Fermentation CH4 Research Articles

Improved Biohythane Production from Rice Straw in an Integrated Anaerobic Bioreactor under Thermophilic Conditions

This study evaluated the feasibility of continuous biohythane production from rice straw (RS) using an integrated anaerobic bioreactor (IABR) at thermophilic conditions. NaOH/Urea solution was employed as a pretreatment method to enhance and improve biohythane production. Results showed that the maximum specific biohythane yield was 612.5 mL/g VS, including 104.1 mL/g VS for H2 and 508.4 mL/g VS for CH4, which was 31.3% higher than the control RS operation stage. The maximum total chemical oxygen demand (COD) removal stabilized at about 86.8%. COD distribution results indicated that 2% of the total COD (in the feed) was converted into H2, 85.4% was converted to CH4, and 12.6% was retained in the effluent. Furthermore, carbon distribution analysis demonstrated that H2 production only diverted a small part of carbon, and most of the carbon flowed to the CH4 fermentation process. Upon further energy conversion analysis, the maximum value was 166.7%, 31.7 times and 12.8% higher than a single H2 and CH4 production process. This study provides a new perspective on lignocellulose-to-biofuel recovery.

Evaluation of a novel pretreatment of NaOH/Urea at outdoor cold-winter conditions for enhanced enzymatic conversion and hythane production from rice straw

A novel pretreatment using NaOH/Urea (NU) solution at outdoor cold-winter conditions was developed to enhance the enzymatic saccharification and hythane production from rice straw (RS). Results revealed that the reducing sugar conversion of RS reached 90.02% after NU pretreatment at outdoor freezing temperature. Chemical composition analysis showed that the lignin removal was up to 62.74% with cellulose and hemicellulose loss of 0.56% and 18.87% after 3%–6% NU pretreatment at 100% solid loading for 3 months. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis confirmed that the surface of pretreated RS exposed more cellulose and hemicellulose due to the disruption of resistant structure of lignocellulose. Subsequently, the enzymatic hydrolysate of pretreated RS was used as substrate to produce hythane by two-stage fermentation with the yield of 225.1 mL H2/g sugar and 112.8 mL CH4/g sugar. The energy conversion efficiency of hythane fermentation attained 10.4%, which was 22.8% and 190.5% higher than that for single H2 and CH4 fermentation. These results demonstrated that NU pretreatment at outdoor cold-winter conditions was practically and feasible way for improved hythane recovery from lignocellulosic biomass.

In situ integration of microbial electrochemical systems into anaerobic digestion to improve methane fermentation at different substrate concentrations

Microbial electrochemical system (MES) was integrated into anaerobic digestion (AD) to improve the overall process efficiency by enhancing methane (CH4) production. CH4 fermentation at various glucose concentrations (2, 4, 8 and 10 g/l) was evaluated along with corresponding control (without electrodes) operations. The maximum CH4 yield of 0.34 l- CH4/g COD was obtained with both 2 and 4 g/l glucose concentrations (MES), which was about 1.4 and 2.4 times, respectively, higher than the values obtained with corresponding control operations. However, at 10 g/l, similar performance (∼0.07 l- CH4/g COD) was observed with both control and MES operations, which might be due to pH drop occurred by volatile fatty acids (VFAs) buildup in the process. Substrate removal was amplified in the presence of MES with faster degradation of VFAs at all substrate concentrations except 10 g/l. This enhanced utilization of VFAs in the MES process is an important aspect to recover from initial pH drops, especially at higher substrate concentration to maintain the optimum pH for methane fermentation. The current generation and cyclic voltammetric profiles suggest that the enhanced CH4 production in MES was attributed to the bioelectrochemical reactions on the electrodes.

Mitigating Greenhouse Gas and Ammonia Emissions from Beef Cattle Feedlot Production: A System Meta-Analysis.

