Microbial community acclimatization for enhancement in the methane productivity of anaerobic co-digestion of fats, oil, and grease

Sustainable valorization of slaughterhouse waste through anaerobic digestion: A circular economy perspective

Slaughterhouse waste (SHW) poses significant environmental challenges due to its complex composition. In response, a novel review exploration of anaerobic digestion (AD) as a means of valorising SHW within the context of the circular economy (CE) is presented. The physicochemical properties of individual SHW, representing key parameters for the correct management of the AD process, are scrutinized. These parameters are further connected with identifying suitable pretreatment methods to enhance biogas production. Subsequently, the review examines the diverse technologies employed in the AD of SHW, considering the complexities of mono- or co-digestion. Various AD systems are evaluated for their effectiveness in harnessing the substantial biogas production potential from SHW, encompassing key parameters, reactor configurations, and operational conditions that influence the AD process. Moreover, the review interestingly extends its scope to the recovery and management of digestate, the by-product of AD. Along with the digestate composition, strategies for various utilization of this by-product are discussed. This investigation thus underscores, within the principles of the CE, the dual sustainable benefits of SHW processing via AD in biogas production and utilization of the resultant nutrient-rich digestate in various sectors.

Development of oriented multi-enzyme strengthens waste activated sludge disintegration and anaerobic digestion: Performance, components transformation and microbial communities

Low methane production and long retention time are the main dilemmas in current anaerobic digestion (AD) of waste activated sludge (WAS). This work used WAS as only substrate to prepare oriented multi-enzyme (ME) that directly used for WAS pretreatment. Under the optimal parameters, the highest activities of protease and amylase in ME could respectively reach 16.5 U/g and 580 U/g, and the corresponding methane production attained 197 mLCH4/g VS, which was increased by 70.4% compared to blank group. It was found that ME pretreatment could strengthen WAS disintegration and organic matters dissolution, lead to the soluble chemical oxygen demand (SCOD) was increased from the initial 486 mg/L to 2583 mg/L, and the corresponding volatile suspended solid (VSS) and extracellular polymeric substances (EPS) were reduced by 27% and 73.8%, respectively. The results of three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform infrared spectroscopy (FTIR) indicated that protein disintegration may be the critical step during the process of WAS hydrolysis with ME, of which the release of tyrosine-like proteins achieved the better biodegradability of WAS, while the results of X-ray photoelectron spectroscopy (XPS) showed that the formation of protein derivatives was the main harmful factor that could extend the lag phase of AD process. Microbial communities analysis further suggested that ME pretreatment facilitated the enrichment of acetogenic bacteria and acetotrophic methanogens, which caused the transition of the methanogenesis pathway from hydrogenotrophic to acetotrophic. This study is expected to furnish valuable insight for ME pretreatment on enhancing WAS disintegration and methane production.

Sequential bio-treatment of ammonia-rich wastewater from Chinese medicine residue utilization: Regulation of dissolved oxygen

To effectively treat actual ammonia-rich Chinese medicine residue (CMR) resource utilization wastewater, we optimized an anaerobic-microaerobic two-stage expanded granular sludge bed (EGSB) and moving bed sequencing batch reactor (MBSBR) combined process. By controlling dissolved oxygen (DO) levels, impressive removal efficiencies were achieved. Microaeration, contrasting with anaerobic conditions, bolstered dehydrogenase activity, enhanced electron transfer, and enriched the functional microorganism community. The increased relative abundance of Synergistetes and Proteobacteria facilitated hydrolytic acidification and fostered nitrogen and phosphorus removal. Furthermore, we examined the impact of DO concentration in MBSBR on pollutant removal and microbial metabolic activity, pinpointing 2.5 mg/L as the optimal DO concentration for superior removal performance and energy conservation.

Microbial community changes and metabolic pathways analysis during waste activated sludge and meat processing waste anaerobic co-digestion

Waste activated sludge (WAS) and meat processing waste (MPW) were acted as co-substrates in anaerobic co-digestion (AcD), and biochemical methane potential (BMP) test was carried out to investigate the methane production performances. Microbial community structure and metabolic pathways analyses were conducted by 16S rRNA high-throughput sequencing and functional prediction analysis. BMP test results indicated that AcD of 70% WAS+30% MPW and 50% WAS+50% MPW (VS/VS) could significantly improve methane yield to 371.05 mL/g VS and 599.61 mL/g VS, respectively, compared with WAS acting as sole substrate (191.87 mL/g VS). The results of microbial community analysis showed that Syntrophomonas and Petrimonas became the dominant bacteria genera, and Methanomassiliicoccus and Methanobacterium became the dominant archaea genera after MPW addition. 16S functional prediction analysis results indicated that genes expression of key enzymes involved in syntrophic acetate oxidation (SAO), hydrogenotrophic and methylotrophic methanogenesis were up-regulated, and acetoclastic methanogenesis was inhibited after MPW addition. Based on these analyses, it could be inferred that SAO combined with hydrogenotrophic and methylotrophic methanogenesis was the dominant pathway for organics degradation and methane production during AcD. These findings provided systematic insights into the microbial community changes and metabolic pathways during AcD of WAS and MPW.

Unlocking the potential of sugarcane leaf waste for sustainable methane production: Insights from microbial pre-hydrolysis and reactor optimization

Sugarcane leaf waste, a byproduct of the growing global sugar industry, challenges agricultural waste management. This study explores its potential for methane production via anaerobic digestion. A microbial pre-hydrolysis, using lignocellulose-degrading bacteria, enhanced soluble chemical oxygen demand at an optimal initial substrate concentration of 40 g-volatile solid/L. Comparative analysis with untreated and bioaugmented leaves revealed the pre-hydrolyzed leaves achieved the highest methane production rate (MPR) at 14.0 ± 0.5 mL-CH4/L·d, surpassing others by 1.47 and 1.67 times. Two continuous stirred tank reactors were employed to assess the optimal hydraulic retention time (HRT). Results showed a stable methane production with an HRT of 25 days, yielding high MPRs: 88.70 ± 0.63 mL-CH4/L·d from pre-hydrolyzed sugarcane leaves and 82.57 ± 1.22 mL-CH4/L·d from microbial consortium-augmented leaves. A 25-day HRT fosters high microbial diversity with Bacteroidota, Firmicutes, Chloroflexi, and Verrucomicrobiota dominance, indicating favorable conditions. Conversely, a 20-day HRT results in lower diversity due to unfavorable factors like low pH during organic overloading, leading to increased concentrations of volatile fatty acids and lactic acid, with Firmicutes as the predominant phylum. This study highlights sugarcane leaf waste's potential as a valuable resource for sustainable methane production.

