Multi-objective optimization of biomass to biomethane system

The superstructure optimization of biomass to biomethane system through digestion is conducted in this work. The system encompasses biofeedstock collection and transportation, anaerobic digestion, biogas upgrading, and digestate recycling. We propose a multicriteria mixed integer nonlinear programming(MINLP) model that seeks to minimize the energy consumption and maximize the green degree and the biomethane production constrained by technology selection, mass balance, energy balance, and environmental impact. A multi-objective MINLP model is proposed and solved with a fast nondominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ). The resulting Pareto-optimal surface reveals the trade-off among the conflicting objectives. The optimal results indicate quantitatively that higher green degree and biomethane production objectives can be obtained at the expense of destroying the performance of the energy consumption objective.

Carbohydrate Yield and Biomethane Potential from Enzymatically Hydrolysed <i>Saccharina latissima</i>and Its Industrial Potential

The demand for fuel for utilisation of machinery and transport has culminated in large amounts of fossil fuel usage in the last century. The environmental dangers attached with the usage of fossil fuels have created a large demand for alternative sources of fuels. There is an array of polysaccharides contained within macroalgae, such as mannitol, cellulose and laminarin. These polysaccharides have potential for production of alternative biofuels;however, they are not easily accessible for biological digestion. By pretreatment of macroalgae with enzymes, these polysaccharides may be easier to access by microbes, allowing effective utilization in anaerobic digestion. Saccharina latissima, available in abundance on the Norwegian coast line, is a brown macroalgae with a high level of carbohydrates. This study assesses the ability for utilisation of enzymatically pre-treated Saccharina latissima for production of biogas through anaerobic digestion. The harvested Saccharina latissima was analysed to contain 30.11 ± 2.30 g of reducing sugars per 100 g of dry sample upon enzymatic hydrolysis. This was able to yield 459 ± 30 mL per gVS of biogas through anaerobic digestion, with a methane content of 56%. This suggests a biomethane potential of 1760 m3 per ha of productive sea floor growing Saccharina latissima. An evaluation of this process has been performed to demonstrate the industrial potential of Saccharina latissima in biogas production.

Effects of Heavy Metal Ions (Fe³⁺, Cu²⁺, Zn²⁺and Cr³⁺) on the Productivity of Biogas and Biomethane Production

It was shown that the concentration of heavy metal ions Fe3+, Cu2+, Cr3+ and Zn2+, which are contained in the fermentation medium, affects the process of biogas production. The aim of this paper was to establish the concentration of ions, which makes it possible to increase the yield of biogas and the methane content in it. The total yield of biogas per unit of dry organic matter, methane and the kinetics of changes in the yield of biogas during fermentation of cattle manure in the presence of different concentrations of metal ions in the anaerobic environment. It was established that the content of Fe3+, Cu2+ is up to 80 mg/dm3, Cr3+ and Zn2+ is up to 50 mg/dm3 in the medium lead to increased methane production by anaerobic association of microorganisms due to the effect on the activity of enzyme systems in comparison with the sample without the addition of metal ions. It was found that the rational concentrations to increase the methane yield in the biogas obtained by fermentation of cattle manure are: Fe3+-20 - 40 mg/dm3, Cu2+-40 - 60 mg/dm3, Cr3+-10 mg/dm3. The increase in the concentration of metal ions above rational values leads to a decrease in the methane content in biogas. It was shown that zinc ions have a positive effect on methane production, but reduce the total biogas yield and, accordingly, the degree of conversion of organic raw materials. Therefore, the rational concentration of Zn2+ in the fermentation medium is 10 mg/dm3.

Improving biomethane yield by strengthening acidification of maize stover in two-phase anaerobic digestion

In this study,the acidification and two-phase anaerobic digestion(AD)were conducted in batch and continuous stirred tank reactors,respectively,to determine the effect of acidification on methane production in AD.The results showed that two-phase AD achieved an observable enhancement in the methane production under optimal acidification conditions(organic loading rate of 60 g TS/L,the ratio of raw material to inoculum(based on dry weight)of 2:1,the temperature of 45℃,urea concentration of 4%,and time of 6 d).Under these conditions,the daily biogas and biomethane productions were 0.48 L/g TS and 0.30 L/g TS,respectively,which were 26.32%and 57.89%higher than those of the untreated group,respectively.The ammonia nitrogen(AN),alkalinity,and pH value of the methanogenic phase of C4 continued to increase up to 956 mg/L,5680 mg/L,and 7.41,respectively,after 60 d,which might have destroyed the stability of the system.Therefore,for the purpose of reusing the nitrogen source,reducing AN,and maintaining the stability of the reaction system,another set of acidification and two-phase AD with water pretreatment using the discharge of the methanogenic phase of C4 as the inoculum was subsequently conducted.The results showed that the daily biogas productions of single-phase and two-phase AD were 5.26%and 15.79%higher than that of the untreated group,respectively;similarly,their daily methane yields were 10.42%and 21.05%higher than that of the untreated group.