Beef cattle production systems are the largest contributors of greenhouse gas (GHG) and ammonia (NH3) emissions in the livestock industry. Here, we present the first meta-analysis and integrated assessment of gaseous emissions and mitigation potentials for a typical beef cattle feedlot system, including methane (CH4), nitrous oxide (N2O), and NH3 losses from enteric fermentation and manure management based on data from 104 studies. A total of 14 integrated emission factors (EF) and the mitigation efficiencies (ME) of 17 available options were provided. The estimated GHG and NH3 emissions from the baseline feedlot system were 2786 ± 108 kg carbon dioxide equivalents (CO2-eq) per animal unit (AU) per year and 49.1 ± 1.5 kg NH3 AU-1 year-1, respectively. Enteric CH4 fermentation and manure on the feedlot contributed 67.5% and 80.8% of the total system GHG and NH3 emissions, respectively. The highest ME values were found for lipid additives for enteric CH4 fermentation and urease inhibitor additives (UI) for NH3 emissions from manure on the feedlot, being -14.9% ( p < 0.05) and -59.5% ( p < 0.001), respectively. The recommended mitigation combinations of a low-crude-protein (CP) diet and a UI additive for manure on the feedlot could reduce the GHG of the system by 4.9% and NH3 by 50.9%. The results of this study have important implications for developing sustainable beef cattle feedlot systems from the viewpoint of GHG and NH3 mitigation.

Enhancement of methane production from various microalgae cultures via novel ozonation pretreatment

In this work, the application of ozone, an unexplored pretreatment to improve methane production from three mixed microalgae sources was investigated. Ozonation at various, culture-dependent dosages was employed and its impact on the efficiency of subsequent anaerobic digestion was examined in comparison with untreated biomass. Regardless of the O3 pretreatment conditions, the methane yield in all cases could be increased by various extents (6–66%). The highest methane production (432.7mLCH4g−1VSalgal, equaling to 259.6mLCH4g−1CODin) was attained with the culture composed of 35% Scenedesmus, 30% Dictyosphaerium, 15% Keratococcus, 10% Oscillatoria, 8% Monoraphidium and 2% Nitzchia, using the highest dosage of ozone (382mgO3g−1VSalgal) for pretreatment. Electron microscopic assessment revealed the devastating effect of O3 on algal cell wall structure and integrity, which was thus identified as the key-contributor to the improvement of CH4 fermentation.

Enhanced energy recovery from cassava ethanol wastewater through sequential dark hydrogen, photo hydrogen and methane fermentation combined with ammonium removal

Cassava ethanol wastewater (CEW) was subjected to sequential dark H2, photo H2 and CH4 fermentation to maximize H2 production and energy yield. A relatively low H2 yield of 23.6mL/g soluble chemical oxygen demand (CODs) was obtained in dark fermentation. To eliminate the inhibition of excessive NH4+ on sequential photo fermentation, zeolite was used to remove NH4+ in residual dark solution (86.5% removal efficiency). The treated solution from 5gCODs/L of CEW achieved the highest photo H2 yield of 369.7mL/gCODs, while the solution from 20gCODs/L gave the lowest yield of 259.6mL/gCODs. This can be explained that photo H2 yield was correlated to soluble metabolic products (SMPs) yield in dark fermentation, and specific SMPs yield decreased from 38.0 to 18.1mM/g CODs. The total energy yield significantly increased to 8.39kJ/gCODs by combining methanogenesis with a CH4 yield of 117.9mL/gCODs.

Enhanced Productions and Recoveries of Ethanol and Methane from Food Waste by a Three-Stage Process

A three-stage process that consisted of saccharification, ethanol fermentation of the saccharified liquid, and anaerobic treatment of the saccharified residue to convert food waste (FW) to ethanol and CH4 was developed. Results revealed that high sugar recovery (i.e., 61.7%) from FW could be achieved after saccharification and 15.2% saccharified sugar was retained in saccharified residue after solid–liquid separation. A high ethanol yield was obtained during ethanol fermentation of the saccharified liquid. This high yield indicates the superiority of the system. The ethanol productivity in the ethanol fermentation stage was 0.9 g L–1 h–1. A CH4 yield of 248.4 mL/g of volatile solid (VS) was achieved in the CH4 fermentation stage, whereas that in the single-stage fermentation system was 252.6 mL/g of VS. A comparison of the two fermentation systems based on material balance and energy outcome demonstrated that the three-stage process achieved a 27.5% increase in the FW decomposition rate, a 51.8% reduction...

