Anaerobic Co-digestion Of Food Waste Research Articles

Anaerobic co-digestion of food waste and cardboard in different mixing ratios: Impact of ultrasound pre-treatment on soluble organic matter and biogas generation potential at varying food to inoculum ratios

The aim of the present work is to investigate the impact of acetic acid assisted ultrasound pre-treatment of food waste (FW) and cardboard (CB) to overcome the barriers of substrate characteristics. Anaerobic co-digestion (ACoD) experiments were conducted with FW and CB in the mixing ratios of 100:0, 80:20, 60:40 and 50:50 at a food to inoculum (F/I) ratio of 1:1 and 1:2 to investigate its impact on biogas yield, volatile solids (VS) removal, solubilization of organic matter and the specific energy (SE) required. Results revealed that the biogas yield obtained from ultrasound pre-treated samples regardless of mixing ratio was higher at a F/I ratio of 1:2 compared to 1:1. The formation of bubbles, cavities and floc matrix significantly increased and the particle size decreased from 100 μm to 10 μm for FW:CB of 60:40 and 50:50 after pre-treatment. Ultrasound pre-treatment for 45 min was adequate for FW:CB of 100:0 and 80:20 while it was 60 min for 60:40 and 50:50 for increased sCOD between 37 % - 53 %. The VS removal efficiencies increased between 3–15 % from pre-treated samples compared to untreated. The CB mixing ratio is inversely related to SE while directly related to sCOD. Overall, during ACoD of FW and CB, the FW:CB of 80:20 gave a higher biogas yield of 471 mL/g VSadded followed by 60:40 and 50:50.

Understanding the fate and impact of capsaicin in anaerobic co-digestion of food waste and waste activated sludge

Anaerobic co-digestion is an attractive option to treat food waste and waste activated sludge, which is increasingly applied in real-world situations. As an active component in Capsicum species being substantially present in food waste in many areas, capsaicin has been recently demonstrated to inhibit the anaerobic co-digestion. However, the interaction between capsaicin and anaerobic co-digestion are still poorly understood. This work therefore aims to deeply understand the fate and impact of capsaicin in the anaerobic co-digestion. Experiment results showed that capsaicin was completely degraded in anaerobic co-digestion by hydroxylation, O-demethylation, dehydrogenation and doubly oxidization, respectively. Although methane was proven to be produced from capsaicin degradation, the increase in capsaicin concentration resulted in decrease in methane yield from the anaerobic co-digestion. With an increase of capsaicin from 2 ± 0.7 to 68 ± 4 mg/g volatile solids (VS), the maximal methane yield decreased from 274.6 ± 9.7 to 188.9 ± 8.4 mL/g VS. The mechanic investigations demonstrated that the presence of capsaicin induced apoptosis, probably by either altering key kinases or decreasing the intracellular NAD+/NADH ratio, which led to significant inhibitions to hydrolysis, acidogenesis, and methanogenesis, especially acetotrophic methanogenesis. Illumina Miseq sequencing analysis exhibited that capsaicin promoted the populations of complex organic degradation microbes such as Escherichia-Shigella and Fonticella but decreased the numbers of anaerobes relevant to hydrolysis, acidogenesis, and methanogenesis such as Bacteroide and Methanobacterium.

Anaerobic digestion of food waste at varying operating conditions

Food waste is one of the major problems contributing to the degradation of the environment, and thus needs serious attention. Among different options, anaerobic digestion is possibly the most effective technique for managing degradable waste, and produce renewable energy and fertilizer. Despite multiple-use and benefits of the technology, its application is limited due to a few technical challenges. This study focuses on the anaerobic digestion of food waste with the addition of different percentages of digested cow manure as inoculum to it, at different total solid content in ambient temperature. Anaerobic digestion of food waste in batch and semi-continuous processes were carried out in three different trials at an average temperature range of 20-26℃: Food waste with 20% inoculum, food waste with 50%, 100%, and 200% inoculum and 10% total solid content in batch process and food waste with 20% inoculum with 6% and 10% total solids content in the semi-continuous process. During each trial, some amount of gas production was observed, however, the gas composition showed a negligible amount of methane production (maximum 13% of CH4). There were two common problems detected in each trial: the inability to complete the methanogenesis process, and instability of the overall process due to the high degradability and acidic nature of food waste. Therefore, this study suggests that the mono digestion of food waste is not a suitable option. However, anaerobic co-digestion of food waste with different organic substrate might provide a favorable condition for stable anaerobic digestion as seen from preliminary results.