Biomethane use for automobiles towards a CO_(2)-neutral energy system

To pursue the goal of sustainable mobility,two main paths can be considered:the electrification of vehicles and the use of biofuels,replacing fossil fuels,in internal combustion engine(ICE)vehicles.This paper proposes an analysis of different possible scenarios for automobiles towards a CO_(2)-neutral energy system,in the path of the use of biofuels and the production,distribution and use of biomethane.The study,an update of work presented previously,focuses on different scenarios that take into account numerous parameters that affect the overall efficiency of the production-and-use process.A Well-to-Wheel analysis is used to estimate the primary energy savings and reduction in greenhouse-gas emissions compared both to the use of fossil-based methane and to other fuels and automotive technologies.In particular,the study shows that the Non-Renewable Primary Energy Consumption(NRPEC)for biomethane is slightly higher(+9%)than that of biodiesel,but significantly lower than those of all the other power trains analysed:-69%compared to the battery electric vehicle(BEV)and-55%compared to bioethanol.Compared to the use of fossil natural gas,the NRPEC is reduced to just over a third(2.81).With regard to CO_(2) emissions,biomethane has the lowest values:-69%compared to BEV,-176%compared to bioethanol and-124%with respect to biodiesel.Compared to the use of fossil natural gas,the CO_(2) emissions are reduced over a third(3.55).Moreover,the paper shows that biomethane can completely cover the consumption of fossil methane for vehicles in Italy,proposing two different hypotheses:maximum production and minimum production.It is evident,therefore,that biomethane production can completely cover the consumption of fossil methane for vehicles:this means that the use of biomethane in the car can lead to a reduction in NRPEC equal to 28.9×10^(6) GJ/year and a reduction of CO_(2) emissions equal to 1.9×10^(6) t/year.

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.

Recent progress in supercritical fluid science for biofuel production from woody biomass

Owing to an environment-friendly utilization of resources, increased attention has been focused on fuels and chemicals from biomass as an alternative to fossil resources. In addition, supercritical fluid technology has been considered to be an environmentally-benign treatment. Therefore, its technology was applied for a conversion of biomass to useful fuels and chemicals in order to mitigate environmental loading. For example, supercritical water treatment has demonstrated that lignocellulosics can be hydrolyzed to become lignin-derived products for useful aromatic chemicals and carbohydrate-derived products, such as polysaccharides, oligosaccharides and monosaccharides of glucose, mannose and xylose used for subsequent ethanol fermentation. If this treatment is prolonged, lignocellulosics were found to be converted to organic acids such as formic, acetic, glycolic and lactic acids which can be converted to methane for biofuel. When alcohols, such as methanol and ethanol, were used instead of water, some other useful products were achieved, and its liquefied products were found to have a potential for liquid biofuel. In this study, therefore, our research achievements in supercritical fluid science of woody biomass will be introduced for clean and green chemistry for a sustainable environment.

Effect of ultrasonic assisted KOH pretreatment on physiochemical characteristic and anaerobic digestion performance of wheat straw

In this study,ultrasonic field was applied during potassium hydroxide(KOH) pretreatment of wheat straw(WS).Three concentrations of KOH(2%,4%,and 6%) were tested during pretreatment.The results showed that there was a significant influence of the ultrasonic assisted KOH pretreatment(KOH(Upt)) on physiochemical characteristics of WS during pretreatment as well as on digester performance.The pretreatment time was optimized to 36 h for all KOH concentrations.The highest total volatile fatty acid(TVFA) productions(3189 mg·L^-1) from 6%KOHupt samples were observed.Similarly,the SEM analysis and FTIR observation revealed that KOH(Upt) effectively disrupted the physical morphology of WS and successful breaking of lignin and hemicellulose linkage between carboxyl groups.Moreover,the highest biogasification(555 ml·(g VS(loaded))^-1) and biomethane productions(282 ml·(g VS(loaded))^-1) from 4%KOH(Upt) digesters,with 69% of biodegradability,indicated significant availability of organic matter from KOH(Upt).The R^2 values(0.993-0.998) in Modified Gompertz Model indicated that the model was feasible to predict methane yield for this study.Similarly,the Bo values for 4%KOH(Upt)(283.30±2.74 ml·(gVS(loaded))^-1) were also in agreement to the experimental methane yield.These results suggested that ultrasonic addition during KOH pretreatment of WS can effectively increase the organic yield during pretreatment.Moreover,the increase in methane production from 4% KOH(Upt) suggested that digester performance can be improved with lower KOH concentrations using this pretreatment.