Microbial community acclimatization enhances bioplastics biodegradation and biogas production under thermophilic anaerobic digestion

This paper reports the results of a novel study of microbial acclimatization for bioplastics anaerobic degradation and conversion into biogas. Three sequential anaerobic digestion (AD) runs were carried out to favour microbial acclimatization to two different bioplastics, starch-based (SBS) and polyactic-acid (PLA). AD of SBS and PLA bioplastics was favoured by the acclimatization of the inoculum to the substrate after each run of AD. SBS conversion into biogas increased by 52 % (from 94 to 143 NL kgVS-1) and it was correlated with the enhanced growth of starch degrading bacteria such as Hydrogenispora, Halocella and Haloplasma. PLA anaerobic degradation increased by 97 % (from 395 to 779 NLbiogas kgVS-1) and it was related to the acclimatization of known PLA-degraders such as Tepidimicrobium, Methanothermobacter and Tepidanaerobacter. Microbial acclimatization appears a suitable and low-cost strategy to enhance bioplastics circularity by promoting their anaerobic biodegradation and conversion into biogas.

The migration regularity and removal mechanism of antibiotic resistance genes during in situ enzymatic hydrolysis and anaerobic digestion of food waste

This study developed a high efficiency compound enzyme (fungal mash) produced in situ from food waste (FW) used for improving hydrolysis and anaerobic digestion (AD) efficiency of FW. Results showed that the soluble COD and methane yield were respectively increased by 67.80% and 16.58% after 24 h in situ enzymatic hydrolysis of food waste by fungal mash. Furthermore, most of target ARGs in FW were also reduced by 45-94% after 24 h in situ enzymatic hydrolysis, while the total tested ARGs and intI1 were respectively further removed by 44-55% and 21-73% in subsequent AD process. In-depth analysis showed that fungal mash could effectively reduce potential hosts and control the horizontal transfer of ARGs during the in situ enzymatic hydrolysis and AD process. Ultimately, correlation analysis and redundancy analysis indicated that the evolution of bacterial communities and changes in intI1 where the common driving forces for the fate of ARGs.

Acclimatizing waste activated sludge in a thermophilic anaerobic fixed-bed biofilm reactor to maximize biogas production for food waste treatment at high organic loading rates

Thermophilic anaerobic digestion (TAD) provides a promising solution for sustainable high-strength waste treatment due to its enhanced methane-rich biogas recovery. However, high organic loading rates (OLR) exceeding 3.0 kgCOD/m3/day and short hydraulic retention times (HRT) below 10 days pose challenges in waste-to-energy conversion during TAD, stemming from volatile fatty acids (VFAs) accumulation and methanogenesis failure. In this study, we implemented a stepwise strategy for acclimatizing waste activated sludge (WAS) in a thermophilic anaerobic fixed-bed biofilm reactor (TA-FBBR) to optimize methanogen populations, thereby enhancing waste-to-energy efficiencies under elevated OLRs in food waste treatment. Results showed that following stepwise acclimatization, the TA-FBBR achieved stable methane production of approximately 5.8 L/L-reactor/day at an ultrahigh OLR of ∼20 kgCOD/m3/day and ∼15 kgVS/m3/day at 6-day HRT in food waste treatment. The average methane yield reached 0.45 m3/kgCODremoval, attaining the theoretical production in TAD. Moreover, VFA concentrations were stabilized below 1000 mg/L at the ultrahigh OLR under 6-day HRT, while maintaining an acetate/propionate ratio of > 1.8 and a VFA/TAK ratio of < 0.3 serving as effective indicators of system stability and methane yield potential. The microbial community analysis revealed that the WAS acclimatization strategy fostered the microbial diversity and abundance of Methanothermobacter and Methanosarcina. Methanosarcina in the biofilm were observed to be twice as abundant as Methanothermobacter, indicating a potential preference for biofilm existence among methanogens. The findings demonstrated an effective strategy, specifically the stepwise acclimatization of WAS in a thermophilic fixed-bed biofilm reactor, to enhance the food waste treatment performance at high OLRs, contributing valuable mechanistic and technical insights for future sustainable high-strength waste management.

Dissemination of sulfonamide resistance genes in digester microbiome during anaerobic digestion of food waste leachate

The preeminence of sulfonamide drug resistance genes in food waste (FW) and the increased utilization of high-strength organic FW in anaerobic digestion (AD) to enhance methane production have raised severe public health concerns in wastewater treatment plants worldwide. In this regard, the dissemination patterns of different sulfonamide resistance genes (sul1 and sul2) and their impact on the digester core microbiota during AD of FW leachate (FWL) were evaluated. The presence of various sulfonamide antibiotics (SAs) in FWL digesters improved the final methane yield by 37 % during AD compared with FWL digesters without SAs. Microbial population shifts towards hydrolytic, acidogenic, and acetogenic bacteria in the phyla Actinobacteriota, Bacteroidota, Chloroflexi, Firmicutes, Proteobacteria, and Synergistota occurred due to SA induced substrate digestion and absorption through active transport; butanoate, propanoate, and pyruvate metabolism; glycolysis; gluconeogenesis; the citrate cycle; and pentose phosphate pathway. The initial dominance of Methanosaeta (89-96 %) declined to 47-53 % as AD progressed and shifted towards Methanosarcina (40 %) in digesters with the highest SA concentrations at the end of AD. Dissemination of sul1 depended on class 1 integron gene (intl1)-based horizontal gene transfer to pathogenic members of Chloroflexi, Firmicutes, and Patescibacteria, whereas sul2 was transmitted to Synergistota independent of intl1. Low susceptibility and ability to utilize SAs during methanogenesis shielded methanogenic archaea against selection pressure, thus preventing them from interacting with sul or intl1 genes, thereby minimizing the risk of antibiotic resistance development. The observed emergence of cationic antimicrobial peptide, vancomycin, and β-lactam resistance in the core microbiota during AD of FWL in the presence of SAs suggests that multidrug resistance caused by bacterial transformation could lead to an increase in the environmental resistome through wastewater sludge treatment.

