Effect Of Sludge Retention Time And Temperature On Continuous Short-chain Fatty Acids (SCFAs) Production From Waste Activated Sludge

The studies on the anaerobic fermentation of sludge in the literature mainly focus on the treatment of the primary or its mixture with waste activated sludge(WAS). However, there are few studies regarding the anaerobic fermentation of single waste activated sludge .And researches on continuous short-chain fatty acids (SCFAs) production from waste activated sludge have not been reported till now. Considering the continuous operation in practical wastewater treatment plant , the effect of sludge retention time(SRT) and temperature on SCFAs production from waste activated sludge by alkaline pH controlling or adding surfactant was investigated in a series of continuous-flow reactors in this paper.Firstly, the effect of different SRT and temperature on waste activated sludge hydrolysis and acidogenesis by alkaline pH controlling(pH10) or adding surfactant(sodium dodecylbenzene sulfonate, SDBS) was investigated in continuous reactors. The experimental results showed that under a certain SRT, the soluble protein and carbohydrate maintained a stable value within the research time. And the increase of SRT benefited the hydrolysis of WAS. SCFAs accumulation improved along the increase of SRT when SRT was less than 12 days .Primary experimental results showed that the best SRT was 12d for both only controlling pH10 and adding SDBS conditions ,and the average SCFAs concentration was 934mgCOD/L and 1149.7mgCOD/L respectively ,which was 3.6 and 4.4 times of the SCFAs concentration in blank test. Acetate was the most content among six kinds of individual SCFAs , iso-valeriate and propionate were the second and the third , n-butyric and n-valeriate were the least content compositions of the SCFAs under every SRT within the research extent. Under only controlling pH10 and SDBS conditions, the percentage of acetate and propionate accounting for total SCFAs were respectively 40.1% and 16%,56.3%and8.5%. SDBS benefited the acetate and pH10 benefited the propionate properly. And the increase of SRT benefited the release of ammonia in the sludge. Further research showed that the hydrolysis of WAS and the concentration of SCFAs were improved when the temperature increased from 10℃to 35℃. Greater SCFAs concentration rising rate was found when the temperature increased from 10℃to 30℃compared to the SCFAs concentration rising rate when the temperature increased from 30℃to 35℃, thus properly increase of the temperature benefited the concentration of SCFAs. And increase of the temperature benefited the release of ammonia and phosphate in the sludge.The effect of combination of alkaline pH controlling and adding surfactant on waste activated sludge hydrolysis and acidogenesis in continuous-flow reactors were also investigated under SRT was 12d and the temperature was 20℃. The results showed that the soluble protein and carbohydrate maintained a stable value within the research time. Persistant controlling pH 10 benefited the hydrolysis of waste activated sludge compared to the mothed of controlling the sludge pH10 for 8 days and then adding SDBS to the reactor. Controlling pH10 and adding SDBS to the reactor at the same time improved the hydrolysis and the SCFAs production (2055.8mgCOD/L )of the WAS compared to only controlling pH 10 or adding SDBS. The percentage of acetate and propionate accounting for total SCFAs were respectively 49.6%andl2.2 % when controlling pH10 and adding SDBS to the reactor at the same time, which between the value of only controlling pH 10 and adding SDBS. More ammonia release was found when combination of alkaline pH controlling and adding surfactant compared to only controlling pH 10 or adding SDBS.The decrease of the volatile suspended solids(VSS) was found when only controlling pH 10,only adding SDBS and the combination of controlling pH 10 and adding SDBS conditions , which was 39.4%,33.8%and 31.6% respectively.