Anaerobic Co-digestion Of Food Waste Research Articles

Anaerobic Co-Digestion of Food Waste and Microalgae at Variable Mixing Ratios: Enhanced Performance, Kinetic Analysis, and Microbial Community Dynamics Investigation

There is an urgent need for clean recycling strategies to address the increase in food waste (FW) and the harvesting of microalgae (MA). In this study, biogas production potential and operational stability were evaluated by testing combinations of FW and MA mixed at five different ratios. Co-digestion of FW and MA improved substrate biodegradability, achieving a decomposition rate of 0.45/d (FW/MA = 1:1), which is 1.25 to 1.55 times higher than that of MA or FW alone. Co-digestion of FW and MA resulted in a synergistic effect, improving biogas yield by 2.04–26.86%. Four mathematical models were applied to estimate biological degradation and biogas production kinetics, and the Cone model performed better than the other models in terms of reliability and accuracy. The abundance of Bacteroidetes, Firmicutes, and Synergistetes peaked at FW/MA = 1:1. At the same ratio, the genera Methanospirillum, Methanocorpusculum, and Methanomethylovorans were also found to have increased in abundance. The optimal ratio was found to be 1:1 for co-digestion of FW and MA, which is a feasible approach for simultaneous bioenergy production and biomass waste co-disposal.

Biowaste management by hydrothermal carbonization and anaerobic co-digestion: Synergistic effects and comparative metagenomic analysis

The feasibility of anaerobic co-digestion in semicontinuous mode of two major urban biowaste, food waste (FW) and garden and park waste (GPW) (75 % FW and 25 % GPW) as well as the co-digestion of FW with the process water originated from the hydrothermal carbonization of GPW (95 % FW and 5 % process water), both on a COD basis, has been assessed. The effect of varying organic loading rate (OLR) from 1.5 to 3.5 g COD/L·d on methane yield, gross energy recovery, and microbiome population was evaluated. For comparison, anaerobic digestion of FW was also conducted to determine the best strategy for sustainable biowaste management. This study showed an optimal OLR of 2.5 g COD/L·d. Acetic and propionic acid content increased as OLR raised for each condition studied, while methane yield decreased at the highest OLR tested indicating overloading of the system. The anaerobic co-digestion of FW and process water showed a 10 % increase on methane production compared to anaerobic digestion of FW (324 vs. 294 mL CH4 STP/L·d). Moreover, it enhances the process due to a greater abundance and diversity of hydrolytic and acidogenic bacteria belonging to Bacterioidota, Firmicutes, and Chloroflexi phyla, as well as promotes the hydrogenotrophic pathway under higher propionic concentrations which is not usually favoured for methane production. The integration of hydrothermal carbonization of GPW with the anaerobic co-digestion of 95 % FW and 5 % of process water results in the highest potential energy recovery and could be a good strategy for sustainable management of urban biowaste.

Anaerobic co-digestion of food waste and bio flocculated sewage sludge towards bio-methane production

The existing sewage treatment plants are energy consumers rather than producers and integration of anaerobic reactor can be a viable approach for enhancing their commercial viability. Therefore, anaerobic co-digestion of food waste and bio-flocculated sewage sludge was studied in a continuous stirred tank reactors (R1 and R2) having a working volume of 6.5 Litre at organic loading rates of 2.5 and 2.4 g VS L−1D−1. At mesophilic temperature, the stabilisation of inoculum was performed in batch mode for 60 days followed by continuous mode feeding for 120 days. The feeding ratio was decided based on availability of food waste and bio-flocculated sewage sludge from a typical domestic household for analysing the effect of volatile fatty acids accumulation on reactor performance. The R1 was fed with equal proportion of bio-flocculated sewage sludge and food waste while R2 was fed in 98:2 (v/v), respectively. To analyse the mixing and temperature distribution within the digester, the velocity and temperature profiles were obtained using Ansys Fluent. In R1, more biogas yield were observed than R2 due to 80% average VS reduction as compared to 55% in case of R2. The highest volatile fatty acids accumulation of 10951 mg L−1 was observed in R1 whereas R2 showed 2800 mg L−1, respectively. The more fluctuations in pH were observed in R1 as compared to R2 due to more food waste concentration and maximum bio-methane production was 133 and 233 mL CH4 g−1 VSadded in R1 and R2, respectively.

