Methane and hydrogen sulfide production during co-digestion of forage radish and dairy manure

Forage radish, a winter cover crop, was investigated as a co-substrate to increase biogas production from dairy manure-based anaerobic digestion. Batch digesters (300 cm³) were operated under mesophilic conditions during two experiments (BMP1; BMP2). In BMP1, the effect of co-digesting radish and manure on CH₄ and H₂S production was determined by increasing the mass fraction of fresh above-ground radish in the manure-based co-digestion mixture from 0 to 100%. Results showed that forage radish had 1.5-fold higher CH₄ potential than dairy manure on a volatile solids basis. While no synergistic effect on CH₄ production resulted from co-digestion, increasing the radish fraction in the co-digestion mixture significantly increased CH₄ production. Initial H₂S production increased as the radish fraction increased, but the sulfur-containing compounds were rapidly utilized, resulting in all treatments having similar H₂S concentrations (0.10–0.14%) and higher CH₄ content (48–70%) in the biogas over time. The 100% radish digester had the highest specific CH₄ yield (372 ± 12 L kg⁻¹ VS). The co-digestion mixture containing 40% radish had a lower specific CH₄ yield (345 ± 2 L kg⁻¹ VS) but also showed significantly less H₂S production at start-up and high quality biogas (58% CH₄). Results from BMP2 showed that the radish harvest date (October versus December) did not significantly influence radish C:N mass ratios or CH₄ production during co-digestion with dairy manure. These results suggest that dairy farmers could utilize forage radish, a readily available substrate that does not compete with food supply, to increase CH₄ production of manure digesters in the fall/winter.     

Starting-up low temperature dry anaerobic digestion of cow feces and wheat straw

Psychrophilic dry anaerobic digestion (PDAD) of animal manures and agriculture residues is of high interest in cold-climate regions. This paper reports the results of a start-up experiment (113 days) of PDAD of cow feces and wheat straw mixture (at two total solids (TS) of 18 and 21%) in laboratory scale sequence batch reactor (SBR) at 20 °C. An average specific methane yield (SMY) of 96.1 ± 5 L of CH₄ per kg of volatile solid (VS) corrected to standard pressure and temperature (101.3 kPa and 273 K) (_NL CH₄ kg⁻¹ VS) has been achieved for a feed with TS of 18% along with an organic loading rate (OLR) 4.0 g total chemical oxygen demand (TCOD) kg⁻¹ inoculum day⁻¹ and a treatment cycle length (TCL) of 21 days. An average SMY of 149.9 ± 14 _NL CH₄ kg⁻¹ VS with a maximum daily CH₄ production rate of 7.2 ± 0.7 _NL CH₄ kg⁻¹ VS day⁻¹ have been obtained for a feed with total solid of 21% along with an average daily inoculum OLR of 4.2 g TCOD kg⁻¹ inoculum day⁻¹ and TCL of 21 days. The rapid decrease in volatile fatty acids concentration after 7 days of treatment and their low concentration thereafter indicated that hydrolysis was the reaction limiting step. The results indicate that PDAD of cow feces and wheat straw is feasible at feed TS of 21%.     

Effects on the biogas and methane production of cattle manure treated with urease inhibitor

Urease inhibitors are in general known as potential measure for reducing ammonia emissions in dairy and cattle housing systems. Due to the application of the urease inhibitor on the exercise areas within a housing system the inhibitor is “mixed” with cattle manure and this “mixture” remains unchanged during manure storage. In Germany, a large part of the total stored cattle manure is utilized as a substrate in biogas plants. Therefore, the aim of the current study was to test if different concentrations of urease inhibitor mixed with typical cattle slurry will have any (negative) effects on the biogas and methane yield. The Hohenheim Biogas Yield Test (HBT) was used to determine if the biogas and methane production of cattle manure is influenced by the admixture with urease inhibitor. Altogether, four urease inhibitor concentrations (0%, 0.1%, 1% und 10% of total Kjeldahl nitrogen) were tested in the HBT experiments with two different substrates, cattle manure and cellulose, as a reference, in repetitions each. The average biogas and methane production of cellulose was 740 L_N/kg_ODM and 403 L_N/kg _ODM and of cattle manure 471 L_N/kg_ODM and 295 L_N/kg_ODM. Both substrates treated with urease inhibitor showed no significant change in the biogas and methane production compared to the untreated ones. The use of urease inhibitors to reduce ammonia is harmless from the view of biogas plants.     

