Substrate For Methane Production Research Articles

Coupling protein recovery to methane and lactic acid production to valorize duckweed used in selenate remediation

Duckweed (DW) can be used for metal bioremediation, but can also serve as a renewable feedstock for various processes such as protein production, acidogenesis and methanogenesis. In this study, a selenate (3 mg L−1) supplemented modified Steinberg medium was used as a feed for DW cultivation, which gave a selenate removal efficiency of 55%. Thereafter, an optimized protein extraction protocol was developed yielding a∼20% protein extraction efficiency from both the control and selenate-enriched DW. The solid fraction obtained during protein extraction was utilised for lactic acid (LA) production (upto 5 g L-1), whereas the liquid fraction (after protein extraction) was used as the substrate for methane production (∼150 mL gCOD−1). Selenate enriched DW achieved faster LA production and showed better methane production kinetics when compared to the control DW. This study shows that bioenergy and biocommodity production can be efficiently coupled to selenium removal from polluted wastewaters using DW.

Biohydrogen and Biomethane Production from Acid Pretreated Water Hyacinth and Kinetics

In this study, several ratios of water hyacinth to acid solution were varied from 1:10, 1:20, 1:30, and 1:40, in order to find the optimum ratio for biohydrogen and biomethane production. The pretreated water hyacinth was used as substrates to produce hydrogen in the first stage anaerobic digestion. Then the residue from hydrogen production was used as substrate for methane production in the second stage. The results showed that cumulative hydrogen production slightly increased with the substrate to acid solution (2 % v/v H2SO4) ratio. The highest cumulative hydrogen produced (77.47 mL with 7.75 mL H2/gVS) at 1:40 substrate to acid solution, however the highest hydrogen content obtained at 1:20 (40.1 %). Hydrogen could not be produced from water hyacinth without acid pretreatment, only 4 mL hydrogen was detected from control case. In the second stage, methane was generated from the residue of first stage fermentation and found that the highest cumulative methane was obtained from 1:30 substrate to acid solution ratio. The methane content was not significantly different for control (53.68 %), 1:10 (54.45 %), 1:20 (53.46 %), and 1:30 (52.10 %) cases. The modified Gompertz, modified Logistic, and Cone model were best fit models for hydrogen production since the fermentation needed lag phase time before the hydrogen can be generated. The calculated lag phase time from modified Gompertz model increased from 0.0531 to 0.9775 day, and those from modified Logistic model increased from 0.3867 to 1.0305 day. On the other hand, the Cone model, first order model, and Transference function agreed very well with the second stage methane production data where lag phase time was nearly zero.
 HIGHLIGHTS
 
 Biohydrogen cannot be produced from water hyacinth without acid pretreatment
 The optimum substrate to acid solution ratio for pretreating water hyacinth for hydrogen production is at 1:20 with highest hydrogen content. Higher acid ratio produced more undesired gases
 Biomethane can be produced from water hyacinth without acid pretreatment. Only mechanical size reductionand heating pretreatment are enough to facilitate the process
 Hydrogen production were best described by the modified Gompertz, modified Logistic, and Cone model. On the other hand, second stage biomethane production were best described by the Cone model, first order model, and Transference function
 
 GRAPHICAL ABSTRACT

Methane production from ethanolic and acid fermentations of the organic fraction of municipal solid waste under different pH and reaction times

Thermodynamically, lactic acid and ethanol allow the best energy recovery among all common metabolites for methane production. When faster methane production is required, previously fermented organic fraction of municipal solid waste (OFMSW) can be essential for methane production. This research deals with OFMSW fermentation in batch reactors at pH values of 4, 5, and 6 at 35 °C. Samples were taken at reaction times of 1, 3, and 6 days for every pH, characterized, and exposed to methane production at 35 °C. The results show that lower pH and shorter fermentation times allow better ethanol and lactic acid production. Without exception, the fermented liquid fractions produce more methane than the solid ones. Fermented OFMSW produced 19% more methane than unfermented ones. The first methanization stage of the liquid fractions required 1–2 days and the solid fractions from 4 to 8 days. According to Michaelis & Menten, the reaction rate Vmax values are significantly higher for the liquid fractions than for the solid ones. Vmax shows that the lowest tested pH (4) during fermentation delivers the best substrate for methane production. The liquid digestates show significantly lower Km values than the solid ones, indicating a good affinity of the methanogens for the substrate. These results show the possibility of producing methane fast and efficiently using liquid fermented digestates. The solid fraction produces methane, but only slower than the liquid fraction.

