Solid-state Anaerobic Digestion Research Articles

Solid state anaerobic digestion of food waste and sewage sludge: Impact of mixing ratios and temperature on microbial diversity, reactor stability and methane yield

Food waste (FW) and sewage sludge (SS) were anaerobically co digested under solid state conditions (Total solids >15%) and observed that mixing ratio of 3:1 and 2:1 is optimum for mesophilic and thermophilic conditions respectively. The VS reduction and methane yield at optimized ratio was 76% and 0.35 L CH4/(g VS reduced) respectively at mesophilic temperature whereas it was 88% and 0.42 L CH4/(g VS reduced) at thermophilic temperature. The metagenomic analysis for these cases were done and high throughput DNA sequencing revealed that diversified bacterial groups that participate in the different metabolisms (hydrolysis, acidogenesis and acetogenesis) were mainly dominated by the phylum Firmicutes and Bacteriodetes. Genus Methanothrix is found to be dominant which is capable of generating methane by any methanogenic pathway among all the archaeal communities in the reactors followed by Methanolinea and Methanoculleus. However, it was understood through metagenomic studies that acetotrophic pathway is observed to be the major metabolic pathway in the reactors.

The impact of immersed liquid circulation on anaerobic digestion of rice straw bale and methane generation improvement

Immersed liquid circulation is assumed to improve solid-state anaerobic digestion (SS-AD) with digestate flow convection on the surface of solid-state bed (SSB), which depends on SSB concentration and circulation rate (CR). In this study, the impact of CR on rice straw SS-AD was investigated within a 30 L pilot digester. Results showed that SSB threshold concentration for efficient biogas conversion was 10%–12% TS, achieving the methane yield of 185.3 mL/g VS. Within the threshold, methane production progress and VFAs release could be enhanced simultaneously by rational CR increasing, but no significant methane yield improvement was observed; above, the rapid and stable biogas generation could be acquired with a competitive methane yield of 174.7 mL/g VS (150% CR). No matter within or above the threshold, efficient lingo-cellulosic degradation was always accompanied by the moderate CR for effective methane generation. SSB was proposed to be above threshold for industrial application.

Enhanced CH4 Production from Corn Stover by Simultaneous Lime Treatment

Calcium hydroxide (lime) treatment and solid-state anaerobic digestion (SSAD) of corn stover (CS) were carried out simultaneously with different lime doses (0, 2, 3.5, and 5%) and feedstock to seed sludge (F/S) ratios (6, 8, and 10). It was found that the addition of 3.5% lime improved CH4 yield from 118 mL/g VS to 182 mL/g VS (54% increase) during SSAD of CS when F/S ratio was at 6. The improved CH4 production is consistent with increased relative abundance of several microbes that might play important roles in biomass degradation and CH4 generation. At higher F/S ratios (8 and 10), SSADs with different lime doses (0–5%) were all upset with accumulation of volatile fatty acids. Addition of 3.5% lime can obtain a net benefit of $18.4/tonne TS which are 44% of the gross benefit of power production ($41.5/tonne TS) via SSAD of CS and combined heat and power system.

Solid-state anaerobic co-digestion of organic fraction of municipal waste and sawdust: impact of co-digestion ratio, inoculum-to-substrate ratio, and total solids.

Municipal solid waste contains mainly organic wastes that can be a good source for anaerobic digestion. Solid-state anaerobic digestion is an affordable and suitable technique to mitigate the organic fraction of municipal solid waste (OFMSW). However, as the organic loading of OFMSW is high, co-digestion with other materials can improve the system's performance. This study aimed to investigate the performance of the co-digestion of OFMSW and sawdust and study the parameters affecting its performance. Based on the experiments, the optimum sawdust/OFMSW ratio was achieved 1:2 with the methane production of 0.3L/g VS. In addition, the inoculum-to-substrate ration (I/S) was investigated at 1:4, 1:2, 1:1, 2:1 ratios. The best result was obtained at 2:1 ratio with a total methane yield of 0.28 L/g VS. The results also indicated that I/S ratios less than 1:1 led to fatty acid accumulation and acidic pH condition. The effect of total solids content on the co-digestion process was also examined in this study. According to the results, as the total solids increased, the biomethane yield decreased while the biogas content increased.

