.The concentration monitoring of LCFA showed that the contents of two major LCFA,i.e.oleic acid(C18:1)and linoleic acid(C18:2),decreased significantly in the rapid accumulation phase of VFA in the experimental group of 1200 mg S/L,and the sulfate radical of the system decreased rapidly.Sulfate radical coupling GAC could shorten the time to reach the maximum amount of volatile fatty acid on the basis of maintaining the fermentation efficiency.The ratio of acetic acid to TVFA in single sulfate and GAC coupled sulfate addition was about 80%,which improved the purity of organic acids.High-throughput sequencing revealed that the rapid accumulation of acetic acid in the 1200 mg S/L reactor might be related to the increase of Desulfotulus(Sulfate-reducing bacteria),which significantly promoted the oxidation of LCFA to VFA under exprimental conditions. |
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