Effect of calcium peroxide and sodium hydroxide on hydrogen and methane generation during the co-digestion of food waste and cow dung

Anaerobic co-digestion of food waste, cow dung, and sludge solution was experimentally evaluated to produce hydrogen and methane considering the effect of calcium peroxide (CaO2) and sodium hydroxide (NaOH) addition with the feedstock. The various substrate to inoculum ratios (v/v) of 1:1(S1), 1:2(S2), 1:3(S3), 1:4(S4), and 1:5(S5) were evaluated in separate fermentative and methanogenic reactors. The optimum hydrogen and methane production was observed in S3 compared to the other samples. The biogas generation was increased up to 17% with an enhancement of methane concentration up to 10% by using NaOH compared to CaO2. The cumulative methane yield was increased by 12% due to the addition of NaOH as compared to CaO2. The maximum hydrogen concentration was improved by 7% with a substantial enhancement of cumulative hydrogen yield up to 37% by adding CaO2 with the feedstock as compared to NaOH. It was evident from the experiment that the production of hydrogen was significantly enhanced by adding CaO2 while the methane generation was influenced by the addition of NaOH during the co-digestion.

Effects of long-term acclimatization on the optimum substrate mixture ratio and substrate to inoculum ratio in anaerobic codigestion of food waste and cow manure

The effects of long-term acclimatization on the optimum food waste to cow manure ratio (FW/CM) and substrate to inoculum ratio (S/I) in anaerobic codigestion with FW and CM were investigated by batch trials. For the unacclimated sludge, the highest CH4 yields of 646.6 and 653.4 mL/g VS were achieved under the optimum FW/CM (2.5 VS/VS) and S/I (0.07 VS/VS) ratios, respectively. After more than 550 days of acclimatization, the optimum FW/CM and S/I of the acclimated sludge were improved to 3.4 and 0.68 VS/VS with more anaerobic digestion enzymes and lignocellulose, respectively. Based on high-throughput sequencing analysis, the microbial community structures of bacteria, fungi, and archaea were changed, which was the main reason for the change in the optimum FW/CM and S/I. Therefore, the FW/CM and S/I should be periodically optimized during the long-term operation of codigestion to improve the codigestion efficiency for biogas production.

Highly efficient anaerobic co-digestion of food waste and horticultural waste using a three-stage thermophilic bioreactor: Performance evaluation, microbial community analysis, and energy balance assessment

The thermophilic anaerobic co-digestion of food waste and horticultural waste with a three-stage bioreactor was investigated to produce renewable energy, focusing on performance evaluation, microbial community analysis, and energy balance assessment. The results of this study indicated that the average methane yield (0.42 ± 0.06 L/gVS) in the bench-scale three-stage thermophilic bioreactor was approximately 45% and 31% higher than that of the one and two-stage bioreactors, respectively. The average volatile solid (VS) reduction achieved in the bench-scale three-stage thermophilic bioreactor was 63.0 ± 8.2%, which was 61% and 32% higher than that of the one and two-stage bioreactors, respectively. Pyrosequencing analysis of microbial communities in simulated thermophilic three-stage co-digestion experiments showed that bacterial phyla Firmicutes, Thermotogae and Bacteroidetes dominated in all three types of bioreactors. However, significant differences were observed at the genus level of bacterial communities between the one, two and three-stage bioreactors. Indeed, due to selective enrichment, the dominant methanogenic pathways in the three-stage bioreactor shifted from hydrogenotrophic methanogenesis at a low organic loading rate (OLR) to a balance of hydrogenotrophic and acetoclastic pathways at high OLR. Furthermore, assessments of the energy balance and the economic viability of the bench-scale system demonstrated that the three-stage thermophilic co-digestion could be a promising process for the treatment of food waste and horticultural waste as well as for bioenergy recovery at an industrial scale.

