Study on Influencing Factors of Methane Production Efficiency of Microbial Electrolytic Cell with CO_(2) as Carbon Source

Reducing CO_(2) to produce methane through microbial electrolytic cell(MEC)is one of the important methods of CO_(2) resource utilization.In view of the problem of low methanogenesis rate and weak CO_(2) conversion rate in the reduction process,theflowfield environment of the cathode chamber is changed by changing the upper gas cir-culation rate and the lower liquid circulation rate of the cathode chamber to explore the impact on the reactor startup and operation and products.The results showed that under certain conditions,the CO_(2) consumption and methane production rate could be increased by changing the upper gas recirculation rate alone,but the increase effect was not obvious,but the by-product hydrogen production decreased significantly.Changing the lower liquid circulation rate alone can effectively promote the growth of biofilm,and change the properties of biofilm at the later stage of the experiment,with the peak current density increased by 16%;The methanogenic rate decreased from the peak value of 0.561 to 0.3 mmol/d,and the CO_(2) consumption did not change signifi-cantly,which indicated that CO_(2) was converted into other organic substances instead of methane.The data after coupling the upper gas circulation rate with the lower liquid circulation rate is similar to that of only changing the lower liquid circulation rate,but changing the upper gas circulation rate can alleviate the decline of methane pro-duction rate caused by the change of biofilm properties,which not only improves the current density,but also increases the methane production rate by 0.05 mmol/d in the stable period.This study can provide theoretical and technical support for the industrial application scenario offlowfield regulation intervention of microbial elec-trolytic cell methanogenesis.

Effects of Fe and Mn in Paddy Soils Derived from Different Parent Materials on Methane Production and Emission

Three types of paddy soils, derived from granite, Quaternary red clay andbasalt, respectively, were selected to study the effects of Fe and Mn in paddy soils on methaneproduction and emission through pot and incubation experiments. The results indicated that thedifference of Fe and Mn in paddy soils was one of the important factors causing obvious differencesin methane emission from different soil types. Soil Fe and Mn affecting methane emission from thepaddy soils was likely through affectingsoil Eh and forming Fe and Mn plagues on rice roots.Different rates and valences of added Fe and Mn significantly affected methane production from paddysoils. Therefore, this study enhanced understanding of processes controlling methane emission frompaddy soils and may help to improve modeling and estimating regional and global methane emissionfrom paddy soils.

Monoclinic KNbO3 Nanowires for Photocatalytic Methane Production and Dye Degradation

The room temperature stabled monoclinic KNbO3 nanowires were found to act as photocatalyst for photocatalytic methane production and dye degradation in this work. Higher activities have been observed for monoclinic phase compared to the reference（orthorhombic phase）. In the photoreduction of CO2 reaction, the monoclinic KNbO3 nanowires exhibited a CH4 evolution rate of 0.025 μmol·g-1·h-1, which was higher than 0.021 μmol·g-1·h-1 of orthorhombic KNbO3 nanowires. In the photodegradation of rhodamine B（Rh B）, almost all the Rh B were degraded after 90 min light illumination for monoclinic KNbO3 nanowires. But for orthorhombic KNbO3 nanowires, the concentration of Rh B only decreased to 62% of the initial value.

Investigation of Barree-Conway non-Darcy flow effects on coalbed methane production

Coalbed gas non-Darcy flow has been observed in high permeable fracture systems,and some mathematical and numerical models have been proposed to study the effects of non-Darcy flow using Forchheimer non-Darcy model.However,experimental results show that the assumption of a constant Forchheimer factor may cause some limitations in using Forchheimer model to describe non-Darcy flow in porous media.In order to investigate the effects of non-Darcy flow on coalbed methane production,this work presents a more general coalbed gas non-Darcy flow model according to Barree-Conway equation,which could describe the entire range of relationships between flow velocity and pressure gradient from low to high flow velocity.An expanded mixed finite element method is introduced to solve the coalbed gas non-Darcy flow model,in which the gas pressure and velocity can be approximated simultaneously.Error estimate results indicate that pressure and velocity could achieve first-order convergence rate.Non-Darcy simulation results indicate that the non-Darcy effect is significant in the zone near the wellbore,and with the distance from the wellbore increasing,the non-Darcy effect becomes weak gradually.From simulation results,we have also found that the non-Darcy effect is more significant at a lower bottom-hole pressure,and the gas production from non-Darcy flow is lower than the production from Darcy flow under the same permeable condition.