Improvement of solid-state anaerobic digestion of broiler farm-derived waste via fungal pretreatment

Fungus, Trichoderma longibrachiatum, was used for the pretreatment of broiler farm derived-lignocellulosic bedding material (rice husk) to enhance the subsequent solid-state anaerobic digestion (SS-AD). Fungal pretreatment efficacy was evaluated through a series of batch studies with respect to carbon-to-nitrogen (C/N) ratio and pretreatment time. Lignocellulosic outer layer structure disruption of the rice husk was prominent under the best fungal pretreatment condition evaluated (C/N ratio of 18.9 and pretreatment time of 7 days). Consequently, the resulting methane yield of 438.1 ± 20.0 NmL/gVSadded was obtained which was ~2.0-folds higher than that of the control (without pretreatment). Furthermore, in semi-continuous SS-AD, fungal pretreatment could significantly enhance digestibility of organic substance in high solid loading (30% total solids) AD process by 3.2-folds and improve microbial kinetic parameters with subsequent daily methane yield improvement by 2.4-folds. Thus, fungal pretreatment could be an environmentally-friendly and effective low-cost approach for broiler farm-derived waste management to enhance SS-AD efficacy.

Anaerobic digestion of agricultural wastes from liquid to solid state: Performance and environ-economic comparison

Performance and environ-economic impacts were compared for anaerobic digestion (AD) of dairy manure and cucumber residues from liquid to solid state. Environ-economic evaluation of the overall AD process at different total solids (TS) was performed with the estimated treatment capacity of 9600 tons/year and service life of 20 years. Results showed that TS increase from 6% to 22% enhanced both cumulative and volumetric methane (CH4) production. Further TS increase to 25%, however, reduced CH4 yield. Environ-economic assessment indicated that TS increase enhanced volumetric waste treatment capacity and thus AD environmental footprints. Environmental credits from digestate and biogas utilization could compensate the adverse environmental impacts of other processes in AD plants. Furthermore, biogas and nutrients in digestate determined AD net-present value. As a result, solid state AD was more profitable with higher CH4 yield and more nutrients in both biosolids and digested effluent of digestate than its liquid and hemi-solid counterparts.

Solid-State Anaerobic Digestion of Chicken Manure and Corn Straw with Different Loading Amounts

Solid-State Anaerobic Digestion of Chicken Manure and Corn Straw with Different Loading Amounts

Development of a novel reactor for simultaneous production of biogas from oil-palm empty fruit bunches (EFB) and palm oil mill effluents (POME)

A novel reactor was developed in this research to simultaneously produce biogas from solid- and liquid-state anaerobic digestions in one container for the first time. Excess heat from the outer liquid-state anaerobic digestion (OL-AD) of POME was transferred to the inner solid-state anaerobic digestion (IS-AD) of EFB for promoting thermophilic digestions (55 °C and 70 °C). Continuous operations at various hydraulic retention times were performed. Bacteria and archaea communities were identified. The results showed that the maximum methane yields were 507.07 and 125.84 mL-CH4/g-VS for OL-AD and IS-AD, respectively. In OL-AD, raising temperature increased the methane yield by 6.4%. In IS-AD, the yield was not significantly affected by elevated temperature. However, the pretreatment of EFB with NaOH increased the methane yield by 14.1%. The main bacteria and archaea communities in OL-AD and IS-AD were found similar. The novel reactor could save energy, reduce costs and digester space, and increase the methane yield.

The effect of amylase and cellulase enzymes on biogas production from rice husk waste using solid-state anaerobic digestion (SS-AD) method

Biogas comes from an anaerobic biological decomposition process. Biogas is an alternative energy that potential to be developed in Indonesia. One of the various raw materials that can be used in biogas production is rice husk waste. This study analyzes the effect of pretreatment using amylase and cellulase enzymes on the production of biogas from rice husk waste in the Solid-State Anaerobic Digestion (SS-AD) method. Rice husk waste was used as a substrate with a C/N ratio of 25%, and the total solids used was 21%. Rice husk is biomass that is difficult to degrade because it has high lignin content; therefore, pretreatment is necessary. One of them is biological pretreatment using enzymes. The enzymes used are amylase and cellulase enzymes with various concentrations of 9%, 12%, 15%, and 18%. The biogas produced was then measured every two days for 40 days of the study with the volume of biogas as the observed parameter. The results showed that pretreatment with the addition of amylase and cellulase enzymes could increase biogas production. The highest biogas production was obtained by pretreatment of 18% amylase enzyme, namely 1466 mL, and by pretreatment of 18% cellulase enzyme, namely 1075 mL.