Two-Stage Anaerobic Codigestion of Crude Glycerol and Micro-Algal Biomass for Biohydrogen and Methane Production by Anaerobic Sludge Consortium

Optimization of factors affecting biohydrogen production from the codigestion of crude glycerol and microalgal biomass by anaerobic sludge consortium was conducted. The experiments were designed by a response surface methodology with central composite design. The factors affecting the production of hydrogen were the concentrations of crude glycerol, microalgal biomass, and inoculum. The maximum hydrogen production (655.1 mL-H2/L) was achieved with 13.83 g/L crude glycerol, 23.1 g-VS/L microalgal biomass, and 10.3% (v/v) inoculum. The hydrogenic effluents obtained under low, high, and optimal conditions were further used as substrates for methane production. Methane production rates and methane yield of 868.7 mL-CH4/L and 2.95 mL-CH4/L-h were attained with the effluent produced under optimum conditions. The use of crude glycerol and microalgal biomass as cosubstrates had an antagonistic effect on biohydrogen production and a synergistic effect on methane fermentation. The two-stage process provided a more attractive solution, with a total energy of 1.27 kJ/g-VSadded, than the one-stage process.

Effect of nanobubble water on anaerobic methane production from lignin

Lignocellulosic biomass is abundant in the environment, which can be used as the substrate for methane production via anaerobic digestion (AD). However, the methane production efficiency from lignocellulosic biomass is relatively low, mainly due to its refractory components, of which lignin is the major barrier to bioconversion and also resists the hydrolysis of lignocellulose, thus limiting the AD process. This study compared the effects of two different gases (N2 and CO2) nanobubble water (NBW) on methane production from lignin using mono-digestion and co-digestion with acetic acid (HAc) at four different total organic carbon (TOC) ratios of HAc to lignin (97.5%:2.5%, 95%:5%, 90%:10%, and 80%:20%). Results show that N2-NBW is the promising NBW which can enhance methane production by 22% compared to the control. In addition, co-digestion of lignin with acetic acid reflects a higher methane production potential in comparison with the mono-digestion of lignin, achieving a much higher methane production (824–1061 mL CH4/g-TOCremoved) when lignin content was less than 20% (TOC basis) and the highest lignin reduction (43%) at the TOC ratio of HAc to lignin of 95%:5%.

Effects of biochar on methane emission from paddy soil: Focusing on DOM and microbial communities

Biochar can be used as a soil amendment. However, it generally possesses unique physicochemical properties and complex organics, which could affect soil methanogenesis. In this study，straw-based biochars obtained at 300 °C (BC300), 500 °C (BC500) and 700 °C (BC700) were added to the paddy soil. Compared with the blank group, BC300 significantly increased paddy soil methane emissions by about 38%. However, this promoting effect gradually disappeared with the increase of pyrolysis temperature, and the inhibition even appeared in the BC700 group with the methane reduction by 18.2%. This might be related to the organics released from biochar. Van Krevelen (VK) diagram showed that the aromaticity of BC700 and BC500 were significantly higher than BC300. Fluorescent analysis further revealed that BC300 increased the amount of degradable fluorescent organics in the soil, which could provide more substrate for methane production. Moreover, as pyrolysis temperature increased, the fluorescent organics released were more likely to be non-biodegradable humus. In addition, it was shown that BC700 could adsorb some inherent organics in the soil, and thus reduced the total organic content and inhibited soil methane emissions. Microbial analysis showed that methanogenesis had a positive correlation with the abundance of syntrophic bacteria (e.g. Desulfobacca and Clostridium) which had ability to further degrade various types of organics and provided substrates to the methanogens. This article provides a deeper understanding regarding for the effects of biochar on methane emission from paddy soil in terms of organics and microbial perspectives.

