Effect of optimized intermittent mixing during high-solids anaerobic co-digestion of food waste and sewage sludge: Simulation, performance, and mechanisms

Simultaneously enhancement of methane production and active phosphorus transformation by sludge-based biochar during high solids anaerobic co-digestion of dewatered sludge and food waste: Performance and mechanism

Biochar has been proved to improve methane production in high solids anaerobic co-digestion (HS-AcoD) of dewatered sludge (DS) and food waste (FW), but its potential mechanism for simultaneous methane production and phosphorus (P) transformation has not been sufficiently revealed. Results showed that the optimal preparation temperature and dosage of sludge-based biochar were selected as 300 °C and 0.075 g·g-1, respectively. Under this optimized condition, the methane production of the semi-continuous reactor increased by 54%, and the active phosphorus increased by 18%. The functional microorganisms, such as Methanosarcina, hydrogen-producing, sulfate-reducing, and iron-reducing bacteria, were increased. Metabolic pathways associated with sulfate reduction and methanogenesis, especially hydrogenotrophic methanogenesis, were enhanced, which in turn promoted methanogenesis and phosphorus transformation and release. This study provides theoretical support for simultaneously recovery of carbon and phosphorus resources from DS and FW using biochar.

Significance of homogeneous operation in light-assisted fixed-bed bioprocess under ammonia stress: Optimization, long-term operation and metagenomic analysis

Activating microbes with light is a promising strategy for addressing ammonia-stressed anaerobic digestion (AD). However, as a critical in-process parameter, homogenous operation, in light-assisted AD amended by bio-fixed bed has received limited attention. This research endeavors to establish a uniform-illuminated biosystem and assess its practical feasibility through a 90-day semi-continuous operation at pilot scale under solar light illumination. With optimal stirring mode (intermittent stirring for 3 min every 15 min), robust methane yields were achieved across various organic loads, reaching 88.7-94.3% of theoretical yield under high ammonium stress (3500 mg/L). The metagenomic analysis unveiled that uniform illumination triggered synergistic effects in AD, fostering a diversified microbial consortium, enhancing carbohydrate and methane metabolism, and facilitating the formation of an electroactive bio-cluster. This study underscores the significance of homogenous illumination in AD systems for efficient waste-to-energy conversion, highlighting the implementation of solar light as a greener approach for scale-up application.

Mass Transfer Enhancement in High-Solids Anaerobic Digestion of Organic Fraction of Municipal Solid Wastes: A Review

The increasing global population and urbanization have led to a pressing need for effective solutions to manage the organic fraction of municipal solid waste (OFMSW). High-solids anaerobic digestion (HS-AD) has garnered attention as a sustainable technology that offers reduced water demand and energy consumption, and an increased biogas production rate. However, challenges such as rheology complexities and slow mass transfer hinder its widespread application. To address these limitations, this review emphasizes the importance of process optimization and the mass transfer enhancement of HS-AD, and summarizes various strategies for enhancing mass transfer in the field of HS-AD for the OFMSW, including substrate pretreatments, mixing strategies, and the addition of biochar. Additionally, the incorporation of innovative reactor designs, substrate pretreatment, the use of advanced modeling and simulation techniques, and the novel conductive materials need to be investigated in future studies to promote a better coupling between mass transfer and methane production. This review provides support and guidance to promote HS-AD technology as a more viable solution for sustainable waste management and resource recovery.

Enhancing of pretreatment on high solids enzymatic hydrolysis of food waste: Sugar yield, trimming of substrate structure

The development of high solids enzymatic hydrolysis (HSEH) technology is a promising way to improve the efficiency of bioenergy production from solid waste. Pretreatment methods such as ultrasound (USP), freeze-thaw (FTP), hydrothermal (HTP), and dried (DRD) were carried out to evaluate the effect and mechanism of the pretreatment methods on the HSEH of FW. The reducing sugar of HTP and DRD reached 94.75% and 94.92% of the theoretical value. HTP and DRD could reduce the crystallinity of FW. DRD resulted in lower alignment and the occurrence of fractures of the substrate and exposed the α-1,4 glycosidic bond of starch. The high destructive power of HTP and DRD reduced the obstacles caused by the high solid content. Moreover, DRD consumed only 27.62% of the total energy of HTP. DRD could be a promising pretreatment methods for glucose recovery for its high product yield, significant substrate destruction, and economic feasibility.

