Solid-state Anaerobic Digestion Research Articles

Alkali-Microwave Co-Pretreatment to Enhance the Solid-State Anaerobic Digestion Performance of Vinegar Residue

Large amounts of vinegar residue generated in the vinegar brewing process have been a severe threat to the environment. In this study, solid-state anaerobic digestion has been applied for sensible utilization of vinegar residue. Besides, alkali pretreatments, microwave pretreatment, and their combinations were introduced to enhance the degradation of vinegar residue in solid-state anaerobic digestion. Results showed alkaline hydrogen peroxide and microwave co-pretreatment performed better in regard to the cumulative methane yield, showing a remarkable increase of 34.6% (p<0.01) compared with untreated. The kinetic behavior of solid-state anaerobic digestion was successfully simulated using the modified Gompertz model. Scanning electron microscopy and X-ray diffraction analysis measurements indicated great destruction and transformation of the lignocellulosic structure of vinegar residue after the co-pretreatment. This research not only afforded a hopeful pretreatment approach for the efficient methane production of vinegar residue but also evaluated the feasibility of methane production after pretreatment under solid-state anaerobic digestion condition, which will also lay a good foundation for the utilization of other biowastes in the future.

Effect of Pretreatment by Freeze Vacuum Drying on Solid-State Anaerobic Digestion of Corn Straw

As a common agricultural waste, corn straw (CS) has a refractory structure, which is not conducive to anaerobic digestion (AD). Appropriate pretreatment is crucial for addressing this problem. Thus, freeze vacuum drying (FVD) was proposed. In this study, fresh CS (F-CS) pretreated (5 h, −40 °C) by FVD and naturally dried CS (D-CS) were compared. Differences in substrate surface structure and nutrient composition were first investigated. Results show that a loose and porous structure, crystallinity, and broken chemical bonds, as well as higher proportions of VS, C, N, cellulose, hemicellulose, and crude proteins in F-CS show a potential for methane production. Besides, process performance and stability were also examined in both high (4, VS basis) and low (1, VS basis) S/I ratio AD. A higher degradation ratio of hemicellulose as well as richer dissolved microbial metabolites, coenzymes, tyrosine-like proteins, and hydrolysis rate of particulate organic matter in the F-CS system enhanced the efficiency of methane conversion. The cumulative methane yield increased from 169.66 (D-CS) to 209.97 (F-CS) mL/gVS in the high S/I ratio system (p = 0.02 < 0.05), and 156.97 to 171.89 mL/gVS in the low S/I ratio system. Additionally, 16S-rRNA-gene-based analysis was performed. Interestingly, the coordination of key bacteria (Clostridium_sensu_stricto_1, Bacillus, Terrisporobacter, Clostridium_sensu_stricto_7, Thermoclostrium, UCG-012, and HN-HF0106) was more active. Poorer Methanosarcina and Methanomassiliicoccus as well as richer Methanobrevibacter and Methanoculleus stimulated the co-relationship of key archaea with diverse methanogenesis pathways. This study aims to verify the positive effect of FVD pretreatment on AD of CS, so as to provide a reference for applications in waste management.

Enhancing biogas production from livestock manure in solid-state anaerobic digestion by sorghum-vinegar residues

This study investigated the performance of sorghum vinegar residue to enhance methane production from livestock manures during solid-state anaerobic digestion. Sorghum vinegar residue was co-digested with cattle, sheep, and pig manure, respectively. Results show that co-digesting vinegar residue with livestock manures effectively diluted inhibitory substances (e.g. ammonium, sodium ion, and potassium ion) to alleviate the accumulation of volatile fatty acids and amend microbial composition to enhance digester stability and thus methane production by 10.1 – 58.2%. The highest increase was observed for cattle manure, possibly due to its low inhibitory substances to induce effective synergistic effects with vinegar residue in co-digestion. Modified Gompertz model well fitted the experimental methane yield and exhibited an increase in the maximum methane production rate of livestock manures by 35.2 –58.0% to corroborate their enhanced methanogenesis kinetics with the addition of vinegar residue. Further microbial analyses also indicated that co-digesting vinegar residue with livestock manures enriched hydrolytic bacteria (e.g. the genus vadinBC27_wastewater-sludge_group ), acetogenic bacteria (e.g. the genera Syntrophomonas and Petrimonas ) and aceticlastic methanogens (e.g. the genera Methanosarcina and Methanosaeta ) to promote substrate biodegradation and secure methane production. • Sorghum vinegar residue was co-digested with livestock manures at solid state. • Digester stability and methane production were enhanced in anaerobic co-digestion. • Modified Gompertz model corroborated enhanced methanogenesis kinetics in co-digestion. • Vinegar residue addition enriched functional microbes to sustain methane production.