Molecular insights informing factors affecting low temperature anaerobic applications: Diversity, collated core microbiomes and complexity stability relationships in LCFA-fed systems

Fats, oil and grease, and their hydrolyzed counterparts-long chain fatty acids (LCFA) make up a large fraction of numerous wastewaters and are challenging to degrade anaerobically, more so, in low temperature anaerobic digestion (LtAD) systems. Herein, we perform a comparative analysis of publicly available Illumina 16S rRNA datasets generated from LCFA-degrading anaerobic microbiomes at low temperatures (10 and 20 °C) to comprehend the factors affecting microbial community dynamics. The various factors considered were the inoculum, substrate and operational characteristics, the reactor operation mode and reactor configuration, and the type of nucleic acid sequenced. We found that LCFA-degrading anaerobic microbiomes were differentiated primarily by inoculum characteristics (inoculum source and morphology) in comparison to the other factors tested. Inoculum characteristics prominently shaped the species richness, species evenness and beta-diversity patterns in the microbiomes even after long term operation of continuous reactors up to 150 days, implying the choice of inoculum needs careful consideration. The generalised additive models represented through beta diversity contour plots revealed that psychrophilic bacteria RBG-13-54-9 from family Anaerolineae, and taxa WCHB1-41 and Williamwhitmania were highly abundant in LCFA-fed microbial niches, suggesting their role in anaerobic treatment of LCFAs at low temperatures of 10-20 °C. Overall, we showed that the following bacterial genera: uncultured Propionibacteriaceae, Longilinea, Christensenellaceae R7 group, Lactivibrio, candidatus Caldatribacterium, Aminicenantales, Syntrophus, Syntrophomonas, Smithella, RBG-13-54-9, WCHB1-41, Trichococcus, Proteiniclasticum, SBR1031, Lutibacter and Lentimicrobium have prominent roles in LtAD of LCFA-rich wastewaters at 10-20 °C. This study provides molecular insights of anaerobic LCFA degradation under low temperatures from collated datasets and will aid in improving LtAD systems for treating LCFA-rich wastewaters.

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

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

Methanogenic treatment of dairy wastewater: A review of current obstacles and new technological perspectives

Methanogenic treatment can effectively manage wastewater in the dairy industry. However, its treatment efficiency and stability are problematic due to the feature of wastewater. This review comprehensively summarizes the dairy wastewater characteristics and reveals the mechanisms and impacts of three critical issues in anaerobic treatment, including ammonia and long-chain fatty acid (LCFA) inhibition and trace metal (TM) deficiency. It evaluates current remedial strategies and the implementation of anaerobic membrane bioreactor (AnMBR) technology. It assesses the use of nitrogen-removed effluent return to dilute the influent for solving protein-rich dairy wastewater treatment. It explores the methodology of TM addition to dairy wastewater in accordance with microbial TM content and proliferation. It analyzes the multiple benefits of applying high-solid AnMBR to lipid-rich influent to mitigate LCFA inhibition. Finally, it proposes a promising low-carbon treatment system with enhanced bioenergy recovery, nitrogen removal, and simultaneous phosphorus recovery that could promote carbon neutrality for dairy industry wastewater treatment.

Complexity of acclimatization substrate affects anaerobic digester microbial community response to organic load shocks

This study elucidated the changes in the short-term response to organic load shocks of the anaerobic digestion (AD) microbiome acclimatized to a simple substrate and a complex substrate. Batch vial reactors were inoculated with AD sludge acclimatized to either a simple (starch and hipolypeptone) or a complex (dog food and starch) substrate, both with carbon-to-nitrogen ratio of 25. Organic loads in the form of an easily degradable substrate mix (starch and hipolypeptone) with concentrations varying from 0 to 5 g VS/L were applied to the reactors. Runs utilizing the inoculum acclimatized to a complex substrate sustained its methane productivity despite the high organic load shocks which the inoculum acclimatized to a simple substrate was unable to handle efficiently. The alpha-diversity of the microbiome decreased with increase in organic load for inoculum acclimatized with a simple substrate but was unaffected for the case of the inoculum acclimatized with a complex substrate. LactobacillalesandCloacimonadales were inferred to be major players in starch degradation pathways for the inoculum acclimatized using a simple substrate as predicted by the bioinformatics package PICRUSt2. However, acclimatizing using a complex substrate did not support their growth and were replaced by Coriobacteriales which provided higher flexibility in terms of the predicted regulated metabolic functions. The predicted functional regulation of Synergistales and Syntrophales increased with acclimatization using a complex substrate which also showed increase in the flexibility of the microbiome towards handling organic load shocks. Acetoclastic pathway was upregulated with increase in organic load regardless of the acclimatization substrate while the hydrogenotrophic pathway was downregulated. Overall, acclimatization using a complex substrate increased the robustness and flexibility of the microbiome towards organic load shocks.

Integrative biohydrogen- and biomethane-producing bioprocesses for comprehensive production of biohythane

The production of biohythane, a combination of energy-dense hydrogen and methane, from the anaerobic digestion of low-cost organic wastes has attracted attention as a potential candidate for the transition to a sustainable circular economy. Substantial research has been initiated to upscale the process engineering to establish a hythane-based economy by addressing major challenges associated with the process and product upgrading. This review provides an overview of the feasibility of biohythane production in various anaerobic digestion systems (single-stage, dual-stage) and possible technologies to upgrade biohythane to hydrogen-enriched renewable natural gas. The main goal of this review is to promote research in biohythane production technology by outlining critical needs, including meta-omics and metabolic engineering approaches for the advancements in biohythane production technology.

