Free Ammonia-Based Pretreatment Promotes Short-Chain Fatty Acid Production from Waste Activated Sludge

Abstract

This work reports a new waste activated sludge (WAS) pretreatment method based on free ammonia (FA) for promoting the generation of short-chain fatty acids (SCFAs). Experimental results showed that pretreatment of WAS for 3 days with FA largely improved WAS disintegration, with the highest dissolution (soluble chemical oxygen demand (COD), 3400 ± 120 mg/L at initial FA level of 237.8 mg/L) being 4.5-fold that without FA pretreatment. The pretreatment method by FA facilitated the breakdown of extracellular polymeric substances and cell envelope of sludge cells and killed more live microbial cells, which thereby accelerated the dissolution of substances from WAS. It was also found that FA severely suppressed the SCFA consumption process, but the acetogenesis process was unaffected. Although FA also inhibited hydrolysis, acidogenesis, and homoacetogenesis to some extent, the inhibitions did not largely affect the biodegradation of the relevant substances at all the tested FA levels. Finally, using FA to pretreat WAS for SCFA enhancement was confirmed. When FA concentrations ranged from 53.5 to 176.5 mg/L, the maximum generation of SCFA was enhanced from 196.8 to 267.2 mg COD/g VSS, which was 2.3−3.2 times that of the blank. Further FA leveling (237.8 mg/L) caused a slight decline of maximum SCFA generation (226.9 mg COD/g VSS). The findings reported may instruct engineers to develop an economic and effective strategy to enhance SCFA production, which might support the operation of wastewater treatment plants in sustainable paradigms with low energy input in the future.

Effect of free ammonia inhibition on NOB activity in high nitrifying performance of sludge

“…In recent years, some researchers have proposed a new strategy to increase bioenergy recovery from wastewater or sludge treatment using FA. [15][16][17][18] They demonstrate that pre-treatment of the activated sludge with FA for 24-40 h could reduce sludge yields by 20%. At the same time, the NOB activity could be decreased to some extent without any adverse impact on the reactor performance.…”

Feasibility of enhancing short-chain fatty acids production from waste activated sludge after free ammonia pretreatment: Role and significance of rhamnolipid

“…Previous study also showed that 40 mg FA/L posed 80% inhibition to the activity of methanogens (Mccarty and Mckinney, 1961). When 178.4 mg FA/L was applied to pretreat sludge 3 d, the maximum SCFA production (267.2 mg COD/g VSS) was achieved at fermentation time of 8 d, which was 3.2-fold of that from the control (without FA pretreatment) (Zhang et al, 2018). Although FA was an effective and validated pretreatment method with significant contribution, the maximal SCFA production required long fermentation time (8 d) and more than 60% of VSS could not be degraded during anaerobic fermentation, which inevitably, to some extent, weakens the its values, hindering its further application in real-world situations.…”

Dehydrated apple‐based snack supplemented with Agave fructans exerts prebiotic effect regulating the production of short‐chain fatty acid in mice

“…SCFA are a subset of saturated fatty acids with six or less carbon molecules (e.g., acetate, propionate, and butyrate). These are produced by acidogenesis, acetogenesis, and homoacetogenes bacterial processes (Zhang et al, ). Besides, SCFA may be further re‐captured for energy recovery which might later be used as a raw substrate for other microorganism reactions (Wang et al, ).…”

“…These are produced by acidogenesis, acetogenesis, and homoacetogenes bacterial processes (Zhang et al, 2018). Besides, SCFA may be further re-captured for energy recovery which might later be used as a raw substrate for other microorganism reactions .…”