Solid-state Anaerobic Digestion Research Articles

Solid-state anaerobic digestion of sweet corn waste: The effect of mixing and recirculation interval

The mixing and sludge recirculation interval is one of the key successes of the solid-state anaerobic digestion process, a promising technology for converting high-solid agro-industrial wastes to renewable energy. This study employed a pilot-scale completely stirred tank reactor to examine biogas production from sweet corn waste, including corn cobs, husks, and seeds. The reactor was operated as solid-state anaerobic digestion at an ambient temperature. The mixing and recirculating intervals were set to non-mixing and mixing for 10 minutes every 3, 6, and 12 hours. The initial total solid of the feedstock was 25%, while the hydraulic retention time was 30 days. The results showed that during the mixing and recirculation every three hours, the highest chemical oxygen demand, total solid, and volatile solid (VS) removal efficiencies were 85.42%, 62.92%, and 64.59%, respectively. The ratio between volatile fatty acid and alkalinity ranged between 0.20 and 0.30 without any sign of system failure. The highest specific methane yield of 766 L/kg VSadded was obtained in the experiment with mixing and recirculating intervals every 3 hours. It was found that the modified Gompertz model could effectively fit the methane yields with an R2 of 0.9667. The modeled methane production potential and the maximum methane production rate were 867.40 NL/kg VSadded and 132.01 NL/kg VSadded-d, respectively. Additionally, the levelized cost of the biogas produced from the solid-state anaerobic digestion of the sweet corn waste was calculated to be 0.61 USD/kg. The findings of this study can serve as a guide for the design and operation of the SS-AD system, which aims to transform various types of lignocellulosic waste into environmentally friendly energy.

Optimizing feedstock organic composition to regulate humification and heavy metal passivation during solid-state anaerobic digestion

This study uncovered the impacts of feedstock organic composition, comprising proteins, lignocellulose, and lipids, on humification and passivation of heavy metals (HMs) in solid-state anaerobic digestion (SSAD). Mantel tests and partial least squares structural equation modeling (PLS-SEM) results revealed that copper (Cu) and zinc (Zn) passivation predominantly occurred through complexation with humic acid (HA). In contrast, lead (Pb) and chromium (Cr) passivation were pH-dependent as influenced by substrate conditions in SSAD. Increasing protein content in the feedstock facilitated lignocellulose biodegradation to enhance HA formation, and thus augmenting Cu and Zn passivation. Furthermore, the improved biodegradation of organic components elevated the substrate pH, further enhancing Pb and Cr passivation. Such improvement was notable when the protein: lignocellulose: lipid ratio of feedstock was regulated to 4.1:3.7:2.2, which increased HA contents to 35.25% and pH to 9 to enhance the passivation of Cu, Pb, and Cr by 0.48%, 52.0%, and 17.9%, respectively.

Enhancing methane production from distillers’ grains by cattle manure in solid-state anaerobic digestion: Focusing on biodegradability, acidification and indigenous microorganisms

Distillers’ grains has high potential in methane production but the process is affected by the acidification in anaerobic digestion. To enhance the methane production in solid-state anaerobic digestion, distillers’ grains was co-digested with cattle manure in different proportions in this study. Compared to distillers’ grains, cattle manure performed lower biodegradability but higher alkalinity and nutrients, hence relieved acidification and drove microbial succession for methane enhancement in the co-digestion with distillers’ grains. The highest increase in total methane yield (10.67 %) was observed in the co-digestion of distillers’ grains and cattle manure at the proportion of 70:30 (T3). This was the synergistic action of reduced acidification, relatively high biodegradability of feedstocks, and balanced composition of hydrolytic bacteria, syntrophic bacteria and acetoclastic methanogens. Further analysis revealed the positive effects of indigenous microorganisms derived from distillers’ grains and cattle manure in methane enhancement. The enrichment of Sedimentibacter, Desulfitibacter, Tepidanaerobacter from distiller's grains, and Eubacterium, Methanoculleus, Methanobacterium, Methanobrevibacter mainly from cattle manure synergistically promoted organics conversion and methane production in T3. This study further affirmed the potential use of distillers’ grains in solid-state anaerobic digestion and provided a favorable strategy for its better methane production.