Effect of the degradation performance on carbon tetrachloride by anaerobic co-metabolism under different external energy sources

In this research, a comprehensive study was carried out on the removal of carbon tetrachloride (CT) in the anaerobic co-metabolism (ACM) reactor. The experiments showed that when the hydraulic retention time (HRT) was 36 h, pH was 7, and influent CT was 2.5mg/L, the average removal efficiency reached 82.45 ± 2.56% in the glucose co-metabolism substrate reactor, exhibiting a dramatic excellent difference in reaction performance from the other two reactors (p < 0.05) and a favorable tolerance on the CT shock loading. The content of extracellular polymeric substances (EPS) and volatile fatty acids (VFA) demonstrated that glucose could supply more energy to protect the microorganisms, which was the appropriate external energy source. Moreover, microbial community structure and biostatistics analysis demonstrated that Pseudomonas was the most important dechlorination bacteria in ACM reactors, which might via dehalogenation process mediate the transformation of CT. The succession of methanogenic bacteria further demonstrated that CT degradation using co-digestion require to destroy hydrogenotrophic methane generation pathway and the external energy substances could make up the lack of hydrogen in the treatment of CT. The change of intermediate products hinted that anaerobic dechlorination process of CT in an ACM reactor was a sequential dechlorination process, and major transformation products measured were CF. Overall, this study has improved our understanding of the roles of CT degradation process in ACM reactors.

Dynamics of microbial community in response to co-feedstock composition in anaerobic digestion

To enable the utilization of seasonal biomasses in e.g., farm-scale biogas plants, the process should be flexible and ensure stable gas production. However, information about microbial community dynamics in long-term co-digestion with versatile co-feedstocks is lacking. This study investigated the effects of co-feedstock changes on the performance and evolution of microbial consortia during 428-day anaerobic digestion of cow slurry. Co-feedstocks consisted of hydrocarbon-, protein- and lipid-rich materials. A high throughput 16S ribosomal RNA gene sequencing was used to analyze the taxonomic profile of microbial communities. Due to the low loading rate, the changes were subtle in bacteria, but a shift on archaeal genera in response to different and changing feedstock compositions was observed. Despite drastic changes in co-feedstock composition, stable and flexible anaerobic digestion with relatively constant core microbiome can be achieved with cautious operation of the process.

Complex network analysis of slaughterhouse waste anaerobic digestion: From failure to success of long-term operation

The study explored slaughterhouse waste (SHW) as prime feedstock associated with and without supplement of an external slowly degradable lignocellulosic carbon source to overcome the synergistic co-inhibitions of ammonia and fatty acids. Long-term solid-state digestion (SSD) and liquid-state digestion (LSD) were investigated using a mixture of pork liver and fat. At 2.0 g volatile solids (VS) L^-1 d^-1 of organic loading rate (OLR), the two reactors of SSD experienced operational instability due to ammonia inhibition and volatile fatty acid (VFA) accumulation while LSD successfully produced 0.725 CH₄ L CH₄ g^-1VS during 197 d of working days under unfavorable condition with high total ammonia nitrogen (>4.7 g/L) and VFAs concentration (>1.9 g/L). The network analysis between complex microflora and operational parameters provided an insight for sustainable biogas production using SHW. Among all, hydrogenotrophic methanogens have shown better resistance than acetoclastic methanogens.

Dissecting the roles of conductive materials in attenuating antibiotic resistance genes: Evolution of physiological features and bacterial community

Supplying conductive materials (CMs) into anaerobic bioreactors is considered as a promising technology for antibiotic wastewater treatment. However, whether and how CMs influence antibiotic resistance genes (ARGs) spread remains poorly known. Here, we investigated the effects of three CMs, i.e., magnetite, activated carbon (AC), and zero valent iron (ZVI), on ARGs dissemination during treating sulfamethoxazole wastewater, by dissecting the shifts of physiological features and microbial community. With the addition of magnetite, AC, and ZVI, the SMX removal was improved from 49.05 to 71.56-92.27 %, while the absolute abundance of ARGs reducing by 26.48 %, 61.95 %, 48.45 %, respectively. The reduced mobile genetic elements and antibiotic resistant bacteria suggested the inhibition of horizontal and vertical transfer of ARGs. The physiological features, including oxidative stress response, quorum sensing, and secretion system may regulate horizontal transfer of ARGs. The addition of all CMs relieved oxidative stress compared with no CMs, but ZVI may cause additional free radicals that needs to be concerned. Further, ZVI and AC also interfered with cell communication and secretion system. This research deepens the insights about the underlying mechanisms of CMs in regulating ARGs, and is expected to propose practical ways for mitigating ARGs proliferation.

Influence of organic loading rate and temperature fluctuation caused by solar energy heating on food waste anaerobic digestion

Anaerobic digestion, one of the most currently remarkable techniques for biogas production, has provided a method of high organic solid waste disposal. Operating temperature, especially in the winter of northern city, makes biomass degradation less efficient. The microorganisms that take on the role of gas production are greatly affected by temperature. In our study, solar energy was selected for anaerobic digestion and winter was selected as the experimental environment. Anaerobic digestion was performed with solar heating and electric heating separately. Parameters were tested (pH, soluble chemical oxygen demand, total ammonia nitrogen, total volatile fatty acids), and microbial structure was monitored. The volume of methane produced was measured over 60 days. The methane yield differed by 15.92% under different conditions. It is clearly shown that methane yield can be improved by a steady temperature environment. Nevertheless, dominant bacteria and microbial structure did not seem to be much different. This study may provide more energy-saving ideas for winter anaerobic digestion projects in northern regions.

Syntrophic bacteria- and Methanosarcina-rich acclimatized microbiota with better carbohydrate metabolism enhances biomethanation of fractionated lignocellulosic biocomponents

An inadequate lignocellulolytic capacity of a conventional anaerobic digester sludge (ADS) microbiota is the bottleneck for the maximal utilization of lignocellulose in anaerobic digestion. A well-constructed microbial consortium acclimatized to lignocellulose outperformed the ADS in terms of biogas productivity when fractionated biocomponents of rice straw were used to achieve a high methane bioconversion rate. A 33.3 % higher methane yield was obtained with the acclimatized consortium (AC) compared to that of ADS control. The dominant pair-wise link between Firmicutes (18.99-40.03 %), Bacteroidota (10.94-28.75 %), and archaeal Halobacteriota (3.59-20.57 %) phyla in the AC seed digesters indicated that the keystone members of these phyla were responsible for higher methane yield. A high abundance of syntrophic bacteria such as Proteiniphilum (1.22-5.19 %), Fermentimonas (0.71-5.31 %), Syntrophomonas (0.87-3.59 %), and their syntrophic partner Methanosarcina (4.26-18.80 %) maintained the digester stability and facilitated higher substrate-to-methane conversion in the AC seed digesters. The present combined strategy will help in boosting the 'biomass-to-methane" conversion.