Batch anaerobic co-digestion of food waste and sludge: a multi criteria decision modelling (MCDM) approach

The present study investigates the application of Multi Criteria Decision Modelling (MCDM) on batch anaerobic co-digestion of kitchen food waste (FW) and the fresh septic tank sludge (STS) for robust output. The batch experiment was carried out at a temperature of 37 ± 2 °C. Different ratio of FW and STS (FW: STS:100:0; 75:25; 60:40; 50:50; 25:75; 0:100) were adopted based on volatile solid (VS) basis as co digestion strategy for 90 days digestion period. Results revealed that experimentally, mono-digestion of FW showed maximum biogas yield (544 ± 65 mL/g VS) followed by blending ratio of 75:25 (FW: STS). However, mono-digestion of STS showed only 150 ± 15 mL/g VS of biogas yield and also showed negative effect on co digestion with FW for every blending on VS basis as STS was high in minerals. MCDM revealed that the FW is the best possible alternative amongst the other blends with STS considering pH, chemical oxygen demand, VS reduction, alkalinity, C/N and biogas yield as output.

Biogas yield assessment from the anaerobic co-digestion of food waste and cymbopogon citratus

This study, aimed at maximizing the biogas yield from the co-digestion of food waste (FW) and cymbopogon citratus (CC) was done in reactors (Rs) I–V at temperature of 36 ± 2 °C. Rs I, II, III, IV and V with respective FW: CC of 100:0; 80:20; 60:40; 40:60; 0:100 had mean biogas yield of 0.41 ± 0.02, 0.68 ± 0.05, 0.49 ± 0.02, 0.29 ± 0.01, and 0.22 ± 0.03 L/gVS, respectively. From the modeling result, while R I had the least latency (λ) of 3.9, RV had the highest value of 11.2 days. RII also had a reasonably low latency (λ) of 5.2 days. Top maximum specific biogas yield (Rm) of 0.48 L/gVS/day and maximum biogas production potential (A) of 19.9 L/gVS were obtained from RII. The high R2 values of 0.99–0.89 obtained from the simulation analysis showed a good fit with the modified Gompertz model. The study has revealed that FW: CC of 80: 20% could be most appropriate for optimal biogas production.

Optimization of methane production parameters during anaerobic co-digestion of food waste and garden waste

Anaerobic digestion is an alternative process to organic waste treatment, which enables energy production from biogas. Additionally, the volume of total waste that goes to landfills decreases, resulting in an increase in landfills lifespan. When considering different organic waste sources, food waste is highly important as it is generated and usually disposed of in large amounts. In this context, the goal of this research was to evaluate to which extent the addition of lignocellulosic waste (also known as garden waste – GW) influences the performance of food waste (FW) anaerobic digestion, focusing on process optimization as a function of the quantity and quality of the produced biogas. The experiment was conducted in two pilot-scale reactors. They were operated at the same time and contained a volume of 500 L each. Both reactors were adapted with agitators (30 rpm) and temperature controllers (36 °C). The reactor’s feeding was performed in a semi-continuous process with a gradual increase in the Organic Loading Rate (OLR), from 0.24 to 0.54 kg VS m−3d−1. Operational control parameters, such as pH, alkalinity, VFA, and process performance, characterized by volatile solids, biogas production, and methane content, were carried out to monitor the anaerobic co-digestion. The results showed that a substitution of 20% of the food waste OLR to the lignocellulosic substrate improved both the biogas production and specific methane yield. Also, the organic material conversion efficiency, related to volatile solids (VS), reached 83%. These results indicate that the FW and GW co-digestion can be used as an alternative to organic waste treatment. The process also assists in the control of the monitoring parameters, such as pH, alkalinity and volatile fatty acids, during anaerobic digestion.

