Impact Of Surfactant On Fermentation Of Waste Activated Sludge

The city sewage treatment plants produce massive sludge. If the sludge could be reused, not only its environmental pollution can be reduced, but also its application value can be improved. As one part of the work of National Science Foundation and Fok Ying Tung Education Foundation, this paper focused on the fermentation of waste activated sludge (WAS) with surfactant, compared the influence of four surfactants on the acidogenesis of waste activated sludge, studied with emphasis on the effect of sodium dodecyl sulfate (SDS) and linear alkylbenzene sulphonates (LAS) respectively on the acidogenesis of WAS, researched the improvement of SDS to the acidogenesis under different pH, and analyzed their mechanism preliminarily. These results have been published in Acta Scientiae Circumstantiae and applied for China patent for invention.It’s the first time to find that volatile fatty acids (VFA) production was enhanced by surfactant. The VFA production of WAS was obviously higher with addition of surfactant than that in blank test, and SDS showed the highest VFA production comparing the effect of four surfactants on the fermentation of WAS.Further studies indicated that the maximum VFA production increased with the dosage of SDS. However, longer time was needed for WAS treated with higher SDS dosage to reach its own maximum VFA production than that treated with lower SDS dosage. Therefore, 0.10 g/g at a ratio of surfactant dosage to dry sludge was the desirable dosage for SDS according to cost and effectivess. Concentrations of soluble carbohydrate and protein increased with the dosage of SDS, providing large amount of subtrates for acidogenic bacterias. As SDS may be degraded into VFA, so LAS, which can not degrade under anaerobic condition, was choosen to testify whether the hydrolysis and acidification of WAS can be greatly improved by surfactant. It also showed that VFA production was significantly enhanced in the presence of LAS, and concentrations of soluble carbohydrate and protein increased with the dosage of LAS, suggesting again that surfactant influenced the fermentation of WAS. Compared with SDS, the desirable dosage for LAS is lower, which is 0.02 g/g. It was also observed that the influence of SDS on WAS fermentation varied with pH value. It’s not good for SDS to improve the fermentation of WAS at pH=4.0, 5.0 or 6.0, while it’s enhanced by SDS at pH=7.0, 8.0, 9.0 or 10.0. VFA production from WAS treated with SDS at pH =10.0 was the highest.As influence of surfactant on the fermentation of WAS was discovered for the first time, its mechanism was not clear and need further investigation. The reason for large amount of VFA accumulation in the presence of SDS was due to the improvement of hydrolysis of sludge and the inhibition of methanogenesis by SDS. Also, the production of VFA from fermentation of WAS was proved to be the microbiological effect.