Search

In Pakistan, bioenergy from agricultural residues (AR) plays a remarkable contribution to mitigating environmental pollution due to immense quantity of AR being produced. Pretreatment is a well-matured technique to disintegrate lignocellulose matter. This study evaluated pretreatment of rice straw (RS), canola straw (CS), and banana plant substrate (BPS) to be co-digested with buffalo dung in order to optimize the methane potential. Five different concentrations (0.1, 0.2, 0.3, 0.4, and 0.5%) of calcium hydroxide (Ca(OH)2) reagent were utilized for disintegrating residues at ratios of RS:BD (30:70), CS:BD (40:60), and BPS:BD (60:40). Co-digestion experiment was conducted on 5-g volatile solids (VS). The experiments revealed that Ca(OH)2 pretreatment significantly enhanced the methane yield. Maximum methane yield of 346.7, 417.3, and 284.3 mLCH4/gVS was obtained at a concentration of 0.4%, 0.4%, and 0.3% for RS, CS, and BPS respectively. However, maximum cellulose biodegradability was observed at 0.5% about 45.1% in CS. In addition, cumulative methane yields were kinetically assessed by S-Gompertz. Based on R2 simulated values, i.e., 0.9968, 0.9971, and 0.9940 for RS, CS, and BPS, the applied model validates optimal experimental results. Regarding optimization, CS generates the highest yield of methane than RS and BPW due to carbon content and oilseed substrate. [ABSTRACT FROM AUTHOR]

This study assessed the impacts of wheat straw as a cosubstrate on coal biocoverion into methane and the associated mechanism within methane metabolic pathways. Co-digestion of coal with varying wheat straw concentrations resulted in a remarkable (1246.05%) increase in methane yield compared to that of the control (CK). Moreover, microbial analysis revealed a uniform distribution of Methanosarcinaceae (51.14%) and Methanobacteriaceae (39.90%) in the co-digestion of coal and wheat straw (CWS1) at a ratio of 3:1 (w/w) compared to other treatments such as coal and wheat straw (CWS2) at a ratio of 3:0.5. In addition, Hungatieclostridiaceae and Rhodobacteriaceae were abundant in both co-digesters, whereas the bacterial communities in the CK group were significantly different and more abundant than those in the Peptostreptococcaceae and Enterobacteriaceae groups. The key enzymes related to methanogenic metabolic pathways, including EC: 1.2.99.5 and EC: 2.1.1.86 (facilitating the conversion of CO2 into methane), and EC:1.12.98.1 exhibited significant abundance within CWS1. Aromatic compounds such as 4-(2-chloroanilino)-4-oxobutanoic acid and phthalic acid were substantially more abundant in CWS1 and CWS2 than in CK, indicating the increased bioavailability of coal to microbial activities. This novel approach demonstrates that wheat straw co-digestion with coal during anaerobic digestion modulates microbial communities and their metabolic pathways to enhance methane production from complex substrates such as coal. [ABSTRACT FROM AUTHOR]

Anaerobic fermentation (AF) can effectively dispose of kitchen waste (KW) without the shortcomings of traditional methods such as incineration and sanitary landfill. However, KW has a high organic content, which easily leads to acidification and ammonia inhibition during digestion. To mitigate this issue, anaerobic co-digestion (AnCoD) with other substrates helps to adjust the carbon to nitrogen ratio (C/N) and enhance the stability of the reaction system. The hydrolysis of substrate is the rate-determining step in AF, prompting the adoption of necessary pretreatment methods to accelerate substrate hydrolysis. Among physical, chemical, and enzymatic pretreatments, the latter is more efficient. And the enzymatic pretreatment does not need additional equipment or reagents. Therefore, coupling enzyme treatment before AnCoD received more attention. In this review, we conduct a comparative analysis of the biogas production efficiency of enzymatic pretreatment against other pretreatment methods. The challenges and strategies concerning enzymatic pretreatment coupled with AnCoD system were discussed. Finally, the pilot-scale study and industrial application for KW co-digestion are also analyzed. [ABSTRACT FROM AUTHOR]

Copyright of Advances in New & Renewable Energy is the property of Editorial Office of Advances in New & Renewable Energy and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wheat straw (WS) is a promising substrate for biogas production by anaerobic digestion (AD) due to its high carbohydrate content. An estimated 0.603 million t yr−1 of WS are generated from wheat production systems in South Africa. This is equivalent to an energy potential of 11 PJ. Despite this, WS is still undervalued as a bioenergy resource in South Africa due to its structural complexity and low nitrogen content. WS disposal methods, such as use in livestock bedding, burning and burying into the soil, inter alia, are not sustainable and may contribute to global warming and climate change. The commercialization of the AD of WS needs to be further developed and promoted. Pre-treatment (i.e., physical, chemical, biological and hybrid methods) and anaerobic co-digestion (AcoD) are novel strategies that can support the conversion of WS into biogas and other value-added products. Current and future research should focus on optimizing pre-treatment and AcoD conditions towards industrialization of WS into valuable products. This paper focuses on the potential use of WS for biogas production in South Africa. The aim is to create information that will promote research and development, and encourage policy makers and stakeholders to participate and invest in WS biogas technology. Were WS biogas technology fully adopted, we believe that it would alleviate energy insecurity and environmental degradation, and sustain the livelihoods of citizens in South Africa. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is an efficient technology for treating organic solid wastes, and the volatile fatty acids (VFAs) produced during AD have significant value due to their wide range of applications and higher added value compared to methane. This study investigated the long-term effects of high solid content and straw proportion in mixed substrates (straw, sludge, and food wastes) on VFAs production through semi-continuous reactors under thermophilic and mesophilic conditions. Results showed that both reactors achieved a maximum VFAs concentration of ~ 22 g/L as the straw proportion increased to 50%. Acetate (48.3 – 64.5%) was the main component of produced VFAs in both reactors, while butyrate and propionate production in thermophilic temperature were superior compared to mesophilic conditions. Microbial community analysis revealed that Defluviitoga plays a pivotal role in acidogenesis within both reactors; besides, unclassified Hungateiclostridiaceae and Caproiciproducen were found to be dominant in thermophilic reactor, while Lachnospiraceae_NK3A20_group and Rikenellaceae_RC9_gut_group were essential for VFAs production under mesophilic conditions. These findings provide valuable insights for the biotechnological exploration of acidogenic fermentation for large-scale mechanized production of VFAs from agricultural wastes. [ABSTRACT FROM AUTHOR]

We report the relationship between enrichment of adapted populations and enhancement of community functional resilience in methanogenic bioreactors. Although previous studies have shown the positive effects of acclimation, this work directly investigated the relationships between microbiome dynamics and performance of anaerobic co-digesting reactors in response to different levels of an environmental perturbation (loading of grease interceptor waste [GIW]). Using the methanogenic microbiome from a full-scale digester, we developed eight sets of microbial communities in triplicate using different feed sources. These substrate-specific microbiomes were then exposed to three independent disturbance events of low-, mid- and high-GIW loading rates. This approach allowed us to directly attribute differences in community responses to differences in community composition. Despite identical inocula, environment (digester operation, substrate loading rate, and feeding patterns) and general whole-community function (methane production and effluent quality) during the cultivation period, different substrates led to different microbial community assemblies. Lipid pre-acclimation led to enrichment of a pool of specialized populations, along with thriving of sub-dominant communities. The enrichment of these populations improved functional resilience and process performance when exposed to a low level of lipid-rich perturbation compared with less-acclimated communities. At higher levels of perturbation, the communities were not able to recover methanogenesis, indicating a loading limit to the resilience response. This study extends our current understanding of environmental perturbations, feed-specific adaptation, and functional resilience in methanogenic bioreactors. [ABSTRACT FROM AUTHOR]

