Anaerobic Digestion Of Food Waste Research Articles

Lipase pretreatment enhances biochar‐assisted anaerobic digestion of food waste

AbstractAnaerobic digestion is a promising technology for the treatment of food waste (FW) but it requires optimization to improve its performance. This study investigated whether combining the addition of biochar with lipase pretreatment could improve the anaerobic digestion of FW. The results showed that biochar stimulated the release of soluble substances, resulting in an increase in the methane yield of groups with added biochar by 16.24% to 19.36% in comparison with the group without biochar. Lipase pretreatment substantially shortened the fermentation time required to complete the anaerobic digestion, from 15 to 9 days. Lipase pretreatment further improved microbial abundance and promoted the enrichment of functional microbes in the anaerobic digestion of FW mediated by biochar. It also changed the methane production pathway from acetotrophic to hydrogenotrophic, thereby ensuring the stability of the anaerobic digestion system in the presence of a high ammonia nitrogen concentration.

Optimizing food waste anaerobic digestion in Kuwait: Experimental insights and empirical modelling using artificial neural networks.

This study investigates, for the first time, the anaerobic digestion of food waste in Kuwait to optimize methane production through a combination of artificial neural network (ANN) modelling and continuous reactor experiments. The ANN model, utilizing eight hidden neurons and a 70-20-10 split for training, validation and testing sets, yielded mean squared error values of 0.0056, 0.0048 and 0.0059 and coefficient of determination (R²) values of 0.9942, 0.9986 and 0.9892, respectively. Methane percentages in biogas were predicted using six parameters: biomass type, pH, organic loading rate (OLR), hydraulic retention time (HRT), temperature and reactor volume. To validate the ANN results, continuous reactor experiments were conducted under an OLR of 3 kg VS m⁻³ d⁻¹ and HRT of 20 days at varying temperatures (35°C, 40°C, 45°C, 50°C and 55°C). The experiments demonstrated optimal methane production in the mesophilic range, with ANN predictions closely aligning with experimental data up to 45°C. However, deviations were observed at higher temperatures, particularly under thermophilic conditions beyond 50°C. This study provides novel insights into waste-to-energy initiatives in Kuwait and highlights the potential of integrating computational models with empirical data to enhance biogas production processes.

Efficient resource recovery from food waste digestate via hydrothermal treatment and its application as organic fertilizer

With the continuous recognition of green, organic and non-polluting products, organic fertilizers play an increasingly vital role in agricultural production. Among them, hydrochar-based organic fertilizer has attracted widespread attention recently. The present study evaluated the potential of digestate from anaerobic digestion of food waste for the preparation of hydrochar-based organic fertilizer by straw-based, FeCl3-catalyzed hydrothermal carbonization (HTC). Under the optimal conditions, a hydrochar-based organic fertilizer with > 25 wt% humus content and limited pollution risk was successfully prepared. The pot experiment demonstrated the feasibility of improving the physicochemical properties of red soil and promoting crop growth after adding hydrochar in place of commercial fertilizer. In addition, the function of zeolite on nutrient recovery in hydrothermal liquid (HTL) was analyzed, and preparing the slow-release organic fertilizer by mixing the nutrient-rich zeolite with hydrochar in a mass ratio of 1:4 was proposed. This work has significant implications for achieving the efficient resource recovery of digestate.

Mass flow and ecological risk of heavy metals in anaerobic digestion of food waste

