Solid-state Anaerobic Digestion Process Research Articles

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.

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.

Impact of continuous leachate recirculation during solid state anaerobic digestion of Miscanthus

Continuous leachate recirculation was performed in a solid-state anaerobic digestion (SS-AD) in an attempt to enhance and improve the biogas (methane) production from Miscanthus sp. Furthermore, microbial community dynamics was analysed, and liaised with the process performance and stability. Results showed that the SS-AD process without leachate recirculation showed significantly higher degradation degree of cellulose/hemicellulose (35% higher) as well as methane yield (65% higher) compared to the leachate recirculation processes. Continuous recirculation led to the transpose of active microbial groups from the main reactor to the leachate holding vessel, a condition which could be attributed to the poor degradation efficiency. Therefore, for the enhancement of biogas production in a SS-AD of structural mono-substrate with leachate recirculated process, the recirculation speed should be carefully chosen and optimized to minimize the disturbance and wash-out of the viable microbial consortium.

Ultrasonic pretreatment on biogas production from wood-dust mahogany (swietenia mahagoni) with solid-state anaerobic digestion method: effect of time and pretreatment temperature

The availability of fossil energy as the main energy source makes its availability running low. One alternative energy source is biomass and it can be converted into biogas through a solid-state anaerobic digestion process. One of the many biomass types found in Indonesia is the wood-dust mahogany. The content of lignin contained in wood-dust mahogany makes the process of hydrolysis runs slowly. This causes the biogas production rate to be slow. This study examined the effects of temperature and duration of ultrasonic pretreatment on the characteristics of wood-dust mahogany and the rate of biogas formation along with kinetic study. This research was conducted in three stages, beginning with characterization stage to know the character of wood-dust mahogany, followed by ultrasonic pretreatment stage with time variation (10,20,30) minutes without heating and with heating temperature 70°C. The last stage was fermentation by using bioreactor for 60 days. The biogas produced was measured volume in every two days and the data obtained were used to create a biogas production kinetics simulation by using Gompertz and Richards modification models. The results of the evaluation indicated that the ultrasonic pretreatment process leaded to changes in surface morphology and wood-dust mahogany structure has a positive impact on increasing the rate of biogas formation. The longer the time and the higher the temperature of the ultrasonic pretreatment leaded to an increase in the rate of biogas production. The kinetic model of Richards modification equation gave the result of R2 0.999-0.985 value better than Gompertz modification equation model which is only 0.998-0.968.

Enhancement of the solid-state anaerobic digestion of rice straw by liquor supplementation

Solid-state anaerobic digestion (SS-AD) has gained attention in recent years because it is robust, cheap and easy to operate. However, at high loads, the SS-AD is often plagued by acidification and poor methane yields. Mesophilic and thermophilic SS-AD at the different substrate to inoculum ratios (S/I) aided by liquor supplementation was studied in batch mode. Results demonstrated that the liquor supplementation reinvigorated the failed or inhibited SS-AD processes giving methane yields as high as 260.3 ± 5 mL CH4/g VS and improved process stability evidenced low VFA accumulation (˂1 g/L). The achieved methane yield was 85% of the biochemical methane potential achieved under unlimiting batch assay. This study, therefore, revealed that the methane yield in an SS-AD of lignocellulosic biomass can be significantly boosted at high loads by simply adding recycled water or sludge supernatant especially in an inhibited SS-AD process.

Effect of inoculum and substrate/inoculum ratio on the performance and methanogenic archaeal community structure in solid state anaerobic co-digestion of tomato residues with dairy manure and corn stover

Effects of methanogenic community of inoculum (liquid anaerobic digestion effluent (L-AD effluent), waste activated sludge (WAS), and anaerobic granular sludge (AGS)) and substrate/inoculum ratio (S/I) on reactor performance in solid state anaerobic digestion (SS-AD) were investigated. L-AD effluent, which can provide sufficient microbes and enough buffering capacity to the reactor at an S/I ratio of 6, was found to quickly initiate SS-AD processes. The highest methane production was obtained in reactor inoculated with WAS at an S/I ratio of 2. Higher volatile fatty acids and total ammonia nitrogen concentrations were found when AGS was used as inoculum, which led to a low methane production. Methanosaetaceae, Methanosaetaceae, and Methanosaetaceae together with Methanobacteriaceae were the dominant methanogens in reactors inoculated with L-AD effluent, WAS, and AGS, respectively. These findings suggest among the three inoculum, L-AD effluent is the most effective inoculum for SS-AD of on farm organic waste.

