Dry Thermophilic Anaerobic Digestion Research Articles

Thermophilic Fungi as the Microbial Agents of Choice for the Industrial Co-Fermentation of Wood Wastes and Nitrogen-Rich Organic Wastes to Bio-Methane.

The novel industrial approach of co-fermenting wood wastes with agricultural wastes that are rich in nitrogen such as animal manures to produce bio-methane (renewable natural gas) fuel via thermophilic anaerobic digestion mimics an analogous process occurring in lower termites, but it relies instead on thermophilic fungi along with other thermophilic microorganisms comprising suitable bacteria and archaea. Wood microbial hydrolysis under thermophilic temperatures (range of 55 °C to 70 °C) and aerobic or micro-aerobic conditions constitutes the first step of the two-step (hydrolysis and fermentation) dry thermophilic anaerobic digestion industrial process, designated as "W2M3+2", that relies on thermophilic fungi species, most of which grow naturally in wood piles. Eleven thermophilic fungi have been identified as likely agents of the industrial process, and their known growth habitats and conditions have been reviewed. Future research is proposed such that the optimal growth temperature of these thermophilic fungi could be increased to the higher thermophilic range approaching 70 °C, and a tolerance to partial anaerobic conditions can be obtained by modifying the fungal microbiome via a symbiotic existence with bacteria and/or viruses.

Dry Anaerobic Digestion of the Organic Fraction of Municipal Solid Waste: Biogas Production Optimization by Reducing Ammonia Inhibition

The aim of this work is to optimize biogas production from thermophilic dry anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) by comparing various operational strategies to reduce ammonia inhibition. A pilot-scale plug flow reactor (PFR) operated semi-continuously for 170 days. Three scenarios with different feedstock, namely solely OFMSW, OFMSW supplemented with structural material, and OFMSW altered to have an optimal carbon-to-nitrogen (C/N) ratio, were tested. Specific biogas production (SGP), specific methane production (SMP), the biogas production rate (GPR), and bioenergy recovery were evaluated to assess the process performance. In addition, process stability was monitored to highlight process problems, and digestate was characterized for utilization as fertilizer. The OFMSW and the structural material revealed an unbalanced content of C and N. The ammonia concentration decreased when the optimal C/N ratio was tested and was reduced by 72% if compared with feeding solely OFMSW. In such conditions, optimal biogas production was obtained, operating with an organic loading rate (OLR) equal to 12.7 gVS/(L d). In particular, the SGP result was 361.27 ± 30.52 NLbiogas/kgVS, the GPR was 5.11 NLbiogas/(Lr d), and the potential energy recovery was 8.21 ± 0.9 MJ/kgVS. Nevertheless, the digestate showed an accumulation of heavy metals and low aerobic stability.

Effect of microaeration combined with ferric chloride pretreatment on anaerobic digestion of corn stalk

ABSTRACT In this study, microaeration combined with ferric chloride pretreatment was used to improve the methanogenic performance for thermophilic dry anaerobic digestion. Parameter optimization and mechanism analysis were explored for combined pretreatment in anaerobic digestion by response surface methodology and microbial diversity and community. The results showed that both microaeration and ferric chloride had significant effects on the cumulative methane production, and the effect of microaeration was greater than that of ferric chloride. The optimal pretreatment parameters were predicted at oxygen loading rate of 0.76 mL/g VS and ferric chloride addition rate of 4.04 mg/g VS. The methane production of anaerobic digestion was 114.05 mL/g VS with the optimal pretreatment parameters, which was 17.78% higher than that without pretreatment. In addition, microbial community analysis showed that combined pretreatment enhanced methanogenesis by enhancing the hydrogenotrophic pathway.