The yield of green energy from solid-state anaerobic co-digestion (SSAD) has recently been enhanced by incorporating innovative pretreatment methods and nanoparticles. However, the environmental consequences of employing new processes have not been fully examined. In this study, the environmental impacts of three high-methane-yielding scenarios including SSAD of corn stover blended with dairy manure (DM) denoted as (SYM1), calcium hydroxide-pretreated corn stover (CpCS) blended with DM (SYM2), and the CpCS blended with DM and nanoparticles (SYM3) were assessed and compared the baselines of solid-state and semi-solid-state anaerobic digestion using a life cycle assessment (LCA) approach. The approach investigated the best management practices that would result in high methane yield and low environmental impact. Results of the life cycle assessment indicate the inclusion of calcium hydroxide and nanoparticle has minimal negative environmental impact. There was an environmental gain in GWP when corn stover was co-digestion with DM (SYM1) relative to DM mono-digestions (baselines) and the carbon footprint of SYM1 was less by more than 85% compared to SYM2 and SYM3. However, the large volume of untreated corn stover harnessed for SYM1 scenario resulted in over 75% fossil fuel depletion compared to the other scenarios. The surplus methane from the SYM3 (at least twofold of other scenarios and baselines) in conjunction with being the least with the environmental implication makes the scenario the most attractive option for on-farm practice capable of harnessing the growing organic waste volume. These outcomes can guide trade-off between pretreatment and nanoparticle application to reduce solid-state anaerobic digestion's negative environmental impact. [ABSTRACT FROM AUTHOR]

Considering the difficulty of digesting coffee husk (CH) and water hyacinth (WH) due to the lignin content, the present study investigated the influence of feedstock mixing ratios on the co-digestion performance of CH and WH with food waste (FW) at 38 ± 1 °C and its kinetics. Food waste was considered as co-substrate due to its ease of digestion. Batch experiments were conducted using CH/WH/FW ratios (100:0:0, 0:100:0, 35:35:30, 30:30:40, 25:25:50, 20:20:60, and 0:0:100 w/w) with total solids (TS) content of about 9.5% (w/v). The results indicated that the addition of FW significantly enhanced WH and CH digestion performance, with the maximum biogas yield of 572.60 ± 2.30 mL/gVS, best synergistic effect of 1.5, highest biodegradability of 89.22%, and a biodegradation rate of 57.82% obtained at a mix ratio of 25:25:50, which was improved by 179.71% compared to CH mono-digestion. In addition, the organic conversion efficiency of TS and volatile solids reached 69.86 and 81.48%, respectively. Conversely, CH mono-digestion yielded the lowest biogas yield of 204.71 ± 10.74 mL/g VS, highlighting its unfeasibility. The modified logistic equation showed the best fit to the experimental data. The optimum CH/WH/FW ratio of 25:25:50 demonstrated the highest biogas yield and methane content at 66.30 ± 0.76%. [ABSTRACT FROM AUTHOR]

The utilization of palm oil mill residues for sustainable biogas production presents a promising avenue to mitigate environmental challenges associated with waste disposal and energy demand in palm oil processing. The study explores the use of palm oil mill residues for sustainable biogas production, focusing on the impact of mixing ratios of POME and three raw milled residues on biogas yield through anaerobic co-digestion. Results indicate that co-digestion significantly enhanced biogas production compared to mono-digestion of POME alone. The highest biogas yield of 370 ml was recorded in the digester with 40% residues followed by 50% with a cumulative biogas of 190 ml. The two digesters were higher than 80 ml recorded for POME alone. The findings underscore the potential of integrating palm oil mill residues into biogas systems to achieve dual objectives of waste management and renewable energy generation. [ABSTRACT FROM AUTHOR]

Orange peel waste (OPW) and crude glycerol (CG) can be used in anaerobic processes. To avoid inhibition due to D‐limonene from OPW, the process can be carried out in two stages. Thus, this work aimed to evaluate the generation of methane in biogas through the anaerobic digestion of OPW and CG, individually and mixed, in a single‐stage and two‐stage batch system. For this purpose, the biochemical methane potential (BMP) of the wastes, separately and mixed, was determined in a single‐stage system (methanogenic phase) and in a two‐stage system (acidogenic and methanogenic), following the German standard VDI 4630. The results obtained were statistically analyzed using Shapiro−Wilk and non‐parametric tests. For OPW, the BMP value found was 160.5 m3 CH4. tonSV−1. For CG, the result for BMP was 344.8 m3 CH4. tonVS−1. The result of these mixed wastes was equivalent to 501.3 m3 CH4. tonSV−1, for BMP. Through the statistical tests used, it was found that the use of OPW and CG, separately and mixed, in the two‐stage system does not present a statistically significant difference in the production of biogas when using the same wastes in a single‐stage system. However, it was found that the co‐digestion of these wastes is promising for biogas generation and contributes to managing these agro‐industrial wastes. [ABSTRACT FROM AUTHOR]

In this study, the optimum mixing ratio of food waste (FW) and livestock manure (LM) was investigated to improve the methane yield efficiency and prohibit the inhibition factors (organic loading rate and NH4+) from inhibiting the anaerobic co-digestion of FW and LM under mesophilic and thermophilic conditions. The research involved the following: (I) the analysis of the characteristics of FW and LM, (II) the evaluation of the potential and toxicity of the anaerobic digestion of I have confirmed that there is no problem. FW and LM using the biochemical methane potential (BMP) and anaerobic toxicity assay (ATA) tests, (III) the evaluation of the anaerobic co-digestion of FW and LM using the BMP test, and (IV) the evaluation of the optimum mixing ratio using mathematical modeling. The characteristics of FW and LM were analyzed to evaluate the theoretical methane potential and inhibition factor. The BMP test was carried out to evaluate the concentration of the biodegradable organic matter, biogas production rate, and methane yield. The ATA test was carried out to evaluate the impact of the inhibition concentration. Ultimately, mathematical models, such as a first-order reaction and a modified Gompertz model, were implemented to evaluate the optimum mixing ratio for the anaerobic co-digestion of FW and LM. FW had a higher concentration of degradable organic matter than LM. The initial operational parameters of the anaerobic digestion were determined to be appropriate at an organic matter concentration of less than 2.5 g/L and a TN concentration of 2,000 mg/L. In conclusion, as a result of evaluation through mathematical models, it was determined that anaerobic microorganisms were more sensitive to inhibitory factors under the thermophilic condition than under the mesophilic condition, and the optimum mixing ratio of FW to LM was 5:1 (vol:vol) based on kinetic results (k: 0.080; Bu: 0.23 L CH4/g VSadded; P: 100.84 mL; Rm: 10.23 mL/day; λ: 1.44 days). [ABSTRACT FROM AUTHOR]