Powdered activated carbon facilitates methane productivity of anaerobic co-digestion via acidification alleviating: Microbial and metabolic insights

Low methanogenic efficiency caused by excess acidification is a challenge during anaerobic digestion. This study indicated that both granular activated carbon (GAC) and powdered activated carbon (PAC) promoted the start-up of methanogenesis and methane output in anaerobic co-digestion of food waste and fruit-vegetable waste. Moreover, PAC performed better than GAC. Specifically, the highest cumulative methane yield and shortest lag phase were observed in 5 g/L PAC and 10 g/L PAC group, 22.0% higher and 62.5% shorter than that without activated carbon supplementation, respectively. PAC facilitated the methane productivity by effectively accelerating volatile fatty acids (VFAs) consumption and thereby alleviating acidification. Syntrophic VFAs oxidizing bacteria (Gelria and Syntrophomonas) and direct interspecies electron transfer related microorganisms (Geobacter and Methanosarcina) were remarkably enriched by PAC. Furthermore, metagenomic analysis showed that both PAC and GAC might facilitate the electron transfer between microbes by acting as the electrical bridge and enhance both hydrogenotrophic and aceticlastic pathways.

Energy generation from anaerobic co-digestion of food waste, cow dung and piggery dung

The study investigated bioenergy generation from anaerobic co-digestion of food wastes (FW), cow dung (CD) and piggery dung (PD). The physicochemical parameters of the substrates were determined before and after digestion following standard procedures after mechanical pretreatment. Throughout the study, pH remained slightly alkaline while temperature varied between 26 and 32 °C. The highest cumulative biogas yield of 0.0488 L was recorded from the digestion of FW + CD + PD on the ninth day. After analyses, the highest methane content of 64.6 was obtained from the digestion of FW + PD while the lowest (54.0%) was from the digestion of FW only. Overall, cumulative biogas production for the four digestion regimes followed the order: FW + CD + PD, FW + PD, FW + CD and FW only respectively. Accumulation of VFAs was recorded at a slow rate during the digestions.

Opportunities and challenges: Experimental and kinetic analysis of anaerobic co-digestion of food waste and rendering industry streams for biogas production

Large amounts of food waste and sewage sludge exert a hazardous environmental impact in several countries. Producing biogas and digestate from food and industrial waste is one of the solutions for waste management, stabilization of sludge, resource and energy recovery and reductions in the amount of waste. However, biogas production from such substrates has challenges in degradation efficiency, inhibitory effects and other challenges, and thus co-digestion and pretreatment techniques could be applied to enhance biogas production. The aim of this study is to explore the effects of co-digestion of food waste, meat and bone meal and rendering wastewater sludge. First, thermal pretreatment was performed (35°C, 5 days) by adding the rendering-industry streams to food waste in the amounts of 0, 5, 10 and 15% on a total solid basis, and further anaerobic digestion (40.5°C, ca. 40 days) was then performed. Both experimental and kinetic analysis were conducted, and the major factors regarding opportunities and challenges in the two-stage process are discussed. Results have shown that both co-substrates from rendering industry decreased the biogas yield of food waste. When 5% of them was added to food waste, meat and bone meal decreased biogas production by 12%, and wastewater sludge decreased it by 23%. Both co-substrates, on the other side, increased the rate of reaction of food waste digestion when applying different common kinetic models.

Characterization of food waste and sewage sludge mesophilic anaerobic co-digestion under different mixing ratios of primary sludge, secondary sludge and food waste

The main aim of the present work was to characterize the mesophilic anaerobic co-digestion of food waste (FW) and sewage sludge (SS) by considering different mixing ratios of primary sludge (Pr), secondary sludge (Sc) and food waste. The experiments were carried out using batch reactors (R1-R7). The applied ratios included VSPr:VSSc (1:1 and 2:1) and VSFW:VSSS (0:4, 1:3, 2:2 and 4:0) with VSx (g) as the volatile solids content of the substance x within the total feed of each reactor and VSSS as the sum of VSPr and VSSc. According to the obtained results, ratio of carbon to nitrogen (C:N) was much more effective than VSPr:VSSc ratio considering VS reduction and biogas production efficiencies. A second-order polynomial curve fitted well the data of VS reduction vs. C:N, representing an optimum C:N around 16 to achieve the highest VS removal. A high R-squared linear correlation was found between data of gas production and C:N ratio according to which, with increasing the C:N within the test range (8–19.7), the biogas production increased steadily. Doubling VSPr:VSSc under lower ratios of VSFW:VSSS (0:4 and 1:3) positively affected both VS reduction and biogas production, while under higher VSFW:VSSS ratio (2:2) it influenced adversely. Doubling VSPr:VSSc also improved the digestate dewaterability under all applied ratios of VSFW:VSSS. A synergistic gas production was observed for the reactors with 50% share of VSFW (VSFW:VSSS of 2:2) between which, R5 with VSPr:VSSc of 1:1 showed the highest synergistic gas production. The highest methane content (70.3%) also belonged to R5.