Anaerobic Digestion of the Organic Fraction of Municipal Solid Waste in Plug-Flow Reactors: Focus on Bacterial Community Metabolic Pathways

The aim of this study is to investigate the performance of a pilot-scale plug-flow reactor (PFR) as a biorefinery system to recover chemicals (i.e., volatile fatty acids (VFAs)), and biogas during the dry thermophilic anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). The effects of the hydraulic retention time (HRT) on both outputs were studied, reducing the parameter from 22 to 16 days. In addition, VFA variation along the PFR was also evaluated to identify a section for a further valorization of VFA-rich digestate stream. A particular focus was dedicated for characterizing the community responsible for the production of VFAs during hydrolysis and acidogenesis. The VFA concentration reached 4421.8 mg/L in a section located before the end of the PFR when the HRT was set to 16 days. Meanwhile, biogas production achieved 145 NLbiogas/d, increasing 2.7 times when compared to the lowest HRT tested. Defluviitoga sp. was the most abundant bacterial genus, contributing to 72.7% of the overall bacterial population. The genus is responsible for the hydrolysis of complex polysaccharides at the inlet and outlet sections since a bimodal distribution of the genus was found. The central zone of the reactor was distinctly characterized by protein degradation, following the same trend of propionate production.

Plug-flow reactor for volatile fatty acid production from the organic fraction of municipal solid waste: Influence of organic loading rate

This work experimentally assessed the production of total and specific volatile fatty acids (VFAs) by dry thermophilic anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) in a semi-continuous pilot-scale plug-flow reactor (PFR). The experimental test compared the two organic loading rates (OLR) of 7.5 and 14 gVS/(L d) for an overall duration of 150 days. The results revealed that OLR positively affects the production of total VFAs, since their overall concentration reached a maximum of 12136 mg/L with OLR of 14 gVS/(L d). In addition, the productivity increased by 150.9% and the yield increased by 49.2% compared to the lowest OLR tested. Propionate dominated during the whole experimental period ranging between 86.2% and 64.4% of total VFAs. As the OLR increased, the concentration of iso-valeric and butyric acids increased as well, accounting for 15.7% and 9.6% of total VFAs, respectively. Meanwhile, the specific biogas production (SGP) decreased from 280.8 ± 72.8–196.3 ± 24.4 NLbiogas/kgVS diminishing by 30.6%, and the oxygen uptake rate (OUR) raised from 46.4 ± 0.6–124.8 ± 10.9 mmolO2/(kgVS h) increasing by 169.1%.

Development of a Sensitivity Analysis method to highlight key parameters of a dry Anaerobic Digestion reactor model

Global sensitivity analysis enables to identify model parameters that have the most significant impact on model outputs and therefore require an estimation effort. This work demonstrates the reliability of a global sensitivity analysis methodology based on Definitive Screening Design and multiple linear regression analysis that requires a low number of runs. The method is applied to a simplified anaerobic digestion model. The model is firstly used to simulate a case study of a thermophilic dry anaerobic digestion of a potential agricultural waste. Then, the influence of the kinetic and mass transfer parameters of the model on the biogas flowrate, the percentage of methane in the biogas and the pH are estimated and discussed. The sensitivity analysis reveals that the slow hydrolysis constant and the upper pH inhibition limit of the hydrolytic biomass are decisive in correctly describing the biogas flowrate. The methane percentage in the biogas slightly varies with kinetic parameters, between 53 % and 55 %. Moreover, the mass transfer coefficient has significant impact on the pH through CO2 desorption. The method simplicity and reliability make its application easy to any type of model.

Performance evaluation and microbial community analysis of microaerobic pretreatment on thermophilic dry anaerobic digestion

Abstract In this study, microaerobic pretreatment (MP) was used to improve the system stability and biogas production performance of the thermophilic dry anaerobic digestion (AD). The results showed that proper MP made the AD have better methane-producing performance and the maximum cumulative methane production was 108.31 mL/g VS with an oxygen load of 5 mL/g VS, which was 13.20 % higher than that of control group (G1, 95.68 mL/g VS). Specific microaerobic conditions promoted the generation of volatile fatty acid (VFA) and reduced propionic acid content in the digestive system. In addition, the volatile solid (VS) removal rate of the digestive substrates was improved in the presence of limited oxygen, which can reduce environmental risks. Microbial community diversity indicated that MP increased the relative abundance of Firmicutes to promote substrate hydrolysis and accelerated the growth of hydrogenotrophic methanogens to improve AD performance.