Abstract This study assessed the impacts of wheat straw as a cosubstrate on coal biocoverion into methane and the associated mechanism within methane metabolic pathways. Co-digestion of coal with varying wheat straw concentrations resulted in a remarkable (1246.05%) increase in methane yield compared to that of the control (CK). Moreover, microbial analysis revealed a uniform distribution of Methanosarcinaceae (51.14%) and Methanobacteriaceae (39.90%) in the co-digestion of coal and wheat straw (CWS1) at a ratio of 3:1 (w/w) compared to other treatments such as coal and wheat straw (CWS2) at a ratio of 3:0.5. In addition, Hungatieclostridiaceae and Rhodobacteriaceae were abundant in both co-digesters, whereas the bacterial communities in the CK group were significantly different and more abundant than those in the Peptostreptococcaceae and Enterobacteriaceae groups. The key enzymes related to methanogenic metabolic pathways, including EC: 1.2.99.5 and EC: 2.1.1.86 (facilitating the conversion of CO2 into methane), and EC:1.12.98.1 exhibited significant abundance within CWS1. Aromatic compounds such as 4-(2-chloroanilino)-4-oxobutanoic acid and phthalic acid were substantially more abundant in CWS1 and CWS2 than in CK, indicating the increased bioavailability of coal to microbial activities. This novel approach demonstrates that wheat straw co-digestion with coal during anaerobic digestion modulates microbial communities and their metabolic pathways to enhance methane production from complex substrates such as coal.

Anaerobic digestion (AD) of feedstocks yields biogas, a potentially useful new energy source. This study looked into the anaerobic co-digestion of cow dung and organic garbage to produce biogas. An anaerobic biodigester, with a volume of 20 L, was used to digest organic waste (OW) and to trace the changes that occur during the AD process. It was equipped with tools that ensure complete control of the conditions affecting anaerobic biological reactions such as temperature, pH function, and mixing speed. Therefore, an anaerobic biodigester was designed to contain such biological transformations and to improve the biogas production process from OW. Based on the present investigation, the AD of OW was improved by integrating the substrate with sewage sludge or cow manure (CM) during the digestion process to provide the basic microorganisms to complete the digestion process. Feeding into the digester was a blend of 100 kg of cow dung (CM) and OW per day, diluted 1:1 with water. A gasbag was used to capture the methane that resulted. Biogas production began on the seventh day after the substrate was fed into the digester. A performance test was carried out on the produced biogas to determine its composition. For OW–CM, the generated biogas’s methane (CH4) concentration was determined to be 60%, but the rates of decline for TS and VS were 57 and 50.6%, respectively. Anaerobic biodegradation of OW–CM experiments was observed at 37°C, a mesophilic temperature. For OW–CM, the pH value was 6.7. After being adjusted to standard circumstances, the cumulative volume of methane produced which had been recorded as 4,914 mL became 3964.5 mL.

Abstract Anaerobic digestion (AD) is an efficient technology for treating organic solid wastes, and the volatile fatty acids (VFAs) produced during AD have significant value due to their wide range of applications and higher added value compared to methane. This study investigated the long-term effects of high solid content and straw proportion in mixed substrates (straw, sludge, and food wastes) on VFAs production through semi-continuous reactors under thermophilic and mesophilic conditions. Results showed that both reactors achieved a maximum VFAs concentration of ~ 22 g/L as the straw proportion increased to 50%. Acetate (48.3 – 64.5%) was the main component of produced VFAs in both reactors, while butyrate and propionate production in thermophilic temperature were superior compared to mesophilic conditions. Microbial community analysis revealed that Defluviitoga plays a pivotal role in acidogenesis within both reactors; besides, unclassified Hungateiclostridiaceae and Caproiciproducen were found to be dominant in thermophilic reactor, while Lachnospiraceae_NK3A20_group and Rikenellaceae_RC9_gut_group were essential for VFAs production under mesophilic conditions. These findings provide valuable insights for the biotechnological exploration of acidogenic fermentation for large-scale mechanized production of VFAs from agricultural wastes.

The study aimed to assess the effects of ultrasound-assisted thermal pretreatment on biogas production by co-digesting stress-adapted microalgae (Synechocystis sp.) with a combination of mixed municipal and industrial sewage sludge under anaerobic conditions. The pretreatment process involved subjecting the microalgae biomass to thermal pretreatment at temperatures of 70, 90, and 110oC while utilizing ultrasound pretreatment for the sludge (with an average solids content of 16.7 g/L) at a frequency of 25 kHz and power output of 400 W for durations of 3, 9, and 15 minutes before the main digestion process. The experiment was designed using response surface methodology (RSM) with a central composite design. The results revealed that the model exhibited statistical significance, with a probability value (Prob > F) of less than 0.05. Pre-treated samples demonstrated a substantial increase in biogas production compared to untreated samples, showing an average 1.4 to 5.6-fold enhancements. Optimization analysis indicated that the highest cumulative biogas production, amounting to 706 NmL, could be achieved after two weeks by pre-heating the microalgae cells at 110oC for one hour and subjecting the sewage sludge to ultrasound pretreatment for three minutes. These findings highlight the potential of ultrasound-assisted thermal pretreatment technology as a strategy to enhance biogas production through the co-digestion of stress-resilient microalgae and sewage sludge.

Anaerobic co-digestion of source-separated blackwater (BW) and food and kitchen waste (FW) offers decentralized circular economy solutions by enabling local production of biogas and nutrient-rich byproducts. In this study, a 2 m3 pilot-scale continuously stirred tank reactor (CSTR) operated under mesophilic conditions was utilized for co-digestion of BW and FW. The process obtained a CH4 yield of 0.7 ± 0.2 m3/kg influent-volatile solid (VS), reaching a maximum yield of 1.1 ± 0.1 m3/kg influent-VS, with an average organic loading rate of 0.6 ± 0.1 kg-VS/m3/d and HRT of 25 days. The CH4 production rate averaged 0.4 ± 0.1 m3/m3/d, peaking at 0.6 ± 0.1 m3/m3/d. Treatment of digestate through flocculation followed by sedimentation recovered over 90% of ammonium nitrogen and potassium, and 80–85% of total phosphorus in the liquid fraction. This nutrient-rich liquid was used to cultivate Chlorella vulgaris, achieving a biomass concentration of 1.2 ± 0.1 g/L and 85 ± 3% and 78 ± 5% ammonium nitrogen and phosphorus removal efficiency, respectively. These findings not only highlight the feasibility of anaerobic co-digestion of source-separated BW and FW in local biogas production but also demonstrate the potential of microalgae cultivation as a sustainable approach to converting digestate into nutrient-rich algae biomass. HIGHLIGHTS Anaerobic co-digestion of blackwater and food waste in a 2 m3 CSTR.; The maximum CH4 production rate was 0.6 ± 0.1 m3 per m3 reactor volume per day.; CH4 productivity was 50 ± 1% higher on the pilot-scale than in laboratory-scale BMPs.; Flocculation followed by sedimentation preserved >90% of macronutrients in digestate.; Chlorella vulgaris treatment reduced total and dissolved COD by 50 ± 10%.;

Anaerobic co-digestion is one potential strategy for maximizing the infrastructure's capacity for treatment while improving biogas output. It involves the addition of two or more substrates being digested simultaneously in the process. Anaerobic co-digestion's primary goal is to increase biogas, mostly bio-methane for domestic heating activities and electricity. By increasing bio-methane yields, anaerobic co-digestion becomes an effective and proficient method for reducing the limitations of mono-digestion and enhancing the commercial efficiency of existing anaerobic co-digestion amenities. By co-treating two or more waste streams, improved biogas generation can be accomplished through anaerobic co-digestion.