Optimization of Biogas Production from Organic Municipal Waste: Development of Activated Sludge as Digesters Inoculum

This study is a contribution to the optimization of organic fraction of municipal waste bioconversion into biomethane, by activated sludge production as inoculum for digesters. The wastewater (WW) and cow dung (CD) samples were taken from the slaughterhouse of Ouagadougou town, Burkina Faso. Different mixtures were made, enriched with mineral solution and cellulose at 5% (w/v) as: 10% CD + 90% WW (C7), 30% CD + 70% WW (C6), 50% CD + 50% WW (C5), 70% CD + 30% WW (C4), 90% CD + 10% WW (C3), 100% CD (C2) and 100% WW (C1). The pH evolution and biogas (CH4 and CO2) production were followed for 25 days. Cultures tend to acidify with increase in cow dung proportion. Biogas production was significantly higher (p < 0.05) in C5 (880.0 mL), C6 (862.0 10 mL) and C7 (772.0 mL). Mixture C5 had a highest level of CO2 production (40%). Also C7 and C6 retained in the experiment contained respectively organic matter, volatile fatty acids (VFA) and total alkalinity (TAC) as 41.06%, 47.02%, 1320 mg acetic acid/L, 3036 mg Acetic acid/L and 520 mg CaCO3/L, 1310 mg CaCO3/L. Mixture C6 was the best medium for microorganism proliferation stability with 3.5 × 105 UFC/ml of methanogens bacteria. It also possessed buffering capacity, which prevents acidification of medium during VFAs production.

Anaerobic Mono-Digestion of Turkey Manure: Efficient Revaluation to Obtain Methane and Soil Conditioner

This work demonstrates the possibility to make a full valuation of a solid waste such as turkey manure, to obtain methane and a soil conditioner/fertilizer from turkey manure anaerobic digestion in a mesophilic pilot-scale continuous stirred tank reactor at different organic loading rates (OLR) (from 0.5 to 2.5 kgVS/m3d). The application of the anaerobic mono-digestion for the turkey manure treatment was an efficient alternative, because high volatile solids removal and methane were obtained in addition to obtaining a stabilized solid waste that can be applied as soil conditioner, based on its nutritional parameters and humic substances content. In this way, the turkey manure anaerobic digestion can be applied avoiding the co-digestion of the manure with other wastes and allows a process devoid of pollutant emissions, obtaining two products. The reactor operation depends on the OLR, and its operation does not allow an OLR above 1.5 kgVS/m3d. Higher OLR produced a decrease in the TS and VS removals and methane productivity.

Determination of the Experimental Calorific Performance of Passion Fruit Spreading Waste

Brazil is the world’s largest producer and consumer of passion fruit,being a tropical fruit that produces a lot of waste in its process.As this residue is more than 60%of the mass of the fruit,there is a problem directed to the discard of the same.One way to add economic and financial value to the passion fruit industry would be to use the waste as a source of fuel in a process of converting biomass to energy.The objective of this work was to characterize samples of passion fruit residues by analyzing the moisture content and the experimental calorific value,aiming at its energy utilization,in order to obtain initial information to help define the best conversion path of this biomass:thermochemical or biochemical.After analysis,it was concluded that the most appropriate biomass utilization route would be anaerobic biodigestion due to the high moisture content presented in the samples(greater than 80%).However,the same ones,if in dry basis,also have high calorific value,compared,for example,with sugarcane bagasse.With the results,it was demonstrated that the biomass of the passion fruit pulp presents itself as a potential alternative for the energy utilization.

