Co-digestion Of Food Waste Research Articles

Enhancing anaerobic co-digestion of primary settled-nightsoil sludge and food waste for phosphorus extraction and biogas production: effect of operating parameters and determining phosphorus transformation.

The study aimed to comprehensively determine P extraction efficiency and co-digestion of food waste (FW) and primary settled-nightsoil sludge (PSNS) process performance influenced by different hydraulic retention times (4, 7, 10, and 15days) and mixture ratios of FW:PSNS in substrates (100:0, 75:25, 50:50, 25:75, and 0:100). P-transformation was evaluated to identify P fractionation in both supernatant and sludge accumulated in reactors. The results showed that anaerobic co-digestion was inhibited by the accumulation of undigested feedstock due to higher %PSNS found in AD4 (25FW:75PSNS) and AD5 (100PSNS). A more stable process was found in AD2 (75FW:25PSNS) under hydraulic retention time (HRT) 15days in which COD removal efficiency and P release were 97.2 and 80.2%, respectively. This recommended condition allowed a high organic loading rate (OLR) at 12 gVS/L/day resulting in the highest biogas yield of 0.93 L/L/day. Distribution of P data demonstrated that most of P in feedstock was deposited and accumulated in sediment up to 97.8%. Poor biodegradability resulting from using shortened HRT led to high increased P-solid content in effluent. In addition, available P in effluents and accumulated P-solids in sediment obtained from the AcoD process has the potential to serve as sources for P recovery.

Biorefinery-oriented full utilization of food waste and sewage sludge by integrating anaerobic digestion and combustion: Synergistic enhancement and energy evaluation

Biorefinery-oriented full utilization of organic wastes by integrating anaerobic digestion and combustion is a promising approach. The objectives of this study were to investigate the effect of the co-treatment of food waste and sewage sludge on the performance of the combined system in terms of methane production, combustion characteristics and total energy output. The anaerobic co-digestion of food waste with sewage sludge showed a clear synergistic enhancement at the optimal food waste/sewage sludge ratio of 2:2, where the methane yield increased by 99 mL/g VSadded compared with the theoretical value. The analysis of aqueous products suggested that the synergistic effect was attributed to reduced volatile fatty acids accumulation and ammonia inhibition. Furthermore, the digestate at a ratio of 2:2 showed the best combustion characteristics with the highest comprehensive combustion index and combustion stability index of 4.87 × 10−7%2 min−2 °C−3 and 4.80 × 103%2 min−2 °C−3, respectively, which could be resulted from the more stable organic components and the catalytic effects of inorganic minerals. Finally, the energy evaluation showed that the co-treatment would increase the daily energy output and specific energy output of 100 t/d full-scale plant by 14.3 GJ/day-33.7 GJ/day and 0.3 GJ/t-0.6 GJ/t, respectively. These findings could provide some valuable information for anaerobic digestion-combustion-based biorefinery of organic wastes.

Monitoring of produced biogas volume and composition from co-digestion of Cow-dung and organic-kitchen-waste

This is an experimental study on produced biogas volume and volume from co-digestion of cow dung and food waste. This study was carried out at ambient condition. A gas meter was used for the measurement of gas composition, biodigester operating parameter were measured using a multi meter while gas volume was obtained from the observation of the floating drum. Four floating drum digesters were used for the experiment. The digesters held 3300 g of feed each with varying ratios of 70:30 (Sample A), 50:50 (Sample B), 40:60 (Sample C), and 30:70 (Sample D) of cow dung to kitchen waste respectively. The dilution ratio was 1:3 of feed to water which had a retention time of 30 days. The gas composition (CH4, CO, CO2, H2S), substrate pH and temperature were monitored to observe the changes. The results gotten were graphed and tabulated. The gas gotten from the biogas burnt which shows that the biodigesters produced methane (CH4) of more than 40% of the gas composition at certain points during the retention time.