Energy,economic and environmental assessment of photocatalytic methane production:a comparative case study between Japan and Malaysia

Photocatalytic methane(CH_(4))production wherein CO_(2)is reduced to CH_(4) by utilizing solar radiation energy is gaining research and industrial focus because of its environmental-friendly notion.It offers twofold advantages:reduction in CO_(2)emission and production of artificial natural gas(methane)at the same time.In this paper,comparative energy,economic and environmental assessment of such photocatalytic methane production has been carried out between Japan and Malaysian conditions.Assumptions on the photocatalytic methane production plant and estimation of energy production,CO_(2)emission reduction,and economic indicators are made based on previous research and existing technologies.Energy analysis shows that Malaysia has a higher potential for energy production and CO_(2)emission reduction than Japan.Economic analysis reveals that the feasible reaction efficiencies of the plant in Japan and Malaysia are 8%.The slightly higher conversion efficiency in Malaysia is due to the energy price and CO_(2)tax.For the implementation of the photocatalytic methane production plant,the high energy price and CO_(2)tax will work as a driving force.

Influence of main dietary chemical constituents on the in vitro gas and methane production in diets for dairy cows

Background： Modification of chemical composition of diets fed to dairy cows might be a good strategy to reduce methane（CH4） production in the rumen. Notable reductions of CH4 production compared to conventional highroughages rations were more frequently observed for very concentrated diets or when fat supplements were used. In these cases, the reduction in the gas emission was mainly a consequence of an overall impairment of rumen function with a reduction of fiber digestibility. These strategies do not always comply with feeding standards used in intensive dairy farms and they are usually not applied owing to the risks of negative health and economic consequences.Thus, the present study evaluated the effects of seven commercial diets with contents of neutral detergent fiber（NDF）,protein and lipids ranging 325 to 435 g/kg DM, 115 to 194 g/kg DM, and 26 to 61 g/kg DM, respectively, on in vitro degradability, gas（GP）, and CH4 production.Results： In this experiment, changes in the dietary content of NDF, crude protein（CP） and lipids were always obtained at the expense or in favor of starch. A decreased of the dietary NDF content increased NDF（NDFd） and true DM（TDMd） degradability, and increased CH4 production per g of incubated DM（P 〈 0.001）, but not that per g of TDMd. An increase of the dietary CP level did not change in vitro NDFd and TDMd, decreased GP per g of incubated DM（P 〈 0.001）, but CH4 production per g of TDMd was not affected. An increased dietary lipid content reduced NDFd, TDMd,and GP per g of incubated DM, but it had no consequence on CH4 production per g of TDMd.Conclusions： It was concluded that, under commercial conditions, changes in dietary composition would produce small or negligible alterations of CH4 production per unit of TDMd, but greater differences in GP and CH4 production would be expected when these amounts are expressed per unit of DM intake. The use of TDMd as a standardizing parameter is proposed to account for possible difference in DM intake and productivity.

Methodological factors affecting gas and methane production during in vitro rumen fermentation evaluated by meta-analysis approach

Effects of some methodological factors on in vitro measures of gas production（GP, mL/g DM）, CH4production（mL/g DM） and proportion（% CH4 on total GP） were investigated by meta-analysis. These factors were considered：pressure in the GP equipment（0 = constant; 1 = increasing）, incubation time（0 = 24; 1 = ≥ 48 h）, time of rumen fluid collection（0 = before feeding; 1 = after feeding of donor animals）, donor species of rumen fluid（0 = sheep; 1 =bovine）, presence of N in the buffer solution（0 = presence; 1 = absence）, and ratio between amount of buffered rumen fluid and feed sample（BRF/FS; 0 = ≤ 130 mL/g DM; 1 = 130–140 mL/g DM; 2 = ≥ 140 mL/g DM）. The NDF content of feed sample incubated（NDF） was considered as a continuous variable. From an initial database of 105 papers, 58 were discarded because one of the above-mentioned factors was not stated. After discarding 17 papers,the final dataset comprised 30 papers（339 observations）. A preliminary mixed model analysis was carried out on experimental data considering the study as random factor. Variables adjusted for study effect were analyzed using a backward stepwise analysis including the above-mentioned variables. The analysis showed that the extension of incubation time and reduction of NDF increased GP and CH4 values. Values of GP and CH4 also increased when rumen fluid was collected after feeding compared to before feeding（＋26.4 and ＋9.0 mL/g DM, for GP and CH4）,from bovine compared to sheep（＋32.8 and ＋5.2 mL/g DM, for GP and CH4）, and when the buffer solution did not contain N（＋24.7 and ＋6.7 mL/g DM for GP and CH4）. The increase of BRF/FS ratio enhanced GP and CH4production（＋7.7 and ＋3.3 mL/g DM per each class of increase, respectively）. In vitro techniques for measuring GP and CH4 production are mostly used as screening methods, thus a full standardization of such techniques is not feasible. However, a greater harmonization of analytical procedures（i.e., a reduction in the number of available protocols） would be useful to facilitate comparison between results of different experiments.