Alkaline and co-digestion pretreatments: process optimization for enhancing the methane yield of Jatropha press cake

Oil extraction and biodiesel production process produce a massive amount of by-products like Jatropha press cake (JPC) and crude glycerol (CG), which could be used as a potential substrate for methane production. However, the higher lignocellulosic and nitrogen content in the JPC act as a recalcitrant and inhibitor, respectivly, for microbes that are involved in the anaerobic digestion (AD) process. Therefore, the present study aimed to enhance the methane yield of JPC by optimizing the alkaline pretreatment and co-digestion process conditions. The effects of NaOH concentration, incubation temperature, and retention time on methane and soluble chemical oxygen demand (sCOD) yields were evaluated and modeled by employing a response surface methodology coupled with central composite design (RSM-CCD). Moreover, a series of batch experiments with various feedstock concentrations (FCs) were tested to investigate the methane yield of JPC when co-digested with CG at different levels. The methane yields of all pretreated samples were significantly higher when compared with these of the untreated JPC. Pretreating the JPC using 7.32% NaOH at 35.86 °C for 54.05 h was the optimum conditions for maximum methane increment of 40.23% (353.90 mL g−1 VS), while co-digesting 2% CG with JPC at 2 g VS L−1 FC enhanced the methane yield by 28.9% (325.47 mL g−1 VS). Thus, the methane yield of JPC was effectively increased by alkaline pretreatment and co-digesting with CG. However, the alkaline pretreatment was relatively more effective compared with the co-digestion process.

From waste to fuel: Energy recovery from household food waste via its bioconversion to energy carriers based on microbiological processes

In the present study the bioconversion of dried household food waste (FORBI) to energy carriers was investigated aiming to its sustainable management and valorization. FORBI was either directly fermented towards ethanol and hydrogen or was previously subjected to extraction with water resulting to a liquid fraction (extract) rich in sugars and a solid residue, which were then fermented separately. Subsequently, the effluents were assessed as substrates for methane production via anaerobic digestion (AD). Mono-cultures and co-cultures of C5 and C6 yeasts were used for the alcoholic fermentation whereas for the production of hydrogen, mixed acidogenic consortia were used. Taking into account the optimum yields of biofuels, the amount of recoverable energy was estimated based for each different approach. The maximum ethanol yield was 0.16 g ethanol per kg of FORBI and it was achieved for separate fermentation of liquid and solid fractions of the waste. The highest hydrogen yield that was observed was 210.44 L ± 4.02 H2/kg TS FORBI for 1% solids loading and supplementation with cellulolytic enzymes. Direct AD of either the whole FORBI or its individual fractions led to lower overall energy recovery, compared to that obtained when fermentation and subsequent AD were applied. The recoverable energy was estimated for the different exploitation approaches of the waste. The maximum achieved recoverable energy was 21.49 ± 0.57 MJ/kg.

An overall perspective for the energetic valorization of household food waste using microbial fuel cell technology of its extract, coupled with anaerobic digestion of the solid residue

The valorization of typical household food waste (HFW) produced at municipality level was studied for the production of electricity in a microbial fuel cell (MFC) from its extract, and methane, through anaerobic digestion of the solid extraction residue. HFW, after heat drying and shredding, was subjected to extraction using warm water, which resulted in a liquid fraction (extract) and a solid residue. The rich in soluble chemical oxygen demand extract was used for electricity production in a four air– cathodes single chamber MFC, operating under different organic loading rates, while the solid residue from the extraction process was used as substrate for methane production in biochemical methane potential experiments. On the basis of the energy outputs estimated for the optimum operational conditions of both aforementioned processes, it can be concluded that the exploitation of dried HFW is quite appealing as it leads to promising energy recovery.

Co-Digestion of Napier Grass and Its Silage with Cow Dung for Bio-Hydrogen and Methane Production by Two-Stage Anaerobic Digestion Process