Co-digestion of cow manure and food waste for biogas enhancement and nutrients revival in bio-circular economy

Anaerobic co-digestion (AcoD) with suitable substrate ratios may have the potential to improve biogas process and could play a better role in nutrient management for biocircular economy. The goal of this study was to enhance biogas yield from AcoD of cow manure (CM) and canteen food waste (CFW), and pertinent co-digestion of suitable substrate ratios for nutrient management i. e NPK from linear to biocircular economy, using ruminant intestinal fluid as a source of inoculum. A mesophilic (37 ± 1 °C) laboratory-scale AcoD with varying CFW/CM ratios of (0:1, 1:4, 2:3, 1:1, 3:2, 4:1, and 1:0) based on wet weight was performed. The AcoD systems of different CFW/CM ratios were evaluated with a loading rate of 400 g/L in the presence of 100 g cow intestinal fluid (CIF) inoculation. All experimental AcoD systems yielded greater biogas (147–300 cm3/g VS) than the mono-digestion in which only CM (135 cm3/g VS) and CFW (146 cm3/g VS) were digested anaerobically. The AcoD system of CFW/CM with 4:1 showed the highest biogas yield (300 cm3/g VS), and VS and COD reduction rate (39.51% and 65.15%, respectively), and nutrient contents (6.53%). Moreover, the experiment results were verified by modified Gompertz model. This work provided a window of opportunity to examine the anaerobic co-digestion technology beyond biogas production and to put the current low-cost technology to use for nutrient management and as a better component of the biocircular economy for agriculture in Pakistan in order to achieve sustainable development goals.

Effect of initial pH and substrate to inoculum ratio on the production of methane and hydrogen from food waste

“Anaerobic co-digestion of food waste, cow dung, and sludge solution is experimented by varying the pH to produce hydrogen and methane as a source of renewable energy. The substrate to inoculum ratio (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. A maximum hydrogen and methane concentration of 19.73% and 64.81% respectively are obtained in S3. The methane concentration of 53.67%, 64.81% and 59.64% is observed at the pH variation of 6.5, 7, and 7.5 respectively. The obtained result shows the substrate to inoculum ratio of 1:3 to be the optimal combination for the highest methane and hydrogen production during the anaerobic co-digestion process”.

Anaerobic co-digestion of food waste with sewage sludge from wastewater treatment plant of Sequele, Luanda-Angola

This work aimed to evaluate the potential for methane production from anaerobic co-digestion of the organic fraction of urban solid wastes with sewage sludge. The tests were carried out using Bioprocess AMPTS II batch reactors operated at 37 °C in two different runs. In each run, a different food waste sample, inoculated with sludge, was tested varying the inoculum to substrate ratio (ISR) in each reactor. The experimental cumulative methane production by the mixture at the end of the tests was compared with the expected methane production in order to identify synergistic effects. The modified Gompertz model was fitted to experimental substrate cumulative methane yields. The results of this study suggest the suitability of this model to describe the degradation kinetics. ISR was found to be an important parameter for an efficient methane production, values ≥ 2 are recommended in order to prevent the pH drop in reactors. For one of the food waste samples, the highest substrate methane yield achieved was 91% of the theoretical value. For the other one, synergistic effects were observed in the mixtures of inoculum and substrate, that were attributed to an enhanced methane production by the sewage sludge when mixed with the food waste. The anaerobic co-digestion of food waste with sewage sludge from the Sequele WWTP is a sustainable treatment option for both organic wastes, which can be implemented in this WWTP where the sludge is simply discarded after dehydration.

Green biohydrogen production in a Co-digestion process from mixture of high carbohydrate food waste and cattle/chicken manure digestate

This study was investigated biohydrogen production on the effects of different ratio of food waste to seed digestate and pH value from co-digestion process in anaerobic reactor. The seed digestate was mixture of cattle manure 45%, corn silage 25%, chicken manure 15%, and olive pomace 15% which was collected from the biogas plant in central Italy. It was found that the peaks of total biogas and the biohydrogen productions were 1355 ± 26 and 436 ± 10 mL whereas the biohydrogen yield was 50.4 mL/g-VS (45.8 mL/g-COD) with 43.33% COD removal rate, the bacteria to substrate volatile solids (VS) ratio was 2:1 where seed digestate to food waste was 6:4 under pH 6.5. As a consequence, food waste with a high COD concentration can be adapted C/N ratio by the cattle manure and chicken manure in the seed digestate which resulted in a high biohydrogen production. The food waste co-digestion system mixed with biogas plant digestate is one of approach to increase total biogas production.

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.