Effects of woody biochar on dry thermophilic anaerobic digestion of organic fraction of municipal solid waste

This study presents the results of semi-pilot scale anaerobic digestion tests conducted under dry thermophilic conditions with the addition of biochar (6% on fresh mass basis of inoculum), derived from an industrial gasification plant, for determining biogas and biomethane production from organic fraction of municipal solid waste. By using two types of inocula (from a full-scale dry anaerobic digestion plant and from lab-scale biomethanation tests), the obtained experimental results did not show significant increase in methane yield related to the presence of biochar (330.40 NL CH4 kgVS−1 using plant inoculum; 335.41 NL CH4 kgVS−1 using plant inoculum with biochar, 311.78 NL CH4 kgVS−1 using lab-inoculum and 366.43 NL CH4 kgVS−1 using lab-inoculum with biochar), but led to significant changes in the microbial community composition. These results are likely related with the specific biochar physical-chemical features and low adsorption potential.Resulting digestate quality was also investigated: biochar-enriched digestates were characterized by increased biological stability (809 ± 264 mg O2 kgVS−1 h−1 vs. 554 ± 76 mg O2 kgVS−1 h−1 for biochar-free and biochar-enriched digestates, respectively), lower heavy metals concentrations (with the exception of Cd), but higher polycyclic aromatic hydrocarbons content, with a reported maximum concentration of 8.9 mgPAH kgTS−1 for biochar-enriched digestate derived from AD test with lab-inoculum, which could trigger non-compliance with regulation limits for agricultural reuse of digestates. However, phytotoxicity assessments showed a decreased toxicity of biochar-containing digestates when compared to biochar-free digestates.

The influence of the total solid content on the stability of dry-thermophilic anaerobic digestion of rice straw and pig manure

Dry anaerobic digestion is a promising technology for the recycling of agricultural waste to produce energy and fertilizer. Adding water to the substrate enables better handling and avoid inhibition caused by high total solid (TS) content in the reactor; however, it also increases leachate and operational costs. To assess the extent to which the amount of water added can be reduced, it was examined how the TS content in the reactor influenced the production of biogas. A semi-batch dry thermophilic anaerobic digester was fed with substrate (rice straw and pig manure) at a constant organic loading rate, and varied the TS contents (27%, 32%, 37%, and 42%) of the substrate by adding different amounts of water (representing 0–36% of the total substrate). During incubation, the TS content in the reactor gradually increased from 18% to 31%. Biogas production was stable and high (564 ± 13–580 ± 36 N m3 t−1 VS), and there was no accumulation of volatile fatty acids when the TS content of the reactor was between 18% and 27%. However, the rate decreased sharply and propionate and acetate were also produced when the TS content of the reactor exceeded 28%. By applying a simple TS balance model, it was found that stable biogas production could be achieved at a substrate TS content of 32%, at which reactor TS content reached 23% at steady-state condition.

Biogas Production from Distilled Grain Waste by Thermophilic Dry Anaerobic Digestion: Pretreatment of Feedstock and Dynamics of Microbial Community

Distilled grain waste (DGW) eluted from the Chinese liquor making process poses potential serious environmental problems. The objective of this study is to evaluate the feasibility of converting DGW to biogas by thermophilic dry anaerobic digestion. To improve biogas production, the effects of dilute H2SO4 and thermal pretreatment on DGW were evaluated by biochemical methane potential (BMP) tests. The results indicate that 90°C thermal pretreatment provided the highest methane production at 212.7mL/g-VTSadd. The long-term thermophilic dry anaerobic digestion process was conducted in a 5-L separable flask for more than 3years at a volatile total solid (VTS) loading rate of 1g/kg-sludge/d, using synthetic waste, untreated and 90°C thermal pretreated DGW as the feedstock, respectively. A higher methane production, 451.6mL/g-VTSadd, was obtained when synthetic waste was used; the methane production decreased to 139.4mL/g-VTSadd when the untreated DGW was used. The 90°C thermal pretreated DGW increased the methane production to 190.5mL/g-VTSadd, showing an increase of 36.7% in methane production compared with that using untreated DGW. The microbial community structure analysis indicates that the microbial community in the thermophilic dry anaerobic digestion system maintained a similar structure when untreated or pretreated DGW was used, whereas the structure differed significantly when synthetic waste was used as the feedstock.