Mitigation of greenhouse gas emissions by adopting anaerobic digestion technology on dairy,sow and pig farms in Finland

The impact of anaerobic digestion (AD) technology on mitigating greenhouse gas (GHG) emissions from manure management on typical dairy, sow and pig farms in Finland was compared. Firstly, the total annual GHG emissions from the farms were calculated using IPCC guidelines for a similar slurry type manure management system. Secondly, laboratory-scale experiments were conducted to estimate methane (CH₄) potentials and process parameters for semi-continuous digestion of manures. Finally, the obtained experimental data were used to evaluate the potential renewable energy production and subsequently, the possible GHG emissions that could be avoided through adoption of AD technology on the studied farms. Results showed that enteric fermentation (CH₄) and manure management (CH₄ and N₂O) accounted for 231.3, 32.3 and 18.3 Mg of CO₂ eq. yr^?1 on dairy, sow and pig farms, respectively. With the existing farm data and experimental methane yields, an estimated renewable energy of 115.2, 36.3 and 79.5 MWh of heat yr^?1 and 62.8, 21.8 and 47.7 MWh of electricity yr^?1 could be generated in a CHP plant on these farms respectively. The total GHG emissions that could be offset on the studied dairy cow, sow and pig farms were 177, 87.7 and 125.6 Mg of CO₂ eq. yr^?1, respectively. The impact of AD technology on mitigating GHG emissions was mainly through replaced fossil fuel consumption followed by reduced emissions due to reduced fertilizer use and production, and from manure management.     

Overview analysis of bioenergy from livestock manure management in Taiwan

The emissions of greenhouse gases (GHGs) from the livestock manure are becoming significant energy and environmental issues in Taiwan. However, the waste management (i.e., anaerobic digestion) can produce the biogas associated with its composition mostly consisting of methane (CH₄), which is now considered as a renewable energy with emphasis on electricity generation and other energy uses. The objective of this paper was to present an overview analysis of biogas-to-bioenergy in Taiwan, which included five elements: current status of biogas sources and their energy utilizations, potential of biogas (methane) generation from livestock manure management, governmental regulations and policies for promoting biogas, benefits of GHGs (i.e., methane) emission reduction, and research and development status of utilizing livestock manure for biofuel production. In the study, using the livestock population data surveyed by the Council of Agriculture (Taiwan) and the emission factors recommended by the Intergovernmental Panel on Climate Change (IPCC), the potential of methane generation from livestock manure management in Taiwan during the period of 1995–2007 has been estimated to range from 36 to 56 Gg year⁻¹, indicating that the biogas (methane) from swine and dairy cattle is abundant. Based on the characteristics of swine manure, the maximum potential of methane generation could reach to around 400 Gg year⁻¹. With a practical basis of the total swine population (around 4300 thousand heads) from the farm scale of over 1000 heads, a preliminary analysis showed the following benefits: methane reduction of 21.5 Gg year⁻¹, electricity generation of 7.2 × 10⁷ kW-h year⁻¹, equivalent electricity charge saving of 7.2 × 10⁶ US$ year⁻¹, and equivalent carbon dioxide mitigation of 500 Gg year⁻¹.     

Co-digestion of poultry manure and residues from enzymatic saccharification and dewatering of sugar beet pulp

This study investigates the co-digestion of poultry manure (PM) with sugar beet pulp residues (SBPR) obtained from saccharification and dewatering of sugar beet pulp. The laboratory-scale experiments were conducted under batch and semi-continuous conditions at mesophilic temperatures (35 °C). Batch tests gave specific biogas and methane yields of 590 dm³/kgVS_fed and 423 dm³CH₄/kgVS_fed, respectively for SBPR, whereas the corresponding values for PM were 434 dm³/kgVS_fed and 300 dm³CH₄/kgVS_fed. The co-digestion of PM with SBPR was found to increase biogas and methane yields compared to the manure alone. In semi-continuous reactor experiments, the highest methane yield of 346 dm³ CH₄/kgVS_fed was achieved for the mixture containing poultry manure with 50% SBPR (weight basis) and a solids retention time (SRT) of 20 days. However, when poultry manure was digested as a sole feedstock, the biogas production was inhibited by ammonia, whereas the co-digestion of PM with 25% SBPR was slightly affected by volatile fatty acids, which concentrations exceeded 4000 g/m³.     