Poultry Litter Solid State Anaerobic Digestion: Effect of Digestate Recirculation Intervals and Substrate/Inoculum Ratios on Process Efficiency

This study evaluated the effect of the substrate:inoculum ratio and digestate recirculation conditions on the biogas and methane yield, free ammonia concentration and solid phase agronomic quality (after treatment) of poultry litter solid state anaerobic digestion (SSAD). Experimental tests were conducted using a central composite design (2²), with four trials at the factorial points and three at the central points, using poultry litter as substrate that was collected after 12 cycles of broiler production (TS 76% (w.w-1)). Three laboratory-scale reactors containing 3 kg of poultry litter each were operated at mesophilic conditions (37°C) and seven experimental runs were performed at retention time of 30 days each. There were three substrate:inoculum ratios (1:1; 1:1.66 and 1:3) and three daily recirculation intervals (2, 3 and 4 times per day), and each recirculation event lasted 15 min. The highest biogas and methane yields were183 LNbiogas.kgVSadd-1and 74 LNmethane.kgVSadd-1, respectively, and they were obtained at the substrate:inoculum ratio of 1:3 with a digestate recirculation frequency of four times a day. Digestate recirculation was the variable that influenced the concentration of free ammonia; the most frequently recirculated tests had lower concentrations (below 60 mgNH3.L-1). After the SSAD process, we identified a transfer of nutrients (N, P, K) from the solid phase to the liquid phase. The nutrient concentrations in the solid phase (Nout = 11 g.kg-1, Kout=5 g.kg-1 and Pout = 7 g.kg-1) indicated that the digested poultry litter still has potential for use in fertilization. In this study, it was estimated that 90 m³biogas.tonspoultrylitter-1 was generated using SSAD. Whereas 100 tons of poultry litter are produced after 12 production cycles, the biogas generation capacity reaches 9,000 m³/year. In this scenario, farmers can use biogas from poultry litter SSAD as an additional source of energy.n capacity reaches 9000 m³/year. In this scenario, farmers can use biogas from poultry litter SSAD as an additional source of energy.

Optimization and microbial community analysis for production of biogas from solid waste residues of palm oil mill industry by solid-state anaerobic digestion

This study investigated the improvement of biogas production from solid-state anaerobic digestion (SS-AD) of oil palm biomass by optimizing of total solids (TS) contents, feedstock to inoculum (F:I) ratios and carbon to nitrogen (C:N) ratios. Highest methane yield from EFB, OPF and OPT of 358, 280 and 324m3CH4ton−1VS, respectively, was achieved at TS content of 16%, C:N ratio of 30:1 and F:I ratio of 2:1. The main contribution to methane from biomass was the degradation of cellulose and hemicellulose. The highest methane production of 72m3CH4ton−1 biomass was achieved from EFB. Bacteria community structure in SS-AD process of oil palm biomass was dominated by Ruminococcus sp. and Clostridium sp., while archaea community was dominated by Methanoculleus sp. Oil palm biomass has great potential for methane production via SS-AD.

Biohythane Production from Co-Digestion of Palm Oil Mill Effluent with Solid Residues by Two-Stage Solid State Anaerobic Digestion Process

Biohythane production from co-digestion of palm oil mill effluent (POME) with empty fruit bunches (EFB) and decanter cake (DC) by two-stage solid state anaerobic digestion process was investigated. The first stage, thermophilic hydrogen fermentation of co-digestion of POME with DC at 10, 30, 50 and 70% of DC in POME has hydrogen yield of 16, 14, 3 and 1ml H2/gVS, respectively. Co-digestion of POME with 10% DC gave the best hydrogen yield of 16ml H2/gVS with hydrogen production of 1.4 m3/ton mixed waste. Co-digestion of POME with 10% EFB gave the best hydrogen yield of 16ml H2/gVS with hydrogen production of 1.4 m3/ton mixed waste. The effluent from the hydrogen production was further converted to methane in the second stage. The methane yield from POME mixed withn10% DC was 391 mlCH4/gVS and from POME mixed with 10% EFB was 240 mlCH4/gVS. The hydrogen and methane content in biogas was 25.33% and 65.21% respectively. The two-stage solid stage anaerobic digestion process can be removal efficiently of cellulose 57-59%, hemicelluloses 35-40% and lignin 16-27%. Result obtained make practical use for the development of two-stage anaerobic digestion process providing hydrogen and methane co-production from palm oil waste residues.

Biogas production from microbial-alkali pretreated corn stover by solid-state anaerobic digestion

Corn stover pretreated by Ceriporiopsis subvermispora was used as substrate to enhance biogas production via solid state anaerobic digestion (SS-AD). Effects of temperature, inoculum volume and alkaline concentration on the biogas production profermance were investigated. The results showed that pretreatment of corn stover by C. subvermispora benefited the biogas production. The optimal conditions were temperature 35°C, inoculum 10:1 (w/w) and adding 5.0% of alkali, under which the maximum productions were obtained for daily and cumulative biogas of 14.07 L/kg VS and 211.09 L/kg VS. During the SS-AD process, the total solids (TS) and volatile solid (VS) were significantly degraded. The volatile fatty acids (VFA) concentration increased to 106 mmol/L and alkalinity decreased by about 23%. The results collectively suggested that microbial-alkali pretreatment of corn stove combining mesophilic condition could be a promising way to produce biogas in SS-AD. Keywords: solid-state anaerobic digestion, corn stover, Ceriporiopsis subvermispora, microbial-alkali pretreatment, biogas production DOI: 10.3965/j.ijabe.20150805.2032 Citation: Zhao P X, Cui F J, Bu L X, Jiang J X. Biogas production from microbial-alkali pretreated corn stover by solid-state anaerobic digestion. Int J Agric & Biol Eng, 2015; 8(5): 96－104.