Anaerobic Co-Digestion to Enhance Waste Management Sustainability at Yosemite National Park

This study evaluated the co-digestion of domestic wastewater solids (WWS) and food waste (FW) at the bench-scale for Yosemite National Park, California, which operates a 1900 m3/d wastewater treatment plant in El Portal, California. A 35-day biochemical methane potential test was performed on varying amounts of FW as a percentage of total waste (WWS plus FW) on a volatile solids basis (%FW). Specific methane yield and volumetric methane yield increased substantially with increasing %FW. A higher %FW was also associated with slower degradation kinetics but higher methane content in biogas. The 75 %FW treatment had relatively rapid kinetics, a high cumulative specific methane yield (453 mL CH4/g VS), and an elevated methane content in biogas, and is suggested as an upper limit %FW mixture for full-scale co-digestion. This, coincidently, is near the estimated ratio of WWS and FW production at the Park (70 %FW). Co-digesting the Park’s feedstock of FW with WWS in existing anaerobic digestion facilities could increase methane production five-fold. Combusting this methane in a combined heat and power system would produce about twice the energy needed to heat anaerobic digestors and power the treatment plant.

Two-stage anaerobic membrane bioreactor for co-treatment of food waste and kitchen wastewater for biogas production and nutrients recovery

Co-digestion of organic waste and wastewater is receiving increased attention as a plausible waste management approach toward energy recovery. However, traditional anaerobic processes for co-digestion are particularly susceptible to severe organic loading rates (OLRs) under long-term treatment. To enhance technological feasibility, this work presented a two-stage Anaerobic Membrane Bioreactor (2 S-AnMBR) composed of a hydrolysis reactor (HR) followed by an anaerobic membrane bioreactor (AnMBR) for long-term co-digestion of food waste and kitchen wastewater. The OLRs were expanded from 4.5, 5.6, and 6.9 kg COD m−3 d−1 to optimize biogas yield, nitrogen recovery, and membrane fouling at ambient temperatures of 25–32 °C. Results showed that specific methane production of UASB was 249 ± 7 L CH4 kg−1 CODremoved at the OLR of 6.9 kg TCOD m−3 d−1. Total Chemical Oxygen Demand (TCOD) loss by hydrolysis was 21.6% of the input TCOD load at the hydraulic retention time (HRT) of 2 days. However, low total volatile fatty acid concentrations were found in the AnMBR, indicating that a sufficiently high hydrolysis efficiency could be accomplished with a short HRT. Furthermore, using AnMBR structure consisting of an Upflow Anaerobic Sludge Blanket Reactor (UASB) followed by a side-stream ultrafiltration membrane alleviated cake membrane fouling. The wasted digestate from the AnMBR comprised 42–47% Total Kjeldahl Nitrogen (TKN) and 57–68% total phosphorous loading, making it suitable for use in soil amendments or fertilizers. Finally, the predominance of fine particles (D10 = 0.8 μm) in the ultrafiltration membrane housing (UFMH) could lead to a faster increase in trans-membrane pressure during the filtration process.

Enhancing methane production in anaerobic co-digestion of sewage sludge and food waste by regulating organic loading rate

This study presented mechanistic insights into the long-term effects of stepwise-increasing organic loading rates (OLRs) on anaerobic co-digestion (AcoD) of sewage sludge and food waste. The maximum methane (CH4) yield of 500.0 ± 10.5 mL CH4/g VSfed was achieved at medium OLR of 3.5 g VS/L/d. This excellent performance was associated with the high hydrolysis efficiency (78.4%), three-fold enhancement in the acidogenesis enzyme activity, and 87.0% enhanced methanogen activity. Soluble intermediates (carbohydrates and proteins) were largely degraded (>98.5%), especially tyrosine-like and tryptophan-like aromatic proteins. The particulates were effectively decomposed from macromolecules to micromolecules, and the crystallinity of cellulosic substances decreased by 24.5%. The newly-shaped combined syntrophic acetate oxidation-hydrogenotrophic methanogenesis pathway dominated enhanced CH4 production. Energy balance analysis based on medium OLR demonstrated the high energy recovery potential in full-scale AcoD. These findings suggest the optimal medium OLR can facilitate the bioconversion of organics to CH4 through a new metabolic pathway.

Long-term evaluation of the anaerobic co-digestion of food waste and landfill leachate to alleviate ammonia inhibition