Optimization of the methane production in batch anaerobic digestion of maize straw by adjustment of total solid and substrate-to-inoculum ratio based on kinetics

Anaerobic digestion(AD)operating under conditions of organic overload stress typically exacerbates the potential for process instability,thereby resulting in significant economic and ecological ramifications.In this investigation,an augmented substrate-to-inoculum ratio(S/I)along with varying total solid content(TS)levels was employed to replicate diverse organic loadings,utilizing maize straw and cattle manure.The findings reveal that a moderate augmentation in S/I and TS proves advantageous in augmenting methane yield,while an excessive substrate loading diminishes methane yield,hampers the kinetics of methane production,and even induces severe process instability.Kinetic study also displayed the variation of the model parameters for the first-order model,the modified Gompertze model,and the transfer function model.Both the modified Gompertze model and transfer function model exhibited the same environmental stress trend.Thus,both the increase in particulate content and the increase in S/I had a substantial effect on the substrate conversion rate to methane.Microbial analysis demonstrates the dominant influence of Firmicutes and Methanosarcina under different organic loading stresses.From both a kinetic and a microbiological point of view,this work provides novel insights into the fundamental processes that regulate anaerobic digestion(AD)under varying loading stress.Furthermore,it has significant implications for improving the operating efficiency of AD,which is a significant benefit.

New microbial electrosynthesis system for methane production from carbon dioxide coupled with oxidation of sulfide to sulfate

Microbial electrosynthesis system (MES) is a promising method that can use carbon dioxide,which is a greenhouse gas,to produce methane which acts as an energy source,without using organic substances.However,this bioelectrical reduction reaction can proceed at a certain high applied voltage when coupled with water oxidation in the anode coated with metallic catalyst.When coupled with the oxidation of HS–to SO_(4)^(2-),methane production is thermodynamically more feasible,thus implying its production at a considerably lower applied voltage.In this study,we demonstrated the possibility of electrotrophic methane production coupled with HS–oxidation in a cost-effective bioanode chamber in the MES without organic substrates at a low applied voltage of 0.2 V.In addition,microbial community analyses of biomass enriched in the bioanode and biocathode were used to reveal the most probable pathway for methane production from HS–oxidation.In the bioanode,electroautotrophic SO_(4)^(2-)production accompanied with electron donation to the electrode is performed mainly by the following two steps:first,incomplete sulfide oxidation to sulfur cycle intermediates (SCI) is performed;then the produced SCI are disproportionated to HS^(–)and SO_(4)^(2-).In the biocathode,methane is produced mainly via H_(2)and acetate by electronaccepting syntrophic bacteria,homoacetogens,and acetoclastic archaea.Here,a new ecofriendly MES with biological H_(2)S removal is established.

Degradation of polyacrylamide (PAM) and methane production by mesophilic and thermophilic anaerobic digestion: Effect of temperature and concentration

Polyacrylamide(PAM)is generally employed in wastewater treatment processes such as sludge dewatering and therefore exists in the sludge.Furthermore,it degrades slowly and can deteriorate methane yield during anaerobic digestion(AD).The impact or fate of PAM in AD under thermophilic conditions is still unclear.This study mainly focuses on PAM degradation and enhanced methane production from PAM-added sludge during 15 days of thermophilic(55°C)AD compared to mesophilic(35°C)AD.Sludge and PAM dose from 10 to 50 g/kg TSS were used.The results showed that PAM degraded by 76%to 78%with acrylamide(AM)content of 0.2 to 3.3 mg/L in thermophilic AD.However,it degraded only 21%to 30%with AM content of 0.5 to 7.2 mg/L in mesophilic AD.The methane yield was almost 230 to 238.4 mL/g VSS on the 8th day in thermophilic AD but was 115.2 to 128.6 mL/g VSS in mesophilic AD.Mechanism investigation revealed that thermophilic AD with continuous stirring not only enhanced PAM degradation but also boosted the organics release from the sludge with added PAM and gave higher methane yield than mesophilic AD.