Enhancement of Biogas Production Through Solid-State Anaerobic Co-Digestion of Food Waste and Corn Cobs

Although biogas has been primarily produced through liquid anaerobic digestion, this method leads to the floating and stratification of fibers and non-homogeneous mixing, which can reduce the biogas yield. Alternatively, biogas can be produced by the solid-state anaerobic digestion (SS-AD) of organic material with a high solid content, such as corn cobs. We investigated the co-digestion of food waste and corn cobs as a biomass feedstock for SS-AD in biogas production. We measured the effects of the total solid (TS) content, percentage of food waste, and reduction in volatile solids (VS), from which we determined its appropriate kinetic model. We found that the SS-AD of food waste with corn cobs produced a high biogas yield of 543 mL/g VS at a TS content of 22% and a food waste content of 20%. The first-order kinetics model for biogas production during SS-AD of the tested corn cob and food waste yielded an R2 value in the range of 0.91–0.94. The main contributor to the biogas production during the SS-AD of the corn cobs and food waste was the reduction in VS. A positive linear relationship was observed between the biogas yield and the reduction of VS.

Effects of pretreatment methods on biomethane production kinetics and microbial community by solid state anaerobic digestion of sugarcane trash

Solid state anaerobic digestion (SS-AD) of lignocellulose is effective in improving biomethane productivity but is limited by low biomass digestibility and lack of substrate-specific working microorganisms. In this study, the effects of different pretreatment methods on biomethane production by SS-AD of sugarcane trash were studied. The biomethane production, fitted to a modified Gompertz’s model, predicted a maximum methane yield of 214.2 L/kg volatile solids (VS) and productivity of 6.9 L/kg VS/day from KOH-pretreated trash, respectively. Microbial community analysis showed that bacterial community was significantly associated with volatile acids and pretreatment types while archaeal community was significantly associated with methane yield. Microbial community dynamics was revealed in SS-AD. Main genera related to pretreatment method were identified and discussed. This study generated important information on SS-AD of lignocellulosic biomass pretreated by different methods, which is useful for developing bioaugmentation strategies to improve biomethane production by SS-AD.

Solid-state anaerobic digestion of rice straw pretreated with swine manure digested effluent

Solid-state anaerobic digestion (SSAD) is a key technology for utilization of agricultural waste due to higher volumetric methane productivity, having a high load of organics, and nearly no effluent produced. The swine manure digested effluent (SMDE) containing high concentrations of ammonia nitrogen (1000, 1500, and 2000 mg L−1, respectively) were innovatively used to pretreat rice straw replacing alkaline chemicals at 30 °C for 2d, 4d, 6d, 8d, and downstream processed in SSAD loaded with solid digestate of swine manure (SDSM). After pretreatment, the surface structure of rice straw was obviously destroyed, and the removal rates of lignin, cellulose and hemicellulose were 1.3–20.4%, 1.3–26.3% and 13.9–28.4%, respectively. The concentrations of ammonia nitrogen in the pretreatment system were reduced by 16.75–75.47%. In the subsequent SSAD process, the accumulative methane yields in the digester loaded with pretreated rice straw increased by 93.25–261.08%, and the technical digestion time to achieve 80% of the maximum cumulative methane yield (T80) occurred 10–14 days earlier. The highest daily methane yield and accumulative methane yield of 7.37 mL/(g·VSadded·d) and 105.27 mL/(g·VSadded), respectively, were noted in the digester loaded with 2000 mg/L ammonia pretreated rice straw. Overall, SMDE pretreatment could significantly improve the biodegradability and anaerobic digestibility of rice straw, and improve the production efficiency of SSAD. The novel integrated approach to reutilization of SMDE, rice straw and SDSM not only reduced the environmental pollution, but also stimulated the sustainable development of swine farms, and promoted the carbon neutrality and economic development via effective bioenergy production as well. A large-scale trial and wide application of this approach could be expected in future.