Semi-continuous co-digestion of solid slaughterhouse waste, manure, and fruit and vegetable waste

The potential of semi-continuous mesophilic anaerobic digestion (AD) for the treatment of solid slaughterhouse waste, fruit-vegetable wastes, and manure in a co-digestion process has been experimentally evaluated. A study was made at laboratory scale using four 2 L reactors working semi-continuously at 35 °C. The effect of the organic loading rate (OLR) was initially examined (using equal proportion of the three components on a volatile solids, VS, basis). Anaerobic co-digestion with OLRs in the range 0.3–1.3 kg VS m⁻³ d⁻¹ resulted in methane yields of 0.3 m³ kg⁻¹ VS added, with a methane content in the biogas of 54–56%. However, at a further increased loading, the biogas production decreased and there was a reduction in the methane yield indicating organic overload or insufficient buffering capacity in the digester.In the second part of the investigation, co-digestion was studied in a mixture experiment using 10 different feed compositions. The digestion of mixed substrates was in all cases better than that of the pure substrates, with the exception of the mixture of equal amounts of (VS/VS) solid cattle–swine slaughterhouse waste (SCSSW) with fruit and vegetable waste (FVW). For all other mixtures, the steady-state biogas production for the mixture was in the range 1.1–1.6 L d⁻¹, with a methane content of 50–57% after 60 days of operation. The methane yields were in the range 0.27–0.35 m³ kg⁻¹ VS added and VS reductions of more than 50% and up to 67% were obtained.     

Bioenergy production from cotton straws using different pretreatment methods

Cotton straws are one of the most produced agricultural wastes in Turkey and getting attention by not being consumed as animal feed or an industrial stock and having a huge potential in clean energy production. In this study, different pretreatment methods for the conversion of cotton straw to sugar then biohydrogen and biomethane production from cotton straw were examined. The energy potential of cotton straw in case of an evaluation of these biomass residues was also determined using fuel cell technology. Acid pretreatment provided the highest yield in biogas formation as well as sugar extraction from the raw sample. The highest biohydrogen and biomethane production were obtained as 33 mL H₂/g VS and 83 mL CH₄/g VS, respectively. Concomitantly, the maximum power peaks in PEM fuel cell studies were observed as 0.45 W/cm² and 0.23 W/cm² with current densities of 1.086 A/cm² and 0.522 A/cm² when the fuel cell was fed with pure H₂ and biogas, respectively. This suggested that acid pretreatment is more suitable for cotton straw management in sustainable and renewable ways and the results demonstrated that PEM fuel cell is a promising clean technology for energy generation from cotton straw.     

Mild alkaline pre-treatments loosen fibre structure enhancing methane production from biomass crops and residues

Three ligno-cellulosic substrates representing varying levels of biodegradability (giant reed, GR; fibre sorghum, FS; barley straw, BS) were combined with mild alkaline pre-treatments (NaOH 0.05, 0.10 and 0.15 N at 25 °C for 24 h) plus untreated controls, to study pre-treatment effects on physical-chemical structure, anaerobic digestibility and methane output of the three substrates. In a batch anaerobic digestion (AD) assay (58 days; 35 °C; 4 g VS l⁻¹), the most recalcitrant substrate (GR) staged the highest increase in cumulative methane yield: +30% with NaOH 0.15 N over 190 ml CH₄ g⁻¹ VS in untreated GR. Conversely, the least recalcitrant substrate (FS) exhibited the lowest gain (+10% over 248 ml CH₄ g⁻¹ VS), while an intermediate behaviour was shown by BS (+15% over 232 ml CH₄ g⁻¹ VS). Pre-treatments speeded AD kinetics and reduced technical digestion time (i.e., the time needed to achieve 80% methane potential), which are the premises for increased production capacity of full scale AD plants. Fibre components (cellulose, hemicellulose and acid insoluble lignin determined after acid hydrolysis) and substrate structure (Fourier transform infra-red spectroscopy and scanning electron microscopy) outlined reductions of the three fibre components after pre-treatments, supporting claims of loosened binding of lignin with cellulose and hemicellulose. Hence, mild alkaline pre-treatments were shown to improve the biodegradability of ligno-cellulosic substrates to an extent proportional to their recalcitrance. In turn, this contributes to mitigate the food vs. fuel controversy raised by the use of whole plant cereals (namely, maize) as feedstocks for biogas production.     