To evaluate the feasibility of the co-digestion of food waste (FW) and landfill leachate (LL) to alleviate ammonia inhibition, a series of batch co-digestion experiments were conducted to explore the optimal substrate mixing ratio, and semi-continuous experiments were conducted to evaluate the long-tern effects of LL addition on methane generation and digestate characteristics of the anaerobic co-digestion system under ammonia stress. The optimum methane generation and digestate properties were observed when the concentration of LL in the dilution liquid in the co-digestion reactor was 40 % (v/v). Significant volatile fatty acid accumulation and lower methane yields were both observed during the long-term FW mono-digestion when the total ammonia nitrogen (TAN) concentration reached 3391.27 mg·L–1. However, stable methane generation was observed in the co-digestion system, even when the TAN was 3721.59 mg·L–1, confirming that the LL alleviated the ammonia inhibition of the FW-based anaerobic digestion (AD) system. Microbial analysis of the AD reactors demonstrated that the relative abundance of Pelotomaculum was higher in the co-digestion system than in the mono-digestion system. Analysis of the phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) confirmed the enrichment of genes involved in butyrate, propionate, and methane metabolism in the co-digestion system. In addition, analysis of the digestate characteristics (i.e., dewaterability, germination index, and heavy metals concentrations) indicated that there was no ecological risk for utilization of the digestate after long-term co-digestion operation. These results aim to provide guidance for using LL to promote the processing of FW in the future.

Comparative study of the effect of loading increments on the mesophilic codigestion of waste activated sludge and food waste: Reactor performance, stability analysis, and microbial community

The performance and stability of mesophilic codigestion of waste activated sludge (WAS) and food waste (FW) were compared in two parallel, continuously stirred tank reactors using high- and low-magnitude loading increments for the loading regimes. The results indicated that a high methane (CH4) production of 6.98 L L−1·d−1 was realized without volatile fatty acid accumulation via low-magnitude loading increments at a high loading of 26.5 g-COD·L−1·d−1, and this system was more stable and achieved a higher efficiency than the codigestion system that used high-magnitude loading increments at similar loading and operating conditions. Furthermore, higher CH4 yields of 258–334 mL-CH4·g-COD−1, TCOD removal efficiencies of 64–79%, conversion ratios of 62–88%, and methanogenic activities of 0.37–0.40 g-CH4-COD·g-VS−1·d−1 were consistently maintained via the low-magnitude loading increments during the high-rate period. High abundances of the phyla Firmicutes (63.3%) and genus Methanosarcina (94.5%) contributed to the high rates and stable operating conditions of the mesophilic system for WAS and FW codigestion using low-magnitude loading increments.

Solid-state anaerobic co-digestion of food waste, rice straw, and rice husk supplemented with cattle digesta under thermophilic conditions

Solid-state anaerobic co-digestion of food waste, rice straw, and rice husk supplemented with cattle digesta under thermophilic conditions

Biogas production from anaerobic co-digestion of sewage sludge and food waste in continuously stirred tank reactor

The purpose of current investigation was to explore the scope of integrating an anaerobic digester in a decentralized municipal wastewater treatment plant for in-situ treatment of household waste. The present work intends to identify the potential of sewage sludge and food waste for biogas generation. The study was conducted in lab scale continuous stirred tank reactor having a working volume of 6.5 L at mesophilic temperature. The paper mill sludge was used as inoculum and was stabilised using food waste substrate for initial 50 days in batch mode. Co-digestion of food waste (FW) and bio-flocculated sewage sludge (BFS) was performed using continuous feeding for maintaining OLR of 2.5 gVSL−1D−1at HRT of 4 days for 120 days. 2% FW and 98% BFS (by volume) was feeded in the reactor throughout the experimental duration. The highest VFA accumulation of 1902 mg L−1 were observed and maximum bio-methane yield was found to be 127.05 mLCH4 g−1 VSadded. The pH with current feeding ratio was found stable during the reactor operation without adding external alkalinity source.

Methanogenic diversity changes in full-scale anaerobic digesters by co-digestion of food waste and sewage sludge

Methanogenic diversity changes in full-scale anaerobic digesters by co-digestion of food waste and sewage sludge

Anaerobic co-digestion of sewage sludge pretreated by thermal hydrolysis and food waste: gas production, dewatering performance, and community structure

ABSTRACT Anaerobic co-digestion can effectively break the limitations of mono-digestion. However, there are still some problems such as long residence time, unsatisfactory methane yield, and unstable performance for co-digestion of sewage sludge (SS) and food waste (FW). Therefore, the SS in the reactor treating co-digestion of SS and FW is considered to be pretreated by thermal hydrolysis. In this work, the anaerobic co-digestion of SS of thermal hydrolysis pretreatment (THP) and FW significantly improved the stability, methane production of the digestive reactor, and dewaterability of the digested sludge. The R6 obtained the most cumulative methane production (315.76 mL/g VS). In addition, compared to R3, the cumulative methane production and maximum methane production rate of R5 increased by 9.93% and 14.56%, respectively. The dewaterability of R4, R5, and R6 was improved, while the dewatering performance of the R3 decreased to a greater extent. The results of the kinetic model fitting were consistent with the experimental results. Among them, the hydrolysis constants (Kh) of anaerobic co-digestion of THP-SS and FW were 0.121, 0.130, and 0.114 d−1, respectively, which were higher than those of other groups. And the estimated lag time (λ) of co-digestion was also lower than that of mono-digestion groups. Microbial community analysis indicated that the bacterial diversity and richness of anaerobic co-digested groups of THP-SS and FW were enhanced, while the methanogens with acetoclastic pathway became the main methanogenic microorganisms. This work provides essential information on anaerobic co-digestion containing different THP-SS contents.