Anaerobic digestion of poultry manure to power a poultry farm in Ba: Pilot and techno-economic study

Although poultry is the largest meat by volume produced in Fiji, there has not been any established study, nor application of the anaerobic digestion (AD) of poultry manure (PM) in the country. This paper aims to determine the techno-economic feasibility of the AD of PM to power a poultry farm in Fiji. A pilot scale study was first conducted with mono-digestion batches of poultry manure, and co-digestions with kitchen waste (KW) and newspaper waste (NPW). Solid state anaerobic digestion (SSAD) was employed in all the batches, and the key operational parameters of AD were studied, along with its influence on biogas production. The pilot study revealed that even slight changes in environmental temperature had the greatest effect on biogas production. The most resilient to the temperature changes were the co-digested feedstocks of KW. Yet, given a substantial AD period, the anaerobes in the mono-digesters were able to eventually acclimatize to the SSAD environment, and produce the overall highest biogas production. The pilot study results were then used to conduct a feasibility study of the full-scale design. The analysis showed that the SSAD system would generate 189.46 MWh of electricity annually, with a levelized cost of energy of FJ$0.17/KWh.

A coupling strategy combined with acid-hydrothermal and novel DES pretreatment: Enhancing biomethane yield under solid-state anaerobic digestion and efficiently producing xylo-oligosaccharides and recovered lignin from poplar waste

Lignocellulose is an abundant renewable bio-macromolecular complex, which can be used to produce biomethane and other high-value products. The lignin, presents in lignocellulose is typically regarded as an inhibitor of anaerobic digestion. Therefore, it is crucial to develop a novel selective separation strategy to achieve efficient biomethane production and all-component utilization of biomass. Hence, a combination of two-step pretreatment and solid-state anaerobic digestion was employed to enhance the production of biomethane and to generate valuable chemicals from poplar waste. Optimal conditions (4 % acetic acid, 170 °C, and 40 min) resulted in 70.85 % xylan removal, yielding 50.28 % xylo-oligosaccharides. The effect of a strong acid 4-CSA-based novel three-constituent DES on delignification was investigated from 80 °C to 100 °C; the cellulose content of DES pretreated poplar increased from 64.11 % to 80.92 %, and the delignification rate increased from 49.0 % to 90.4 %. However, high delignification of the pretreated poplar (DES-100 and DES-110) led to a rapid accumulation of volatile organic acids during the hydrolysis and acidogenesis stages, resulting in methanogenesis inhibition. The highest biomethane yield of 208 L/kg VS was achieved with DES-80 (49.0 % delignification), representing a 148 % improvement compared over untreated poplar. This approach demonstrates the potential for comprehensive utilization of all components of biomass waste.

Evaluating the Environmental Impacts of Pretreatment and Nanoparticles in Solid-State Anaerobic Digestion Using Life Cycle Assessment

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.

The Biogas Production Potential and Community Structure Characteristics of the Co-Digestion of Dairy Manure and Tomato Residues

Anaerobic digestion is an important means to turn agricultural waste into resources and an important way to address the challenges in treating vegetable residues in China. In this study, the co-digestion of dairy manure with tomato residue was investigated to clarify the effect of the total solids (TS) of the digestion substrate on methane’s production and mechanism using the self-made anaerobic digestion device. The results showed that all treatments could rapidly ferment methane and that the daily methane production showed a trend of increasing first and then decreasing. The optimal concentrations of the digestion substrate for liquid anaerobic digestion (L-AD), hemi-solid-state anaerobic digestion (HSS-AD), and solid-state anaerobic digestion (SS-AD) were 10%, 18%, and 25%, respectively. Compared with SS-AD and HSS-AD, L-AD gas production peaked 3–6 days earlier. Treatment TS25 had the best cumulative methane production, reaching 117.4 mL/g VS. However, treatment TS6 had acid accumulation and a very unstable system. The cumulative methane production of SS-AD was higher than that of HSS-AD and L-AD. Firmicutes and Bacteroidetes were the dominant flora, and Methanoculleus, Methanosarcina, and Methanobrevibacter were the main archaeal groups. The TS significantly changed the microbial community composition of the digestion system, especially the low TS treatment. The results presented herein indicated that TS significantly changed the bacterial and archaeal community composition of the digestion system, and thus with the increase in TS from 6% to 25%, the methane yield increased.