Anaerobic co-digestion was conducted on the solid residues after three-phase separation of kitchen waste (KWS) and waste-activated sludge (WAS), the synergistic effects and process performance were studied during co-digestion at different ratios of KWS to WAS. KWS and WAS mix ratios of 0:1, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1 and 1:0 (based on TS). The results showed that a ratio of KWS to WAS of 1:1 got a very high methane recovery with a methane yield of 310.45 ± 30.05 mL/g VSadded. The highest concentration of free ammonia among all reaction systems was only 70.23 ± 5.53 mg/L, which was not enough to produce ammonia inhibition in the anaerobic co-digestion system. However, when the KWS content exceeded 50%, methane inhibition and prolongation of the lag phase were observed due to the accumulation of volatile fatty acids (VFAs), and during the lag phase. Microbial community analysis showed that various bacterial groups involved in acid production and hydrolysis were mainly dominated by phylum Firmicutes, Chloroflexi, Proteobacteria and Bacteroidetes. Hydrogenotrophic methanogen was found to dominate all archaeal communities in the digesters. Co-digestion of KWS with WAS significantly increased the relative abundance of Methanobacterium compared with anaerobic digestion of WAS alone. HIGHLIGHTS Anaerobic co-digestion of solid residue after three-phase separation of kitchen waste and waste-activated sludge.; When the ratio of KWS to WAS was 1:1, the methane recovery was higher and was 310.45 + 30.05 mL/g VSadded.; As the amount of KWS added increased, the protein-like fluorescence intensity increased in the co-digestion system.; Hydrogenotrophic methanogen (Methanobacterium) dominated all archaeal communities in the digesters.;

Abstract The study investigates the potential of anaerobic co-digestion (AcoD) as a sustainable solution for managing putrescible organic waste generated by leather processing. Three experiments were conducted to assess the impact of various tannery wastes, pretreatment methods, and waste combinations on methane production. Experiment 1 demonstrated that co-digesting tannery wastewater primary sludge (TWPS) and fleshings significantly increased methane yield compared to digesting TWPS alone, though the addition of chromium- and vegetable-tanned leather wastes decreased yield. Experiment 2 explored TWPS pretreatment methods and found that ultrasonic pretreatment increased soluble chemical oxygen demand (SCOD) but did not significantly improve methane yield, suggesting that pretreatment may not be necessary. Experiment 3 revealed that increasing the proportion of fleshings to TWPS resulted in higher methane yield, ranging from 226.52 mL/gVS with 6% fleshings to 395.71 mL/gVS and 538.34 mL/gVS with 12% and 20% of fleshings, respectively. Additionally, this increase in fleshings also led to a reduction in digester volume. These findings highlight the importance of AcoD in addressing both environmental and economic challenges in the leather industry. Graphical Abstract

Anaerobic digestion (AD) of food waste (FW) is considered an environmentally sustainable process that can divert the disposal of FW to landfill and prevent greenhouse gas (GHG) emissions in managing the FW. Although several studies have attempted to demonstrate the AD of FW, low methane yields and a high incidence of process instability have been reported due to the rapid generation and accumulation of volatile fatty acids (VFAs). This paper reviews the recent research and development with high variation in FW composition, such as the carbon-to-nitrogen (C/N) ratio and, consequently, the effect of its physicochemical composition on process performance and methane yields. The paper highlights the significance of optimizing the anaerobic co-digestion (AcoD) of FW with carbon-rich substrates such as garden waste (GW) and/or the addition of trace elements as strategies that can improve the process performance and methane yields from FW. This review focuses on the factors effecting the feasibility of food organics and garden organics (FOGO) as a substrate for methane production. The review also critically analyses the prospects of enhancement of biomethane yield by optimizations of the impactful parameters. The progress in research related to these methods and identifying existing limitations to efficient AD of FOGO are the key findings of this review. This review also assesses the impact of nanotechnology on the process performance of the digester. The integration of FO and GO in AD processes has demonstrated enhanced biogas yields, improved process stability, and better waste management outcomes compared to the digestion of either substrate alone. Despite these advantages, challenges such as feedstock variability, process optimization, and the need for advanced pretreatment methods remain. Addressing these issues through continued research and technological innovations will be crucial for maximizing the efficiency and scalability of AD systems. Moreover, the economic feasibility and policy frameworks supporting AD need further development to promote broader adoption. [ABSTRACT FROM AUTHOR]

Effective nitrogen removal from anaerobic co-digestion is a major challenge to achieving dual-carbon goals. This study explored the acclimatization process of a lab-scale two-stage partial nitritation and anammox process of a stepwise increase in the percentage of raw anaerobic co-digestion liquor from kitchen waste, human feces, and municipal sludge in a venous industrial park in China, which has not been reported yet. Under limited dissolved oxygen (below 0.5 mg/L) and high ammonia levels (200–1500 mg/L), based on adjusting aeration rates, partial nitritation rapidly started up in 50 days. After acclimatization, partial nitritation still performed efficiently and stably, with the final total nitrogen loading rate (TNLR) of 1.24 ± 0.09 gN/L/d, nitrite accumulation rate of 99 ± 4%, and ratio of eff. nitrite/ammonia of 1.32 ± 0.13. In the anammox process, the final total nitrogen removal efficiency, total nitrogen removal rate, and TNLR reached 94 ± 5%, 1.27 ± 0.03 gN/L/d, and 1.36 ± 0.05 gN/L/d, respectively. Chemical oxygen demand (COD) was also reduced in both reactors, with COD removal rates of 0.7 gCOD/L/d in the partial nitritation and 0.4 gCOD/L/d in the anammox process. Overall, the PNA system demonstrated its feasibility in adapting to high ammonia, salinity, and iron levels, when treating anaerobic co-digestion liquor, particularly regarding resource recovery in venous industrial parks. [ABSTRACT FROM AUTHOR]

The study aimed to assess the effects of ultrasound-assisted thermal pretreatment on biogas production by co-digesting stress-adapted microalgae (Synechocystis sp.) with a combination of mixed municipal and industrial sewage sludge under anaerobic conditions. The pretreatment process involved subjecting the microalgae biomass to thermal pretreatment at temperatures of 70, 90, and 110oC while utilizing ultrasound pretreatment for the sludge (with an average solids content of 16.7 g/L) at a frequency of 25 kHz and power output of 400 W for durations of 3, 9, and 15 minutes before the main digestion process. The experiment was designed using response surface methodology (RSM) with a central composite design. The results revealed that the model exhibited statistical significance, with a probability value (Prob > F) of less than 0.05. Pre-treated samples demonstrated a substantial increase in biogas production compared to untreated samples, showing an average 1.4 to 5.6-fold enhancements. Optimization analysis indicated that the highest cumulative biogas production, amounting to 706 NmL, could be achieved after two weeks by pre-heating the microalgae cells at 110oC for one hour and subjecting the sewage sludge to ultrasound pretreatment for three minutes. These findings highlight the potential of ultrasound-assisted thermal pretreatment technology as a strategy to enhance biogas production through the co-digestion of stress-resilient microalgae and sewage sludge. [ABSTRACT FROM AUTHOR]