Effects of different alkalis on hydrolysis of swine manure during dry anaerobic digestion and resultant nutrients availability

Hydrolysis is regarded as the rate-limiting step for dry anaerobic digestion (AD) of organic solid wastes. This study investigated the effect of different alkalis (Ca(OH)2, CaO, KOH and NaOH) on hydrolysis of swine manure during thermophilic dry AD at initial pH 10 and nutrients availability of the digestate by evaluating soluble organics production, hydrolase activity, nitrogen mineralization degree and phosphorus fractionation. Compared to their initial values, addition of Ca(OH)2 promoted the hydrolysis rate by 140% and enhanced volatile fatty acids (VFAs) production by 320%. Nitrogen mineralization was enhanced from 56% of control group to 64% when Ca(OH)2 was applied for initial pH adjustment, while decrease in P bioavailability was unavoidable. Both addition of NaOH and KOH achieved an increase around 250% on soluble total organic carbon (TOC) after 18 days’ fermentation, while little VFAs production and ammonia nitrogen were detected. In addition, the correlation between hydrolase activity and solid organics solubilization was also addressed. Further work is necessary to shed light on the mechanisms of dry AD after alkali addition to manure wastes.

A new approach for concurrently improving performance of South Korean food waste valorization and renewable energy recovery via dry anaerobic digestion under mesophilic and thermophilic conditions

Dry semicontinuous anaerobic digestion (AD) of South Korean food waste (FW) under four solid loading rates (SLRs) (2.30–9.21kg total solids (TS)/m3day) and at a fixed TS content was compared between two digesters, one each under mesophilic and thermophilic conditions. Biogas production and organic matter reduction in both digesters followed similar trends, increasing with rising SLR. Inhibitor (intermediate products of the anaerobic fermentation process) effects on the digesters’ performance were not observed under the studied conditions. In all cases tested, the digesters’ best performance was achieved at the SLR of 9.21kg TS/m3day, with 74.02% and 80.98% reduction of volatile solids (VS), 0.87 and 0.90m3 biogas/kg VSremoved, and 0.65 (65% CH4) and 0.73 (60.02% CH4) m3 biogas/kg VSfed, under mesophilic and thermophilic conditions, respectively. Thermophilic dry AD is recommended for FW treatment in South Korea because it is more efficient and has higher energy recovery potential when compared to mesophilic dry AD.

河川敷で発生する植物バイオマスの高温乾式メタン発酵特性

河川敷で発生する植物バイオマスの高温乾式メタン発酵特性

Mass and Energy Balances of Dry Thermophilic Anaerobic Digestion Treating Swine Manure Mixed with Rice Straw.

To evaluate the feasibility of swine manure treatment by a proposed Dry Thermophilic Anaerobic Digestion (DT-AD) system, we evaluated the methane yield of swine manure treated using a DT-AD method with rice straw under different C/N ratios and solid retention time (SRT) and calculated the mass and energy balances when the DT-AD system is used for swine manure treatment from a model farm with 1000 pigs and the digested residue is used for forage rice production. A traditional swine manure treatment Oxidation Ditch system was used as the study control. The results suggest that methane yield using the proposed DT-AD system increased with a higher C/N ratio and shorter SRT. Correspondently, for the DT-AD system running with SRT of 80 days, the net energy yields for all treatments were negative, due to low biogas production and high heat loss of digestion tank. However, the biogas yield increased when the SRT was shortened to 40 days, and the generated energy was greater than consumed energy when C/N ratio was 20 : 1 and 30 : 1. The results suggest that with the correct optimization of C/N ratio and SRT, the proposed DT-AD system, followed by using digestate for forage rice production, can attain energy self-sufficiency.