Role of the Thickness of Medium on Solid-State Anaerobic Digestion

Role of the Thickness of Medium on Solid-State Anaerobic Digestion

Substrate-to-inoculum ratio drives solid-state anaerobic digestion of unamended grape marc and cheese whey.

Inoculation dose is a key operational parameter for the solid-state anaerobic digestion (SS-AD) of lignocellulosic biomass, maximum methane recovery, and stable digester performance. The novelty of this study was the co-digestion of unamended full-strength grape marc and cheese whey for peak methane extraction at variable inoculation levels. An acclimatised digestate from a preceding anaerobic treatment was used as a downstream inoculum. The impact of inoculum size (wet weight) was evaluated at 0/10, 5/5, 7/3 and 9/1 substrate-to-inoculum (S/I) ratios, corresponding to an initial concentration of 20–30% total solids (TS) in digesters over 58 days at 45°C. The optimal 7/3 S/I produced the highest cumulative methane yield, 6.45 L CH4 kg-1 VS, coinciding with the lowest initial salinity at 11%; the highest volumetric methane productivity rate of 0.289±0.044 L CH4 LWork-1 d-1; the highest average COD/N ratio of 9.88; the highest final pH of 9.13, and a maximum 15.07% elemental carbon removal; for a lag time of 9.4 days. This study identified an optimal inoculation dose and opens up an avenue for the direct co-digestion of grape marc and cheese whey without requirements for substrate pretreatment, thus improving the overall bioenergy profile of the winery and dairy joint resource recovery operations.

A coupling model for solid-state anaerobic digestion in leach-bed reactors: Mobile-Immobile water and anaerobic digestion model

A coupling distributed solid-state anaerobic digestion model was developed and performed considering a simplified AM2 model and a saturated Mobile-Immobile water Model (MIM). This model allows considering both microporosity and macroporosity evolutions as well as the impact on biological kinetics. This model was adapted, implemented and validated on cattle manure in mesophilic conditions and carried out in a solid-state leach-bed reactor. Three 60 L sacrificial leach-bed reactors were used to determine hydrodynamics and kinetic parameters in a calibration-validation approach. A sensitivity analysis was conducted and has shown a high value of hydrolysis kinetics on outputs variables (until 92% for accumulated methane yield and 72% for volatile fatty acids accumulation) which confirmed the necessity to identify accurately the hydrolysis parameter before calibration step. Finally, the solutes present inside each mobile and immobile region evolved in a different way confirming the model relevance.

Exploring Interactions Between Fruit and Vegetable Production in a Greenhouse and an Anaerobic Digestion Plant—Environmental Implications

Greenhouse fruit and vegetable production uses large amounts of energy and other resources, and finding ways of reducing its impact may increase sustainability. Outputs generated from solid-state anaerobic digestion (SS-AD) are suitable for use in greenhouses, which creates a need to investigate the consequences of the possible interactions between them. Connecting the fruit and vegetable production with the resource flows from an SS-AD process, e.g., biogas and digestate, could increase circularity while decreasing the total environmental impact. There are currently no studies where a comprehensive assessment of the material flows between greenhouses and SS-AD are analyzed in combination with evaluation of the environmental impact. In this study, material flow analysis is used to evaluate the effects of adding tomato related waste to the SS-AD, while also using life cycle assessment to study the environmental impact of the system, including production of tomatoes in a greenhouse and the interactions with the SS-AD. The results show that the environmental impact decreases for all evaluated impact categories as compared to a reference greenhouse that used inputs and outputs usually applied in a Swedish context. Using the tomato related waste as a feedstock for SS-AD caused a decrease of biomethane and an increase of carbon dioxide and digestate per ton of treated waste, compared to the digestion of mainly food waste. In conclusion, interactions between a greenhouse and an SS-AD plant can lead to better environmental performance by replacing some of the fertilizer and energy required by the greenhouse.