The objective of this study was to efficiently utilize the napier grass and its silage to produce bio-hydrogen and methane by a two-stage process in batch mode. First, the production of hydrogen from a co-digestion of grass with cow dung and silage with cow dung by Clostridium butyricum Thailand Institute of Scientific and Technological Research (TISTR) 1032 was conducted. The results indicated that bio-hydrogen production by C. butyricum TISTR 1032 gave a higher hydrogen yield (HY) than without C. butyricum addition. The HY of 6.98 and 27.71 mL H2/g-Volatile solidadded (VSadded), were obtained from a co-digestion of grass with cow dung and silage with cow dung by C. butyricum, respectively. The hydrogenic effluent and solid residue left over after hydrogen fermentation were further used as substrates for methane production (Batch I). Methane yield (MY) from hydrogenic effluent of grass with cow dung and silage with cow dung were 169.87 and 141.33 mL CH4/g-CODadded (COD: chemical oxygen demand), respectively. The maximum MY of 210.10 and 177.79 mL CH4/g-VSadded, respectively, were attained from solid residues left over after bio-hydrogen production pretreated by enzyme (cellulase cocktail) and alkali (NaOH). Afterward, solid residue left over after methane production (Batch I) was used as the substrate for methane production (Batch II). A maximum MY of 370.39 and 370.99 mL CH4/g-VSadded were achieved from solid residue repeatedly pretreated by alkaline plus enzyme, respectively. The overall energy yield in the two-stage bio-hydrogen and methane production process was derived from a bio-hydrogen production, a methane production from hydrogenic effluent, methane production of pretreated solid residue (Batch I) and methane production of repeatedly pretreated solid residue (Batch II), which yielded 480.27 and 204.70 MJ/g-VSadded, respectively.

Dairy manure wastewater in serial UASB reactors for energy recovery and potential effluent reuse

Abstract This manuscript addresses the use of dairy manure wastewater (DMW) as a substrate for methane production in a high rate system - two serial UASB reactors - and the characterization of the effluent in the different phases of the treatment. Two experimental conditions were applied. In the first, the organic load rate (OLR) was 6.2 gCODtotal L-1 d-1 and the hydraulic retention time (HRT) was 12 days, whereas in experiment 2 they were 14.2 gCODtotal L-1 d-1 and 7.5 days, respectively. The reactors showed a high capacity of removal of COD and solids, i.e., above 71%, which led to bioenergy productivities of 0.55 and 0.73 L CH4 L-1 d-1 in experiments 1 and 2,respectively. The methane yield in UASB1 was 0.19 and 0.08 L CH4g CODrem.-1, respectively, inexperiments 1 and 2. The methane yield in UASB1 was greater than UASB2, with approximately 70% of methane content in the biogas in this reactor.The effluent characterization showed micro and macronutrients - some in high concentrations, as nitrogen, phosphorous, K, and Fe between 12.1 and 521.4 mg L-1, and others in low concentrations, as Ca, Mg, Zn and Mn between 0.6 and 13 mg L-1. Na was not removed from the UASB systems and its concentration in the effluent was raised to 23.5% in comparison with the substrate.

Effect of aerobic pre-treatment on hydrogen and methane production in a two-stage anaerobic digestion process using food waste with different compositions

Aerobic pre-treatment was applied prior to two-stage anaerobic digestion process. Three different food wastes samples, namely carbohydrate rich, protein rich and lipid rich, were prepared as substrates. Effect of aerobic pre-treatment on hydrogen and methane production was studied. Pre-aeration of substrates showed no positive impact on hydrogen production in the first stage. All three categories of pre-aerated food wastes produced less hydrogen compared to samples without pre-aeration. In the second stage, methane production increased for aerated protein rich and carbohydrate rich samples. In addition, the lag phase for carbohydrate rich substrate was shorter for aerated samples. Aerated protein rich substrate yielded the best results among substrates for methane production, with a cumulative production of approximately 351ml/gVS. With regard to non-aerated substrates, lipid rich was the best substrate for CH4 production (263ml/gVS). Pre-aerated P substrate was the best in terms of total energy generation which amounted to 9.64kJ/gVS. This study revealed aerobic pre-treatment to be a promising option for use in achieving enhanced substrate conversion efficiencies and CH4 production in a two-stage AD process, particularly when the substrate contains high amounts of proteins.

Influence of carbon dioxide, temperature, medium kind and light intensity on the growth of algaeChlamydomonas reinhardtiiandScenedesmus obliquus

Microalgae attracts the attention of scientists because of the possibility of using in the energy industry as one of the substrates for the production of renewable energy. So far, the greatest emphasis was put on attempts to obtain strains, and technologies of their culturing, in order to efficiently acquire fat from cells and its further conversion to biodiesel using transesterification reaction. Increasingly, algae are considered also as an efficient biomass producer, which can be used as a substrate for methane production in biogas plants. In this study the influence of different physical and chemical conditions, on the growth of two algae species: Chlamydomonasreinhardtii and Scenedesmus obliquus was investigated. Based on the literature and the data obtained for the algae growth on the standard medium and the digestate remaining after fermentation, one may suggest further investigations on the use of other liquid waste from agriculture and industry for algae breeding, including chemical. analysis and supplementation of these mediums so as to provide the best conditions for their growth.