Re-evaluating the impact of feeding shock on anaerobic co-digestion of food waste and waste activated sludge: Trade-off between efficiency and stability

To optimize the feeding strategy of anaerobic digestion (AD) treating food waste and waste activated sludge, the impact of relative feeding shock (RFS) on the trade-off between efficiency and stability was re-evaluated at six feeding conditions from 1/96 (approximate continuous feeding) to 1. The results showed that increasing the RFS from 1/96 to 1/3 increased the CH4 yield from 293.23 mL CH4/g-total solid (TS) to the maximum value of 345.11 mL CH4/g-TS, which was due to the highest specific microbial growth rates (μmax) of acetate (1.05d-1) and propionate (0.48d-1) and a balanced reaction rate between acidogenesis and methanogenesis. However, when the RFS increased to 1, the total volatile fatty acids (TVFA) concentration increased from 0.51 to 5.90 g-COD/L, with the predominant VFAs changing from acetate to propionate, limiting methanogenesis. Meanwhile, the stability coefficient decreased to 0.37, leading to decreased CH4 yield and μmax. In addition, the high hydrogen partial pressure caused by high RFS increased the Gibbs free energy by 17 %, aggravating the thermodynamic disadvantages. The abundant methanogens shifted from Methanosaeta to Methanosarcina, which cooperated with a syntrophic partner-Syntrophomonas to ensure the smooth VFAs degradation at RFS of 1/3. These findings provide prima facie insights into the optimization of operational conditions for AD treating organic wastes.

Biochar enhanced methane yield on anaerobic digestion of shell waste and the synergistic effects of anaerobic co-digestion of shell and food waste

Mesophilic anaerobic bacteria rely on a relay degradation process to convert chitin-containing waste into methane. This study investigated the effects of biochar on the anaerobic digestion (AD) of shell waste (SW) and explored the impact on methane yield in the anaerobic co-digestion of food waste with SW. The biochar (BC) added for AD of SW increased the methane yield by 18.45 %. Compared to the inoculum, the relative abundance of Pseudomonas decreased by 72.69 % in the SW group and 91.18 % in the SW + BC group. The second experiment with the same total volatile solids (VS) content showed that the group with an VS of 20 % SW had the highest methane yield, significantly surpassing the yields of the 0 % SW group by 25.24 %. The results presented in this study demonstrated that SW synergistically promotes methane yield in the AD of food waste by reducing lag time and facilitating methanogenic archaeal community colonization.

Intermittent mixing facilitates energy recovery and low carbon emissions from high-solids anaerobic co-digestion of food waste and sewage sludge

Mixing inside high-solids anaerobic co-digestion (HS-AcoD) is essential for process feasibility and economic sustainability. This study developed a proper energy assessment for a high solids anaerobic digestion-combined heat and power (AD-CHP) system to clarify the impact of mixing on methane production, energy recovery and carbon emission reduction during HS-AcoD of food waste (FW) and sewage sludge (SS). Results indicated that intermittent mixing enhanced methane production and shortened the lag phase compared with unmixing and continuous mixing. The modified Gompertz model yielded better fitting than the logistic and transfer function models via kinetic analysis. In the case of a scaled-up AD-CHP system, intermittent mixing with 15 min/h boosted energy output (2.14 × 103 kWh/tonne VS) at 21 d. Compared with continuous mixing, 15 min/h intermittent mixing at 13 d improved the energy recovery ratio from 31% to 45% and carbon emissions reduction from 0.25 t CO2/t VS to 0.35 t CO2/t VS. For a high availability of FW and SS in China, the AD-CHP system with intermittent mixing would have higher net energy output (128.4 × 109 kWh) and carbon emission reduction (15.3 million tonnes) by the full utilization of these biomasses. These results are expected to provide theoretical support for the high solids AD-CHP system in determining the optimal mixing strategy with maximum energy production for FW and SS disposal.