Enhanced methane production during long-term UASB operation at high organic loads as enabled by the immobilized Fungi

Anaerobic digestion is widely applied in organic wastewater treatment coupled with bioenergy production,and how to stabilize its work at the high organic loading rate(OLR)remains a challenge.Herein,we proposed a new strategy to address this issue via involving the synergetic role of the Aspergillus sydowii 8L-9-F02 immobilized beads(AEBs).A long-term(210-day)continuous-mode operation indicated that the upflow anaerobic sludge bed(UASB)reactor(R1,with AEBs added)could achieve the OLR as high as 25.0 kg/(m^(3)×d),whereas the control reactor(R0,with AEBs free)could only tolerate the maximum OLR of 13.3 kg/(m^(3)×d).Remarkably,much higher COD removal(85.9%vs 23.9%)and methane production(5.4 m^(3)/(m^(3)×d)vs 2.2 m^(3)/(m^(3)×d))were achieved in R1 than R0 at the OLR of 25.0 kg/(m^(3)×d).Such favorable effect results from the facts that fungi inhibit VFAs accumulation,favor the pH stabilization,promote the generation of more extracellular polymeric substance,and enhance the sludge granulation and settleability.Moreover,fungi may enhance the secretion of acetyl-coenzyme A,a key compound in converting organic matters to CO_(2).In addition,fungi are favorable to enrich methanogenic archaea even at high OLR,improving the activity of acetate kinase and coenzyme F_(420) for more efficient methanogenic pathway.This work may shed new light on how to achieve higher OLR and methane production in anaerobic digestion of wastewater.

Effects of cow manure ratios on methane production and microbial community evolution in anaerobic co-digestion with different crop wastes

The present study investigated the effects of cow manure ratios mixed with maize stover,rice straw,and wheat stalk at 3,2,1(total solid based,TS-based),respectively,on methane production and microbial community structure during the anaerobic co-digestion process.Results showed cow manure co-digested with maize stover,wheat stalk,and rice straw at ratios of 2,1,and 3 had the highest cumulative methane yields(272.99,153.22167.73 mL/g volatile solid(VS),respectively)and better stability(e.g.pH,volatile fatty acids(VFAs)and their component).The main microbe evolution had a similar trend which was Petrimonas and Methanosaeta in the early digestion process(Days 0-7)and then evolved into Longilinea,Ruminofilibacter,and Methanosarcina with the progress of digestion,but the relative abundance of these microbes in each reactor was different.It was worth noting that Caldicoprobacter in cow manure to maize stover ratio of 2,and to rice straw ratio of three reactors had a relatively higher proportion than reactor of cow manure to wheat stalk ratio of 1,and Hydrogenophaga was the specific bacterium in cow manure to wheat stalk ratio of 1 reactor.In addition,Petrimonas showed positive relationship with VFAs and Longilinea was the opposite.Methanosaeta and Methanobacterium contributed the most during the peak period of methane production in cow manure and maize stover co-digested reactor,and showed positive relationship with acetic acid.However,Methanosarcina and Methanospirillum made a great contribution during the peak period of methane production in cow manure co-digested with wheat stalk and rice straw reactors.These findings could provide further information on the application of cow manure co-digested with crop wastes.

Enhanced methane production in an anaerobic digestion and microbial electrolysis cell coupled system with co-cultivation of Geobacter and Methanosarcina

The anaerobic digestion（AD）and microbial electrolysis cell（MEC）coupled system has been proved to be a promising process for biomethane production.In this paper,it was found that by co-cultivating Geobacter with Methanosarcina in an AD–MEC coupled system,methane yield was further increased by 24.1%,achieving to 360.2 m L/g-COD,which was comparable to the theoretical methane yield of an anaerobic digester.With the presence of Geobacter,the maximum chemical oxygen demand（COD）removal rate（216.8 mg COD/（L·hr））and current density（304.3 A/m3）were both increased by 1.3 and 1.8 fold compared to the previous study without Geobacter,resulting in overall energy efficiency reaching up to 74.6%.Community analysis demonstrated that Geobacter and Methanosarcina could coexist together in the biofilm,and the electrochemical activities of both were confirmed by cyclic voltammetry.Our study observed that the carbon dioxide content in total gas generated from the AD reactor with Geobacter was only half of that generated from the same reactor without Geobacter,suggesting that Methanosarcina may obtain the electron transferred from Geobacter for the reduction of carbon dioxide to methane.Taken together,Geobacter not only can improve the performance of the MEC system,but also can enhance methane production.