Use of a marine microbial community as inoculum for biomethane production

Marine substrates are prominent candidates for the production of biofuels, especially for biogas, which is a well-established technology that accepts different types of substrates for its production. However, the use of marine substrates in bioreactors may cause inhibition of methanogenic bacteria due to the addition of seasalts. Here, we explore a simple and economically viable way to circumvent the problem of inoculum inhibition. Based on the current knowledge of the diversity of microorganisms in marine sediments, we tested the direct use of methanogenic bacteria from an anoxic marine environment as inoculum for biomethane production. Both marine and freshwater substrates were added to this inoculum. No pretreatment (that may have enhanced methane production, but would have made the process more expensive) was applied either to the inoculum or to the substrates. For comparison, the same substrates were added to a standard inoculum (cow manure). Both the marine inoculum and cow manure produced methane by anaerobic digestion of the substrates added. The highest methane production (0.299 m3 kg VS−1) was obtained by adding marine microalgae biomass (Chlorella sp. and Synechococcus sp.) to the marine inoculum. No inhibitory effects were observed due to differences in salinity between the inocula and substrates. Our results indicate the potential of using both marine inoculum and substrates for methane production.

Methane production from acid hydrolysates of Agave tequilana bagasse: Evaluation of hydrolysis conditions and methane yield

Evaluation of diluted acid hydrolysis for sugar extraction from cooked and uncooked Agave tequilana bagasse and feasibility of using the hydrolysates as substrate for methane production, with and without nutrient addition, in anaerobic sequencing batch reactors (AnSBR) were studied. Results showed that the hydrolysis over the cooked bagasse was more effective for sugar extraction at the studied conditions. Total sugars concentration in the cooked and uncooked bagasse hydrolysates were 27.9g/L and 18.7g/L, respectively. However, 5-hydroxymethylfurfural was detected in the cooked bagasse hydrolysate, and therefore, the uncooked bagasse hydrolysate was selected as substrate for methane production. Interestingly, results showed that the AnSBR operated without nutrient addition obtained a constant methane production (0.26LCH4/gCOD), whereas the AnSBR operated with nutrient addition presented a gradual methane suppression. Molecular analyses suggested that methane suppression in the experiment with nutrient addition was due to a negative effect over the archaeal/bacterial ratio.

A methanotrophic community in a tropical peatland is unaffected by drainage and forest fires in a tropical peat soil

The effects of drainage and forest fires on the methanotrophic activity and community structure of peat soils in a tropical forest were studied by analyzing methane fluxes and the population of methanotrophs. A denaturing gradient gel electrophoresis (DGGE) analysis was used to target particular methane monooxygenase genes (pmoA). An incubation experiment was performed to investigate methane production activity relative to the effects of flooding and litter fall. Low levels of methane fluxes were observed in the soils in drained forest, natural forest and burned forest sites. These fluxes did not differ significantly among the sites (–0.02 ± 0.01–0.36 ± 0.30 mg C m−2 hr−1). The water-filled pore space (WFPS) showed a statistically significant positive relationship with methane fluxes and a statistically significant negative relationship with the populations of methanotrophs. A DGGE profile targeted on pmoA gene fragments showed no apparent differences in the gene patterns among the various soil types. Four of the excised bands showed identical sequences closely related to type 1 methanotrophs, Methylomonas spp. An incubation experiment showed stronger methane oxidation than methane production in the absence of litter, even under flooded conditions. These results indicated that labile organic carbon or intact photosynthetic products, such as litter, may act as the principal substrate for methane production in the flooded condition and that the recalcitrant woody organic matter preserved under flooded anaerobic conditions in the peat soils for a long period would, most likely, play only a subordinate role. Under these environmental conditions, the methanotrophic community may consist primarily of type 1 methanotrophs irrespective of drainage and forest fires, and its activity could be controlled by WFPS by adjusting the oxygen supply to the peat soils.