Mitigation of Greenhouse Gas Emissions by Water Management in a Forage Rice Paddy Field Supplemented with Dry-Thermophilic Anaerobic Digestion Residue

Dry-thermophilic anaerobic co-digestion (DTAD) can be used to treat forage rice straw and pig manure and generate biogas as an energy source. Solid residue produced from DTAD process can be used as a fertilizer in forage rice fields, while addition of the residue could increase methane (CH4) and nitrous oxide (N2O) emissions from the soil. We evaluated the effects of adding DTAD residue and water management on CH4 and N2O emissions from a forage rice field. Three treatments were evaluated: (a) 100 kg N · ha−1 chemical fertilizer and continuous flooding (CC); (b) residue addition (300 kg N · ha−1 DTAD residue) with continuous flooding (RC); and (c) residue addition with intermittent irrigation (RI). RC and RI showed higher CH4 fluxes than CC throughout the growing period. After a midsummer drainage, RI showed higher soil Eh values and lower CH4 fluxes (mean, 7.6 mg C · m−2 · h−1) than those in RC (mean, 18.6 mg C · m−2 · h−1). Abundance of mcrA gene copy number was not different between RC and RI, suggesting CH4 flux was reduced by suppression of methanogenic activity by intermittent irrigation. Cumulative CH4 emissions during the cultivation period were 105, 509, and 306 kg C · ha−1 in CC, RC, and RI, respectively. N2O fluxes were within detection limits in all treatments. Our results, to our knowledge, are the first to show greenhouse gas emission from forage rice fields supplemented with DTAD residue and of the effectiveness of water management in CH4 mitigation.

Effect of moisture of municipal biowaste on start-up and efficiency of mesophilic and thermophilic dry anaerobic digestion

Methane production from biowaste with 20–30% dry matter (DM) by box-type dry anaerobic digestion and contributing bacteria were determined for incubation at 20, 37 and 55°C. The same digestion efficiency as for wet anaerobic digestion of biowaste was obtained for dry anaerobic digestion with 20% DM content at 20, 37 and 55°C and with 25% DM content at 37 and 55°C. No or only little methane was produced in dry anaerobic reactors with 30% DM at 20, 37 or 55°C.Population densities in the 20–30% DM-containing biowaste reactors were similar although in mesophilic and thermophilic biowaste reactors with 30% DM content significantly less but phylogenetically more diverse archaea existed. Biogas production in the 20% and 25% DM assays was catalyzed by Methanosarcinales and Methanomicrobiales. In all assays Pelotomaculum and Syntrophobacter species were dominant propionate degraders.

Effect of pretreatment and total solid content on thermophilic dry anaerobic digestion of Spartina alterniflora

The effect of pretreatment [thermo-lime with 0.09g Ca(OH)2/g total solid (TS) of biomass at 120°C for 4h and hot water at 120°C for 4h] and TS content on the thermophilic anaerobic digestion of Spartina alterniflora was assessed in six batch reactors and three leaching bed reactors. The componential change in solid biomass was analyzed to understand the changes in biogas production. The biogas production rate but not the biogas yield of the sample pretreated with thermo-lime was improved compared with that of raw and hot-water pretreated samples. The biogas yield (206.8mL/g TS) and production rate constant (k; 0.052d−1) of the hot–water pretreated sample were obviously higher than those of the thermo-lime-pretreated sample (168.3mL/g TS and 0.028d−1) because more biodegradable matter were preserved in the former sample. Dry anaerobic digestion at high TS content caused a high componential reduction. However, the digestion also led to organic metabolite accumulation because of mass transfer limitations, which decreased biogas yield and production rate. A decrease in TS content from 20.8% to 17.9% increased 29.6% of biogas yield and 67.9% of k values. Process stability was enhanced with decreasing TS content.