High-efficiency anaerobic co-digestion of food waste and mature leachate using expanded granular sludge blanket reactor

Anaerobic digestion of food waste receives more and more attention for waste-to-energy conversion, while easy acidification and limited efficiency hinder its wide application. To improve anaerobic digestion of food waste, its anaerobic co-digestion with mature leachate was performed using an expanded granular sludge blanket reactor. With the chemical oxidation demand (COD) removal of around 80%, the methane production and organic loading rate of the reactor reached 5.87 ± 0.45 L/L/d and 23.6 g COD/L/d, respectively. The rate of COD converted to methane was ranging from 74% to 87%. The addition of mature leachate provided ammonium to avoid acidification and trace metals for microbial growth, and the efficiencies of four stages of anaerobic digestion were all enhanced. The predominant methanogenic genera were shifted to adapt the changing condition, thus stabilizing the system. These findings support high-efficiency bioenergy recovery from food waste and leachate in practice.

Insights into the anaerobic digestion of fecal sludge and food waste in Tanzania

With the increasing demand for renewable energy and environmental protection, biogas technology has attracted considerable attention around the world. Fecal sludge (FS) is rich in organic matter, and it contains high concentrations of excreted pathogens that cause gastro-intestinal infection. In Tanzania, fecal sludge management from on-site sanitation systems poses a threat on environmental safety. This study aimed to assess the feasibility of the use of anaerobic digestion (AD) for the treatment of FS and the production of biogas as renewable energy to achieve multiple benefits in Tanzania. For the experiments, FS and food waste (FW) were used as feedstock, and rice straw-derived biochar (RSB) was added as an additive to improve biogas production. The mesophilic anaerobic digestion resulted in a methane yield of 287.5 ml/g VS for FS + FW co-digestion and 396 ml/g VS for FS + FW + RSB co-digestion. At ambient temperature (20–26°C), the system produced a methane yield of 234 ml/g VS for FS + FW co-digestion and 275 ml/g VS for FS + FW + RSB co-digestion. Three different scenarios (digester with volumes of 4, 100, and 400 m3, respectively) and strategies for FS treatment by AD in Tanzania were proposed and analyzed. These treatments can produce methane volumes of 1.95, 49.5, and 199.5 m3 with pay-back periods of 3, 5, and 15 years and net present values of + 28, +1,337, and +52,351 USD, respectively. The calculations also showed that the heat value from the produced biogas and energy needed to heat the digester at 26–37°C resulted in energy balance values of + 0.012, + 0.53, and + 2.22 GJ/day for the 4, 100, and 400 m3 digester volumes, respectively.

Anaerobic Co-Digestion of Sugarcane Leaves, Cow Dung and Food Waste: Focus on Methane Yield and Synergistic Effects

Anaerobic co-digestion (AcoD) of food waste (FW) and lignocellulose waste is a promising technology for methane production. This work investigated the methane generation from AcoD of FW, sugarcane leaves (SLs), and cow dung (CD) under mesophilic conditions in a batch test. As for AcoD of two feedstocks (SL and FW or CD and FW), introduction of SL and CD (25%, volatile solid (VS) basis) showed slight improvement in methane production from FW. In contrast, positive synergistic effect (synergy index = 1.03–1.14 > 1) was observed in all the AcoD reactors of the three feedstocks (SL, CD, and FW). The optimum mixing ratio of FW:SL:CD (VS basis) was 85:11.25:3.75 with a synergy index of 1.07, achieving a methane yield rate and methane content of 297.16 mL/g VS and 73.26%, respectively. This group cumulative methane production was an improvement of 110.45 and 444.72% higher than mono-digestion of SL and CD. The biodegradability, soluble chemical oxygen demand (SCOD), and VS removal rate were 56.44, 44.55 and 55.38%, respectively. The optimum results indicated that AcoD of FW, SL, and CD have higher potentials for energy recovery and provided forceful scientific evidence for their energy utilization.