Effects of citrus peel biochar on anaerobic co-digestion of food waste and sewage sludge and its direct interspecies electron transfer pathway study

Effects of citrus peel biochar on anaerobic co-digestion of food waste and sewage sludge and its direct interspecies electron transfer pathway study

Inactivation of carbapenemase-producing Enterobacterales during anaerobic co-digestion of food waste and pig manure

Animal manures and food wastes are significant reservoirs of antimicrobial resistant bacteria, among which carbapenemase-producing Enterobacterales (CPE) are resistant to almost all antibiotics and have been detected in these wastes. This study investigated the inactivation of three different CPE strains (KPC-3, OXA-48 and NDM-1 carbapenemase-producing Klebsiella pneumoniae) during anaerobic co-digestion of food waste and pig manure at various total solids (TS) contents. The results showed that the elimination of CPE strains was more efficient at higher TS contents. While increasing the TS contents from 5% to 20%, the survival time of CPE decreased from 9 days to 2 days. Statistical analysis revealed significant negative correlations between total volatile fatty acids (VFAs) and the survival time of two CPE strains (KPC-3 and OXA-48 producing Klebsiella pneumoniae) (P < 0.05), indicating the possible elimination effects of VFAs on antibiotic resistant bacteria.

An experimental approach to produce hydrogen and methane from food waste using catalyst

Anaerobic co-digestion of food waste, cow dung, and sludge solution is experimented in the presence of calcium peroxide (CaO2) as the catalyst to produce hydrogen and methane as a source of renewable energy. The substrate to inoculum ratios (v/v) of 1:1(S1), 1:2(S2), 1:3(S3), 1:4(S4) and 1:5(S5) are investigated in separate fermentative and methanogenic reactors. The result from the fermentative reactors indicate maximum hydrogen concentration of 26.34% with cumulative yield of 114.1 mL/g total solid (TS) in S3 compared to the other samples. Methanogenic reaction shows the highest methane concentration of 54.13% in S3. The highest daily (average) and cumulative biogas yield of 5.36 mL/g TS and 201.9 mL/g TS respectively are identified in S3. A maximum carbon dioxide concentration of 63.11% is found in S1. Overall, the substrate to inoculum ratio of 1:3 is spotted to be optimal for effective hydrogen and methane production during the anaerobic co-digestion process.

Impact of Nanoscale Magnetite and Zero Valent Iron on the Batch-Wise Anaerobic Co-Digestion of Food Waste and Waste-Activated Sludge

As a potential approach for enhanced energy generation from anaerobic digestion, iron-based conductive nanoparticles have been proposed to enhance the methane production yield and rate. In this study, the impact of two different types of iron nanoparticles, namely the nano-zero-valent-iron particles (NZVIs) and magnetite (Fe3O4) nanoparticles (NPs) was investigated, using batch test under mesophilic conditions (35 °C). Magnetite NPs have been applied in doses of 25, 50 and 80 mg/L, corresponding to 13.1, 26.2 and 41.9 mg magnetite NPs/gTS of substrate, respectively. The results reveal that supplementing anaerobic batches with magnetite NPs at a dose of 25 mg/L induces an insignificant effect on hydrolysis and methane production. However, incubation with 50 and 80 mg/L magnetite NPs have instigated comparable positive impact with hydrolysis percentages reaching approximately 95% compared to 63% attained in control batches, in addition to a 50% enhancement in methane production yield. A biodegradability percentage of 94% was achieved with magnetite NP doses of 50 and 80 mg/L, compared to only 62.7% obtained with control incubation. NZVIs were applied in doses of 20, 40 and 60 mg/L, corresponding to 10.8, 21.5 and 32.2 mg NZVIs/gTS of substrate, respectively. The results have shown that supplementing anaerobic batches with NZVIs revealed insignificant impact, most probably due to the agglomeration of NZVI particles and consequently the reduction in available surface area, making the applied doses insufficient for measurable effect.