Methane yield optimization using mix response design and bootstrapping: application to solid-state anaerobic co-digestion process of cattle manure and damp grass

Optimization of solid-state anaerobic digestion on cattle manure and damp grass were performed simultaneously and combined to a bootstrapping tool to significantly decrease the number of experiments for a methane yield optimization. 15 batch reactors at lab scale were launched two times respecting a mix surface response methodology. A numerical method called Bootstrapping was used to verify results significance. Results have shown a significant influence with a p-value between 10−8 and 10−11: the optimal parameter values depend on the substrate composition with a maximal p-value of 5.60.10−2. The methane yield reached 156.19 NL · kgVS−1 for a mixture of cattle manure and damp grass, and 142.92 NL · kgVS−1 for cattle manure only. The bootstrapping were validated with a standard error lower than 3% in comparison with ANOVA method, which confirms that the mix surface response methodology combined to bootstrapping is an innovative and efficient way to optimize solid-state anaerobic digestion process.

Comparison of Initial pH Adjustment Prior to Thermophilic Anaerobic Digestion of Lime-Treated Corn Stover via Liquid Digestate or CO2

Neutralization with liquid digestate and CO2 was compared herein to adjust the pH of lime-treated corn stover. The effects on the thermophilic (55 °C) anaerobic digestion were also analyzed. Liquid digestate neutralization (LDN) caused a decrease in pH from 10.5 to 7.5 in 60 h and accumulation of acetic/isobutyric acids. The CO2 neutralization (CN) under solid-state conditions reduced the pH from 10.5 to 8.5 in 30 min, which is faster than that of LDN and did not affect the subsequent anaerobic digestion. Biomethane production rate indicates that LDN contributed to the performance of anaerobic digestion, but this was not sufficient to compensate for the loss of total biomethane yield, resulting in a negative net profit (i.e., revenue from increased energy production minus reagent cost). For CN under solid-state conditions, the biomethane production was highest in both liquid- and solid-state anaerobic digestion, and also obtained a net profit of 98.74–100.89 RMB/tonne dry biomass. Therefore, the solid-state condition CN is a more efficient and economic method for adjusting initial pH of lime-treated corn stover.

Effects of digestion duration on energy efficiency, compost quality, and carbon flow during solid state anaerobic digestion and composting hybrid process

This study investigated the effects of anaerobic digestion duration on methane yield, net energy production, and humification of compost during solid state anaerobic digestion (SSAD) and composting hybrid process for food waste treatment. Carbon flow and balance were used to evaluate organic methanation and humification inclination of carbon in the whole SSAD and aerobic composting system. Results showed that SSAD for 15 (AD-15) and 21 days (AD-21) could increase net energy production and degraded organic matter contained in the mixtures to achieve high biological stability. The cumulative net energy production between the AD-15 and AD-21 treatments was not significantly different, which was 8.3% higher than that in SSAD for 30 days (AD-30). Furthermore, digestate (AD-15 and AD-21) composting for 3 days reached maturity and absence of phytotoxic substances. Carbon fixed into humus of the AD-21 treatment (11.6%) was not significantly different from that of AD-15 (12.0%). However, the total amount of carbon fixed into compost in AD-15 was 6.6% higher than that in AD-21. Moreover, the CO2 -C loss of the AD-15 treatment (22.9%) was slightly higher than that of AD-21 (20.6%). Thus, AD-21 treatment achieved the most effective use of carbon during SSAD and composting hybrid process for food waste treatment. These results could provide valuable insights for the effective management of food waste in practice.