Mesophilic Process and Kinetics Studies of Selected Biomolecules as Potential Enhancers of Biomethanization of Cow Dung in an Anaerobic Tubular Batch Reactor

Mesophilic biogas production and substrate decomposition is one of the significant limiting steps in biogas generation. The rate of generation and quality often affect the viability of biogas systems. This study assessed the potential for biogas process catalysis using powdered Sorghum bicolor L., Zea mays, and Pennisetum glaucum. The kinetics and biogas generation processes were studied. Experiments were conducted in 1 m3 tubular batch reactors, where batches were dosed with various organic biomolecules. Results show that the use of P. glaucum L. and S. bicolor L. reduced the biogas retention times significantly. Biogas generation commenced after the first day for digesters fed with S. bicolor L. and P. glaucum L. while one with Z. mays and control occurred on day two. The rate of biomethanation and methane content were enhanced. S. bicolor L. led to the highest methane content. Findings reveal that locally available organic biomolecules improved biogas quality and quantity.

VALORIZATION OF BIOGAS THROUGH SIMULTANEOUS CO_(2) AND H_(2)S REMOVAL BY RENEWABLE AQUEOUS AMMONIA SOLUTION IN MEMBRANE CONTACTOR

Upgrading biogas into biomethane not only improves the biogas utilization as vehicle fuel or natural gas substitute,but also reduces the greenhouse gases emissions.Considering the principle of engineering green energy process,the renewable aqueous ammonia(RAA)solution obtained from biogas slurry was used to remove H_(2)S and CO_(2) simultaneously in the hollow fiber membrane contactor.RAA was mimicked in this study using the ammonia aqueous solution mixed with some typical impurities including ethanol,acetic acid,propionic acid,butyric acid and NH4HCO_(3).Compared with the typical physical absorption(i.e.,pure water)removing 48%of H_(2)S from biogas,RAA with 0.1 mol·L^(−1) NH_(3) could remove 97%of H_(2)S.Increasing the NH3 concentration from 0.1 to 0.5 mol·L^(−1) could elevate the CO_(2) absorption flux from 0.97 to 1.72 mol·m^(−2)·h^(−1) by 77.3%.Among the impurities contained in RAA,ethanol has a less impact on CO_(2) absorption,while other impurities like CO_(2) and acetic acid have significant negative impacts on CO_(2) absorption.Fortunately,the impurities have a less influence on H_(2)S removal efficiency,with more than 98%of H_(2)S could be removed by RAA.Also,the influences of operating parameters on acid gases removal were investigated to provide some engineering suggestions.

Maximal methane potential of different animal manures collected in northwest region of China

Maximum methane potential(B0)is an important parameter used in assessing suitability of a substrate for biogas production.This study examined maximum methane potential of different manures generated from three major Chinese livestock,namely chicken,hog and cattle,and evaluated the important factors that affect the maximum methane potential of a substrate.The livestock manures collected from the local farms were incubated under a thermophilic anaerobic condition(55℃).The results showed that the maximum methane potential(B0)of cattle,hog and chicken manures were 292.0 mL/g VS,272.0 mL/g VS and 266.4 mL/g VS,respectively.The B0 value decreases with increasing contents of crude protein and crude fat,while increases with increasing the contents of carbohydrates and crude fiber in manures.The content of NH4+-N in chicken manure was significantly higher during the digestion period,reached as high as 1962.5 mg/L by the end of incubation period.Heavy metals of Cu and Zn in the manure also affect the B0.Empirical relationships that describe the B0 decrease in response to increase of Zn and Cu contents in manure were developed and used as a simple tool to assess the effects of these metals on the B0.It was concluded that the protein,Cu and Zn contents of manure are most important chemical compositions that negatively affect maximum methane potential.Based on the three experimental manures,the maximum methane potential was limited by either ammonium content or Cu and Zn content in the manure.For a commercial biogas production facility using these manures as main feedstock,one should consider to add co-substrate or co-substrates to reduce concentration of these chemicals to maximize biogas production.

A comparison of process performance during the anaerobic mono-and co-digestion of slaughterhouse waste through different operational modes

The use of consecutive feeding was applied to investigate the response of the microbial biomass to a second addition of substrates in terms of biodegradation using batch tests as a promising alternative to predict the behavior of the process. Anaerobic digestion（AD） of the slaughterhouse waste（SB） and its co-digestion with manure（M）, various crops（VC）, and municipal solid waste were evaluated. The results were then correlated to previous findings obtained by the authors for similar mixtures in batch and semi-continuous operation modes. AD of the SB failed showing total inhibition after a second feeding. Co-digestion of the SB ＋ M showed a significant improvement for all of the response variables investigated after the second feeding, while co-digestion of the SB ＋ VC resulted in a decline in all of these response variables. Similar patterns were previously detected, during both the batch and the semi-continuous modes.