혐기성 수소발효를 결합한 생물학적 2단공정의 유기성폐자원 처리 및 바이오에너지 생산

This study was performed to investigate the application of dark H2 fermentation to two-stage bioprocesses for organic waste treatment and energy production. We reviewed information about the two-stage bioprocesses combining dark H2 fermentation with CH4 fermentation, photo H2 fermentation, microbial fuel cells (MFCs), or microbial electrolysis cells (MECs) by using academic information databases and university libraries. Dark fermentative bacteria use organic waste as the sole source of electrons and energy, converting it into H2. The reactions related to dark H2 fermentation are rapid and do not require sunlight, making them useful for treating organic waste. However, the degradation is not complete and organic acids remain. Thus, dark H2 fermentation should be combined with a post-treatment process, such as CH4 fermentation, photo H2 fermentation, MFCs, or MECs. So far, dark H2 fermentation followed by CH4 fermentation is a promising two-stage bioprocess among them. However, if the problems of manufacturing expenses, operational cost, scale-up, and practical applications will be solved, the two-stage bioprocesses combining dark H2 fermentation with photo H2 fermentation, MFCs, or MECs have also infinite potential in organic waste treatment and energy production. This paper demonstrated the feasibility of two-stage bioprocesses combining dark H2 fermentation as a novel system for organic waste treatment and energy

Microalgae-bacteria flocs (MaB-Flocs) as a substrate for fermentative biogas production

Biogas production from the microalgae-bacteria flocs (MaB-Flocs) in batch reactors was conducted in this study. A batch test was performed to determine optimum inoculums that were taken from a running biogas plant (BP), a municipal wastewater treatment plant (MWTP) and a river sediment (RS). The maximum biogas yield (304.83±4.23mL per gram volatile solids introduced (mLg-VS−1)) was obtained with the inoculum from MWTP. Subsequently, the effect of substrate–inoculum (S/I) ratios, temperature and pre-treatment methods on fermentative biogas and methane production was investigated. The optimum S/I ratios and incubation temperature were determined as 0.2gVSsubstrate/gVSinoculum and 37±1°C, respectively. The results of the CH4 fermentation show that the methane yields could be increased from 216.72±3.52mLCH4g-VS−1 to 271.34±6.65mLg-VS−1 by using enzymatic pre-treatment at the S/I ratio of 0.2gVSsubstrate/gVSinoculum and mesophilic conditions.

A Critical Assessment of Microbiological Biogas to Biomethane Upgrading Systems.

Microbiological biogas upgrading could become a promising technology for production of methane (CH(4)). This is, storage of irregular generated electricity results in a need to store electricity generated at peak times for use at non-peak times, which could be achieved in an intermediate step by electrolysis of water to molecular hydrogen (H(2)). Microbiological biogas upgrading can be performed by contacting carbon dioxide (CO(2)), H(2) and hydrogenotrophic methanogenic Archaea either in situ in an anaerobic digester, or ex situ in a separate bioreactor. In situ microbiological biogas upgrading is indicated to require thorough bioprocess development, because only low volumetric CH(4) production rates and low CH(4) fermentation offgas content have been achieved. Higher volumetric production rates are shown for the ex situ microbiological biogas upgrading compared to in situ microbiological biogas upgrading. However, the ex situ microbiological biogas upgrading currently suffers from H(2) gas liquid mass transfer limitation, which results in low volumetric CH(4) productivity compared to pure H(2)/CO(2) conversion to CH(4). If waste gas utilization from biological and industrial sources can be shown without reduction in volumetric CH(4) productivity, as well as if the aim of a single stage conversion to a CH(4) fermentation offgas content exceeding 95 vol% can be demonstrated, ex situ microbiological biogas upgrading with pure or enrichment cultures of methanogens could become a promising future technology for almost CO(2)-neutral biomethane production.

