Free nitrous acid serving as a pretreatment method for alkaline fermentation to enhance short-chain fatty acid production from waste activated sludge

Abstract

Alkaline condition (especially pH 10) has been demonstrated to be a promising method for short-chain fatty acid (SCFA) production from waste activated sludge anaerobic fermentation, because it can effectively inhibit the activities of methanogens. However, due to the limit of sludge solubilization rate, long fermentation time is required but SCFA yield is still limited. This paper reports a new pretreatment method for alkaline fermentation, i.e., using free nitrous acid (FNA) to pretreat sludge for 2 d, by which the fermentation time is remarkably shortened and meanwhile the SCFA production is significantly enhanced. Experimental results showed the highest SCFA production of 370.1 mg COD/g VSS (volatile suspended solids) was achieved at 1.54 mg FNA/L pretreatment integration with 2 d of pH 10 fermentation, which was 4.7- and 1.5-fold of that in the blank (uncontrolled) and sole pH 10 systems, respectively. The total time of this integration system was only 4 d, whereas the corresponding time was 15 d in the blank and 8 d in the sole pH 10 systems. The mechanism study showed that compared with pH 10, FNA pretreatment accelerated disruption of both extracellular polymeric substances and cell envelope. After FNA pretreatment, pH 10 treatment (1 d) caused 38.0% higher substrate solubilization than the sole FNA, which indicated that FNA integration with pH 10 could cause positive synergy on sludge solubilization. It was also observed that this integration method benefited hydrolysis and acidification processes. Therefore, more SCFA was produced, but less fermentation time was required in the integrated system.

Enhancing sludge biodegradability through free nitrous acid pre-treatment at low exposure time

“…It is well known that methane production (MP) from waste activated sludge (WAS) is often limited by the slow fermentation rates (hydrolysis and acidification) and its poor biochemical methane potential (BMP) [1][2][3][4][5][6][7][8][9][10]. To overcome this, recent research has been focusing on developing a novel, attractive and economic pre-treatment for WAS based on free nitrous acid (FNA) [6,7,[11][12][13][14].…”

Assessment of free nitrous acid pre-treatment on a mixture of primary sludge and waste activated sludge: Effect of exposure time and concentration

“…AD of waste activated sludge (WAS) is widely used to obtain methane from the organics present in the WAS. However, methane production in these systems is often limited by the slow fermentation rates of this substrate (hydrolysis and acidification) and its poor biochemical methane potential (Carrere et al, 2010;Liu et al, 2012;Wang et al, 2013Wang et al, , 2014Lee et al, 2014;Zhao et al, 2015;Li et al, 2016;Ennouri et al, 2016). To overcome this limitation, research has been focusing on developing novel WAS pretreatment methods to improve sludge biodegradability and enhance biogas production (Carrere et al, 2010;Liu et al, 2012;Lee et al, 2014).…”

Feasibility of short-term fermentation for short-chain fatty acids production from waste activated sludge at initial pH10: Role and significance of rhamnolipid

“…Currently, some methods had been applied to improve SCFAs production from WAS with anaerobic fermentation process, and Table S2 exhibits some typical methods reported in the previous publications. It was clear that, among these available methods, pH = 10 had been known as the most common way to enhance SCFAs production [27,28]. More interesting, SCFAs production could be further enhanced by adding RL into alkaline anaerobic fermentation process with a short-term fermentation time in this study.…”

“…On the other hand, it is cost-effective and operation-convenient, which is of great strategic significance. However, though the SCFAs production can be improved at pH 10, more than 60% of volatile suspended solids (VSS) could not be effectively degraded by microorganisms [27,28]. Thus, it is necessary to couple alkaline with other methods to further harvest improvement of SCFAs production from WAS.…”