Anaerobic co-digestion of rice straw and digested swine manure with different total solid concentration for methane production

This study aimed to investigate potential methane production through anaerobic co-digestion of rice straw and digested swine manure with different total solids.The research was carried out in bench scale with utilizing batch system.To evaluate the stability of anaerobic co-digestion process,the experiment was run in triplicate.The anaerobic co-digestion process was operated in 500 mL batch digesters under constant agitation speed and temperature.The agitation speed was maintained at 270 r/min.Temperature of the batch system was set and maintained at 35℃.Digested swine manure utilized in this experiment was obtained from semi-continuous digesters run at steady state condition,with 25 days of hydraulic retention time under mesophilic condition.Rice straw(RS)generated the highest methane production at 3% total solids(TS)which was around(1814±47.43)mL,where in this concentration,it had C:N ratio at 10.6:1.Rice straw obtained the highest methane yield at 3% TS,which was around(141.4±3.70)mL CH_(4)/g volatile solids(VS)added.Rice straw also had the highest chemical oxygen demand(COD)removal and VS reduction at 3% TS which were around(52.97%±1.46%)and(61.81%±1.04%),respectively.

An advanced anaerobic biofilter with effluent recirculation for phenol removal and methane production in treatment of coal gasification wastewater

An advanced anaerobic biofilter（AF） was introduced for the treatment of coal gasification wastewater（CGW）,and effluent recirculation was adopted to enhance phenol removal and methane production.The results indicated that AF was reliable in treating diluted CGW,while its efficiency and stability were seriously reduced when directly treating raw CGW.However,its performance could be greatly enhanced by effluent recirculation.Under optimal effluent recirculation of 0.5 to the influent,concentrations of chemical oxygen demand（COD） and total phenol in the effluent could reach as low as 234.0 and 14.2 mg/L,respectively.Also,the rate of methane production reached 169.0 m L CH_4/L/day.Though CGW seemed to restrain the growth of anaerobic microorganisms,especially methanogens,the inhibition was temporary and reversible,and anaerobic bacteria presented strong tolerance.The activities of methanogens cultivated in CGW could quickly recover on feeding with glucose wastewater（GW）.However,the adaptability of anaerobic bacteria to the CGW was very poor and the activity of methanogens could not be improved by long-term domestication.By analysis using the Haldane model,it was further confirmed that high effluent recirculation could result in high activity for hydrolytic bacteria and substrate affinity for toxic matters,but only suitable effluent recirculation could result in high methanogenic activity.

Catalytic coal gasification for methane production: A review

Catalytic coal gasification for methane production is a promising technology in the clean coal utilization field.In this review,the technologies for coal-derived natural gas production,the catalytic coal gasification processes and the used reactors were compared.The compared catalysts mainly included single-component,composite,and disposable catalysts.The effects of catalyst properties included composition,preparation method,supporter and loading amount were further illustrated.The influences of coal properties included char preparation method,particle size,and ash content on catalytic performance were investigated.The effects of temperatures and pressures on gasification performance were discussed in details.The evaporation,melting,decomposition,and inactivation of catalyst under various temperatures and pressures were also analyzed.It is expected to provide comprehensive information on the researches of catalytic coal gasification for methane production.

Effects of ceramsite on methane and hydrogen sulphide productions from macroalgae biomass

The easy acidification and high hydrogen sulfide （H2S） production during anaerobic digestion of macroalgae limited its application in biomethane production. In order to investigate the effects of ceramsite on methane and HzS productions during anaerobic digestion of macroalgae, batch experiments ofMacrocystis pyrifera were carried out. Four groups named C0, C1, C2 and C3 added with 0, 1.5, 3.0 and 4.5 g/g substrate of ceramsite, respectively, were studied and compared. The highest cumulative methane yield of 286.3 mL/g substrate is obtained in C2, which is 40.11% higher than that of CO. The cumulative HzS yields of C1, C2 and C3 are 32.67%, 44.66% and 53.21% lower than that of CO, respectively. Results indicate that ceramsite addition permits higher methane yields, shorter lag-phase time and lower HzS yields during anaerobic digestion of Macrocystispyrifera.