A new model for electron flow during anaerobic digestion: direct interspecies electron transfer to Methanosaeta for the reduction of carbon dioxide to methane

Anaerobic conversion of organic wastes and biomass to methane is an important bioenergy strategy, which depends on poorly understood mechanisms of interspecies electron transfer to methanogenic microorganisms. Metatranscriptomic analysis of methanogenic aggregates from a brewery wastewater digester, coupled with fluorescence in situ hybridization with specific 16S rRNA probes, revealed that Methanosaeta species were the most abundant and metabolically active methanogens. Methanogens known to reduce carbon dioxide with H2 or formate as the electron donor were rare. Although Methanosaeta have previously been thought to be restricted to acetate as a substrate for methane production, Methanosaeta in the aggregates had a complete complement of genes for the enzymes necessary for the reduction of carbon to methane, and transcript abundance for these genes was high. Furthermore, Geobacter species, the most abundant bacteria in the aggregates, highly expressed genes for ethanol metabolism and for extracellular electron transfer via electrically conductive pili, suggesting that Geobacter and Methanosaeta species were exchanging electrons via direct interspecies electron transfer (DIET). This possibility was further investigated in defined co-cultures of Geobacter metallireducens and Methanosaeta harundinacea which stoichiometrically converted ethanol to methane. Transcriptomic, radiotracer, and genetic analysis demonstrated that M. harundinacea accepted electrons via DIET for the reduction of carbon dioxide to methane. The discovery that Methanosaeta species, which are abundant in a wide diversity of methanogenic environments, are capable of DIET has important implications not only for the functioning of anaerobic digesters, but also for global methane production.

Methanogens, Methane and Gastrointestinal Motility

Anaerobic fermentation of the undigested polysaccharide fraction of carbohydrates produces hydrogen in the intestine which is the substrate for methane production by intestinal methanogens. Hydrogen and methane are excreted in the flatus and in breath giving the opportunity to indirectly measure their production using breath testing. Although methane is detected in 30%-50% of the healthy adult population worldwide, its production has been epidemiologically and clinically associated with constipation related diseases, like constipation predominant irritable bowel syndrome and chronic constipation. While a causative relation is not proven yet, there is strong evidence from animal studies that methane delays intestinal transit, possibly acting as a neuromuscular transmitter. This evidence is further supported by the universal finding that methane production (measured by breath test) is associated with delayed transit time in clinical studies. There is also preliminary evidence that antibiotic reduction of methanogens (as evidenced by reduced methane production) predicts the clinical response in terms of symptomatic improvement in patients with constipation predominant irritable bowel syndrome. However, we have not identified yet the mechanism of action of methane on intestinal motility, and since methane production does not account for all constipation associated cases, there is need for high quality clinical trials to examine methane as a biomarker for the diagnosis or as a biomarker that predicts antibiotic treatment response in patients with constipation related disorders.

Energy-environmental benefits and economic feasibility of anaerobic codigestion of Iberian pig slaughterhouse and tomato industry wastes in Extremadura (Spain)

Anaerobic digestion of Iberian pig slaughterhouse and tomato industry wastes, as well as codigestion operations from such residues, are reported to achieve 54–80% reduction in Chemical Oxygen Demand and 6–19Nm3/m3 substrate methane production. Furthermore, 0.79–0.88m3water/m3 substrate is seen to be recovered after the above mentioned operations, which might be used as irrigation water, and 0.12–0.21m3agricultural amendment/m3 substrate with 91–98% moisture content.The present paper also reports on the economic feasibility of both an anaerobic codigestion plant operating with 60% slaughterhouse wastes/40% tomato industry wastes (optimal ratio obtained in previous laboratory-scaled experiments), and an anaerobic digestion plant for Iberian pig slaughterhouse waste. Payback times are reported as 14.86 and 3.73years, respectively.

Evaluation of marine biomass as a source of methane in batch tests: A lab-scale study

Marine biomass is considered an important feedstock for anaerobic digestion to generate energy; however, its utilization as an energy source is still minimal around the world. In the current study, the biochemical methane potential test was used to evaluate energy recovery from seaweed, brown algae, green algae, and fish viscera as substrates for methane production. Cumulative CH4 yields of 256 ± 28 and 179 ± 35 mL CH4/g VS were observed using green and brown algae, respectively, after 60 days of digestion. The CH4 content of the biogas was approximately 70% for both substrates. Lower CH4 yields of 127 ± 20 and 102 ± 25 mL CH4/g VS were observed using fish viscera and seaweed, respectively. Given that 44 ± 15% of the TCOD was converted to CH4, a longer adaption period or pretreatment of the marine biomass is necessary to fully convert the TCOD to CH4.