Metagenomic characterization of the enhanced performance of multicomponent synergistic thermophilic anaerobic co-digestion of food waste utilizing kitchen waste or garden waste as co-substrate

Food waste (FW) single-substrate anaerobic digestion usually suffers from rapid acidification and inhibition of oil and salt. To overcome these problems and improve the process efficiency, supplementing other substrates has been used in FW anaerobic digestion. This study investigated the biogas production potential through co-digestion of FW with kitchen waste (KW) or garden waste (GW) in different ratios under thermophilic conditions. The results showed that the optimal ratios were FW:KW=60:40 and FW:GW=80:20 which biogas production improved 73.33% and 68.45% compared with single FW digestion, respectively. The organic matter removal rate of co-digestion was 84.46% for FW+KW group (RFK) and 65.64% for FW+GW group (RFG). Co-digestion increased the abundance of the dominant hydrolytic bacteria Defluviitoga and Hydrogenispora and hydrogenotrophic methanogen Methanoculleus. Furthermore, glycoside hydrolases (GHs), vital carbohydrate-active enzymes (CAZymes), were improved by co-digestion. Co-digestion could also effectively promote the function of cellulase and hemicellulose. This strategy for utilizing different organic wastes together as co-substrate provides a new avenue for bioenergy production.

Pilot-Scale Anaerobic Co-Digestion of Food Waste and Polylactic Acid

Bioplastics are frequently utilized in daily life, particularly for food packaging and carrier bags. They can be delivered to biogas plants through a separate collection of the organic fraction of municipal waste (OFMSW). The increased demand for and use of bioplastics aimed at mitigating plastic pollution raises significant questions concerning their life cycle and compatibility with waste management units. Anaerobic digestion (AD) in OFMSW is a valuable resource for biogas production. In this work, the valorization of poly-L-lactic acid (PLLA) composed of food waste within the Biowaste to Bioplastic (B2B) Project framework was studied in laboratory and pilot-scale anaerobic liquid conditions. Taking into account that the addition of PLLA to biowaste can increase biogas production, we performed laboratory-scale anaerobic tests on food waste enriched with different molecular-weight PLLAs produced from food waste or commercial PLLA at a mesophilic temperature of 37 °C. PLLA with the highest molecular weight was subjected to AD on the pilot scale to further validate our findings. The addition of PLLA increased biogas production and had no apparent negative impact on the operation of the reactors used in the laboratory or on the pilot scale. Biogas production was higher when using PLLA with the lowest molecular weight. In the pilot-scale experiments, co-digestion of FW with PLLA increased biogas production by 1.1 times. When PLLA was added to the feed, biomethane was 8% higher, while volatile solids (VS) and total chemical oxygen demand (TCOD) removal were almost the same. Importantly, no effect was observed in the operation of the digesters.

Anaerobic co-digestion of food waste, bio-flocculated sewage sludge, and cow dung in CSTR using E(C2)Tx synthetic consortia