Environmental Loading in Pig Farming with Solid-state Anaerobic Digestion and High-yielding Rice Cultivation

Environmental Loading in Pig Farming with Solid-state Anaerobic Digestion and High-yielding Rice Cultivation

Renewable energy from the solid-state anaerobic digestion of grape marc and cheese whey at high treatment capacity

Globally, wine production annually generates some 11 million metric tonnes of grape marc (GM) while the cheese-making industry releases over 200 million m3 y−1 of effluent. Where value-creation mechanisms are absent, such wastes may be channelled to landfills. The study aimed to evaluate the bioenergy potential of the combined treatment of such wastes. Digestion of feedstock at a ratio 3/1 GM/CW (w/w) was conducted in unstirred conditions at 45 °C, following optimisation through the Taguchi Method. Cumulative biogas and methane yields were 0.601 m3 gas kg−1 VS and 0.363 m3 CH4 kg−1 VS, respectively. Firmicutes and Bacteroides mediated hydrolysis and acidogenesis, thus providing metabolites to Methanosarcina. Co-digestion can potentially generate 1330 GW h and 482,000 Mt CO2-equivalents avoidance. Wine and dairy industries jointly present a case for value-creation through a circular economy, thereby reducing the dependency on non-renewables, renewing commitment to the Paris Agreement.

Thermophilic Solid-State Anaerobic Digestion of Corn Straw, Cattle Manure, and Vegetable Waste: Effect of Temperature, Total Solid Content, and C/N Ratio.

Thermophilic solid-state anaerobic digestion (SS-AD) of agricultural wastes, i.e., corn straw, cattle manure, and vegetable waste, was carried out in this study. The effects of temperature (40-60°C), initial solid content (ISC, 17.5-32.5%), and C/N ratio (15-32 : 1) on biogas production were evaluated using a Box-Behnken experimental design (BBD) combined with response surface methodology (RSM). The results showed that optimization of process parameters is important to promote the SS-AD performance. All the factors, including interactive terms (except the ISC), were significant in the quadratic model for biogas production with SS-AD. Among the three operation parameters, the C/N ratio had the largest effect on biogas production, followed by temperature, and a maximum biogas yield of 241.4 mL gVS−1 could be achieved at 47.3°C, ISC = 24.81%, and C/N = 22.35. After 20 d of SS-AD, the microbial community structure under different conditions was characterized by high-throughput sequencing, showing that Firmicutes, Bacteroidetes, Chloroflexi, Synergistetes, and Proteobacteria dominated the bacterial community, and that Firmicutes had a competitive advantage over Bacteroidetes at elevated temperatures. The biogas production values and relative abundance of OPB54 and Bacteroidia after 20 d of SS-AD can be fitted well using a quadratic model, implying that OPB54 and Bacteroidia play important roles in the methanogenic metabolism for agricultural waste thermophilic SS-AD.

Design of Solid state digester for biogas production from banana wastes

Processing of banana results in a huge amount of waste generation, leaves, stems and peels etc. Indiscriminate disposal of these wastes when decomposed produces noxious gases such as hydrogen sulphide and ammonia, which pose serious environmental hazards. Thus turning them into biomass feedstock offers a better waste management option and also source of energy production. For the past 30 years, there has been only biogas plants which are developed for treating cow dung as feed material. In those plants only other organic wastes are used as feed material. As banana wastes contain high moisture, they can be treated by the way of solid state digestion. The paper describes the design of solid state digester of 1 m3 capacity of biogas production, exclusively for treating banana wastes by the method of solid state anaerobic digestion. The reactor was designed based on the hydraulic retention time and the total solid content of the banana feedstock in order to complete digest and produce biogas at a faster rate with optimum quantity and methane content. The digester was designed for a feed capacity of 30 kg with 30 days retention time with a gas holder volume of 1 m3. The diameter and height of the digester are 1.09 m and 2.1 m and for gas holder the diameter and height are 1.01 m and 0.9 m respectively. The developed digester was found to convert 90% of the solid content in feed to bioenergy.