Integration of Solid-State Anaerobic Digestion and Hydrothermal Carbonization

Integration of Solid-State Anaerobic Digestion and Hydrothermal Carbonization

Optimising organic composition of feedstock to improve microbial dynamics and symbiosis to advance solid-state anaerobic co-digestion of sewage sludge and organic waste

This study provided new insight to the underlying mechanisms, by which organic compositions, including protein, fat, degradable carbohydrates and lignocellulose, regulate the performance of solid-state anaerobic digestion (SSAD) for synergistic treatment of organic wastes. Results show that the feedstock with a balanced composition of protein, fat, degradable carbohydrates and lignocellulose could maintain SSAD homeostasis to enhance methane (CH4) production by 14–487%. On the other hand, organic waste with a high content of degradable carbohydrates and fat at 39 and 14%, respectively, showed an initially high CH4 production at the beginning but a lower overall CH4 production. This was because of the accumulation of volatile fatty acids (VFAs) and ammonium nitrogen (NH4+-N) at up to 17.3 and 7227.7 mg·L−1, respectively, leading to anaerobic activity inhibition. Microbial dynamic and modular network analyses indicated that the balanced feedstock secured stepwise biodegradation of different organic substances to reduce the relative abundance of hydrolytic bacteria (e.g. Rikenellaceae_RC9_gut_group and Tepidimicrobium), thus alleviating VFAs and NH4+-N stresses. In particular, fat in the balanced feedstock could not only enrich the phylum Firmicutes for macromolecular biodegradation and genes for VFAs production, but also inhibit relative oxidizers (e.g. Synergistes and Acinetobacter) to facilitate propionate and acetate production to strengthen acetotrophic methanogenesis for effective CH4 yield. Results in this study show that a balanced organic composition could regulate microbial dynamics and symbiosis to advance SSAD homeostasis and methanation in synergistic organic waste treatment.

Layer Inoculation as a New Technology to Resist Volatile Fatty Acid Inhibition during Solid-State Anaerobic Digestion: Methane Yield Performance and Microbial Responses

Solid-state anaerobic digestion is easily inhibited by high volatile fatty acid induced by high total solids, although it is a promising technology. Previous studies on volatile fatty acid inhibition mainly focused on total solid content, co-digestion substrates, and external additives. The present study proposed a new inoculation method named layer inoculation and compared it to premixing inoculation in the solid-state anaerobic digestion of pig manure and maize straw. The results showed that the cumulative CH4 yields from layer inoculation (211.5 mL/g-VS) were 5.64 times more than premixing inoculation (37.5 mL/g-VS) under a low inoculation ratio (25%), with the values of total volatile fatty acid being greater than 30.0 mg/g. The concentrations of total VFAs and acetic acid from layer inoculation decreased dramatically during days 18–43. Layer inoculation also showed wider specific methane yield peaks and shorter startup times than premixing inoculation. Methanosphaerula and Methanothrix were the most dominant genera, while the genus Methanosphaerula did not correlate with volatile fatty acids, pH, or total ammonia nitrogen. The hydrogenotrophic methanogen pathway was predominant during solid-state anaerobic digestion; the shift from hydrogenotrophic to acetoclastic occurred in premixing inoculation, and it was stable in layer inoculation (61.20–68.88%). Overall, layer inoculation can effectively enhance methane production under high volatile fatty acid concentrations compared with premixing inoculation.