Biomethanization from sulfate‐containing municipal solid waste: effect of molybdate on microbial consortium

AbstractBACKGROUNDThe effect of molybdate on a microbial consortium of dry thermophilic anaerobic digestion (AD) from sulfate‐containing municipal solid waste was studied.RESULTSThe study showed molybdate inhibition affecting hydrolysis, acidogenesis, and methanogenesis, but the main microbial populations in AD can sustain the molybdate load over a short period of time. Molybdate was not a bactericide for all members of the principal groups, only a few of them are affected. Although all the microbial populations decreased, the weakest groups were sulfate reducing bacteria (SRBs) and butyrate‐utilising acetogens (BUAs) and the most resistant group was propionate‐utilising acetogens (PUAs). Prior to using molybdate, the relative percentages were: Eubacteria:Archaea 80:20; acetogens 25% (BUAs 11% and PUAs 14%) and SRBs 17%. After molybdate addition the relative percentages were: Eubacteria:Archaea were 83:17, acetogens remained over 28% (BUAs 8% and PUAs 20%) and SRBs around 11%. The relation between acetate‐utilising methanogens (AUMs) and hydrogen‐utilising methanogens (HUMs) changed slightly from 55:45 to 53:47.CONCLUSIONAll biochemical reactions in AD were inhibited and an increase in food:microorganism(F:M) ratio was observed. The microorganism's removal rates and growth inhibition rates are indicators of inhibitory effect in all analysed populations by inhibitor addition. © 2013 Society of Chemical Industry

Optimisation of the two-phase dry-thermophilic anaerobic digestion process of sulphate-containing municipal solid waste: Population dynamics

Microbial population dynamics and anaerobic digestion (AD) process to eight different hydraulic retention times (HRTs) (from 25d to 3.5d) in two-phase dry-thermophilic AD from sulphate-containing solid waste were investigated. Maximum values of gas production (1.9 ± 0.2 l H2/l/d; 5.4 ± 0.3 l CH4/l/d and 82 ± 9 ml H2S/l/d) and microbial activities were obtained at 4.5d HRT; where basically comprised hydrolysis step in the first phase (HRT=1.5d) and acidogenic step finished in the second phase as well as acetogenic-methanogenic steps (HRT=3d). In the first phase, hydrolytic-acidogenic bacteria (HABs) was the main group (44-77%) and Archaea, acetogens and sulphate-reducing bacteria (SRBs) contents were not significant; in the second phase (except to 2d HRT), microbial population was able to adapt to change in substrate and HRTs to ensure the proper functioning of the system and both acetogens and Archaea were dominated over SRBs. Decreasing HRT resulted in an increase in microbial activities.

Comparison of mesophilic and thermophilic dry anaerobic digestion of OFMSW: Kinetic analysis

Temperature is a significant variable in anaerobic digestion (AD) since it determines the values of the main kinetic parameters for the process and, hence, the rate of the microbiological process. Thus, in this study, batch AD experiments were carried out, at mesophilic (35°C) and thermophilic (55°C) conditions, with the aim to compare the kinetic of both processes. Tests were performed in dry conditions (concentration of Total Solids (TSs) of 20%) using the Organic Fraction of Municipal Solid Waste (OFMSW) as feedstock.Romero model [1] was used to fit the experimental results from both, the organic matter consumption and the biogas production. This model has been used extensively in the analysis of results of AD process in a wide range of experimental conditions [2–4].The values of the maximum specific growth rate of microorganisms (μMAX) are 27–60% higher for thermophilic process than for mesophilic ones and, therefore, the same level of organic matter degradation and methane production can be achieved in a shorter operating time, 20days in thermophilic instead of 40days in mesophilic. Moreover, the yield coefficient for methane production (αP/S) and the initial amount of active microorganisms (XV0/YX/S) show values 107% and 129% higher, respectively, in thermophilic processes.