Fermentative hydrogen and methane production from microalgal biomass (Chlorella vulgaris) in a two-stage combined process

This study investigated the hydrogen fermentation in a two-stage combined fermentation process (combination of dark fermentation for hydrogen (H2) production from microalgae and methane (CH4) fermentation from residues following H2 production process). Microalgae Chlorella vulgaris culture was used as a substrate. The hydrogen production from C. vulgaris ranges 1.75±1.50–19±2.94ml H2 g-VS−1 at different substrate dosages without enzymatic pre-treatment. A seven-fold increase in H2 production yields (19±2.94–135±3.11ml H2 g-VS−1) was observed with enzymatic pre-treatment (Onozuka R-10 and Macerozyme R-10) of the microalgae. The results of the CH4 fermentation show that the methane yields could be increased from 245±2.46 to 414±2.45ml CH4 g-VS−1 by using enzymatic pretreatment. In addition, the yield of the CH4 fermentation (14.86kJ/g-VS) has approximately the same order of magnitude in comparison to the two-stage combined fermentation process (14.46kJ/g-VS) in terms of energy production.

Hydrogen-methane production from pulp & paper sludge and food waste by mesophilic–thermophilic anaerobic co-digestion

The present study focused on the mesophilic anaerobic bio-hydrogen production from PPS (pulp & paper sludge) and FW (food waste), and the subsequent anaerobic digestion of the effluent for the methane production under thermophilic conditions by a two-stage process. The maximum hydrogen yield of 64.48 mL g−1 VSfed and methane yield of 432.3 mL g−1 VSfed were obtained when PPS and FW were applied with 1: 1 VS ratio as the feedstock. No VFA were cumulated in the reactor during the period of hydrogen - methane fermentation, as well as no NH3–N and Na+ inhibition were found in the process. 71%–87% removal efficiencies of SCOD were attained for hydrogen and methane co-production. pH 4.8–6.4 and alkalinity 794–3316 mg CaCO3 L−1 for H2 fermentation, as well as pH 6.5–8.8 and alkalinity 4165–4679 mg CaCO3 L−1 for CH4 fermentation, were achieved without any adjustment. This work showed that anaerobic co-digestion of PPS and FW for hydrogen-methane co-production was a stable, reliable and effective way for energy recovery and bio-solid waste stabilization by the two-stage mesophilic–thermophilic process.

Hydrogen and methane production from untreated rice straw and raw sewage sludge under thermophilic anaerobic conditions

Bioenergy produced from co-digestion of sewage sludge (SS) and rice straw (RS) as raw materials, without pretreatment and additional nutrients, was compared for the one-stage system for producing methane (CH4) and the two-stage system for combined production of hydrogen (H2) and CH4 in batch experiments under thermophilic conditions. In the first stage H2 fermentation process using untreated RS with raw SS, we obtained a high H2 yield (21 ml/g-VS) and stable H2 content (60.9%). Direct utilization of post-H2 fermentation residues readily produced biogas, and significantly enhanced the CH4 yield (266 ml/g-VS) with stable CH4 content (75–80%) during the second stage CH4 fermentation process. Overall, volatile solids removal (60.4%) and total bioenergy yield (8804 J/g-VS) for the two-stage system were 37.9% and 59.6% higher, respectively, than the one-stage system. The efficient production of bioenergy is believed to be due to a synergistically improved second stage process exploiting the well-digested post-H2 generation residues over the one-stage system.

CH4 Fermentation Using Acclimated-Methanogens on a Continuous Feed Substrate of Mixed Carbon Dioxide and Hydrogen

CH4 Fermentation Using Acclimated-Methanogens on a Continuous Feed Substrate of Mixed Carbon Dioxide and Hydrogen

Methane fermentation of rubber (Hevea brasiliensis) latex effluent.

Four species of bacteria capable of CH4 fermentation of rubber latex effluent were isolated and identified as a Methanococcus, a strain of M. vannielii, a Methanobacterium and a strain of M. omelianskii. Auxanographic tests using the four strains showed growth and CH4 formation on a basal medium containing mineral salts or added H2 and Co2. Varied response was obtained when the basal medium was added to formate, acetate, butyrate, methanol, ethanol, and glucose. Previous work has established acid fermentation of Hevea latex arising from bacterial contamination and decomposition of the non-rubber constituents which consist of N-compounds, 2% quebrachitol, and smaller concentration of carbohydrates. This suggests that reduction of CO2 and fermentation of acids formed during metabolism of Hevea latex are possible pathways of CH4 production.