RESUMEN

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.

RESUMEN

Dry anaerobic digestion (dry-AD) is an attractive process for solid wastes such as agri-food waste. However, some limitations mainly associated to lack of effective mixing, can hinder the methane production capacity of the systems. Bulking agent (BA) has been proposed as a solution to the compaction issues in systems without mechanical agitation, such as leaching bed reactors. However, effects of BA are still not clear, and, thus, the factors to consider for its dose has not been optimized yet. This work studies the effect of BA in dry-AD. Two substrates with different characteristics were proposed as models, bean peel as a lignocellulosic substrate and a mixture of food waste as a readily biodegradable substrate. Inert plastic rings were used as BA at different BA:S ratios. Assessed BA:S ratio did not affect the performance of methane production for the lignocellulosic waste, but it did significantly affect to the easily biodegradable substrate, showing up to a 28% of methane production increase. This result could be due to the presence of lignocellulosic compounds in the bean peel, behaving like a natural BA. In assays with an increased bed height, the compaction of the system was more severe, resulting in the rapid acidification of the processes. At these conditions, the positive effect of BA addition was more marked, allowing methane production and no acidification of the system. Thus, the addition of BA is a suitable strategy for improving methane production or stability in dry-AD systems without requiring the stirring of the systems.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

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 2-15 g 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.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

Solid state anaerobic digestion (SSAD) of lignocellulosic biomass may be attractive solution for its valorisation. Compared to liquid state anaerobic digestion (LSAD), SSAD can handle higher organic loading rates (OLR), requires a less water and smaller reactor volume. It may require lower energy demand for heating or mixing and has higher volumetric methane productivity. Besides numerous benefits of SSAD processes and progress in system design, there are still obstacles, which need to be overcome for its successful implementations. This review aims to compile the recent trends in enhancing the bioconversion of agricultural stubbles in SSAD. Several pretreatment procedures used to breaking lignin and cellulose complex, method to overcome carbon to nitrogen ratio imbalance, use of carbon-based conducting materials to enhance Volatile Fatty Acids (VFA) conversion and additives for achieving nutrient balance will be discussed in this review. Leachate recirculation and its impacts on SSAD of agricultural stubbles are also discussed.

Asunto(s)

RESUMEN

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 0.3 L/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.

Asunto(s)

RESUMEN

The influence of magnetite nanoparticle (nFe3O4) concentrations (20, 50, and 75 mg/L) on reactor performance and retention time was investigated for the first time in an initially upset solid-state anaerobic batch (SSAB) reactor. nFe3O4 mitigated acidification threat, enhanced reactor stability, ensured rapid volatile fatty acids bioconversion, and modified microbial community. The impacts reduced retention time by 27 days relative to the control. Of the nFe3O4 concentrations, 20 mg/L had the highest hemicellulose degradation (93%) and methane yield (191.2 L/kg VS) with no threat to anaerobic microbes. Besides, existing kinetic models, novel models equally well-described methane yield with low root mean square errors (RMSE) < 1.2 and high coefficients of determination (R2) > 98%, therefore could be used for downstream applications. This study provides useful information on the impact of nFe3O4 on reactor stability and reactor performance in an initially upset SSAB reactor.

Asunto(s)

RESUMEN

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.

Asunto(s)

RESUMEN

In this work, techno-economic evaluation of anaerobic digestion (AD) system (8000 metric tons (MT)/year) with singular (dairy manure), binary (dairy manure and corn stalk), and ternary mixture (dairy manure, corn stalk, and tomato residues) under bio-methane and combined heat and power (CHP) pathways based on a plant service life of 20 years were carried out. Solid state-AD (SS-AD) of ternary mixture improved the efficiency of investment, benefited the digestate price, and was shown to be economic viability. The introduction of a CHP unit highly improved the economics of SS-AD. SS-AD of the binary mixture under CHP pathway was able to compensate the initial required investment, however was not financially attractive under bio-methane pathway. Besides, SS-AD of the ternary mixture under CHP pathway had higher net present value (NPV) ($0.60 million vs $0.40 million) and internal rate of return (IRR) (23% vs 20%) than that under bio-methane pathway.