In the current study, a E(C2)Tx synthetic consortia was tested for anaerobic co-digestion of food waste (FW), bio-flocculated sewage sludge (BFS)/ raw wastewater (RW) and cow dung (CD) at varying proportions in 0.25 L and 6.5 L mesophilic continuously stirred tank reactors. Anaerobic co-digestion of FW with CD and RW at the ratio of 1:1:8 in 0.25 L batch-reactor with E(C2)Tx inoculum resulted in the highest H2 production with least CO2 release. The microbial dynamics of FW:CD:RW samples were studied using 16S metagenomic sequencing which indicated a predominance of hydrolysing microbes at the end point of the digestion cycle. Subsequently, the experiments were scaled up in two continuous digesters, namely, R1 (fed with 50% FW and 50% BFS) and R2 (fed with 2% FW and 98% BFS) with 6.5 L working volume at 2.5 g VS L−1D−1 organic loading rate (OLR) for 120 days. The highest VFA production of 19,183 mg L−1 and 3,265 mg L−1 with maximum bio-methane yield of 142.21- and 225.03-mL CH4g−1 VSadded were recorded in reactors R1 and R2, respectively. In addition, a numerical analysis was conducted to visualize the mixing and temperature distribution within the digesters, and the velocity and temperature profiles were obtained using Ansys Fluent.

Synergetic effects of anaerobic co-digestion of food waste and algae on biogas production

Anaerobic co-digestion of food waste and algae was assessed to offset the drawbacks of anaerobic mono-digestion of each substrate. Batch test results indicated that a food waste and algae mixture ratio of 8:2 facilitated the highest CH4 yield (334 mL CH4/g CODInput). This ratio was applied to the anaerobic co-digestion reactor, resulting in a CH4 yield that was twice that of the anaerobic mono-digestion reactors, thereby facilitating high operational stability. In contrast to the anaerobic mono-digestion, anaerobic co-digestion resulted in stable CH4 production by overcoming volatile fatty acid accumulation and a decreased pH, even under a high organic loading rate (3 kg COD/m3∙d). Furthermore, a comparative metagenomic analysis revealed that the abundance of volatile fatty acid-oxidizing bacteria and hydrogenotrophic and methylotrophic methanogens was significantly increased in the anaerobic co-digestion reactor. These findings indicate that the anaerobic co-digestion of food waste and algae significantly improves CH4 production and process stability.

Anaerobic co-digestion of food waste and waste activated sludge for methane production: Evaluation of optimum ratio, microbial analysis, and kinetic modeling

Anaerobic co-digestion of food waste and waste activated sludge for methane production: Evaluation of optimum ratio, microbial analysis, and kinetic modeling

Enhanced methane production from the anaerobic co-digestion of food waste plus fruit and vegetable waste.

Food waste (FW) and fruit, vegetable waste (FVW) are important components of municipal solid waste, yet the performance and related mechanisms of anaerobic co-digestion of FW and FVW for methane production have been rarely investigated. In order to get a deeper understanding of the mechanisms involved, the mesophilic FW and FVW anaerobic co-digestion in different proportions was investigated. The experimental results showed that when the ratio of FW and FVW was 1/1 (in terms of volatile suspended solid), the maximum biomethane yield of 269.9 mL/g TCOD from the codigested substrate is significantly higher than that in FW or FVW anaerobic digestion alone. FW and FVW co-digestion promoted the dissolution and biotransformation of organic matter. When the recommended mixing ratio was applied, the maximum concentration of dissolved chemical oxygen demand (COD) was high as 11971 mg/L. FW and FVW co-digestion reduced the accumulation of volatile fatty acids (VFA) in the digestive system, thus reducing its negative impact on the methanogenesis process. FW and FVW co-digestion process synergistically enhanced microbial activity. The analysis of microbial population structure showed that when FW and FVW were co-digested at the recommended ratio, the relative abundance of Proteiniphilum increased to 26.5%, and the relative abundances of Methanosaeta and Candidatus Methanofastidiosum were also significantly increased. The results of this work provide a certain amount of theoretical basis and technical support for the co-digestion of FW and FVW.