Dynamical model development and parameter identification for solid-state anaerobic digestion of shellfish products: Application to Mytilus edulis

A simplified AM2 model was developed to characterize mussel solid-state anaerobic digestion. This model considers two different substrates for mussels' degradation: the mussel meat and the mussel juice obtained after sanitization. This model was implemented to characterize the anaerobic degradation of Mytilus edulis species. This model was verified, implemented, and validated in 60 L batch reactors in mesophilic conditions. Two different experiments were used to calibrate kinetics using reaction invariants and an interior point optimization method. A conditioning study and a sensitivity analysis were done and had shown a better sensitivity with delayed substrate injections throughout the experiment with a factor of 10. An 88.6 % accumulation of methane yield of the BMP measurement was observed, corresponding to 57.7 % volatile removal with a minimum mass balance of 96.1 %. Additionally, the model proposed in this study was able to successfully predict the two characteristic methane yield peaks observed during solid-state anaerobic digestion.

Recycling cinder in efficient methane production from wheat straw via solid-state anaerobic digestion (SS-AD)

Solid-state anaerobic digestion (SS-AD) has received widespread attention due to its high methane productivity and organic loading, as well as its almost nonexistent wastewater emission. However, local acidification of the reaction system resulted in low material transfer efficiency due to low free water content leading to low energy conversion efficiency. Cinder is a byproduct of the coal chemical industry that has the potential to enhance the SS-AD performance due to its porous structure, electrocatalytic activity, and high trace elements concentration. The effect of cinder addition on SS-AD of wheat straw at 35 °C was studied herein. The cumulative methane of 2.5%, 5.0%, and 10.0% cinder groups were 41.25, 33.34, 28.94, and 26.68 mL/g VS, respectively, which increased 54.61%, 24.96%, and 8.47% compared to control (CK), with 2.5% cinder obtained the highest methane production. Cinder considerably enhanced volatile fatty acids conversion, particularly the propionic acid. The modified Gompertz model was used to predict the methane production potential and found to be able to accurately fit the characteristics of gas production. The maximum methane production of three test groups (2.5%, 5.0%, and 10.0%) was predicted to increase by 53.28%, 26.60%, and 11.56%, respectively, compared to CK. Cinder greatly enhanced the abundance of Methanosarcina, Fibrobacteres, and Spirochaetoma, which contributed to the switch from hydrogenophilic to acetylated methanogenesis. The prediction of the abundance of enzymes associated with microbial metabolism verified that cinder contributed to the greatest abundance of enzymes working in the hydrolysis phase, including peptidases, pyruvate metabolism, and genes encoding methane metabolism. Based on the concept of circular economy, this study presents a significant reference for synergistic and efficient disposal of industrial and agricultural wastes with high-value utilization.

Overview of Numerical Simulation of Solid-State Anaerobic Digestion Considering Hydrodynamic Behaviors, Phenomena of Transfer, Biochemical Kinetics and Statistical Approaches

Anaerobic digestion (AD) is a promising way to produce renewable energy. The solid-state anaerobic digestion (SSAD) with a dry matter content more than 15% in the reactors is seeing its increasing potential in biogas plant deployment. The relevant processes involve multiple of evolving chemical and physical phenomena that are not crucial to conventional liquid-state anaerobic digestion processes (LSAD). A good simulation of SSAD is of great importance to better control and operate the reactors. The modeling of SSAD reactors could be realized either by theoretical or statistical approaches. Both have been studied to a certain extent but are still not sound. This paper introduces the existing mathematical tools for SSAD simulation using theoretical, empirical and advanced statistical approaches and gives a critical review on each type of model. The issues of parameter identifiability, preference of modeling approaches, multiscale simulations, sensibility analysis, particularity of SSAD operations and global lack of knowledge in SSAD media evolution were discussed. The authors call for a stronger collaboration of multidisciplinary research in order to further developing the numeric simulation tools for SSAD.

