Selective acetate production with CO 2 sequestration through acetogen-enriched sludge inoculums in anaerobic digestion

A hyperthermophilic anaerobic fermentation platform for highly efficient short chain fatty acids production from thermal hydrolyzed sludge

In this study, a carboxylate platform of hyperthermophilic (70 ℃) anaerobic fermentation (HAF) for short chain fatty acids (SCFAs) production from thermal hydrolyzed sludge (THS) was established. The long-term performance for SCFAs production and the microbial communities of this HAF under different SRTs were systematically investigated. Under the optimum SRT of 3 d, the HAF had the highest acetate production rate of 1.12 g COD/L/d which accounted for 60% in SCFAs. It also rendered a good performance in SCFAs production, with concentration, production rate and yield of 6.61 g COD/L, 1.86 g COD/L/d and 324 g COD/kg VSSin, respectively. Nearly no biogas produced from this system, which reduced the loss of carbon sources from the system. This was due to the inhibition of methanogenesis by the hyperthermophilic condition and the high content of total ammonia nitrogen (TAN) and free ammonia nitrogen (FAN). Tepidimicrobium, Bhargavaea and XBB1006 were the dominant genus-level biomarkers under the optimum SRT, which facilitated the decomposition of monosaccharides, amino acids, terpenoids and polyketides into SCFAs. This work provides an applicable anaerobic carboxylate platform for highly efficient SCFAs production from excess sludge.

Effect of ultrasonic pretreatment on chain elongation of saccharified residue from food waste by anaerobic fermentation

Converting biowaste into value-added products has raised the researchers' interests. In this study, bioconversion was applied to produce chain acids from food waste by anaerobic fermentation. To improve the caproic acid production, different pretreatments (i.e., ultrasonic, hydrothermal, and alkaline-thermal) were used for investigating their effects on the acidogenic production and microbial communities. The results showed that ultrasonic and hydrothermal pretreatments (207.8 and 210.1 mg COD/g VS, respectively) were very efficient for enhancing the caproic acid production, compared to the alkaline-thermal pretreated samples and control samples (72.6 and 97.5 mg COD/g VS, respectively). The ultrasonic pretreatment was beneficial for reducing volatile fatty acids (VFAs) during the caproic acid production, resulting in converting more lactic acid to caproic acid by adding the hydrothermal pretreatment. The microbial community analysis showed that the acidogenic bacteria Caproiciproducens dominated the fermentation in this bioconversion process of food waste into chain acids. The Caproiciproducens mainly degraded the proteins and carbohydrates from the saccharified residues of food waste to produce caproic acids through chain elongation procedure. The investigation and optimized method may help develop the bioconversion technology for producing VFAs products from food wastes.

A critical review of volatile fatty acids produced from waste activated sludge: enhanced strategies and its applications

This paper reviews the recent achievements in the enhanced production of volatile fatty acids (VFAs) from waste activated sludge (WAS). The enhanced strategies are divided into two approaches. The first strategy focuses on the regulation of carbon-to-nitrogen (C/N) ratio by co-digestion of WAS with carbon-rich substrates, including municipal solid wastes (MSW), marine algae, agricultural residues, and animal manures. The other strategy is to enhance the solubilization and hydrolysis of WAS or inhibit the methanogenesis by applying various pretreatments, such as mechanical, chemical, enzymatic, and thermal pretreatment. Finally, the applications of WAS-derived VFAs are discussed. The future researches in enhancing VFAs production and wide application of the VFAs from both technical and economic perspectives are proposed.

Benefit of solid-liquid separation on volatile fatty acid production from grass clipping with ultrasound-calcium hydroxide pretreatment

Ultrasound-calcium hydroxide (US-Ca(OH)₂) pretreatment effectively enhanced volatile fatty acid (VFA) production from lignocellulosic biomass. In this paper, solid and liquid fraction of pretreated grass clipping was for the first time separately fermented in order to improve organic recovery from liquid fraction and reduce inhibition due to alkaline pretreatment. The total VFA yield and VS removal reached 515 mg/g TS and 59.7% after solid-liquid separation, exhibiting an increase of 116.7% and 91.9% comparing to that of mixture sample. The dominate components of VFAs are acetic and propionate acid, accounting for 80-90% of total VFAs. Kinetic analysis showed that the highest maximum VFA production rate of 690 mg/L·d and the highest cumulative VFA production potential of 3299 mg/L were achieved in the fermentation of solid fraction. Microbial analysis showed that the dominate genera for VFA production were Halocella and Ruminiclostridium, both with a relative abundance of 20.1% in fermentation of solid fraction.