Enhanced anaerobic co-digestion of food waste and solid poultry slaughterhouse waste using fixed bed digester: Performance and energy recovery

Enhanced anaerobic co-digestion of food waste and solid poultry slaughterhouse waste using fixed bed digester: Performance and energy recovery

Comparation of mesophilic and thermophilic anaerobic co-digestion of food waste and waste activated sludge driven by biochar derived from kitchen waste

Anaerobic co-digestion of food waste and wasted sludge is a promising practice to integrate waste management and improve energy balance. In this study, the effects of kitchen waste biochar on the mesophilic and the thermophilic co-digestion were compared. Biochar showed a better performance in thermophilic treatments, and the highest methane production was obtained at 15 g L−1 biochar, while the time for complete digestion was shortened from 20 days in the controls without biochar to 13 days in the 15 g L−1 biochar-assisted treatments. Compared to the mesophilic treatments, thermophilic treatments demonstrated fast pH drop and volatile fatty acids accumulation. Based on the Gompertz model, 15 g L−1 biochar increased the maximum specific methane production rate by 2-fold and reduced the lag time by 31.6%, which was attributed to fast volatile fatty acids consumption and recovery from pH drop. pH, temperature and volatile fatty acids were significant factors shaping the distinct microbial dynamics. Methanosaeta dominated in archaeal community in mesophilic treatments, while Methanosarcina and Methanothermobacter were favored in thermophilic treatments. The higher acetogenesis rate integrated with enriched acetoclastic methanogenesis led to its better performance in biochar-assisted thermophilic co-digestion.

Biochar-promoted methane production and mitigation of acidification during thermophilic anaerobic co-digestion of food waste with crude glycerol: comparison with re-inoculation

Food waste and crude glycerol were anaerobically co-digested for 100 days at 52 ± 1 °C with an organic loading rate of 1.0 g L−1 d−1. This long-term thermophilic anaerobic digestion (AD) system encountered severe inhibition from volatile fatty acids (VFAs). The study investigated the impacts of re-inoculation (RI) and biochar addition (BA) on this AD process, and monitored the variation of pH, VFAs, total alkalinity and total ammonia nitrogen during treatment. RI treatment was effective in the short term by recovering reactivity after inhibited sludge was mixed 1:1 with active inoculant. In the long term, RI could not reverse process imbalance and finally failed on day 56. Superior performance in methane production and process stability was observed in BA reactors when compared with control and RI reactors. Overall, the biochar contributed to alkalinity and facilitated the activation of methanogenesis and stimulated the conversion of VFAs.

Mitigation of the Toxicity of Capsaicin on Anaerobic Codigestion of Food Waste and Waste Activated Sludge Using Calcium Peroxide: A Comprehensive Analysis Using Computational and Biological Approaches

Increasing amounts of food waste with high concentrations of capsaicin are generated globally. Capsaicin concentration has been proven to inhibit methane production in the anaerobic codigestion process; thus, strategies to alleviate this toxicity are urgently needed. This study focuses on the use of calcium peroxide for alleviating the inhibitory effect of capsaicin and methane production promotion in anaerobic codigestion for the first time. Results show that calcium peroxide increases the rate of capsaicin degradation significantly. Based on active site prediction, degradation product identification, and density functional theory calculations, the main pathways of capsaicin degradation are verified to be O-demethylation and hydrogen abstraction. According to the quantitative structure–activity relationship, the main degradation products are less toxic than capsaicin. With an increase of calcium peroxide addition from 0 to 0.10 g/g VS (volatile solid), the methane yield and production rate are promoted from 174.92 ± 7.12 mg/g VS and 10.54 ± 0.32 mL/(g VS·d) to 307.56 ± 10.43 mg/g VS and 23.15 ± 0.72 mL/(g VS·d), respectively. This study provides insights into calcium peroxide-enhanced capsaicin degradation and demonstrates an effective niche to mitigate the capsaicin toxicity toward anaerobic codigestion.