Conversion of food waste (FW) to bioenergy via anaerobic digestion (AD) has become a topic of worldwide research interest. However, the content, distribution, and speciation of heavy metals (HMs) in feedstock and digestate samples throughout the AD process are currently unknown. Especially, the potential ecological risk (PER) of solid digestate with potential of land application was vague. Mass flow of HMs (Cr, Cu, Mn, Ni, Zn, As, Cd, Hg, and Pb) were estimated in a two-stage wet AD of FW plant in Shenzhen, China. Furthermore, the PER of the HMs in solid digestate (SD) was studied. The findings revealed that the variation in the HM contents of the intermediates, as well as the comparatively high HM contents of the SD, were mostly influenced by the total solid contents of the samples, since HMs tend to adhere to the solid matrix. As per mass balance, the Cr and Ni contents of the digestate samples were 4.7 and 5.5 times higher than in the feedstock samples, respectively. The remaining metals were within the range of 82.2126.1%. Furthermore, the enrichment of HMs in SD must be resolved before reclamation. Moreover, the PER of the HMs in SD was 279.6, considered as a considerable risk level, of which Hg and Cd contributed 46.3% and 33.6%, respectively. This research presents a case study for quantitatively assessing the distribution of typical pollutants throughout the AD process, and it offers preliminary data for potential environmental issues caused by digestion product recycling.

Improved Anaerobic Digestion of Food Waste under Ammonia stress by Side-Stream Hydrogen Domestication

High ammonia concentration inhibits archaea's activity, causing the accumulation of H2 and acetate, which suppresses methane production in anaerobic digestion (AD). The study aimed to enhance microbial hydrogen metabolism through a side-stream hydrogen domestication (SHD) strategy, which involves applying hydrogen stimulation to a portion of the sludge separately. SHD maintained a stable methane yield of 407.5 mL/g VS at a high total ammonia nitrogen (TAN) concentration of 3.1 g/L. In contrast, the control group gradually decreased and stopped methane production at a TAN concentration of 2.3 g/L. Further analysis using enzyme activity assays, flow cytometry, and metagenomics explored the mechanisms underlying ammonia tolerance of SHD-treated group. SHD reshaped the microbial community, enriching homoacetogens and Methanosaeta-dominated methanogenic archaea. Key metabolic pathways including homoacetogenesis, butyrate degradation, propionate degradation, and methane production were enhanced. The activity of related enzymes also increased. Gene abundance in energy-generating pathways, such as glycolysis, was enhanced, ensuring adequate ATP production. Additionally, the high gene abundance of ion transport systems contributed to regulating proton imbalance and supplementing intracellular K+. This study provides important insights and practical guidance for developing novel techniques in the field of anaerobic digestion.

Exploring interactive effects of environmental and microbial factors on food waste anaerobic digestion performance: Interpretable machine learning models

Biogas yield in anaerobic digestion (AD) involves continuous and complex biological reactions. The traditional linear models failed to quantitatively assess the interactive effects of these factors on AD performance. To further explore the internal relationship between target variables and AD performance, this study developed four machine learning models to predict biogas yield and consider the interaction among various factors. Results indicated that the highest prediction accuracy of AD performance was achieved by adding bacterial genera dataset with environmental factors. Random forest model exhibited the highest accuracy, with the testing coefficient of determination equal to 0.9879. Among two types of input features, the bacterial genera accounted for 89.9 % of the impact on biogas yield, followed by environmental factors. The results revealed Keratinibaculum and Acetomicrobium as critical bacteria. The volatile fatty acid controlled below 2000 mg/L and the improved stirring system in AD process were recommended to achieve maximum biogas yield.

Eliminated high lipid inhibition in the anaerobic digestion of food waste for biomethane production by engineered E. coli with cell surface display lipase

Food waste (FW) with high content of lipid typically inhibits anaerobic digestion (AD) and methane production. In this study, a novel whole-cell catalyst was created to degrade lipid by displaying lipase on the E. coli cells surface to improve FW anaerobic digestion. The methane production rose, going from 25.78 to 161.77 mL/g VS, with a greater VS removal rate of 66.3% compared to CK group (29.6%). Long-chain fatty acids (LCFAs) was similarly reduced from 1733.6 mg/L to 337 mg/L. Microbial community analysis showed the relative abundance of Acinetbacter and Hydrogenophaga were increased from 1.7% to 6.6% and 1.3%–4.9%, respectively for substrates degradation. The methanogenic Methanosarcina increased from 24.7% to 52.3% for methane production. This study provided a potential approach that might be used to lessen lipid inhibition and improve anaerobic digestion of food waste.