Asunto(s)

RESUMEN

The configuration of the reactor influences the digestion process and thus the product yields; other factors such as the rate of biogas production or biogas loss also affect the process specifically with high solid configuration. With these in mind, the ORganic WAste REsearch (ORWARE) anaerobic digestion sub-model was modified to be able to study solid-state anaerobic digestion (SS-AD) (using plug-flow reactor). The simulation results from the updated model agreed with the operational data with respect to methane yield, digestate yield and energy turnover. The model was found to be sensitive to changes in feedstock composition but to a lesser extent to changes in process temperature and retention time. By applying the model on several cases of liquid anaerobic digestion (L-AD), it was noticed that L-AD at mesophilic condition with 25 retention days seemed to be superior to other cases of L-AD with regard to energy turnover. However, even if similar methane production were observed for L-AD and SS-AD, the model suggested higher energy turnover for the case of SS-AD at thermophilic condition, being 10% more in average in comparison with cases of L-AD.

Asunto(s)

RESUMEN

A high concentration of accumulated volatile fatty acids (VFAs) is one of the most important factors resulting in reactor failure during solid-state anaerobic digestion. In this study, the feedstock-to-inoculum (F/I) ratio (0.5, 2, 3, 4 and 6) and the recovery method after failure (biochar addition or inoculum addition) were investigated in batch solid-state anaerobic digestion fed with rice straw and pig urine. An F/I ratio of 3 was the threshold for stable operation, while the reactors failed at F/I ratios of 4 and 6 because of high accumulated VFAs concentrations (above 30 g HAc/kg). Biochar addition (10% or 20% (wet weight) of the mixture) was as effective as inoculum addition (by adjusting the F/I ratio to 2 or 3) in promoting VFAs degradation in failed reactors within a short period (<1 day). The buffering capacity of biochar was important in promoting VFAs degradation.

Asunto(s)

RESUMEN

Biogas production of palm oil mill effluent (POME) and empty fruit bunches (EFB) was performed by coupled liquid (L-AD) and solid-state (SS-AD) anaerobic digestion processes. POME was fed to L-AD digester, while mixed of effluent from L-AD and EFB was fed to SS-AD digester. The maximum overall methane production of 60.9 m3-CH4·ton-1 waste was obtained at an optimal hydraulic retention time of 30 days and an organic loading rate of 1.66 gVS·L-1-reactor·d-1 for L-AD and 6.03 gVS·L-1-reactor·d-1 for SS-AD with L-AD effluent recycling rate of 16.7 mL·L-1-reactor·d-1. The bacterial community in the L-AD reactor was different from the SS-AD reactor, while the archaeal community was similar in both reactors. Synergistaceae, Caldicoprobacteraceae and Lachnospiraceae were increased in the SS-AD reactor. Coupling L-AD and SS-AD is able to increase energy production by 29% and 71% compared to the L-AD and SS-AD alone, respectively, with no outsource SS-AD inoculum required.

Asunto(s)

RESUMEN

Cellulosic substrates such as dairy cow manure often yield low volumes of biogas and low concentrations of methane when digested anaerobically. Thermal pretreatment of dairy cow manure was investigated to determine if pretreatment temperature and duration can be optimized to maximize biogas yield and methane concentration. A central composite rotatable design was used to select combinations of temperature and duration. Based on measured data, statistical models were generated to estimate the biogas yield and methane concentration during digestion. The highest biogas yields were from the untreated samples and samples treated at the center temperature and duration of the statistical model (125 °C, 37.5 min). The model predicted the optimum pretreatment conditions of 140 °C for 30 minutes. Under the conditions of this experiment, temperature and duration had no significant effect on the biogas yield and methane concentration. This lack of significance may indicate that thermal pretreatment may be an unnecessary step in the anaerobic digestion of dairy cow manure, which could reduce capital and operating costs for the industry.