The adoption of new forms of energy production is one of the challenges faced by countries worldwide due to the progressive depletion of fossil fuels. In this regard, the co-digestion of organic waste in Wastewater Treatment Plants (WWTP) has gained widespread acceptance, as it not only provides an alternative for the utilization of several types of biomasses to meet energy needs but also assists in waste management and nutrient recovery. However, accepting additional substrates for co-digestion requires careful physicochemical studies, as their characteristics can influence both the stability of the process and the quality and production of biogas. In line with the above, this study implemented the case study method through descriptive analysis to evaluate the substrates accepted for anaerobic co-digestion in the Straubing WWTP in Germany (SER GmbH). As a result, it was found that floating fats (C1) and milk with inhibitors (C5) were the substrates that exhibited the highest biogas production per unit of treated mass, 90% more than distillation residues and 70% more than raw sludge. These findings underscore the importance of carefully selecting substrates for codigestion in WWTPs, highlighting the potential to harness valuable resources, as evaluated in this study, to increase efficiency in biogas production and, therefore, promote a more effective transition to sustainable energy sources in the global context. The Straubing WWTP in Germany thus becomes an example of the possibilities offered by co-digestion in sustainable energy generation and waste management. The inclusion of floating fats and milk with inhibitors as successful substrates illustrates how research and careful implementation can optimize the performance of these facilities. [ABSTRACT FROM AUTHOR]

Copyright of Environmental & Social Management Journal / Revista de Gestão Social e Ambiental is the property of Environmental & Social Management Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study quantitatively analyzed the synergistic effects of co-digestion of slaughterhouse waste (SHW) with cattle manure (CM) and pig manure (PM) on methane production by applying statistical methods. The biochemical methane potential of volatile solid concentration-based mixtures showed that the biodegradability (BD) of the co-substrates was improved as the mixing proportion of the highly biodegradable SHW increased. Furthermore, mathematical analysis using the modified Gompertz model showed that an increase in the SHW mixture ratio shortened the lag phase at the initial period by more than 58%. The synergy index (SI) analysis revealed that co-digestion of CM and SHW mixed at an equal ratio of 1:1 in sample S4 resulted in a higher SI of 1.18 compared to 1.10 for PM and SHW in sample S5. An overlay plot based on BD and SI identified the optimal mixture ratio as 26.9:31.0:42.1 (CM/PM/SHW), where both BD and SI reached their maximum values. The study successfully demonstrated that co-digestion of SHW with livestock manure enhances BD through a synergistic effect. [ABSTRACT FROM AUTHOR]

Bioenergy derived from anaerobic digestion has gained attention for a decade because of its ability to convert waste into biogas. The advantages of this biotechnology could substitute conventional energy, lower greenhouse gas emissions, and produce less biodegradable waste. This study focused on methane production from ensiled Napier grass (Pak Chong 1) by co-digestion with anaerobic mixed cultures of an Expanded Granular Sludge Bed (EGSB) from a bakery factory. The ratio of co-digestion between ensiled Napier grass feedstock and inoculum (F/I ratio) was 1:1 and 1:3 based on volatile solids (VS). The potential of methane production was evaluated using a batch experiment for 30 days in the laboratory at room temperature (32-35 ± 5 °C). To enhance biogas production, an alkaline pre-treatment of Napier grass was prepared by adding 1% NaOH. The results demonstrated that the methane production potential of the F/I ratio at 1:1 and 1:3 was 311.11 ± 29 and 255.56 ± 91 mL CH4/g COD, respectively. The maximum energy production based on methane production was approximately 9.17 kJ/L. The range of pH was 6.96 ± 0.2 to 9.93 ± 0.2 and the percentage of SS, TS, and COD removal were 60.10, 24.69, and 48.63, respectively. The results of this study indicated that the feedstock and inoculum ratio (F/I) including pretreatment of feedstock and inoculum is necessary for biogas potential production. The potential biogas production of the CSTR reactor and its economic feasibility should be further considered. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fish wastes and vegetable market wastes generated along with other wastes in the urban cities are disposed of in open landfill sites and lead to water, air and soil pollution. It occupies more and more land area for disposal as the generation of waste also increases day by day. In this current study, a novel approach has been identified to recover energy from mixed fish waste (MFW) and vegetable market waste (VMW) by anaerobic co-digestion. In fish waste, more than 75% of the total solids contribute to volatile solids, indicating that waste content is organic and suitable for anaerobic digestion. Further, MFW showed that the protein content is 4 to 5 times higher than carbohydrate content, indicating nitrogen richness will inhibit the AD process. Hence, co-digestion of MFW with carbon-rich VMW to maintain the stability of AD has been carried out. In this batch study, the biogas potential of these organic nitrogen-rich wastes was evaluated for major fish species (Parastromateus niger, Sillago indica and Scomberomorus cavalla) and mixed fish wastes individually and co-digestion of MFW with vegetable market waste (VMW) in different ratios. Based on the results, the specific biogas yields from Parastromateus niger, Sillago indica, Scomberomorus cavalla and mixed fish waste were 0.301 ± 0.011, 0.291 ± 0.002, 0.306 ± 0.008 and 0.289 ± 0.013 L/g of VS added, respectively. The co-digestion of fish waste with vegetable market waste in different mixing ratio (1:1 to 1:5) showed specific biogas yields of 0.445 ± 0.02 (1:1), 0.462 ± 0.01 (1:2), 0.489 ± 0.013 (1:3), 0.454 ± 0.015 (1:4) and 0.432 ± 0.011 (1:5) L/g of VS added. The results showed that there is an increase in biogas production during the co-digestion process confirming the synergistic potential of fish waste and vegetable market as substrates for the anaerobic digestion process. Further, the cumulative biogas production data were modelled using first-order kinetic, modified Gompertz and logistics models. The model results showed that the logistics model fitted well with experimental data (R2 of 0.99) and the predicted values from this model were less than 1% deviation from experimental biogas production. The results confirmed the suitability of anaerobic digestion for co-digestion of MFW and VMW for enhanced energy recovery for future implementation in an urban area to reduce the waste dumped in landfills. [ABSTRACT FROM AUTHOR]

The study investigates the potential of anaerobic co-digestion (AcoD) as a sustainable solution for managing putrescible organic waste generated by leather processing. Three experiments were conducted to assess the impact of various tannery wastes, pretreatment methods, and waste combinations on methane production. Experiment 1 demonstrated that co-digesting tannery wastewater primary sludge (TWPS) and fleshings significantly increased methane yield compared to digesting TWPS alone, though the addition of chromium- and vegetable-tanned leather wastes decreased yield. Experiment 2 explored TWPS pretreatment methods and found that ultrasonic pretreatment increased soluble chemical oxygen demand (SCOD) but did not significantly improve methane yield, suggesting that pretreatment may not be necessary. Experiment 3 revealed that increasing the proportion of fleshings to TWPS resulted in higher methane yield, ranging from 226.52 mL/gVS with 6% fleshings to 395.71 mL/gVS and 538.34 mL/gVS with 12% and 20% of fleshings, respectively. Additionally, this increase in fleshings also led to a reduction in digester volume. These findings highlight the importance of AcoD in addressing both environmental and economic challenges in the leather industry. [ABSTRACT FROM AUTHOR]