Effects of initial volatile fatty acid concentrations on process characteristics, microbial communities, and metabolic pathways on solid-state anaerobic digestion

Solid-state anaerobic digestion (SSAD) is vulnerable to excess volatile fatty acids (VFA), mainly acetate and propionate. The co-effects of VFAs and microbial dynamics under VFA accumulation were investigated in SSAD of pig manure and corn straw. Adding 2 and 4 mg/g acetate or propionate caused initial increases in total VFAs, followed by decreases after day 6, resulting in ‘mild’ VFA accumulation, while adding 6 mg/g caused similarly increased VFAs, but with no subsequent decrease, causing ‘severe’ VFA accumulation and poor methanation performance. Mild propionate accumulation promoted acetate consumption, whereas acetate accumulation inhibited propionate degradation by affecting crucial redox reactions. Under severe VFA accumulation, hydrolysis and acidification mainly conducted by acid-tolerant Clostridium sp. exacerbated VFA inhibition, causing a competition between Methanosarcina and Methanosaeta, and impairments of acetoclastic and hydrogenotrophic methanogenesis and interspecies formate transfer. This study provides new insights into mechanisms of VFA accumulation in SSAD, and its effects on methanogenesis.

Fermentation characteristics of bedded pack barn dairy cattle manure on methane yield, carbon, and nitrogen content in solid-state anaerobic digestion.

This study aimed to estimate the fermentation characteristics of bedded pack barn dairy cattle manure (BDCM) in terms of methane yield, fibrous material, and nitrogen content in batch solid-state anaerobic digestion (SSAD). SSAD was performed in triplicate using a 1,400 ml polypropylene bottle at a constant temperature of 39 °C until less than 1% methane was produced. The cumulative methane content of BDCM was 142.5 N mL/g volatile solids (VSs). The methane content rapidly increased for 18 days, reaching 63.4 ± 4.6% until the end of the experiment. The ultimate biodegradability and total VS removal of BDCM were 23.1 and 19.0%, respectively. The slopes of the non-fibrous and hemicellulose carbon fractions, and acid detergent insoluble carbon by digestion time were −0.174 (p < 0.001), −0.141 (p = 0.003), and −0.051 (p < 0.001), respectively. The non-fibrous and hemicellulose nitrogen fraction contents quadratically decreased during SSAD (p = 0.001 and p = 0.008). No significant decrease was observed in the acid detergent insoluble nitrogen content (p = 0.840). The results of the present study provide basic data on the digestion characteristics of BDCM and could help determine fermentation conditions in the anaerobic digestion of BDCM.

Food waste humification: a process analysis

Food and Agricultural Organization estimates that roughly 1.3 billion kitchen trash are generated annually on a global scale. By using composting, we could convert our kitchen waste into a properly sanitized, humus-rich, relatively stable product that improves plant growth by conditioning soil Introduction. The main objective of this study is to conduct a review of fundamental of composting, humus, and enhanced humidification. Humus is created from degraded organic compound by the polymerization and condensation of organic components such polyphenols, reducing sugars, and amino acids. Humification can be increased through vermicomposting, the addition of biochar made from digestate, the addition of microbes to food waste compost, the addition of cow manure, multistage inoculation, solid state anaerobic digestion (SSAD), and composting hybrid processes.

Performance of a percolation reactor integrated to solid-state anaerobic garage-type digesters with leachate recirculation for organic fraction of municipal solid waste treatment

Solid-state anaerobic digestion (SSAD) systems have been used for the sustainable treatment of the organic fraction of municipal solid waste (OFMSW). Unlike previous reports considering lab-scale SSAD systems as a unique system, the present study aims to deeper evaluate only the complementary percolation reactor (PR) integrated into the first semi-industrial scale SSAD system in Latin America. An innovative methodology was developed based on the probability function analysis of the monitoring data with target values reported in the literature and a linear correlation matrix to address the relation between different operating parameters. The results indicate that under a maximum organic loading rate of 1.9 kg VS.m−3.d−1, PR achieved a VS removal efficiency of 56 %, producing a highly stabilized inoculum (VS/TS ratio of 0.43). A maximum methane yield of 0.06 m3 CH4.kg VS−1removed and biogas CH4 content up to 76.5 % were reached during the long-term operation of 730 days.