RESUMEN

High-solids anaerobic co-digestion (HS-AcD) has the potential to recover energy and reduce environmental impacts of the organic fraction of municipal solid waste and waste activated sludge. We investigated the impact of substrate to inoculum (S/I) ratios, alkalinity sources (sodium bicarbonate and oyster shells), co-substrate mixing ratios and inoculum acclimation on HS-AcD of food waste, yard waste, and waste activated sludge using batch studies. Long-term HS-AcD performance was evaluated under the optimal conditions through a semi-continuous biodigester study with leachate recirculation. The digester with S/I = 1 using a mixture of crushed oyster shells and sodium bicarbonate as alkalinity sources had the highest methane yields (183 mL CH4/g VS). Addition of waste activated sludge to food waste and yard waste alleviated acidification (pH 6.86 ±â€¯0.12) during the start-up period, which and improved digester stability. Mixtures with FW/YW/WAS = 0.8:1.7:0.5 had higher methane yields (134 ±â€¯15 mL CH4/gVS) than mixtures with FW/YW/WAS = 1:1:1, but required a longer time (10 days) for self-recovery from volatile fatty acid inhibition. The use of an acclimated inoculum eliminated the lag time during start-up and produced 38% higher methane yield. In the semi-continuous biodigester, an average volatile solids reduction of 38% and methane yield of 186 mL/gVS was achieved. Improved performance in the semi-continuous biodigester compared with batch reactors was likely due to leachate recirculation, which can improve mass transfer of substrates to the microbial community. Digestate produced from HS-AcD of waste organics had a 1.7-2.3 fold higher nitrogen, similar phosphorous and 0.2-0.3 fold lower potassium content than commercially available bioorganic fertilizer.

Asunto(s)

RESUMEN

In this study, effect of hardwood biochar on solid state anaerobic digestion of wheat straw has been investigated. The concentration of biochar was 5, 10, 15, 20, 25 and 30 g/L and added in inoculum along with wheat straw for anaerobic action. Results showed that 10 g/L of hardwood biochar led to 2-fold increment in methane yield (223 L/kg VS) compared to the control (110 L/kg VS). However, increasing the concentration of hardwood biochar did not help in significant increase in methane yield and raised pH and alkalinity up to 8.3 and 24.3 g/L respectively. Principal component analysis showed that methane yield is positively correlated with volatile solid reduction while biochar loading is directly correlated with pH as well as alkalinity and inversely correlated with total volatile fatty acid. This study revealed that biochar may help to maintain syntrophy in the anaerobic reactor and enhance methane yield significantly.

Asunto(s)

RESUMEN

Mixing is an important operation in solid-state anaerobic digestion (SS-AD) to improve the mass transfer of the solid phase. This study proposed simple turning by loader in common garage-type digester without commonly used mixer or percolation system (simplified SS-AD). In simplified-SS-AD, turning is conducted in open condition. Thus, oxidation of anaerobic sludge during turning would influence digestion performance. Therefore, in this study, the effect of turning wastes by mixing during digestion on a simplified SS-AD fed with rice straw and pig urine was investigated. Four different mixing frequency levels-no mixing (M0) and mixing once a day (M-1/1), once every 3 days (M-1/3) and once a week (M-1/7)-were conducted. Methane yields of M0, M-1/3 and M-1/7 were comparable with each other. Methane yield and lag period of M-1/1 were approximately 61% and 155% of M0 (351.2  mL/g VS and 4.7 days), respectively. Furthermore, the chemical oxygen demand (COD) of acetate accumulated in the digestate of M-1/1 was comparable to the difference in the COD of methane production between M-1/1 and the other treatments. Mixing every day also resulted in a higher oxidation-reduction potential and carbon dioxide content. These findings suggest that methanogenesis was inhibited in M-1/1 by frequent mixing in the atmosphere. Net energy analysis of SS-AD plant operation showed that M0 can obtain the highest net energy gain, whereas net energy production of M-1/7 was reduced by rewarming after mixing. Therefore, no mixing is the most effective approach for the proposed simplified process.

Asunto(s)