Alleviating "inhibited steady-state" in anaerobic digestion of poultry manure by bentonite amendment: Performance evaluation and microbial mechanism

This study systematically evaluated the effects of bentonite as a possible additive to alleviate the "inhibited steady-state" induced by ammonia and acid accumulation during anaerobic digestion. Continuous stirred tank reactors fed with poultry manure were operated at 35 ± 1 °C either with bentonite or not. The results demonstrate that bentonite amendment increased average specific methane production by 35% as suffered from steady-state at an organic loading rate of 6.25 g VS/L·d. 16S rRNA gene amplicon sequencing revealed that the relative abundance of electron-donating Sedimentibacter and Syntrophomonas, and electrophilic Methanosarcina was increased by 110%, 91%, and 49%, respectively. The genera were identified as crucial for alleviating "inhibited steady-state", through establishment of a more robust syntrophic pathway of methanogenic acetate degradation. The enhancement might result from the accelerated electron transfer by bentonite, which is qualified for serving as an exogenetic electron mediator due to containing abundant redox-active metal elements.

Co-occurrence network analysis reveals loss of microbial interactions in anaerobic digester subjected to repeated organic load shocks

Fluctuations in the anaerobic digestion (AD) organic loading rate (OLR) cause shocks to the AD microbiome, which lead to unstable methane productivity. Managing these fluctuations requires a larger digester, which is impractical for community-scale applications, limiting the potential of AD in advancing a circular economy. To allow operation of small-scale AD while managing OLR fluctuations, we need to tackle the issue through elucidation of the microbial community dynamics via 16S rRNA gene sequencing. This study elucidated the interrelation of the AD performance and the dynamics of the microbial interactions within its microbiome in response to repeated high OLR shocks at different frequencies. The OLR shocks were equivalent to 4 times the baseline OLR of 2 g VS/L/d. We found that less frequent organic load shocks result to deterioration of methane productivity. Co-occurrence network analysis shows that this coincides with the breakdown of the microbiome network structure. This suggests loss of microbial interactions necessary in maintaining stable AD. Identification of species influencing the network structure revealed that a species under the genus Anaerovorax has the greatest influence, while orders Spirochaetales and Synergistales represent the greatest number of the influential species. We inferred that the impact imposed by the OLR shocks shifted the microbiome activity towards biochemical pathways that are not contributing to methane production. Establishing a small-scale AD system that permits OLR fluctuations would require developing an AD microbiome resilient to infrequent organic loading shocks.

Primary Sludge from Dairy and Meat Processing Wastewater and Waste from Biomass Enzymatic Hydrolysis as Resources in Anaerobic Digestion and Co-Digestion Supplemented with Biodegradable Surfactants as Process Enhancers

Incorporation of various alternative resources as co-digestion substrates aids to reduce the consumption of agricultural crops for biogas production. However, the efficiency and limitations of these co-substrates is still not fully understood. Use of biomass waste remaining after enzymatic hydrolysis for high value chemical fermentation, meat processing and dairy wastewater primary sludge as co-substrates in an agricultural resource anaerobic digestion plant is tackled within this study. The results showed that anionic surfactants (<200 ppm) can be used to improve fat, oil and grease (FOG) solubility in water and, at the same time, enhance the biomethane potential of FOG-containing sludge by increasing it from 1374.5 to 1765 mLCH4/gVS for meat processing wastewater primary sludge, and from 534 to 740 mLCH4/gVS for dairy wastewater primary sludge, when agricultural digestate is used as a substrate and sludge loading is not more than 10% from the volatile solids loaded. At the same time, only 549.7 mLCH4/gVS was produced as 30-day BMP when 5% biomass hydrolysis waste was used. Biomass hydrolysis waste co-digestion with primary sludge from dairy and meat processing wastewaters has an antigenic effect, and separate substrate anaerobic digestion gave a better results, thus, showing that excessive combination of various waste resources can be inhibitory for biogas production and the appropriate substrate selection and combination is a technical challenge for the biogas industry.

Anaerobic digestion challenges and resource recovery opportunities from land-based aquaculture waste and seafood processing byproducts: A review

The unprecedented demand for seafood has resulted in land-based recirculating aquaculture systems (RAS), a highly intensive but sustainable fish farming method. However, intensification also results in concentrated waste streams of fecal matter and uneaten feed. Harvesting and processing vast quantities of fish also leads to the production of byproducts, further creating disposal challenges for fish farms. Recent research indicates that anaerobic digestion (AD), often used for waste treatment in agricultural and wastewater industries, may provide a viable solution. Limited research on AD of freshwater, brackish, and saline wastewater from RAS facilities and co-digestion of seafood byproducts has shown promising results but with considerable operational and process stability issues. This review discusses challenges to AD due to low solid concentrations, salinity, low carbon/nitrogen ratio, and high lipid content in the waste streams. Opportunities for recovering valuable biomolecules and nutrients through microbial treatment, aquaponics, microalgae, and polyhydroxyalkanoate production are also discussed.

Principles, Advances, and Perspectives of Anaerobic Digestion of Lipids

Several problems associated with the presence of lipids in wastewater treatment plants are usually overcome by removing them ahead of the biological treatment. However, because of their high energy content, waste lipids are interesting yet challenging pollutants in anaerobic wastewater treatment and codigestion processes. The maximal amount of waste lipids that can be sustainably accommodated, and effectively converted to methane in anaerobic reactors, is limited by several problems including adsorption, sludge flotation, washout, and inhibition. These difficulties can be circumvented by appropriate feeding, mixing, and solids separation strategies, provided by suitable reactor technology and operation. In recent years, membrane bioreactors and flotation-based bioreactors have been developed to treat lipid-rich wastewater. In parallel, the increasing knowledge on the diversity of complex microbial communities in anaerobic sludge, and on interspecies microbial interactions, contributed to extend the knowledge and to understand more precisely the limits and constraints influencing the anaerobic biodegradation of lipids in anaerobic reactors. This critical review discusses the most important principles underpinning the degradation process and recent key discoveries and outlines the current knowledge coupling fundamental and applied aspects. A critical assessment of knowledge gaps in the field is also presented by integrating sectorial perspectives of academic researchers and of prominent developers of anaerobic technology.