Comparison of batch and fed-batch solid-state anaerobic digestion of on-farm organic residues: Reactor performance and economic evaluation

Batch and fed-batch solid-state anaerobic digestion (SS-AD) of on-farm organic residues including cattle manure, cornstalk, and tomato residues (1:1:1.5, wet basis) were compared under mesophilic condition (35 ± 1 °C). Comparing to batch SS-AD, inoculum was needed in fed-batch was reduced by 60%, but increased cumulative methane yield by 45%. However, the overall daily methane yields in fed-batch SS-AD were 35% lower than that of batch SS-AD. The overall volatile solids (VS) reduction were obtained in fed-batch SS-AD was 12% higher than that in batch SS-AD. Furthermore, the effect of particle size of cornstalk on methane yield of fed-batch SS-AD was investigated. The highest cumulative methane yield of 283.3 L/kg VS feed was achieved in fed-batch SS-AD with cornstalk particle size of 40 mm. However, difference in cumulative methane yields caused by cornstalk particle size of 60 mm, 40 mm, and 10 mm in fed-batch SS-AD was not significant. Economic analysis was conducted to evaluate the economic performance of commercial-scale SS-AD (1,000 m 3 ) under batch, fed-batch, and combine fed-batch and batch system with the annual capacities of 6,400 metric tons (MT), 2,400 MT, and 4,800 MT, respectively. Batch SS-AD system has the highest net present value (NPV, 6.35 million US$) and internal rate of return (IRR, 24.7%) concerning economic analysis. However, batch SS-AD only achieved a slightly higher NPV and IRR compared to the combination of fed-batch and batch SS-AD system. Thus, it is more economical to start reactor with fed-batch SS-AD and later change to batch SS-AD under analysis conditions. • 60% less inoculum was needed in fed-batch solid state anaerobic digestion (FBSS-AD). • 45% higher methane yield was obtained in fed-batch SS-AD. • Effect of cornstalk particle size in FBSS-AD on cumulative CH 4 was not significant. • The highest NPV and IRR was achieved in scenario with batch SS-AD. • Combine fed-batch and batch system for SS-AD was financially attractive.

Lignocellulose degradation, biogas production and characteristics of the microbial community in solid-state anaerobic digestion of wheat straw waste

Waste recycling is pivotal for deep space exploration or space habitation in life support systems (LSS) to enhance the material closure. This study investigated the enzymatic pretreatment and solid-state anaerobic digestion (SS-AD) of wheat straw as the major component of biomass waste in LSS for resource reclamation. Wheat straw compounds, such as cellulose, hemicellulose and lignin were significantly degraded after pretreatment with degradation at 37.47%, 46.96%, and 14.05%, respectively. SS-AD with the C/N ratio of 25 resulted in more intense lignocellulose degradation (74.20%) and more biogas yield (77.59 L/kg volatile solid) with 30 days digestion. The microbial community variation and diversity were analyzed that common fiber-degrading bacteria including Firmicutes, Bacteroidetes and Proteobacteria were dominant while the composition of the microbial genera shifted along with the digestion time. Moreover, a potential feasible strategy for biomass waste management in LSS by SS-AD was proposed.

High-Solid Anaerobic Digestion: Reviewing Strategies for Increasing Reactor Performance

High-solid and solid-state anaerobic digestion are technologies capable of achieving high reactor productivity. The high organic load admissible for this type of configuration makes these technologies an ideal ally in the conversion of waste into bioenergy. However, there are still several factors associated with these technologies that result in low performance. The economic model based on a linear approach is unsustainable, and changes leading to the development of a low-carbon model with a high degree of circularity are necessary. Digestion technology may represent a key driver leading these changes but it is undeniable that the profitability of these plants needs to be increased. In the present review, the digestion process under high-solid-content configurations is analyzed and the different strategies for increasing reactor productivity that have been studied in recent years are described. Percolating reactor configurations and the use of low-cost adsorbents, nanoparticles and micro-aeration seem the most suitable approaches to increase volumetric production and reduce initial capital investment costs.