Improving methane production from wheat straw by digestate liquor recirculation in continuous stirred tank processes

Wheat straw is an abundant, cheap substrate that can be used for methane production. However, the nutrient content in straw is inadequate for methane fermentation. In this study, recycling digestate liquor was implemented in single-stage continuous stirred tank processes for enrichment of the nutrient content of straw with the aim of improving the methane production. The VS-based organic loading rate was set at 2 g/(L d) and the solid retention time at 40 days. When wheat straw alone was used as the substrate, the methane yields achieved with digestate liquor recycling was on average 240 ml CH₄/g VS giving a 21% improvement over the processes without recycling. However, over time, the processes suffered from declining methane yields and poor stability evidenced by low pH. To maintain process stability, wheat straw was co-digested with sewage sludge or supplemented with macronutrients (nitrogen and phosphorous). As a result, the processes with digestate liquor recycling could be operated stably, achieving methane yields ranging from 288 to 296 ml CH₄/g VS. Besides, the processes could not be operated sturdily with supplementation of macronutrients without digestate liquor recycling. The highest methane yield (296 ± 16 ml CH₄/g VS) was achieved by co-digestion with sewage sludge plus recycling of digestate liquor after filtration (retention of nutrients and microorganisms). This was comparable to the maximum expected methane yield of 293 ± 13 ml CH₄/g VS achieved in batch test. The present study therefore demonstrated that digestate liquor recycling could lead to a decreased dilution of vital nutrients from the reactors thereby rendering high process performance and stability.     

Production of hydrogen and methane by one and two stage fermentation of food waste

Anaerobic digestion is an attractive process for generation of hydrogen and methane, which involves complex microbial processes on decomposition of organic wastes and subsequent conversion of metabolic intermediates to hydrogen and methane. Comparative performance of a sequential hydrogen and methane fermentation in two stage process and methane fermentation in one stage process were tested in batch reactor at varying ratios of feedstock to microbial inoculum (F/M) under mesophilic incubation. F/M ratios influence biogas yield, production rate, and potential. The highest H₂ and CH₄ yields of 55 and 94 mL g⁻¹ VS were achieved at F/M of 7.5 in two stage process, while the highest CH₄ yield of 82 mL g⁻¹ VS in one stage process was observed at the same F/M. Acetic and butyric acids are the main volatile fatty acids (VFAs) produced in the hydrogen fermentation stage with the concentration range 10–25 mmol L⁻¹. Little concentrations of VFAs were accumulated in methane fermentation in both stage processes. Total energy recovery in two stage process is higher than that in one stage by 18%. This work demonstrated two stage fermentation achieved a better performance than one stage process.     

Biogas production from co-digestion of a mixture of cheese whey and dairy manure

In this study, daily amount of biogas of different mixtures of cheese whey and dairy manure, rates of production of methane, removal efficiencies of chemical oxygen demand (COD), total solid (TS) matter and volatile solid (VS) matter from the mixtures were investigated at 25 and 34 °C. In the experimental studies, two different solid matter rates (8% and 10%) were studied. The hydraulic retention times (HRTs) were 5, 10 and 20 days. Removal efficiencies and amount of biogas produced in each HRT were determined. Maximum daily biogas production was obtained as 1.510 m³ m^?3 d^?1 at HRT of 5 days in the mixture containing 8% total solid matters at 34 °C and the methane production rate was around 60 ± 1% in all experiments. Maximum removal efficiencies for TS, VS and COD were found as 49.5%, 49.4% and 54%, respectively at HRT of 10 days in the mixture containing 8% total solid matters at 34 °C.     

Enhancement of biogas production from sunnhemp using alkaline pretreatment

This study investigates enhancing the biogas production of sunnhemp by pretreatment, before the anaerobic digestion and co-digestion processes, to address the complex and recalcitrant structure of the plant. Fresh sunnhemp harvested at a cutting interval of 50 days is used in the study. Five systems (each with a 5 litre useable volume) are operated semi-continuously with five different ratios of the feedstock by feeding separate feedstocks every five days with a hydraulic retention time (HRT) of 40 days. The system operates at room temperature (30 °C). The study uses sunnhemp as 20% of the feedstock and also considers sunnhemp mixed with cow manure at different ratios, with the weighed sunnhemp being pretreated with dilute sodium hydroxide. Pretreatment of sunnhemp before digestion produces a methane (CH₄) yield 89% greater than that of the untreated sunnhemp. It requires 3.597 kg of dry sunnhemp to produce 1 m³ of CH₄ and the annual CH₄ yield per hectare is 19,015 m³. In the pretreatment of sunnhemp before co-digestion, the increased CH₄ yield depends on the amount of pretreated sunnhemp in the feedstocks. However, the %CH₄, the CH₄ production level and the system stability depend on the optimal ratio of the sunnhemp to cow manure. The initially prepared sunnhemp to cow manure ratio is recommended at 10 g:10 g in 80 mL of water. At this ratio, the %CH₄ and the CH₄ yield are 53.84% and 313 kg chemical oxygen demand (COD) removed, respectively, and the COD removal efficiency is 56.4%. Sunnhemp has high potential and it is worth pretreating before producing biogas. Using sunnhemp to produce biogas is recommended to decrease greenhouse gas emissions and mitigate global warming.     