Microbial β-oxidation of synthetic long-chain fatty acids to improve lipid biomethanation

β-oxidation is a well-known pathway for fatty acid (FA) degradation. However, the wide range of feedstocks, their intermediates, and complex microbial networks involved in anaerobic digestion (AD) make β-oxidation unclear during lipid digestion having a variety of long-chain fatty acids (LCFAs). Here, we demonstrated the detailed metabolic pathway of major bacteria and enzymes responsible for the β-oxidation of individual saturated FAs (C16:0 and C18:0) and unsaturated FAs (C18:1 and C18:2). C16:0 showed no negative impact on AD. The relative enzyme abundance and production of shorter-chain FAs ( Collapse

Key Words

• Biomethanation
• Community response
• Saturated fatty acids
• Unsaturated fatty acids
• Β-oxidation

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Affiliation(s)

Muhammad Usman MOE, Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu, China; Department of Occupational and Environmental Health, School of Public Health, Lanzhou University Lanzhou 730000, Gansu, China
Shuai Zhao MOE, Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu, China
Byong-Hun Jeon Department of Earth Resources and Environmental Engineering, Hanyang University, Seoul 04763, Korea
El-Sayed Salama Department of Occupational and Environmental Health, School of Public Health, Lanzhou University Lanzhou 730000, Gansu, China.
Xiangkai Li MOE, Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu, China.

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Short-term changes in the anaerobic digestion microbiome and biochemical pathways with changes in organic load

Fluctuations in organic loading rate are frequently experienced in practical-scale anaerobic digestion systems. These impose shocks to the microbiome leading to process instability and failure. This study elucidated the short-term changes in biochemical pathways and the contributions of microbial groups involved in anaerobic digestion with varying organic load shocks. A mixture of starch and hipolypeptone corresponding to a carbon-to‑nitrogen ratio of 25 was used as substrate. Batch vial reactors were run using acclimatized sludge fed with organic load varying from 0 to 5 g VS/L. Methane yield decreased with increasing organic load. The microbiome alpha diversity represented as the number of operational taxonomic units (OTUs) and the Shannon index both decreased with organic load indicating microbiome specialization. The biochemical pathways predicted using PICRUSt2 were analyzed along with the corresponding contributions of microbial groups leading to a proposed pathway of substrate utilization. Genus Trichococcus (order Lactobacillales) increased in contribution to starch degradation pathways with increase in organic load while genus Macellibacteroides (order Bacteroidales) was prominent in contribution to bacterial anaerobic digestion pathways. Strictly acetoclastic Methanosaeta increased in prominence over hydrogenotrophic Methanolinea with increase in organic load. Results from this study provide better understanding of how anaerobic digesters respond to organic load shocks.

Filamentous foam disintegration with free nitrous acid: Effect on anaerobic digestion

Sludge foaming is a common problem in wastewater treatment plants negatively affecting operation of anaerobic digestion reactors. Therefore, in common practice, foam is removed from reactors without being fermented, leading to increase in sludge mass for disposal. However, foam is rich in lipids and can be a good source of methane if operational problems can be overcome. In this paper, in a two-stage experiment, we show that foam disintegration with free nitrous acid (FNA) can boost methane production and decrease foaming potential. In the first stage, the biochemical methane potential (BMP) of foam was evaluated to be higher by 19-63% (191-263NmL/gVS) than the BMP of waste activated sludge (WAS) (161 ± 1NmL/gVS) confirming previous assumptions. The main findings of the second stage (continuous experiments) are: (1) foam and WAS co-digestion leads to sludge stratification and thickened biomass accumulation in the upper part of the reactor, (2) FNA disintegration destroyed foam structure, resulting in lower biomass stratification and 14% higher methane production (134 mL/gVS) than observed in the reference reactor, (3) FNA disintegration of both substrates (foam and WAS) does not provide noticeable benefits in terms of biomass stratification. However, it does enhance methane production to 140 mL/gVS and sludge mineralization efficiency. A significantly higher impact of FNA on methane yield from foam than WAS was attributed to the high content of M.parvicella and the ability of these bacteria to adsorb and accumulate lipids. Anaerobic digestion of FNA disintegrated foam leads to substantial benefits in terms of methane production, reactor volume, and reagents consumption.

Rapid initiation of methanogenesis in the anaerobic digestion of food waste by acclimatizing sludge with sulfidated nanoscale zerovalent iron

Although coupling of sulfidated nanoscale zero-valent iron (S-nZVI) into anaerobic digestion of food waste (FW) for improving methanogenesis has been reported, the specific role of S-nZVI during start-up process and its influence on subsequent methanogenesis and system stability remains unknown. In this study, S-nZVI was added into the unacclimatized sludge system to investigate its influence on microbial acclimatization and methanogenic performance. During acclimatization phase, CH₄ production improved and VFAs transformation facilitated with the addition of S-nZVI. Furthermore, enzymatic activity analysis and electrochemical measurements presented direct evidence that electron transfer capacity of acclimatized sludge was significantly improved. S-nZVI favored the transition of microbial community to a robust and specialized population. During evaluation phase, acclimatized sludge still exhibited strong methanogenic ability, but the microbial community inevitably changed under the stress of FW. This research provides a novel perspective on initiating anaerobic digestion of FW for shorter start-up time and stronger methanogenesis.

Synergistic ammonia and fatty acids inhibition of microbial communities during slaughterhouse waste digestion for biogas production

The slaughterhouse waste (SHW) contains high organics which makes SHW a feasible feedstock for anaerobic digestion (AD). The present study systematically assessed the microbiome response and biomethanation along with the production of volatile fatty acids (VFAs) and ammonia under 2%, 4%, 6%, and 8% (w v^-1) loadings of SHW in AD. The optimum loading was 2% SHW which resulted in maximum biomethane production and VFAs consumption. A higher SHW concentration (4% and 6%) resulted in a prolonged lag-phase and decreased biomethane production. High VFAs (28.88 g L^-1) and ammonia nitrogen (>4 g L^-1) accumulation were observed at 8% SHW leading to permanent inhibition of biomethane and methanogenic archaea. An increase in ammonia and VFAs concentration, at 4% and 6% SHW loadings, shifted the methanogenic pathway from acetoclastic to hydrogenotrophic lead by Methanoculleus. Acetoclastic Methanosaeta (77.15%) dominated the reactors loaded with 2% SHW resulting in the highest biomethane production.