Pilot-scale two-phase anaerobic digestion of deoiled food waste and waste activated sludge: Effects of mixing ratios and functional analysis

Anaerobic co-digestion of deoiled food waste (dFW) and waste activated sludge (WAS) can address the challenges derived from mono-digestion of FW. In the present study, a pilot-scale methanogenic bioreactor of a two-phase anaerobic digestion system was developed to explore the impact of dFW/WAS volatile solids ratios on the overall performance, microbial community, and metabolic pathways. Besides, the tech-economic of the system was analyzed. The results showed that the degradation efficiency of soluble chemical oxygen demand (SCOD) was more than 84.90% for all the dFW/WAS ratios (v/v) (1:0, 39:1, 29:1, 19:1 and 9:1). Moreover, the dominant genus of bacteria and archaea with different ratios were Lactobacillus (66.84-98.44%) and Methanosaeta (53.66-80.09%), respectively. Co-digestion of dFW and WAS (29: 1 in v/v ratios) obtained the highest yield of methane (0.41 L CH₄/L_added) with approximately 90% of SCOD being removed. In the pilot-scale experiment, the co-digestion of FW and WAS makes positive contribution to reusing solid waste for improving solid management.

Insights into high-solids anaerobic digestion of food waste concomitant with sorbate: Performance and mechanisms

High-solids anaerobic digestion (HS-AD) of food waste is increasingly applied commercially. Sorbate, a food preservative extensively used in the food industry, induces potential environmental risks. Results indicated sorbate at 0-10 mg/g VS slightly inhibited methane production, and the cumulative methane yield suggested a negative correlation with 25 mg/g VS sorbate, with a reduction of 15.0% compared to the control (from 285.7 to 253.6 mL CH₄/g VS). The reduction in methane yield could be ascribed to the promotion of solubilization and inhibition of acidogenesis and methanogenesis with sorbate addition. Excessive sorbate (25 mg/g VS) resulted in the inhibition of aceticlastic metabolism and the key enzymes activities (e.g., acetate kinase and coenzyme F₄₂₀). This study deeply elucidated the response mechanism of HS-AD to sorbate, supplemented the potential ecological risk assessment of sorbate, and could provide insights to further prevent the potential risk of sorbate in anaerobic digestion of FW.

Anaerobic co-digestion of food waste and sewage sludge in anaerobic sequencing batch reactors with application of co-hydrothermal pretreatment of sewage sludge and biogas residue

The effect of pretreatment technologies and reactor types on conversion efficiency and operating costs of anaerobic co-digestion of food waste and sewage sludge were investigated by 300-day continuous experiments. The volatile solids (VS) removal efficiency increased from 61% to 77% with the application of co-hydrothermal pretreatment of sewage sludge and biogas residue. Deep dewatering reduced the volume of hydrothermally pretreated biogas residue by 85%. When continuous stirred tank reactors (CSTRs) were converted to anaerobic sequencing batch reactors (ASBRs), vS removal efficiencies increased by 6%, attributed to a 1.4-1.6-fold increase in solids retention time (SRT). The bottom drainage of mineralized sludge every 40 days increased ASBR stability. Firmicutes and Methanosphaera dominated the bacterial and archaeal communities, respectively. Operating costs decreased by 14.9 US$/metric ton feedstock by applying ASBRs. Compared to CSTRs, ASBRs achieved higher organic matter conversion efficiency, smaller volume of biogas residue, and lower operating costs.