This study conducted anaerobic co-digestion (AcoD) of chicken manure (CM) and corn straw (CS) with various mixing ratios (1:0, 9:1, 8:2, 7:3, 6:4, 5:5, and 4:6, VS) through batch experiments to investigate gas production performance, changes in biogas slurry fertilizer efficiency, and microbial community. The results indicate that, compared to anaerobic digestion (AD), AcoD promoted methane production and reduced the accumulation of toxic substances, such as ammonia nitrogen. Methane production was the highest when CM and CS were co-digested with a mixing ratio of 7:3 (R-7:3). The degradation rate of organic matter (OM) at R-7:3 was the highest, and both available nitrogen (AN) and available phosphorus (AP) concentrations were at appropriate levels. The concentration of available potassium (AK) increased the most during the digestion process. In addition, the concentrations of heavy metals (Cu, Zn, Cd, Pb, As) in the biogas slurry were below the detection limit. Microbial analysis reveals that Methanosarcina and Sedimentibacter were the primary bacteria responsible for methane production in the system. They are relatively abundant under R-7:3 conditions, which suggests a greater potential for the stability of the AcoD system. Therefore, an appropriate mixing ratio of CM to CS could enhance methane production and system stability, while reducing the risks associated with using biogas slurry in agriculture. [ABSTRACT FROM AUTHOR]

The present study investigated the feasibility of the anaerobic co-digestion (AcoD) of condensate, resulting from drying food waste, with Waste Activated Sludge in a pilot scale continuous stirred tank reactor. Different parameters were assessed in order to enhance the AcoD performance; the condensate potency (condensate A: 13 gCOD/L and condensate B: 4 gCOD/L), the volumetric ratio of condensate to WAS (0–67% v/v) and the hydraulic retention time (HRT) (20, 15 and 12 days). The results showed that increasing the condensate content in the feed from 0 to 67% v/v, enhances the organic load removal (up to 41% increased total COD removal) and the bioenergy production (up to 35% increased biomethane production). Moreover, in the case of condensate A, the reduction of HRT from 20 to 15 days enhanced the bioenergy production (up to 19% increased biomethane production) while the reduction of HRT from 20 to 12 days in the case of condensate B did not significantly affect the reactor's performance. Overall it is concluded that condensate can be safely introduced in existing facilities for anaerobic digestion, while maintaining a more stable operation and improved effluent quality and bioenergy production in comparison with conventional anaerobic sludge digestion. [ABSTRACT FROM AUTHOR]

The tangible effects of climate change and the influence of environmental factors on climate have driven a shift towards cleaner and more sustainable energy sources. This study investigates the effects of biochar and zeolites in the anaerobic digestion (AD) and co-digestion processes of cassava wastewater (CW) with livestock manure, aiming to assess their impact on methane (CH4) and carbon dioxide (CO2) production, as well as process stability. The study employs design of experiments, analysis of variances, design parameter sensitivity, and differential analysis to explore how varying concentrations of biochar and zeolites influence key production parameters and optimize the overall process. Results indicate that increasing biochar and zeolite concentrations produce alternating effects on CO2 and CH4 generation, with CW significantly contributing to CH4 production. Livestock manure shows similar effects on both gases, necessitating calculated trade-offs in prioritizing one over the other. Findings provide insights into enhancing biogas production and waste management, contributing to sustainable bioenergy and wastewater treatment practices. Numerical results demonstrate that increased biochar concentrations in the co-digestion mixtures increased CO2 and CH4 production rates respectively by an approximate factor of 2, contributing 18% and 5% overall effects respectively. Similarly, zeolite concentrations contributed 9% and 5% overall effects to the production rates of CO2 and CH4 respectively, boosting production rates by factors of 1 and −2. The study’s significance lies in its potential to improve biogas yield and process efficiency, fostering advancements in renewable energy and environmental management.

This study investigates the potential of using digestate, a byproduct of anaerobic digestion, as organic manure in sustainable agriculture. The digestate was processed using a constructed screw press, separating it into liquid and solid components, with the liquid stored at room temperature and the solid subjected to a 20-day solar drying process. Four experimental conditions were tested: a control group, soil with chemical fertilizer, soil with solid digestate, and soil with liquid digestate. A fertilization rate of 1 gram per kilogram of soil was used. Over two months, distinct growth patterns emerged, with the liquid digestate group showing the most significant advantages, concluding with 59 leaves compared to 46 leaves in the solid digestate group, 44 in the chemical fertilizer group, and 42 in the control group. However, statistical analysis indicated no significant difference between treatments (p-value: 0.9451). The liquid digestate group also demonstrated superior stem width and crop yield, achieving a total yield of 99 bean seeds. The study highlights the promise of integrating digestate as organic manure in sustainable agriculture. The use of an anaerobic digester and screw press offers a viable solution for waste-to-resource conversion. Despite the encouraging results, further research is recommended to optimize digestate composition and application methods tailored to specific crop needs. This research contributes to eco-friendly agricultural practices and supports the advancement of sustainable waste management and crop cultivation strategies.

The utilization of palm oil mill residues for sustainable biogas production presents a promising avenue to mitigate environmental challenges associated with waste disposal and energy demand in palm oil processing. The study explores the use of palm oil mill residues for sustainable biogas production, focusing on the impact of mixing ratios of POME and three raw milled residues on biogas yield through anaerobic co-digestion. Results indicate that co-digestion significantly enhanced biogas production compared to mono-digestion of POME alone. The highest biogas yield of 370 ml was recorded in the digester with 40% residues followed by 50% with a cumulative biogas of 190 ml. The two digesters were higher than 80 ml recorded for POME alone.The findings underscore the potential of integrating palm oil mill residues into biogas systems to achieve dual objectives of waste management and renewable energy generation.

The biogas production from microalgae has gained attention due to fast depleting of fossil fuels and oil reserves. This study evaluated the anaerobic co-digestion of microalgae in various concentrations with cow manure to enhance biogas production. The biogas production of each experiment was measured using the water displacement method. The results indicated that the addition of microalgae significantly enhanced biogas production. Particularly, high methane yield of Anabaena sp. 50 %, Chlorella sp. 50 %, control was 345 ± 2.88 mL CH4/g VS, 297.96 ± 0.49 mL CH4/g VS, 138.32 ± 0.50 CH4/g VS respectively. The slurry produced by 50 % Anabaena sp. biogas plant exhibited the greatest level of seed germination. The current study demonstrated that Sorgham bicolor had the highest seed germination rate (94.2 %) root and shoot length of all crops. Therefore, it is possible to employ Anabaena sp. (50 %) and Chlorella sp. (50 %) in the rapid production of biogas. Moreover, agricultural output would be increased by using biogas slurry.