Greenhouse gas emissions and net energy production of dark fermentation from food waste followed by anaerobic digestion

There are diverse estimations regarding the carbon reduction effects of alternative hydrogen production technologies. This study assessed the greenhouse gas (GHG) emissions and energy balance of a two-stage process combining dark fermentative hydrogen production and anaerobic digestion from food waste using the cradle-to-gate life cycle assessment (LCA). The system boundary included collection and transportation, pretreatment and feedstock storage, dark fermentation, H2 purification, anaerobic digestion and heat and power generation and the estimated GHG emission was compared with a single anaerobic digestion of food waste. GHG emission of the biohydrogen production was estimated as 2.48 kg CO₂-eq per kg H₂ without considering avoided emissions from heat and power generation. The environmental impacts were majorly influenced by electricity use. The net energy ratio of the two-stage process was calculated to be 8.18, confirming a net energy gain and the potential GHG emission avoidance for electricity and heat use. Given that the single-stage anaerobic digestion of 16 tons of food waste is replaced by the two-stage dark fermentation process, 76.6 kg CO₂-eq would be avoided. Sensitivity analysis revealed that energy-saving strategies are the most sensitive factors for achieving positive net energy production and low global warming potential.

Optimization of Dry Anaerobic Digestion of Food Waste in Leachate Bed Reactors

Optimization of Dry Anaerobic Digestion of Food Waste in Leachate Bed Reactors

Prediction of total organic acids concentration based on FOS/TAC titration in continuous anaerobic digester fed with food waste using a deep neural network model

In this work, the complexities of anaerobic digestion fed with highly degradable feedstock are investigated, focusing on accumulation of organic acids (OA) as a critical monitoring parameter, and the significance of prediction models for total OA concentration. The anaerobic digestion of food waste (FW) was conducted under the organic loading rate (OLR) range of 2.55–8.80 g COD/L/d and hydraulic retention time (HRT) of 30–15 days. The feasibility of flüchtige organische säuren (FOS), totales anorganisches carbonat (TAC), and the FOS/TAC was investigated by predicting the total OA using a deep neural network (DNN) model. Two digesters, Digester 1 and 2, were fed with FW from four distinct sites. When the OA concentration exceeded 2 g/L as CH3COOH, the feeding was paused to recover the methanogens activity. The total OA concentration was successfully predicted with FOS, TAC, and FOS/TAC using the DNN regression model even though applying on the datasets from two distinct digesters, indicating a R-value of 0.9557, R2 of 0.9133, and mean square error of 0.0329. The predictive capability of DNN regression model shows the feasibility of total OA prediction based on the titrimetric method for monitoring and optimizing continuous anaerobic digestion of highly degradable feedstock.

Microbial process in anaerobic digestion of food wastes for biogas production: a review

Microbial process in anaerobic digestion of food wastes for biogas production: a review

Enhancing anaerobic digestion of food waste for biogas production: Impact of graphene nanoparticles and multiwalled nanotubes on direct interspecies electron transfer mechanism

The present research investigated the effect of two carbonaceous materials, multiwalled carbon nanotubes (MWCNTs), and graphene nanoparticles (GNPs), on biogas yield from food waste (FW) in an anaerobic digestion system for 30 days. Lab scale investigations were conducted in batch mode in 250 mL glass reactor bottles and the findings were compared to the control reactor. The performance of the experimental procedure was assessed in terms of biogas output and organic matter reduction. The addition of 100 mg/L multiwalled carbon nanotubes and 100 mg/L GNPs increased the cumulative biogas production (33.55 % and 81.16 %, respectively) while decreasing the total solid content (about 25.95 % and 24.95 %, respectively). However, increasing the concentration of both carbon nanomaterials from 100 mg/L to 500 mg/L reduced the total biogas production compared to the control, which can be attributed to cytotoxic effects. A microbial diversity study was performed using 16S amplicon sequencing to understand the changes occurring in the microbial ecology. The predominant phyla found during diversity analysis were Firmicutes, Proteobacteria, Actinobacteriota, and Bacteroidota. Finally, addition of carbonaceous nanomaterials to the anaerobic reactors favours organic matter degradation through the DIET mechanism. It improves the biogas production kinetics and productivity during the anaerobic digestion of FW up to a certain dose.