Solid-state anaerobic digestion of sugarcane bagasse at different solid concentrations: Impact of bio augmented cellulolytic bacteria on methane yield and insights on microbial diversity

This study investigated the impact of the potential cellulose degrading bacteria that could be bioaugmented in the solid-state anaerobic digestion (SSAD) of bagasse to enhance the methane yield. The prospective anaerobic cellulose degrading bacteria was isolated from the soil. SSAD experiments were organized with & without bioaugmentation with a substrate total solid (TS) of 25%, 30%, 40% and 50% at an optimized feed to microorganism (F/M) ratio of 1:1. The maximum yield of 0.44 L CH4/ (g VS added) was obtained from bioaugmented bagasse at a TS of 40% whereas it was 0.34 L CH4/(g VS added) for non-bioaugmented bagasse. The isolated bacterial strain was identified that belongs species Pseudomonas of Gamma Proteobacteria which exhibited good cellulolytic activity. Metagenomic studies found 90% of archaeal microorganisms affiliated to Methanosaeta, a strict acetoclastic methanogen.

Solid state anaerobic digestion of water poor feedstock for methane yield: an overview of process characteristics and challenges

Solid state anaerobic digestion (SSAD) of water poor feedstock may be a promising technology for energy recovery. Feedstocks having high solid concentration like lignocellulosic biomass, crop residues, forestry waste and organic fraction of municipal waste may be the appropriate feedstock for its biochemical conversion into energy carries like biomethane through SSAD. Compared to liquid state anaerobic digestion (LSAD), SSAD can handle higher organic loading rates (OLR), requires less water and smaller reactor volume and may have lower energy demand for heating or stirring and higher volumetric methane productivity. Besides these, pathogen inactivation may also be achieved in SSAD of biodegradable waste. Around 60% of recently built AD systems have adopted SSAD technology. However, the process stability of an SSAD system may have several constraints like limited mass transfer, process inhibitors and selection of digester type and should be addressed prior to the implementation of SSAD technology. In this article, a comprehensive overview of the key aspects influencing the performance of SSAD is discussed along with the need for mathematical modelling approaches. Further to this, reactor configuration for SSAD and digestate management requirement and practice for solid-state condition are reviewed for a better insight of SSAD technology

Enhancing hydrolysis and syntropy simultaneously in solid state anaerobic digestion: Digester performance and techno-economic evaluation

The present study investigated the effect of alkali and biochar addition for simultaneous increment of hydrolysis and syntropy for higher methane yield from pearl millet straw (PMS) in solid state anaerobic digestion. A taguchi based design of experiment was coupled with grey relation analysis for multiple output optimization. Study showed that 0.5 g (g/100 g PMS) of alkali and 10 g/L of biochar was the optimised dosing. Statistically, contribution of biochar and alkali was 48 and 21% respectively on the multiple output. The confirmation test revealed that hydrolysis rate constant, k and total volatile fatty acid/alkalinity ratio for reactor having optimised conditions was 0.0521 d-1 and 0.36 while for control, it was 0.0595 d-1 and 0.76 respectively. Techno-economic assessment showed US$ 25,652 of net present value and 11.29% of internal rate of return. Sensitivity analysis showed that capital expenditure and methane yield was most sensitive to net present value.

Effects of Pretreatment and Ratio of Solid Sago Waste to Rumen on Biogas Production through Solid-State Anaerobic Digestion

Solid sago waste is a potential source of producing renewable energy in the form of biogas. This study investigated the effects of solid sago waste particle size, biological pretreatment using a microbial consortium of lignocelluloses, pretreatment with NaOH, and the ratio between solid sago waste and cow rumen based on the biogas production rate. Several variations of these conditions were used to achieve this. The anaerobic digestion process was conducted over two months at 30.42 °C ± 0.05 °C, and the biogas production rate was measured every two days. The 1:1 ratio showed better results compared to the 2:1, because it allows the bacteria to achieve metabolic balance. The highest cumulative biogas production (27.91 mL/g TS) was generated when the sago waste underwent milling (±1 mm), pretreatment with 4% NaOH g/g TS, and treatment with microbial consortium 5% v/v at a 1:1 ratio of solid sago waste to the rumen.