The co-digestion of a peach biowaste and parboiled rice effluent mixed with a sludge digester was investigated using a lab-scale biodigester. The biomasses used in the system were characterized by physical-chemical and microbiological analyses. Variations in substrate/inoculum (S/I) ratio of 1:1, 1:2, and 3:2, with different percentages of peach bagasse of 0%, 5%, and 10% in the substrate combination (peach bagasse + effluent), were performed. The study found that co-digestion of peach bagasse and parboiled rice effluent with digester sludge resulted in higher biomethane production, with reactors II and IV showing the best combination of factors both with a proportion of 3:2 (S/I). Reactor IV showed the maximum production of 27.51 mL CH 4 with a substrate composition of 10% peach bagasse and 90% effluent. The physical-chemical properties of the co-digestion substrate were optimal for anaerobic digestion, and the microbial community adapted to enhance biodegradation. The maximum COD removal was found in reactor IV at 88.06%, followed by reactor V at 82.10%. In contrast, the 1:2 (S/I) ratio in reactor I showed the lowest methane production. Furthermore, the co-digestion process resulted in stable and efficient digestion, indicating it is a viable alternative for treating rice parboiling effluent and peach waste. • Alternative for treating rice parboiling effluent and peach waste. • Peach biowaste and parboiled rice effluent characterization. • Maximum production of 27.51 mL CH 4 using anaerobic codigestion process. [ABSTRACT FROM AUTHOR]

A blend of organic municipal solid waste, slaughterhouse waste, fecal sludge, and landfill leachate was selected in different mixing ratios to formulate the best substrate mixture for biomethanation. Individual substrates were characterized, and the mixing ratio was optimized with the help of a response surface methodology tool to a value of 1:1:1:1 (with a C/N ratio of 28±0.769 and total volatile fatty acid (VFA) concentration of 2500±10.53 mg/L) to improve the overall biomethanation. The optimized blend (C/N ratio: 28.6, VFA: 2538 mg/L) was characterized for physicochemical, biological, and microbial properties and subjected to anaerobic digestion in lab-scale reactors of 1000 mL capacity with and without the addition of inoculum. The biogas yield of individual substrates and blends was ascertained separately. The observed cumulative biogas yield over 21 days from the non-inoculated substrates varied between 142±1.95 mL (24.6±0.3 ml/gVS) and 1974.5±21.72 mL (270.4±3.1 ml/gVS). In comparison, the addition of external inoculation at a 5% rate (w/w) of the substrate uplifted the minimum and maximum cumulative gas yield values to 203±9.9 mL (35.0±1.6 mL/gVS) and 3394±13.4 mL (315.3±1.2 mL/gVS), respectively. The inoculum procured from the Defence Research and Development Organisation (DRDO) was screened in advance, considering factors such as maximizing VFA production and consumption rate, biogas yield, and digestate quality. A similar outcome regarding biogas yield and digestate quality was observed for the equivalent blend. The cumulative gas yield increased from 2673±14.5 mL (373.7±2.2 mL/gVS) to 4284±111.02 mL (391.47±20.02 mL/gVS) over 21 days post-application of a similar dosage of DRDO inoculum. The 16S rRNA genomic analysis revealed that the predominant bacterial population belonged to the phylum Firmicutes, with the majority falling within the orders Clostridiales and Lactobacillales. Ultimately, the study advocates the potential of the blend mentioned above for biomethanation and concomitant enrichment of both biogas yield and digestate quality. [ABSTRACT FROM AUTHOR]

This study evaluated the environmental impact and overall benefits of incorporating humus composites in the anaerobic co-digestion of kitchen waste and residual sludge. The life cycle assessment method was used to quantitatively analyze the environmental impact of the entire anaerobic co-digestion treatment process of waste, including garbage collection, transportation, and final product utilization. Moreover, the comprehensive assessment of the environmental impact, energy-saving and emission-reduction abilities, and economic cost of using humus composites in the anaerobic co-digestion treatment process was conducted using a benefit analysis method. The results showed that the anaerobic co-digestion of kitchen waste and residual sludge significantly contributed to the mitigation of global warming potential (GWP), reaching −19.76 kgCO2-eq, but had the least impact on the mitigation of acidification potential (AP), reaching −0.10 kgSO2-eq. In addition, the addition of humus composites significantly increased the production of biogas. At a concentration of 5 g/L, the biogas yield of the anaerobic co-digestion process was 70.76 m3, which increased by 50.62% compared with the blank group. This amount of biogas replaces ~50.52 kg of standard coal, reducing CO2 emissions by 13.74 kg compared with burning the same amount of standard coal. Therefore, the anaerobic co-digestion treatment of kitchen waste and residual sludge brings considerable environmental benefits. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion (AnCoD) presents several advantages over conventional mono-digestion. Various factors can impact the efficiency of the co-digestion process, including the mixing ratio of the feedstocks. This study primarily investigates the effects of different mixing ratios on methane production during the co-digestion of source-separated municipal organic waste (SSO) with thickened waste activated sludge (TWAS). While the C/N or COD/N ratio has generally been used for optimizing the mixing ratios of co-digested feedstocks, a new approach is introduced in this study to evaluate the effects of the lipid, protein, and carbohydrate (L:P:C) ratios on the efficiency of AnCoD with respect to methane production, kinetics, and synergism at mixing ratios of TWAS:SSO of 10:90, 30:70, 50:50, 70:30, and 10:90. AnCoD improved methane production and kinetics relative to TWAS at all mixing ratios, the highest of which was at the 10:90 ratio, corresponding to a methane yield, maximum methane production rate, and an L:P:C ratio of 353 mL CH4/g COD, 25 mL CH4/g COD/d, and 8:1:18, respectively. Improvements in methane yields and kinetics due to synergy were evident at all mixing ratios, with improvements in methane yields ranging from 11 to 23% and improvements in kinetics ranging from 18 to 58%. Improvements in methane yields and kinetics were insensitive to the feedstock composition beyond the 50:50 mixing ratio. [ABSTRACT FROM AUTHOR]

This study aimed to enhance the nutrient balance of municipal solid waste (MSW), characterized by a high carbon-to-nitrogen (C/N) ratio, which is a critical factor in the anaerobic digestion process. The investigation involved the addition of MSW, which is rich in carbon content, to food waste (FW) with high nitrogen content. The goal was to determine an optimal co-substrate mixing ratio of MSW and FW for anaerobic co-digestion at mesophilic temperatures, aiming to improve process stability and performance to achieve higher biogas yield. The co-digestion experiments encompassed five mixing ratios of MSW and FW with C/N ratios of 20, 25, 30, 35, and 40 under mesophilic conditions in a laboratory. The results indicated that the highest specific biogas yield, reaching 827 L/kg VS, was attained when the co-substrate feedstock had a balanced C/N ratio of 20, surpassing the 520 L/kg vs. obtained from MSW digestion alone. As the proportion of MSW increased in the co-substrate mixing feedstock, the biogas production rate decreased. Additionally, the study explored the optimal substrate-to-inoculum (S/I) ratio, focusing on the co-substrate feedstock with a C/N ratio of 20. Four S/I ratios (0.5, 1.0, 1.5, and 2.0) were examined, revealing that the highest specific biogas yield, at 642 L/kg VS, occurred at an S/I ratio of 0.5. An accumulation in volatile fatty acids (VFAs) was observed at higher S/I ratios, attributed to the lower abundance of inoculum microorganisms in the anaerobic digestion process. Overall, the findings suggested that the optimum C/N ratio for co-digestion of MSW and FW falls within the range of 20–25/1, while the preferred S/I ratio is 0.5. [ABSTRACT FROM AUTHOR]