Enhanced anaerobic digestion of food waste by the addition of cobalt iron oxide

In this study, the impact of cobalt iron oxide(CoFe2O4) on the anaerobic digestion (AD) of food waste (FW) was investigated including the variations in pH, VFAs, ORP, Fe2+/Fe3+ concentrations, SCOD, dehydrogenase activity, methane production and microbial community structure. The results showed that CoFe2O4 had a positive effect on the anaerobic digestion of food waste. CoFe2O4 could promote the release of SCOD, increase the dehydrogenase concentration and reduce ORP resulting in an increase of methane production. At a CoFe2O4 concentration of 200 mg/L, the cumulative methane production reached to 414.75 mL/(gVS) which was increased by 79.1% compared to the control group(231.59 mL/(gVS)). Meanwhile, the variation of microbial community showed that CoFe2O4 could increase the relative abundance of Methanobacterium and the methane production pathway in the AD was shifted from acetoclastic to hydrogenotrophic.

Response of food waste anaerobic digestion to the dimensions of micron-biochar under 30 g VS/L organic loading rate: Focus on gas production and microbial community structure

Biochar modification is an effective approach to enhance its ability to promote anaerobic digestion (AD). Focusing on the physical properties of biochar, the impact of different particle sizes of biochar on AD of food waste (FW) at high organic loading rate (OLR) was investigated. Four biochar with different sizes (40–200 mesh) were prepared and used in AD systems at OLR 30 g VS/L. The research results found that biochar with a volume particle size of 102 μm (RBC-P140) had top-performance in promoting cumulative methane production, increasing by 13.20% compared to the control group. The analysis results of the variety in volatile acids and alkalinity in the system did not show a correlation with the size of biochar, but small size has the potential to improve the environmental tolerance of the system to high acidity. Microbial community analysis showed that the abundance of aceticlastic methanogen and the composition of zoogloea were optimized through relatively small-sized biochar. Through revealing the effect of biochar particle size on AD system at high OLR, this work provided theoretical guidance for regulating fermentation systems using biochar.

Anaerobic Digestion of Food Waste with the Addition of Biochar Derived from Microwave Catalytic Pyrolysis of Solid Digestate

Anaerobic Digestion of Food Waste with the Addition of Biochar Derived from Microwave Catalytic Pyrolysis of Solid Digestate

Study on synergistic effect of carrier combined with micro-aeration on anaerobic digestion of food waste

Enhancing the conversion efficiency of methane production from food waste (FW) is always a hot issue. Biological carriers and micro-aeration had demonstrated notable advantages in enhancing anaerobic digestion (AD) efficiency, but their synergistic potential remained largely untapped. This study introduced polyurethane carriers into micro-aeration assisted AD, trying to explore their synergism in enhancing the digestive efficiency of FW. Results revealed that an optimal blend of carriers and micro-aeration pose significant improvement to the digestive performance. Their combination enhanced microbial metabolic activity, accelerated the consumption or conversion of dissolved organic matter (DOM) molecules, promoted the aggregation of microorganisms, which improved their tolerance capacity under the oxygen stress brought by the micro-aeration, ensuring the system stability. It also enriched methane-producing microorganisms, and balanced methane-producing pathways. Additionally, the combination of micro-aeration and carriers promoted key enzyme expression in metabolic pathways, providing ample support for methane production. These findings held significance for optimizing FW treatment, improving methane production efficiency, and reducing the burden of organic waste treatment.

