Effects of ultrasonic-assisted thermophilic bacteria pretreatment on hydrolysis, acidification, and microbial communities in waste-activated sludge fermentation process

Abstract

A novel pretreatment method combining ultrasonic with thermophilic bacteria (Geobacillus sp. G1) was employed to pretreat waste-activated sludge (WAS) for enhancing the WAS hydrolysis and subsequent volatile fatty acids (VFAs) production. The soluble protein and carbohydrate were mostly released from intracellular ultrasonic-assisted Geobacillus sp. G1 pretreatment, and accumulated to 917 ± 70 and 772 ± 89 mg COD/L, respectively, which were 2.53- and 2.62-fold higher than that obtained in control test. Excitation emission matrix (EEM) fluorescence spectroscopy revealed the highest fluorescence intensity (FI) of protein-like substances, indicating the synergistic effect of ultrasonic and Geobacillus sp. G1 pretreatments on WAS hydrolysis. The maximum VFAs accumulation was 4437 ± 15 mg COD/L obtained in ultrasonic-assisted Geobacillus sp. G1 pretreatment test. High-throughput pyrosequencing analysis investigated that the microbial communities were substantial determined by the pretreatment used. The hydrolysis enhancement was caused by an increase in extracellular enzymes, which was produced by one of dominant species Caloramator sp. The positive effect was well explained to the enhancement of WAS hydrolysis and final VFAs accumulation.

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

“…A further increase of SCOD of DOMs was obtained in the case of combined treatment, increasing by 6199 mg/L (11.48 times higher than control test). The more release of SCOD implied that more microbial cells and/or EPSs became soluble substrates from POMs under different pretreatment conditions [11,14,33]. A similar increasing trend was also observed in the case of soluble proteins and polysaccharides ( Fig.…”

“…S3). The two peaks were associated with tryptophan (Ex/Em 275/340, named component 1 (Com.1)) and tyrosine (Ex/Em 275/305, named component 2 (Com.2)) protein-like substances, respectively [11,12,14,42]. As shown in Fig.…”

“…The filtrate was immediately used to analyze SCFAs, polysaccharides, and proteins. The measurements of SCFAs, SCOD, TCOD, polysaccharides, proteins, TSS, VSS and pH were the same as the methods mentioned in our previous publications [11,14,21,33]. The SCFAs were regarded as the sum of acetic (HAc), propionic (HPr), n-butyric (n-HBu), iso-butyric (iso-HBu), n-valeric (n-HVa), and iso-valeric acids (iso-HVa) [11,33,34].…”

“…Details of spectra scan, elimination of inner filtering effect and Raman scattering, and parallel factor analysis (PARAFAC) were used to model EEM fluorescence data, could be found in our previous publication [11,14,33].…”

“…We used EEM spectra to comprehensively reveal the component changes of WAS under different conditions in terms of DOMs, LB-EPSs, and TB-EPSs [11,14,43,44]. And the PARAFAC, a chemometric method with three-way decomposition, was employed to separate the spectra of the main components from overlapped EEM spectra [41][42][43][44].…”