• P and S in organic waste were predicted using NIRS with great accuracy. • S prediction showed a direct correlation with sulfur-related functional groups. • P prediction mainly relied on indirect correlation with organic matter bands. • P prediction success was linked to the samples' homogeneity in organic compound. Near-infrared spectroscopy (NIRS) has recently emerged as a valuable tool for monitoring organic waste utilized in anaerobic digestion processes. Over the past decade, NIRS has significantly improved the characterization of organic waste by enabling the prediction of several crucial parameters such as biochemical methane potential, carbohydrate, lipid and nitrogen contents, Chemical Oxygen Demand, and kinetic parameters. This study investigates the application of NIRS for predicting the levels of Sulfur (S) and Phosphorus (P) within organic waste materials. The results for sulfur prediction exhibited a high level of accuracy, yielding an error of 1.21 g/Kg[TS] in an independently validated dataset, coupled with an R-squared value of 0.84. Conversely, the prediction of phosphorus proved to be slightly less successful, showing an error of 1.49 g/Kg[TS] with an R-squared value of 0.70. Furthermore, the disparities in performance seem to stem from the inherent correlation between the spectral data and the sulfur or phosphorus contents. Significantly, a variable selection technique known as CovSel was employed, shedding light on the differing approaches used for sulfur and phosphorus predictions. In the case of sulfur, the prediction was achieved through a direct correlation with wavelengths associated with sulfur-related functional groups (such as R − S(=O) 2 − OH, -SH, and R-S-S-R) present in the NIR spectra. In contrast, phosphorus prediction relied on an indirect correlation with absorption bands related to organic matter (including CH, CH 2 , CH 3 , –CHO, R-OH, C = O, –CO 2 H, and CONH). [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion is a complex process; therefore, understanding the factors related to kinetics is a prerequisite for optimizing biogas production. In this sense, this study addressed the anaerobic co-digestion of solid waste from vegetables and fruits and anaerobic sewage sludge, focusing on the kinetic modeling of biogas production and investigated synergistic effects of the concentration of total solids (TS) and substrate particle size (SPS). For that, a Factorial Design 3(2-0) was used in which the controlled variables were TS (29.2, 39.9, and 50.5 g/L) and SPS (1.68, 2.9, and 3.36 mm), with tests carried out in 2-L reactors for 200 days to quantify the biogas produced. The modified Gompertz (MG), function transfer (FT), logistic function (LF), modified first-order (FO), and Cone (CN) kinetic models were evaluated in the description of biogas production using the Akaike Information Criterion (AIC) and NRMSE, resulting in the following performance order: LF>CN>FO>MG>FT. The SPS influenced the cumulative biogas production (Mmax) and the hydrolysis constant, so that Mmax increased 221% when the SPS has been reduced from 3.36 to 1.68 mm. TS had an effect on the latency phase time and maximum biogas production rate (Rmax), so that Rmax was optimized by 40% when TS was adjusted from 50.5 to 29.2 g/L. [ABSTRACT FROM AUTHOR]

Biological treatment is a promising alternative for waste management considering the environmentally sustainable concept that the European Union demands. In this direction, anaerobic digestion comprises a viable waste treatment process, producing high energy-carrier gases such as biomethane and biohydrogen under certain operating conditions. The mathematical modeling of this bioprocess can be used as a valuable tool for process scale-up with cost-effective implications. The scope of this work was the evaluation of the well-established Anaerobic Digestion Model 1 (ADM1) for use in two-stage anaerobic digestion of agro-industrial waste. Certain equations for the description of the metabolic pathways for lactate and bioethanol accumulation were implemented in the existing mechanistic model in order to enhance the model’s accuracy. The model presents a high estimation ability regarding the final product (H2 and biogas) reaching the same maximum value for the theoretical as the experimental data of these products (0.0012 and 0.0036 m3/d, respectively). The adapted ADM1 emerges as a useful instrument for designing anaerobic co-digestion processes with the goal of achieving high yields in fermentative hydrogen production, considering mixed biomass growth mechanisms. [ABSTRACT FROM AUTHOR]

Zero-valent iron dosages have an impact on the performance of anaerobic co-digestion of organic fraction of municipal solid waste and activated sludge. Diverse dosages of zero-valent Iron additives within the range of 15–90 mg NP-ZVI/g VS were investigated under mesophilic conditions and a pH reading of 6.0 to deduce their impact on the AD stability in the domain of hydrolysis and acidification percentages, pollutants' uptake, and biogas upgrading rate. It was found that the biogas production was relatively ameliorated with the additives of NP-ZVI at different dosages compared to the non-amended AD process. The results revealed that the threshold of 45 mg NP-ZVI/g VS dosage to a high organic fraction substrate has achieved the most distinguishing features in the AD performance, as distinct through improving the hydrolysis by a factor of 30.5%, acidification percentage by 43.7%, TCOD removal by 89%, methane yield by 18.4%, and biogas production approaches the figure 0.398 Nm3/kg VS with an increase by 36% compared to that of the control test. Whereas a high dosage of 90 mg NP-ZVI /g VS appealed to an acute inhibition on AD that should be avoided, due to the retrogression of methanogenic activity for an anaerobic environment with such additives of concentrated NP-ZVI. Generally, the cumulative biogas production patterns were fitted using a nonlinear least square regression technique. The biogas production of the investigated substrates was adequately predicted by the three-parametric modified Gompertz and logistic models. [ABSTRACT FROM AUTHOR]

This study investigates the co-digestion of hydrothermally pretreated empty fruit bunches (EFB) at 190 °C for 5 min (HTP190-EFB) with decanter cake (DC) to improve biogas production in high solid anaerobic digestion (HSAD). The HTP190-EFB exhibited a 67.98 % reduction in total solids, along with the production of 0.89 g/L of sugar, 2.39 g/L of VFA, and 0.56 g/L of furfural in the liquid fraction. Co-digestion of HTP190-EFB with DC at mixing ratios of 5, 10, and 15 %w/v demonstrated improved methane yields and process stability compared to mono-digestion of HTP190-EFB. The highest methane yield of 372.69 mL CH4/g-VS was achieved in the co-digestion with 5 %w/v DC, representing a 15 % increase compared to digestion of HTP190-EFB (324.30 mL CH4/g-VS) alone. Synergistic effects were quantified, with the highest synergistic methane yield of 77.65 mL CH4/g-VS observed in the co-digestion with 5 %w/v DC. Microbial community analysis revealed that co-digestion of hydrothermally pretreated EFB with decanter cake promoted the growth of Clostridium sp., Lactobacillus sp., Fibrobacter sp., Methanoculleus sp., and Methanosarcina sp., contributing to enhanced biogas production compared to mono-digestion of pretreated EFB. Energy balance analysis revealed that co-digestion of HTP190-EFB with DC resulted in a total net energy of 599.95 kW, 52 % higher than mono-digestion of HTP190-EFB (394.62 kW). Economic analysis showed a shorter return on investment for the co-digestion system (0.86 years) compared to the mono-digestion of HTP190-EFB (1.02 years) and raw EFB (2.69 years). The co-digestion of HTP190-EFB with 5 %w/v DC offers a promising approach to optimize methane yield, process stability, and economic feasibility, supporting the palm oil industry for producing renewable energy and sustainable waste management.