Biological Nutrients Removal Driven By Fermentative Short-chain Fatty Acids From Excessive Sludge Improved By Surfactant

This thesis examined the feasibility of using fermentative Short-chain Fatty Acids (SCFA, which was produced from waste activated sludge affected by surfactant) as the carbon sources of biological nutrient removal (BNR) system, Which has been focused in the research of the metabolic mechanism of nitrogen, phosphorus, SCFA, polyhydroxyalkanoates (PHAs), glycogen et al.Firstly, the research emphasized on two problems, namely dewatering of fermentation liquid and recycling of nitrogen and phosphorus. The experimental results showed that, Polyacrylamide (PAM) can significantly improve the sediment performance and dewatering speed of the fermentation sludge, but to a certain extent, this process also reduced the SCFA concentration of fermentation liquid. For the other hand, the concentrations of nitrogen and phosphorus in fermentation liquid were still very high, so, struvite precipitation was used to handle this ploblem. In this pape, Response surface methodology(RSM) was used to investigate the effect of Mg/N, P/N and pH on the removal of nitrogen and phosphorus. Using the software of Design-Expert, a response surface quadratic model in terms of actual factors was obtained based on the experimental data.The optimum Mg/N, P/N and pH were found to be 1.66, 1.49, and 9.7 respectively and the highest nitrogen and phosphorus removal efficiency(83% and 99% respectively)could be achieved.An enhanced biological phosphorus removal(EBPR) system was developed using fermentative SCFA as the only carbon source .After a period of acclimation, it was observed that the phosphorus removal efficiency was above 95%, n-butyric, propionic and acetic acids were used by PAOs preferentially, The synthesis and degradation of PHV was higher than PHB. Compared with the EBPR system enriched using acetate as the sole carbon sources, fermentative SCFAs caused much higher SOP removal than acetate, which were due to less PHAs used for glycogen synthesis and higher PHAs utilization efficiency for SOP uptake.Process conditions were adjusted to alternating anaerobic/anoxic/aerobic conditions, after a period of acclimation, the system has higher nitrogen and phosphorus removal capacity, TP, NH₄-N and TN removal efficiency were stable at 97%, 95% and 81%, respectively. Further study showed that, in the aerobic phase, PHAs was oxidsed mainly by PAOs to take up excessive amounts of orthophosphate to recover the intracellular polyP levels; in anoxic stage, PHAs was consumed mainly by the denitrifying bacteria as carbon source. In the BNR system using fermentative SCFA as the carbon source, nitrification production in the aerobic phase were mainiy in the form of nitrite, the output ratio of nitrite and nitrate was about 3:1, which means that it's about 75% of the nitrogen was denitrificated through the short - cut nitrification /denitrification ways.