Comparison of methane production performance of vinegar residue under liquid‐ and solid‐state conditions

AbstractVinegar residue (VR), a major by‐product in the vinegar brewing process, is generated at least three million tons annually in China. Currently major part of the disposal of VR is fulfilled by landfill and incineration, however, serious environment pollution along with such processes is a challenging issue. Anaerobic digestion (AD) can provide benefits of environment and renewable methane generation, which seems to be a reasonable alternative to traditional treatment. Noticeably, total solids (TS) is an important influential parameter to AD performance. Therefore, VR was evaluated for methane production and associated kinetic characteristics during the liquid‐state AD (LS‐AD) and solid‐state AD (SS‐AD) in this study. The results indicated that the highest specific methane yield of 194.8 mL gVS−1 and volumetric methane yield of 9.4 Lmethane Lreactor volume−1 were achieved in LS‐AD (TS = 10%) and SS‐AD (TS = 20%), respectively. The kinetic analysis showed a higher specific methane production rate for LS‐AD than SS‐AD, while volumetric methane production rate presented a reverse trend. This study provides useful guidance for the sustainable utilization of VR while contributes to environmental protection and alleviates the dependence on fossil fuels.

Kinetic studies of alkaline-pretreated corn stover co-digested with upset dairy manure under solid-state

Prolonged lag phase and reactor instability make methane yield description and prediction challenging in upset solid-state anaerobic digestion (SSAD). Seven kinetic models (first-order (FOM), modified first-order (MFOM), Fitzhugh (FzM), logistic (LM), modified logistic (MLM), Cone (CM), and modified Gompertz (MGM) were employed for treatment evaluation. The treatments were dairy manure blended with calcium pretreated stover (8% Ca CSDM) or sodium pretreated corn stover (4% Na CSDM) or 2% aqueous ammonia pretreated corn stover (2% NH4 CSDM), or 4% aqueous ammonia pretreated corn stover (4% NH4 CSDM). The LM, CM, MLM with MGM, and MGM best described methane yield for 4% Na CSDM, 2% NH4 CSDM, 4% NH4 CSDM, and 8% Ca CSDM, respectively. Optimal hydraulic retention time predicted for the least inhibited treatment, 8% Ca CSDM, was 60 days. Therefore, non-hydrolysis rate limiting models (LM, MLM, FzM, MGM, and CM) could simulate methane yield, design of reactor’s volume, and develop degradation rate models in full-scale SSAD.

Improvement of empty palm fruit bunches biodegradability and biogas production by integrating the straw mushroom cultivation as a pretreatment in the solid-state anaerobic digestion

Empty fruit bunches (EFB) have low biodegradability and restrict their commercial utilization in biogas plants. Integration of straw mushroom (Volvariella volvacea) cultivation as a function of bio-pretreatment on EFB to improve biodegradability and methane production by solid-state anaerobic digestion (SS-AD) was investigated. The mushroom yield was 47.3 kg·tonne−1 EFB with remaining weight in spent mushroom-EFB (S-mEFB) of 82%. The cellulose, hemicellulose, and lignin of EFB were degraded by 3.3%, 21.3%, and 17.6%, respectively, with an increased surface area of S-mEFB. The biodegradability of S-mEFB (62.7%) was 2 times higher than raw EFB (33.5%) with the highest methane yield and production of 281 mL CH4·g−1 VS and 50.6 m3·tonne−1 S-mEFB, respectively. The co-digestion of S-mEFB with 5% v/w POME had highest methane yield of 405 mL CH4·g−1 VS with biodegradability of 90.8%. Integrating straw mushroom cultivation with SS-AD is a promising strategy for achieving an environmentally friendly and economically feasible process.

Review on the fate of antimicrobials, antimicrobial resistance genes, and other micropollutants in manure during enhanced anaerobic digestion and composting

While manure has been used as nutrient-rich fertilizer for centuries, anaerobic digestion (AD) of manure has only been recognized recently as a promising renewable energy source for producing methane-rich biogas. Various forms of AD have been evaluated for the removal of manure contaminants, such as antimicrobials, antimicrobial resistance genes (ARGs), hormones, and pesticides that pose risks to human health and the environment. Increasing demand for cleaner energy prompts examination of the fate of manure contaminants in conventional and advanced AD techniques. This review reveals that removal of contaminants differs based on type (e.g. antimicrobials vs hormones) or class (e.g. tetracyclines vs sulfonamides) of chemicals being treated. Increasingly, pre-treatment techniques are incorporated into AD systems to enhance biogas production and degrade manure contaminants. For instance, activated carbon with microwave pretreatment removed 87-95% of ARGs. Advanced anaerobic digestion and solid-state anaerobic digestion reduced various ARGs associated with sulfonamides, macrolides, and tetracyclines. Further, total hormone reduction improved using high-temperature pretreatment prior to mesophilic AD. Finally, several studies revealed partial removal of antimicrobials and ARGs during managed composting. Although AD can independently decrease manure contaminants prior to use as fertilizer, augmenting AD with composting and other physical treatment processes can further enhance their removal.