Pilot-scale study of enhanced thermophilic anaerobic digestion of food waste with the addition of trace elements

Thermophilic anaerobic digestion (AD) offers many benefits for food waste treatment but is seldom adopted in industrial plants due to instability issue, particularly under higher loading conditions. This study thus conducted a 160-day continuous operation of a pilot-scale thermophilic AD system on-site. Results from the experiments showed that the system could operate under relatively lower loading but failed when the loading reached up to 5.69 kg·COD/(m3·d). Volatile fatty acids increased to 6000 mg/L at the corresponding hydraulic retention time of 15 days. Trace elements were then introduced, which restored higher process stability by reducing volatile fatty acids to 400 mg/L. The mass balance and materials decomposition resutls revealed the system’s strong resilience. Methanoculleus (92.52 %) and Methanomassiliicoccus (6.55 %) were the dominant methanogens, a phenomenon rarely observed in similar thermophilic systems. This system may tolerate more stressful conditions, as the loading limits had not been reached with the addition of trace elements.

Investigation of start-up strategies and temperature regulation on enhanced methanogenesis in anaerobic digestion of food waste

Temperature is a crucial parameter for anaerobic digestion of food waste. Thermophilic anaerobic digestion (TAD) exhibits high methane production but has a hard initiation. This study compared two start-up strategies, one-step temperature increase and step-wise temperature increase, for achieving rapid TAD initiation. Compared to the step-wise temperature increase, the one-step temperature increase demonstrated stronger stability with slight pH fluctuation. Thermophilic communities were established more rapidly by the one-step temperature increase. Its substrate degradation was more enhanced through improving carbohydrates and lipid metabolisms than step-wise’s. These indicated one-step temperature increase strategy can initiate TAD efficiently. Additionally, a comparative analysis between TAD and mesophilic anaerobic digestion (MAD) was conducted on multilevels. TAD produced 25.29% more methane than MAD. The increased Defluviitoga and Hydrogenispora in TAD promoted hydrogenotrophic methanogenesis. The enriched genes related to the decomposition of glucose and glycerol resulted in higher substrate hydrolysis, acidogenesis, and acetogenesis in TAD than that in MAD. This study elucidated the full stages of TAD, which strengthened methanogenesis.

Anaerobic digestion of food waste with a selective mixed-microbial consortium and its evaluation with different optimization methods

Anaerobic digestion of food waste with a selective mixed-microbial consortium and its evaluation with different optimization methods

Long-chain fatty acids facilitate acidogenic fermentation of food waste: Attention to the microbial response and the change of core metabolic pathway under saturated and unsaturated fatty acids loading

Long-chain fatty acids (LCFAs) are recognized as a significant inhibitory factor in anaerobic digestion of food waste (FW), yet they are inevitably present in FW due to lipid hydrolysis. Given their distinct synthesis mechanism from traditional anaerobic digestion, little is known about the effect of LCFAs on FW acidogenic fermentation. This study reveals that total volatile fatty acids (VFAs) production increased by 9.98 % and 4.03 % under stearic acid and oleic acid loading, respectively. Acetic acid production increased by 20.66 % under stearic acid loading compared to the control group (CK). However, the LCFA stress restricted the degradation of solid organic matter, particularly under oleic acid stress. Analysis of microbial community structure and quorum sensing (QS) indicates that LCFA stress enhanced the relative abundance of Lactobacillus and Klebsiella. In QS system, the relative abundance of luxS declined from 0.157 % to 0.116 % and 0.125 % under oleic acid and stearic acid stress, respectively. LCFA stress limited the Autoinducer-2 (AI-2) biosynthesis, suggesting that microorganisms cannot use QS to resist the LCFA stress. Metagenomic sequencing showed that LCFA stress promoted acetic acid production via the conversion of pyruvate and acetyl-CoA to acetate. Direct conversion of pyruvate to acetic acid increased by 47.23 % compared to the CK group, accounting for the enhanced acetic acid production under stearic acid loading. The abundance of β-oxidation pathway under stearic acid loading was lower than under oleic acid loading. Overall, the stimulating direct conversion of pyruvate plays a pivotal role in enhancing acetic acid biosynthesis under stearic acid loading, providing insights into the effect of LCFA on mechanism of FW acidogenic fermentation.