Development of Solid-State Anaerobic Digestion and Aerobic Composting Hybrid Processes for Organic Solid Waste Treatment and Resource Recovery: a Review

Development of Solid-State Anaerobic Digestion and Aerobic Composting Hybrid Processes for Organic Solid Waste Treatment and Resource Recovery: a Review

Review on solid-state anaerobic digestion of lignocellulosic biomass and organic solid waste.

Sustainable management of organic solid wastes especially the municipal solid waste (MSW) is essential for the realization of various sustainable development goals (SDGs). Resource recovery centric waste processing technologies generate valorizable products to meet the operations and maintenance (O&M) costs while reducing the GHG emissions. Solid-state anaerobic digestion (SSAD) of organic solid wastes is a biomethanation process performed at a relatively higher total solids (TS) loading in the range of 10-45%. SSAD overcomes various limitations posed by conventional anaerobic slurry digesters such as higher degradable matter per unit volume of the bioreactor resulting in a smaller footprint, low freshwater consumption, low wastewater generation, simple upstream and downstream processes, relatively lower operation, and maintenance costs. This review elucidates the recent developments and critical assessment of different aspects of SSAD, such as bioreactor design, operational strategy, process performances, mass balance, microbial ecology, applications, and mathematical models. A critical assessment revealed that the operating scale of SSAD varies between 1000 and 100,000 ts/year at organic loading rate (OLR) of 2-15g volatile solids (VS)/L·day. The SSAD experiences process failures due to the formation of volatile fatty acids (VFAs), biogas pockets and clogging of the digestate outlet. Acclimatization of microbes accelerates the startup phase, steady-state performances, and the enrichment of syntrophic microbes with 10-50 times greater population of cellulolytic and xylanolytic microbes in thermophilic SSAD over mesophilic SSAD. Experimental limitations in the accurate determination of rate constants and the oversimplification of biochemical reactions result in an inaccurate prediction by the models.

Facilitating solid-state anaerobic digestion of food waste via bio-electrochemical treatment

Food waste has become a global environmental concern over emissions of greenhouse gas and odorous pollutants. Anaerobic digestion is gaining increasing attention as an effective food waste disposal method combining waste minimization and bioenergy recovery. Solid-state anaerobic digestion can handle food waste containing high contents of solids and has the merits of higher disposal volumes and less parasitic energy input, however, the low energy/mass transfer impairs the treatment efficiency. This study incorporated bio-electrochemical treatment into solid-state anaerobic digestion of food waste to overcome these shortcomings for enhanced performances. Food waste liquid leachate was used as feedstock to validate the bio-electrochemical treatment effects under different conditions. At a low applied voltage of 0.7 V and initial pH of 8.13, the methane yield increased by 77.5% while the carbon dioxide yield decreased by 16.0% compared with the control without electrodes. Although higher voltages (1.1–2.0 V) contributed to higher methane and hydrogen yields, the fast consumption and breakages of anodes significantly decreased the treatment consistency and material lifespan. Thereby, 0.7 V was selected as the applied voltage when incorporating the bio-electrochemical unit into the solid-state digester treating food waste. Cathodic hydroxide generation increased the buffering capacity, thus contributing to a more stable start-up process. With an immersed electrode surface area of 25.2 cm2/L, the highest methane yield of 526.7 mL/gVS was recorded with lower carbon dioxide and hydrogen contents initially, and the peak gaseous hydrogen sulfide emission was significantly reduced by 71.5% mainly due to the ferrous ions release from low carbon steel anode for sulfide precipitation.