Exploration of microbial communities contributing to effective methane production from scum under anaerobic digestion

Scum is formed by the adsorption of long-chain fatty acids (LCFAs) onto biomass surface in anaerobic digestion of oily substrates. Since scum is a recalcitrant substrate to be digested, it is disposed via landfilling or incineration, which results in biomass washout and a decrease in methane yield. The microbes contributing to scum degradation are unclear. This study aimed to investigate the cardinal microorganisms in anaerobic scum digestion. We pre-incubated a sludge with scum to enrich scum-degrading microbes. Using this sludge, a 1.3-times higher methane conversion rate (73%) and a faster LCFA degradation compared with control sludge were attained. Then, we analyzed the cardinal scum-degrading microbes in this pre-incubated sludge by changing the initial scum-loading rates. Increased 16S rRNA copy numbers for the syntrophic fatty-acid degrader Syntrophomonas and hydrogenotrophic methanogens were observed in scum high-loaded samples. 16S rRNA amplicon sequencing indicated that Syntrophomonas was the most abundant genus in all the samples. The amino-acid degrader Aminobacterium and hydrolytic genera such as Defluviitoga and Sporanaerobacter became more dominant as the scum-loading rate increased. Moreover, phylogenic analysis on Syntrophomonas revealed that Syntrophomonas palmitatica, which is capable of degrading LCFAs, related species became more dominant as the scum-loading rate increased. These results indicate that a variety of microorganisms that degrade LCFAs, proteins, and sugars are involved in effective scum degradation.

Syntrophic metabolism facilitates Methanosarcina-led methanation in the anaerobic digestion of lipidic slaughterhouse waste

Different inoculum to slaughterhouse waste (SHW) ratios (Ino/SHW) influences the digester performance, substrate utilization, and methane yield through microbial shift and their metabolic syntrophy. Acetoclastic Methanosarcina (68-87%) was dominant in the exponential phase, overpowering the initial abundance of Methanosaeta (86% of methanogens) in the SHW digesters. Positive interactions among acetogenic and acetate-oxidizing species of Clostridium (11%) with Methanosarcina (84% of methanogens) improved the methanogenic activity (292 mL g^-1 VS_initial d^-1) and final VS utilization (90%) at the highest Ino/SHW loading. In contrast, significant improvement of methane yield (152% higher than the control) at the lowest Ino/SHW loading was attributed to strong syntrophy among Methanosaeta (24% of methanogens) and its exoelectrogenic partners, Bythopirellula (0.52%) and Mariniphaga (0.08%) and the acetogenic Cloacimonas (0.16%) and Longilinea (0.32%). These syntrophic interactions among the core microbiota induced major metabolic activities, including butanoate, glycine, serine and threonine, methane, propanoate, and pyruvate metabolism, and quorum sensing.

Anaerobic co-digester microbiome during food waste valorization reveals Methanosaeta mediated methanogenesis with improved carbohydrate and lipid metabolism

This study determines the optimum food waste (FW) loading in an anaerobic digester for methane production. Interrelation between the degradation mechanism and microbial community composition was assessed through in-depth metabolic pathway analysis and gene quantification. Higher methane production and short lag phase were observed in the FW reactors with low substrate loadings (<4% v/v) while extended lag phase and incomplete substrate utilization were observed in the reactors fed with higher substrates (>6% v/v). The long-chain fatty acids (LCFAs) degradation was influenced by initial FW loading, and up to 99% LCFA degradation occurred at 4% FW reactor. The addition of 8 to 10% FW substrate inhibited methanogenesis due to the accumulation of volatile fatty acids (VFA) and low LCFA degradation. Under optimal conditions of substrate loading, Methanosaeta and Methanosarcina were abundant, indicating their role in methanogenesis and syntrophic acetogenesis, along with enhanced metabolic pathways specific for carbohydrate and lipid metabolism.

Anaerobic co-digestion of agricultural wastes toward circular bioeconomy

A huge amount of agricultural wastes and waste activated-sludge are being generated every year around the world. Anaerobic co-digestion (AcD) has been considered as an alternative for the utilization of organic matters from such organic wastes by producing bioenergy and biochemicals to realize a circular bioeconomy. Despite recent advancement in AcD processes, the effect of feedstock compositions and operating conditions on the biomethane production processe has not been critically explored. In this paper, we have reviewed the effects of feedstock (organic wastes) characteristics, including particle size, carbon-to-nitrogen ratio, and pretreatment options, on the performance of an anaerobic digestion process. In addition, we provided an overview of the effect of key control parameters, including retention time, temperature, pH of digestate, volatile fatty acids content, total solids content, and organic loading rate. Lastly, based on the findings from the literature, we have presented several perspectives and prospects on priority research to promote AcD to a steppingstone for a circular bioeconomy.

Microbial community composition and metabolic functions in landfill leachate from different landfills of China

Landfill leachate usually harbors complex microbial communities responsible for the decomposition of municipal solid waste. However, the diversity and metabolic functions of the microbial communities in landfill leachate as well as the factors that influence them are still not well understood. In this study, Illumina MiSeq high-throughput sequencing was used to investigate the microbial community composition and metabolic functions in landfill leachate from 11 cities in China. The microbial diversity and structure of different leachate samples exhibited obvious differences. In general, Bacteroidetes, Firmicutes and Proteobacteria were the three dominant microbial communities among the 26 bacterial phyla identified in landfill leachate, regardless of the geographical locations. Diverse bacterial genera associated with various functions such as cellulolytic bacteria (e.g., Sphaerochaeta and Defluviitoga), acidifying bacteria (e.g., Prevotella and Trichococcus) and sulfate-reducing bacteria (e.g., Desulfuromonas and Desulfobacterium) were detected abundantly in the landfill leachate. Moreover, the archaeal community in all leachate samples was dominated by the orders Methanomicrobiales and Methanosarcinales belonging to the Euryarchaeota phylum. Notably, the archaea-specific primer pair covered more diverse archaeal communities than the universal bacteria-archaea primer pair. Seventeen archaeal genera belonging to acetoclastic, hydrogenotrophic, and methylotrophic methanogens were identified, and the composition of the dominant genera in these samples varied greatly. The canonical correlation analysis indicated that landfill age, electrical conductivity, ammonia nitrogen, and total nitrogen were significantly correlated with the microbial community structure. Based on PICRUSt2, a total of 41 metabolic pathways belonging to six metabolic pathway groups were predicted, and the KEGG pathway Metabolism was the most abundant group across all leachate samples. This study provides an important insight into the composition and functional characteristics of the microbial communities in landfill leachate.