Integration of Shiitake cultivation and solid-state anaerobic digestion for utilization of woody biomass

Pretreatment technologies that can not only reduce the recalcitrance of woody biomass but also achieve a high benefit-cost ratio are desirable for bioenergy production from woody biomass. In this study, an integrated process was proposed and conducted by pretreating woodchips via Shiitake cultivation for improved methane yield during solid-state anaerobic digestion (SS-AD), and simultaneously producing mushrooms as a high-value co-product. Shiitake cultivation using woodchips as the main substrate ingredient obtained mushroom yields comparable to those using a commercial substrate. Enzymatic digestibility and cumulative methane yields (133–160Lkg−1VS during 62days of SS-AD) of pretreated substrates (spent mushroom substrate) were at least 1.5times as high as those of untreated woodchips. Compared to a sole SS-AD process, the integrated Shiitake cultivation/SS-AD process increased methane production and solid waste reduction per kilogram of woodchips by about 1.5 and 8times, respectively.

The effects of initial substrate concentration, C/N ratio, and temperature on solid-state anaerobic digestion from composting rice straw

This study investigated the possibilities of improving the biogasification from solid-state anaerobic digestion (SS-AD) of composting rice straw (RS) based on the optimized digestion temperature, initial substrate concentration (ISC) and C/N ratio. RS compounds, such as lignin, cellulose, and hemicellulose, were significantly degraded after composting. A significant interactive effect of temperature, ISC and C/N ratio was found on the biogasification of SS-AD of composting RS, and a maximum biogas production was achieved at 35.6°C, with a 20% ISC and a C/N ratio of 29.6:1. The verification experiment confirmed the optimization results. High-throughput sequencing analysis indicated that microbial communities in the SS-AD mainly consist of Methanobacteria, Bacteroidia, Clostridia, Betaproteobacteria, and Gammaproteobacteria. A dominant Methanobacteria was shifted from Methanobacterium to Methanoculleus during the SS-AD process. This study provides novel information about the interdependent effects and microbial behavior of AD.

Substrate milling pretreatment as a key parameter for Solid-State Anaerobic Digestion optimization

The effect of milling pretreatment on performances of Solid-State Anaerobic Digestion (SS-AD) of raw lignocellulosic residue is still controverted. Three batch reactors treating different straw particle sizes (milled 0.25mm, 1mm and 10mm) were followed during 62days (6 sampling dates). Although a fine milling improves substrate accessibility and conversion rate (up to 30% compared to coarse milling), it also increases the risk of media acidification because of rapid and high acids production during fermentation of the substrate soluble fraction. Meanwhile, a gradual adaptation of microbial communities, were observed according to both reaction progress and methanogenic performances. The study concluded that particle size reduction affected strongly the performances of the reaction due to an increase of substrate bioaccessibility. An optimization of SS-AD processes thanks to particle size reduction could therefore be applied at farm or industrial scale only if a specific management of the soluble compounds is established.

Solid state anaerobic digestion as a possible solution for managing existing mechanical biological treatment plants in a more efficient way: a real case analysis

The exploitation of Mechanical Biological Treatment is quite diffused for treating fractions of Non-Differentiated Waste. A large part of the Italian Mechanical Biological Treatment facilities operate mainly by reducing and stabilizing the Non-Differentiated Waste mass before landfilling. This way of managing Mechanical Biological Treatment can be improved by the adopting a new treatment section, based on the Solid State Anaerobic Digestion process. In this way, the Waste Organic Fraction arising from the mechanical sorting of the Non-Differentiated Waste can be treated before the aerobic stabilization section of the existing Mechanical Biological Treatment. In Italy more than 40% of the working Mechanical Biological Treatment facilities have features suitable for being upgraded with a new Solid State Anaerobic Digestion section. In these plants the amount of the rapidly biodegradable fraction is about 1,100,000 tonnes per year, leading to the production of about 300 GWh of renewable energy. The results concerning a real case study show that, with the adoption of a new Solid State Anaerobic Digestion section, about 150 kWh of electric energy would be able to be produced per each tonne of Waste Organic Fraction. Furthermore, there would be a significant reduction in the Organic Load Rate [kgVS/m3*day] for the existing aerobic section of the plant, leading to additional savings of 160-320 kWh per day, depending on the amount of Waste Organic Fraction diverted from the Solid State Anaerobic Digestion. Results from the economic analysis show that the Solid State Anaerobic Digestion treatment cost ranges from about 6 up to 23 € per each tonne of Non-Differentiated Waste entering the existing Mechanical Biological Treatment plant.