Co-digestion of food waste and hydrothermal liquid digestate: Promotion effect of self-generated hydrochars

Hydrothermal treatment (HTT) can efficiently valorize the digestate after anaerobic digestion. However, the disposal of the HTT liquid is challenging. This paper proposes a method to recover energy through the anaerobic co-digestion of food waste and HTT liquid fraction. The effect of HTT liquid recirculation on anaerobic co-digestion performance was investigated. This study focused on the self-generated hydrochars that remained in the HTT supernatant after centrifugation. The effect of the self-generated hydrochars on the methane (CH4) yield and microbial communities were discussed. After adding HTT liquids treated at 140 and 180 °C, the maximum CH4 production increased to 309.36 and 331.61 mL per g COD, respectively. The HTT liquid exhibited a pH buffering effect and kept a favorable pH for the anaerobic co-digestion. In addition, the self-generated hydrochars with higher carbon content and large oxygen-containing functional groups remained in HTT liquid. They increased the electron transferring rate of the anaerobic co-digestion. The increased relative abundance of Methanosarcina, Syntrophomonadaceae, and Synergistota was observed with adding HTT liquid. The results of the principal component analysis indicate that the electron transferring rate constant had positive correlationships with the relative abundance of Methanosarcina, Syntrophomonadaceae, and Synergistota. This study can provide a good reference for the disposal of the HTT liquid and a novel insight regarding the mechanism for the anaerobic co-digestion.

Impacts of organic loading rate and hydraulic retention time on organics degradation, interspecies interactions and functional traits in thermophilic anaerobic co-digestion of food waste and sewage sludge

This study provided novel insights into the effects of organic loading rate (OLR) and hydraulic retention time (HRT) on thermophilic anaerobic co-digestion of food waste and sewage sludge. The obtained maximum methane (CH4) yield of 328 ± 4 mL CH4/g CODfed at HRT of 15 days (OLR = 5.8 g VS/L/d) was partly attributable to the enhanced acidogenesis, acetogenesis, and methanogenesis phases. The increased key enzyme activities, particularly acetate kinase (improved by 5.2-fold), providing substantial methanogenic substrates for efficient CH4 production. The functional syntrophs that were related to syntrophic decarboxylation, novel acetate oxidation & reductive acetyl-CoA, and β-oxidation pathways could drive trophic interactions with methanogens. This markedly stimulated hydrogenotrophic Methanoculleus thermophilus metabolism and concomitantly enriched mixotrophic Methanosarcina thermophila. The distinctive cross-feeding interspecies interactions significantly affected the assembly and dynamics of thermophilic consortia. These findings shed light on the physicochemical and microbial mechanisms of HRT- and OLR-dependent enhancement of methanogenesis.

Intermittent energization improves microbial electrolysis cell-assisted thermophilic anaerobic co-digestion of food waste and spent mushroom substance

Microbial electrolysis cell-assisted thermophilic anaerobic digestion (MEC-TAD) is a promising method to improve anaerobic co-digestion efficiency; however, its application is restricted by high energy consumption. To improve the energy use efficiency of MEC-TAD, this study investigated the effect of different intermittent energization strategies on thermophilic co-digestion performance. Results revealed that an 18 h-ON/6h-OFF energization schedule resulted in the fastest electron transfer rate and the highest methane yield (364.3 mL/g VS). Mechanistic analysis revealed that 18 h-ON/6h-OFF resulted in the enrichment of electroactive microorganisms and increased abundance of enzyme-coding genes associated with energy metabolism (ntp, nuo, atp), electron transfer (pilA, nfrA2, ssuE), and the hydrogenotrophic methanogenic pathway. Finally, energy balance analysis revealed that 18 h-ON/6h-OFF had the highest net energy benefit (2.52 kJ) and energy conversion efficiency (110.76 %). Therefore, intermittent energization of MEC-TAD using an 18 h-ON/6h-OFF schedule can provide improved performance and more energy savings.

Enzyme pretreatments for anaerobic co-digestion of food waste blended with bioplastics: effects on methane production and microbial community structure

Bioplastic bags mixed with food waste seem inevitable with the growth of waste classification and the banning of non-biodegradable polymers in China.