Improving treatment capacity and process stability via a two-stage anaerobic digestion of food waste combining solid-state acidogenesis and leachate methanogenesis/recirculation

Food waste (FW) accounts for the largest category of municipal solid wastes in the United States and the proper disposal of FW is a unique challenge with urgent environmental concerns. Solid-state anaerobic digestion (SSAD) is a viable option to treat FW but still hindered by poor mass transfer and severe inhibition caused by the accumulation of acidic intermediates. To improve the treatment capacity and process stability using high-solid FW as the sole feedstock via AD, a bench-scale two-stage system comprising of a first-stage solid-state digester (Stage 1; 2 L) and a second-stage liquid digester (Stage 2; 1.4 L) was established and carried out in a semi-batch mode for 99 days. When one-stage SSAD started to encounter acid accumulation and methanogenesis inhibition at a FW loading of 300 g (15% of working volume), the two-stage system secured robust and stable biogas production when the FW loading continued rising to 400 g (20% of working volume), and an increase of 2.4 kJ/gVS (equivalent to 18.2% in one-stage system) in energy yield was achieved. Stage 1 served as a hydrolysis/acidogenesis reactor with a total acids level of 28.5 g/L and a pH of 5.65. A large portion of lactic acid in total acids indicated shifts of metabolic pathways. The transfer of acid-rich leachate from Stage 1 to Stage 2 ensured a high methane yield of 393.0 mL/gVS (90.2% of the biological methane potential), while the liquid effluent recirculation provided buffering to Stage 1. Further increase of FW loading triggered a system instability. The enhanced buffering capacity and increased free ammonia molecules, synergistically induced certain inhibitory effects on FW acidogenesis in Stage 1. To conclude, the two-stage system outpaced the one-stage SSAD with higher FW loading and energy yield.

Optimization of biogas from corn stover using liquid and solid-state anaerobic digestion

The shortage of fossil fuel can be minimized by developing renewable energies such as biogas. The raw material of biogas can be derived from corn stover. Biogas was produced under solid-state anaerobic digestion (SS-AD) and liquid anaerobic digestion (L-AD). The objectives of this study were to compare the biogas yield and analyze the pH value and VS degradation. The results reported that the SS-AD generated a higher biogas yield than L-AD. SS-AD could improve the biogas yield of 71%. Both SS-AD and L-AD had a higher final pH than the initial pH. Moreover, the VS degradation was proportionate to the biogas yield. The highest VS reduction was achieved on SS-AD. Keywords: anaerobic digestion, biogas, liquid state, solid state, volatile solid, renewable energy

Comparison of the Reactor Performance of Alkaline-Pretreated Corn Stover Co-digested with Dairy Manure Under Solid-State

Solid-state anaerobic digestion is a promising path to optimize green energy generation from waste management. This mesophilic study investigated the performance of sodium hydroxide (4%NaOH), ammonium hydroxide (2%NH4OH, and 4%NH4OH), and calcium hydroxide (8%Ca(OH)2) pretreated corn stover (Cs) co-digested with dairy manure (Dm) to achieve 4%NaCsDm, 2%AqCsDm, 4%AqCsDm, and 8%CaCsDm treatments. Results showed that 8%CaCsDm had shortened detention time (79 days) and increased methane yield (178 L/kg VS) in comparison with other treatments. In addition, propionic acid concentration in treatment 4%NaCsDm was elevated beyond a safe threshold (> 0.9 g/L) for methanogens, which is unlike the significant bioconversion that occurred for other treatments. Though, free ammonia concentration for 2%AqCsDm and 4%AqCsDm pre-digestates were within the safe limit (< 53 mg/L) relative to other treatments, 8%CaCsDm sufficiently reduced the initial inhibitory concentration to a safe threshold at the cessation of the experiment. Additionally, 8%CaCsDm treatment had the highest VFA bioconversion rate (80%). Therefore, this study demonstrated that 8%CaCsDm treatment could effectively improve reactor performance in solid-state anaerobic co-digestion.