Effect of the chlortetracycline addition method on methane production from the anaerobic digestion of swine wastewater

Effects of antibiotic residues on methane production in anaerobic digestion are commonly studied using the following two antibiotic addition methods：（1） adding manure from animals that consume a diet containing antibiotics, and（2） adding antibiotic-free animal manure spiked with antibiotics. This study used chlortetracycline（CTC） as a model antibiotic to examine the effects of the antibiotic addition method on methane production in anaerobic digestion under two different swine wastewater concentrations（0.55 and 0.22 mg CTC/g dry manure）. The results showed that CTC degradation rate in which manure was directly added at 0.55 mg CTC/g（HSPIKE treatment） was lower than the control values and the rest of the treatment groups. Methane production from the HSPIKEtreatment was reduced（p 〈 0.05） by 12% during the whole experimental period and 15% during the first 7 days. The treatments had no significant effect on the pH and chemical oxygen demand value of the digesters, and the total nitrogen of the0.55 mg CTC/kg manure collected from mediated swine was significantly higher than the other values. Therefore, different methane production under different antibiotic addition methods might be explained by the microbial activity and the concentrations of antibiotic intermediate products and metabolites. Because the primary entry route of veterinary antibiotics into an anaerobic digester is by contaminated animal manure, the most appropriate method for studying antibiotic residue effects on methane production may be using manure from animals that are given a particular antibiotic, rather than adding the antibiotic directly to the anaerobic digester.

Rumen methane output and fermentation characteristics of gramineous forage and leguminous forage at differing harvest dates determined using an in vitro gas production technique

An in vitro rumen gas production technique was employed to determine the methane production and fermentation characteristics of Leymus chinensis and Medicago ruthenica at differing harvest dates（May 15,May 30,June 30,July 30,August 30 and September 30）,which are sequential phases within a single continuous growth of two 10-year-old pastures.To quantify the rate of degradation and compare in vitro rumen fermentation characteristic,a logistic-exponential model,where initial gas volume was zero（LE_0）,was used to fit gas production and methane output results.Dried,milled forage samples were incubated in vitro for 72 h at 39℃ and gas production was recorded intermittently throughout the incubation and gas samples were collected to measure methane production.Results showed that there were significant interactions between species and harvest for all chemical composition variables（P〈0.001） and condensed tannin content（P〈0.001）.L.chinensis produced more total gas and methane than M.ruthenica（P〈0.001）.Both total gas and methane production decreased lineally（P〈0.001） with advancing harvest date.The degradation rates of L.chinensis and M.ruthenica harvested on September 30 were lower than those on the other harvest dates（P〈0.01）.M.ruthenica fermented fluid had higher concentration of ammonia N（P〈0.05） and molar proportions of isobutyrate（P〈0.01）,valerate（P〈0.001） and isovalerate（P〈0.01） in total volatile fatty acids than L chinensis.Furthermore,concentration of isovalerate decreased cubically with advancing harvest date（P〈0.05）.In conclusion,M.ruthenica produced less methane than L.chinensis and the total gas and methane production decreased with advancing harvest date for both species,which may be due to the changes in contents of chemical compositions and condensed tannin in forages.

Optimization of microwave pretreatment of lignocellulosic waste for enhancing methane production： Hyacinth as an example

The effect of microwave pretreatment on the anaerobic degradation of hyacinth was investigated using response surface methodology （RSM）. The components oflignin and the other constituents of hyacinth were altered by microwave pretreatment. Comparison of the near-infrared spectra of hyacinth pretreated by microwave irradiation and water-heating pretreatment revealed that no new compounds were generated during hyacinth pretreatment by microwave irradiation. Atomic force microscopy observations indicated that the physical structures of hyacinth were disrupted by microwave pretreatment. The yield of methane per gram of the microwave-irradiated substrate increased by 38.3% as compared to that of the substrate pretreated via water-heating. A maximum methane yield of 221 mL·g-sub^-1 was obtained under the optimum pretreatment conditions （substrate concentration （pSC） = 20.1 g·L^-1 and pretreatment time （PT） = 14.6 min） using RSM analysis. A maximum methane production rate of 0.76 mL·h^-1· g-sub^-1 was obtained by applying PSC = 9.5 g·L^-1 and PT= 11 min. Interactive item coefficient analysis showed that methane production was dependent on the PSC and PT, separately, whereas the interactive effect of the PSC and PT on methane production was not significant. The same trend was also observed for the methane production rate.