Rapid recovery of methane yield in organic overloaded-failed anaerobic digesters through bioaugmentation with acclimatized microbial consortium

Acidification during anaerobic digestion (AD) due to organic overloading is one of the major reasons for process failures and decreased methane productivity in anaerobic digesters. Process failures can cause the anaerobic digesters to stall completely, prolong the digester recovery period, and inflict an increased operational cost on wastewater treatment plants and adverse impacts on the environment. This study investigated the efficacy of bioaugmentation by using acclimatized microbial consortium (AC) in recovering anaerobic digesters stalled due to acidosis. Overloading of digesters with food waste leachate (FWL) led to the accumulation of volatile fatty acids (11.30 g L^-1) and a drop in pH (4.67), which resulted in process failure and a 22-fold decline in cumulative methane production compared to that in the initial phase. In the failure phase, the syntrophic and methanogenic activities of the anaerobic digester microbiota were disrupted by a significant decrease in the abundance of syntrophic populations such as Syntrophomonas, Syntrophorhabdus, Sedimentibacter, and Levilinea, and the phylum Euryarchaeota. Bioaugmentation of the failed digesters by adding AC along with the adjustment of pH resulted in the prompt recovery of methane productivity with a 15.7-fold higher yield than that in unaugmented control. The abundance of syntrophic bacteria Syntrophomonas and phylum Euryarchaeota significantly increased by 29- and 17-fold in the recovered digesters, respectively, which showed significant positive correlations with methane productivity. Methanosarcina and acetoclastic Methanosaeta played a major role in the recovery of the digesters; they were later replaced by hydrogenotrophic Methanoculleus. The increase in the abundance of genes associated with biomethanation contributed to digester recovery, according to the functional annotation of 16S rDNA amplicon data. Thus, bioaugmentation with AC could be a viable solution to recover digesters experiencing process failure due to organic overloading.

Does lipid stress affect performance, fate of antibiotic resistance genes and microbial dynamics during anaerobic digestion of food waste?

The dissemination of antibiotic resistance genes (ARGs) in food waste (FW) disposal can pose severe threats to public health. Lipid is a primary composition in FW, while whether lipid stress can affect ARGs dynamics during anaerobic digestion (AD) process of FW is uncertain. This study focused on the impacts of lipid stress on methane production, fate of ARGs and its microbial mechanisms during AD of FW. Results showed that high lipid content increased methane yield but prolonged hydrolysis and lag time of methane production compared to AD of FW without oil. Moreover, variations of ARGs were more susceptible to lipid stress. Lipid stress could facilitate the reduction of total ARGs abundances compared to the group without oil, particularly restraining the proliferation of sul1, aadA1 and mefA in AD systems (P < 0.05). Mantel test suggested that integrons (intl1 and intl2) were significantly correlated with all detected ARGs (r: 0.33, P < 0.05), indicating that horizontal gene transfer mediated by integrons could be the driving force on ARGs dissemination. Network analysis suggested that Firmicutes, Bacteroidetes, Synergistetes and Proteobacteria were the main potential hosts of ARGs. In addition, under the lipid stress, the reduction of host bacteria was responsible for the elimination of several specific ARGs, thereby affecting ARGs profiles. These findings firstly deciphered ARGs dynamics and their driving factors responding to lipid stress during anaerobic biological treatment of FW.

Composition-oriented estimation of biogas production from major culinary wastes in an anaerobic bioreactor and its associated CO2 reduction potential

Despite the wide applications of dry anaerobic digestion (AD), a number of fundamental issues, such as composition-oriented estimation of biogas production and CO₂ reduction potential, were not well understood yet. The objective of this study was to establish composition-oriented models for prediction of biogas production and the associated shift of microbial communities. Three important factors regarding feedstock, including loading, carbon-to-nitrogen ratio, and solid-to-liquid ratio, were found to significantly affect the biogas production. The biogas production and digestion kinetics were evaluated with the response surface methodology. The major contribution to biogas production was found to be hydrogenotrophic methanogens (82.6 ± 0.4%). The net CO₂ reduction potential was assessed from the life-cycle approach, and a substantial amount of CO₂ generation (i.e., 2.8-6.7 tonne/tonne-VS) could be reduced by AD, compared to incineration, revealing that dry AD for food waste treatment should be one of the essential practices in the portfolio of global CO₂ mitigation.

Management and valorization of waste from a non-centrifugal cane sugar mill via anaerobic co-digestion: Technical and economic potential

The main sugarcane wastes from the non-centrifugal cane sugar (NCS) agro-industry, agricultural crop residue (ACR) and sugarcane scum (SCS), were used to produce biogas in a bench-scale semi-continuous anaerobic tubular digester. A two-stage strategy was proposed to achieve the appropriate operability and stability of the digester. In the first stage, the operability of the digester was achieved with ACR mono-digestion. In the second stage, the digester feed was changed until it reached an ACR:SCS ratio (co-digestion) of 75:25, based on volatile solids, and until stability was achieved. The strategy was successful, and specific biogas production of 0.132 m³ kg^-1VS with a methane content of 50.4% was achieved, confirming the technical feasibility of the process. Economic viability was established through a case study at a typical NCS mill. Therefore, anaerobic co-digestion can be consolidated as a technological alternative for the treatment of ACR + SCS and the sustainable benefit of the NCS agro-industry.