Biogas Production from Corn Stover by Solid-State Anaerobic Co-digestion of Food Waste

Biogas has become an alternative fuel to reduce the lack of fossil fuel. Biogas can be produced from organic wastes such as corn stover. Corn stover is a typical lignocellulosic biomass and contains a total solid (TS) content higher of 15%. Biogas production was conducted by solid-state anaerobic digestion with addition co-digestion of food waste. Co-digestion is useful to help the digestion of corn stover. The purposes of this study were to investigate the effect of the percentage of food waste, volatile solid (VS) reduction, and kinetic model on biogas production from corn stover. Results showed that food waste had a significant effect on biogas yield (p &lt; 0.05). The highest biogas yield of 584.49 mL g-1 VS-1 and the highest VS reduction of 40% was obtained at food waste of 20%. The kinetic model of biogas production from corn stover and food waste followed the first-order kinetic model.

Reversibility of propionic acid inhibition to anaerobic digestion: Inhibition kinetics and microbial mechanism

Anaerobic digestion is a technology that simultaneously treats waste and generates energy in the form of biogas. Unfortunately, when a high organic loading rate is applied, anaerobic digestion can suffer from volatile fatty acid accumulation that results in pH drop and decreased biogas production. In particular, propionic acid has shown to inhibit biogas production even at a very low concentration. Therefore, the kinetics of biogas production in relation to propionic acid concentration needs to be investigated. In batch experiments on anaerobic co-digestion of food waste and dairy manure in the present study, cumulative biogas production showed little inhibition by propionic acid in the concentration range of 6.5–14.6 mM, but a lag phase of 9.4, 16.3 and 60.8 d was detected in the digesters with initial propionic acid concentrations of 22.7, 36.2, and 56.4 mM, respectively. After the lag phase, these digesters accelerated to specific biogas yields of 0.59–0.70 L g-VS−1. The similar specific biogas yields across all of the digesters at initial propionic acid concentrations of 6.5–56.4 mM indicated reversibility of the inhibition. The reversibility was made possible by microbial acclimation and the shift to hydrogenotrophic methanogenesis in syntrophy with acetogenic bacteria. Evidently, an increase of hydrogenotrophic Methanobacterium and Methanoculleus abundances was found at 36.2 and 56.4 mM. Batch digestion experiments must be extended beyond the lag phase in order to fully reveal the inhibition kinetics. This paper highlights the need for a standard protocol that experimentally evaluates inhibition in anaerobic digestion.

Mixing strategies – Activated carbon nexus: Rapid start-up of thermophilic anaerobic digestion with the mesophilic anaerobic sludge as inoculum

This study evaluated the mixing – activate carbon nexus in anaerobic digestion with the aim of accelerating start-up of thermophilic anaerobic co-digestion of food waste and chicken manure using mesophilic anaerobic sludge as inoculum. Results showed that the methane yield in the continuous stirred reactor is 71.3% higher than that of intermittent agitated reactor, and the addition of activated carbon can further improve the yield of methane by 18.2%. Continuous mixing mode followed by intermittent mixing was proved to be an alternative strategy to accelerate start-up of thermophilic anaerobic digestion. The optimum mixing time of 120 s/hour were obtained using computational fluid dynamics modeling. Analysis of genomic annotation metabolism indicated that the addition of activated carbon enhanced the dominant metabolism pathways of amino acid, methane and energy. Results of enzymes gene expression suggested that carbohydrates esterases, glycoside hydrolases and glycosyl transferases were dominant, respectively.