Transient performance during start-up of a two-phase anaerobic digestion process demonstration unit treating carbohydrate-rich waste with biochar addition

The paper reports an experimental investigation into the transient performance during the start-up of a pilot-scale two-phase anaerobic digestion (TPAD) process demonstration unit (PDU) treating food waste with biochar addition. Hydrogen (H₂) was produced in the first phase (R1) and methane (CH₄) was produced in the second phase (R2). A fed-batch operation strategy was applied to the start-up of both phases, followed by semi-continuous operation. Production rates and yields of H₂ and CH₄ and volatile fatty acids (VFA) were measured while the pH and temperature were monitored throughout the process. Fed-batch operation allowed microbe enrichment and gradual VFA production in both phases, which was observed to be efficient in starting up the TPAD PDU. Under semi-continuous operation, R1 produced biogas with composition up to 49% of H₂ and at a yield of 46 L H₂.kg ⁻¹ VS. CH₄ composition and yield reached up to 59% and 301 L CH₄.kg⁻¹ VS in the R2.     

Using sugarcane leaves and tops for exploiting higher methane yields: An assessment study

Sugarcane leaves and tops are lignocellulosic agricultural by-products which are considered a significant input for biogas production. Their potential pretreatment by sodium hydroxide prior to co-digestion with cow manure helps increase the methane (CH₄) content, biodegradation efficiency of the lignocellulosic materials and CH₄ yield. The untreated and pretreated sugarcane leaves and tops to cow manure and water of different ratios were digested and co-digested in the 5 L reactors by semi-continuous operation with hydraulic retention time of 40 days. The pretreated sugarcane leaves and tops to cow manure at the initial prepared ratio of 100 g:100 g, in 800 mL water which was corresponding to the organic loading rate (OLR) of 0.61 kg COD/m³·day was recommended. At this ratio, the chemical oxygen demand and total volatile solids degradation efficiency was 68.80 and 72.52%, respectively, the CH₄ content was 44.52% and the CH₄ yield was 331 L/kg COD degraded. According to the results, there is an average of 3.7% deviation between the practical model based on the thermodynamic balance equations carried out using the Aspen Plus and the experimental study. The highest exergy destruction rate is found at 21 kW where the sugarcane leaves and tops, and cow manure ratio is 100 g:100 g, in 800 mL water. The highest energy and exergy efficiencies of the overall system are calculated as 45.53% and 46.02%, respectively.     

Effect of salt and sodium concentration on the anaerobic methanisation of the halophyte Tripolium pannonicum

The halophyte species Sea Aster (Tripolium pannonicum) was grown with different concentrations of artificial seawater. In a second experiment, T. pannonicum was cultivated with a nutrient solution containing different concentrations of NaCl. This halophyte biomass was used to determine the biogas production potential. According to the findings, it is possible to produce high yields of methane using biomass from halophytes cultivated in the presence of salt. Biogas and methane yield are influenced by the salt content of the plant tissue, however, high concentrations of salt in the anaerobic reactors itself inhibit the biogas and methane production. The highest methane yield is obtained using plant substrates grown at 22.5 g L⁻¹ sea-salt with a value of 313 cm³ g⁻¹ of VS. When treating T. pannonicum with different concentrations of NaCl, biogas and methane yields are highest when using plant substrates grown at 30 g L⁻¹ to produce values of 554 cm³ g⁻¹ of VS and 447 cm³ g⁻¹ of VS, respectively. Other research was carried out to study the effect of sodium on the biogas and methane yields using substrate from T. pannonicum cultured under non-saline conditions and adding different amounts of NaCl to the anaerobic reactors. Adding NaCl to the reactors decreases the biogas and methane production but using a salt-adapted inoculum increases the biogas yield in comparison to the non-adapted inoculum.     

Influence of storage on methane yields of separated pig slurry solids

Biogas production from separated pig slurry solids is more profitable than using untreated raw slurry because there is a higher CH₄ potential per unit fresh matter. However, logistics needs to be optimized. A stable storage without losing the high biogas potential could enable deliveries on demand. Self-heating and CH₄ yields of aerobically and anaerobically stored pig slurry solids were analysed and compared. The aerobic storages had run times of 33 and 44 days. Anaerobic storage took 7, 23 and 35 weeks. Anaerobically stored solids show no self-heating and produce CH₄ yields of up to 188 L kg⁻¹ ODM. This is over twice as much as the aerobically stored solids produce and about the same CH₄ yield produced by freshly separated solids. Additionally, a mass loss occurs under aerobic storage that reduces the methane yield of the original material too.     

The impact of inoculum source,inoculum to substrate ratio and sample preservation on methane potential from different substrates

Batch experiments were conducted to evaluate the impact of inoculum sources, inoculum to substrate (IS) ratio and storage conditions on the potential and production rate of methane (CH₄) from different substrates: wheat straw, whole crop maize, cattle manure, grass and cellulose.The results of the test with four inocula and four substrates indicated that inoculum source could have a significant impact on both CH₄ potential (BMP) and the kinetics parameters of different substrates. The two inocula showing the highest BMP and production rates in each period were those coming from a feeding with more than 70% of animal manure under thermophilic conditions. The impact of the IS ratio in the range 0.25–2.5, in terms of g volatile solids (VS) substrate/g VS inoculum, depended on substrate type. Maize silage was more affected to changes in the IS ratio than wheat straw. The optimal IS ratio range for maize was 1.0–1.5, however, a wider IS range can be used in wheat straw (0.5–2.5). The impact of freezing and drying depended on biomass type. Freezing, drying and ensiling of grass increased the CH₄ yield compared to fresh grass. Drying of maize had no impact while freezing reduced the CH₄ potential. Drying and freezing had no impact on straw.     

The effect of waste paper on the kinetics of biogas yield from the co-digestion of cow dung and water hyacinth

The effect of waste paper on biogas yield produced by co-digesting fixed amount of cow dung and water hyacinth in five digesters A-E was studied at room temperature. Waste paper was observed to improve biogas yield in digesters B-E with digester A acting as the control. However, as the amount of waste paper increased the biogas yield was observed to decrease. Kinetic model based on first order kinetic was derived to estimate the maximum, ultimate, biogas yield and also the ultimate methane yield from these biomass mixtures. The maximum biogas yield estimated using this model for digesters B-E were 0.282, 0.262, 0.233, and 0.217 lg⁻¹ VS fed with goodness of fit (R²) of 0.995, 0.99, 0.889, and 0.925 respectively, which were obtained by fitting the experimental biogas yield (y_t) against (exp(kt)−1)/exp(kt). The ultimate biogas and methane yield at very low batch solid load were extrapolated to be 0.34 and 0.204 lg⁻¹ VS fed respectively. In essence, the addition of waste paper in the co-digestion of cow dung and water hyacinth can be a feasible means of improving biogas yield and also alternative means of recycling waste paper. Furthermore, the kinetic model developed can compliment other models used in anaerobic digestion of agricultural and solid waste.     

Bio-methane potential test (BMP) using inert gas sampling bags with macroalgae feedstock

An approach to Bio-methane potential test (BMP) was carried out at mesophilic temperature of 35 °C with Supel™ inert gas sampling bags as biogas collection and storage bags, using selected seaweed (macroalgae) as substrate. Samples were given a range of pre-treatments from washing, drying and macerating. Dried laminaria digitata (DD) with 68.14% VS (%TS) produced the highest BMP of 141 ± 5.77 L CH₄/kg VS, with methane content increasing to about 70%, while the lowest BMP of 93.35 ± 5.03 L CH₄/kg VS with methane content of about 65% was obtained for fresh laminaria digitata (FD) with 72.03% VS (%TS). Methane yields of 97.66 and 67.24 m³ CH₄/t wet weight based on BMP results were obtained for DD and FD. Both DD and FD achieved within 28% and 38% of the theoretical BMP value based on the Buswell equation, respectively. The total methane (V) produced was computed based on;V = X₁ + X₂ – X₃ corrected to Standard temperature and pressure (STP).where X₁ = daily calculated headspace methane volume, X₂ = daily measured volume of methane in gas bags, X₃ = previous day headspace methane volume. An advantage of this approach is the volumetric measurement of gas produced directly from the gas bags, hence it does not require liquid displacement or pressure transducers. Results from a second set of freshly collected sample seaweed sample showed it was in agreement with published BMP values. All analysis were carried out without mineral supplementation.