Methane recovery from water hyacinth through whole-cell immobilization technology

The concepts of feed pretreatment, phase separation, and whole-cell immobilization technology have been incorporated in this investigation for the development of rational and cost-effective two- and three-stage methane recovery systems from water hyacinth (WH)Analyses of laboratory data reveal that a three-stage system could be designed with an alkali pretreatment stage [3.6% Na(2)CO(3) + 2.5% Ca(OH)(2) W/W, 24 h HRT] followed by an open acid reactor (2.1 days HRT) and closed immobilized methane reactor (12 h HRT), providing steady-state COD conversion of 62-65%, TVA conversion of 91-95%, and gas productivity of 4.08-5.36 L/L reactor volume/day with 82% methane. A gas yield of 50 L/kg WH/day (dry wt basis) at 35-37 degrees C is possible with this system. Insulation bricks, with particle size distribution of 500-3000 mum, were used as support material in the reactors at organic loading rate of 20 kg COD/m(3) day. The reactors matured in 15-18 weeksSubstantial reduction in retention time for the conversion of volatile acids in immobilized methane reactors prompted further research on the combined immobilized reactor to make possible an additional reduction in the cost of a WH-based biogas system. Evaluation of laboratory data reveals that a two-stage system could be designed with an open alkali pretreatment stage and a combined immobilized reactor (12 h HRT), providing steady-state COD conversion of 53% and gas productivity of 3.1 L/L reactor volume/day with 86% methane. A gas yield of 44 L/kg WH/day (dry wt basis) at 35-37 degrees C could be obtained from this system. Insulation bricks, with 500-1000 mum particle size distribution, was used as support material at an organic loading rate of 15 kg COD/m(3) day. Notwithstanding the fact that the technology in this study has been developed with water hyacinth as substrate, the implicit principles could be extended to any other organic substrate.     

Liquid-to-Gas Mass Transfer in Anaerobic Processes: Inevitable Transfer Limitations of Methane and Hydrogen in the Biomethanation Process

Liquid-to-gas mass transfer in anaerobic processes was investigated theoretically and experimentally. By using the classical definition of k(L)a, the global volumetric mass transfer coefficient, theoretical development of mass balances in such processes demonstrates that the mass transfer of highly soluble gases is not limited in the usual conditions occurring in anaerobic fermentors (low-intensity mixing). Conversely, the limitation is important for poorly soluble gases, such as methane and hydrogen. The latter could be overconcentrated to as much as 80 times the value at thermodynamic equilibrium. Such overconcentrations bring into question the biological interpretations that have been deduced solely from gaseous measurements. Experimental results obtained in three different methanogenic reactors for a wide range of conditions of mixing and gas production confirmed the general existence of low mass transfer coefficients and consequently of large overconcentrations of dissolved methane and hydrogen (up to 12 and 70 times the equilibrium values, respectively). Hydrogen mass transfer coefficients were obtained from the direct measurements of dissolved and gaseous concentrations, while carbon dioxide coefficients were calculated from gas phase composition and calculation of related dissolved concentration. Methane transfer coefficients were based on calculations from the carbon dioxide coefficients. From mass balances performed on a gas bubble during its simulated growth and ascent to the surface of the liquid, the methane and carbon dioxide contents in the gas bubble appeared to be controlled by the bubble growth process, while the bubble ascent was largely responsible for a slight enrichment in hydrogen.     

Biogas production and valorization by means of a two-step biological process

The scope of this research work was to investigate biogas production and purification by a two-step bench-scale biological system, consisting of fed-batch pulse-feeding anaerobic digestion of mixed sludge, followed by methane enrichment of biogas by the use of the cyanobacterium Arthrospira platensis. The composition of biogas was nearly constant, and methane and carbon dioxide percentages ranged between 70.5–76.0% and 13.2–19.5%, respectively. Biogas yield reached a maximum value (about 0.4 m³_biogas/kgCOD_i) at 50 days-retention time and then gradually decreased with a decrease in the retention time. Biogas CO₂ was then used as a carbon source for A. platensis cultivation either under batch or fed-batch conditions. The mean cell productivity of fed-batch cultivation was about 15% higher than that observed during the last batch phase (0.035 ± 0.006 g_DM/L/d), likely due to the occurrence of some shading effect under batch growth conditions. The data of carbon dioxide removal from biogas revealed the existence of a linear relationship between the rates of A. platensis growth and carbon dioxide removal from biogas and allowed calculating carbon utilization efficiency for biomass production of almost 95%.     

Selective desorption of carbon dioxide from sewage sludge for in situ methane enrichment--part I: pilot-plant experiments

In situ methane enrichment in anaerobic digestion of sewage sludge has been investigated by experiments and by modeling. In this first part, the experimental work on the desorption of carbon dioxide and methane from sewage sludge is reported. The bubble column, had a diameter of 0.3 m and a variable height up to 1.8 m. At operation the dispersion height in the column was between 1 and 1.3 m. Outdoor air was used. The column was placed close to a full-scale sewage sludge digester, at a municipal wastewater treatment plant. The digester was operated at mesophilic conditions with a hydraulic retention time of about 20 days. The bubble column was operated to steady-state, at which carbon dioxide concentration and alkalinity were determined on the liquid side, and the concentration of carbon dioxide and methane on the gas side. Thirty-eight experiments were performed at various liquid and gas flow rates. The experimental results show that the desorption rates achieved for carbon dioxide ranges from 0.07 to 0.25 m(3) CO(2)/m(3) sludge per day, which is comparable to the rate of generation by the anaerobic digestion. With increasing liquid flow rate and decreasing gas flow rate the amount of methane desorbed per amount of carbon dioxide desorbed increases. The lowest methane loss achieved is approximately 2% of the estimated methane production in the digestion process.     

Effects of controlled gas environments in solid-substrate fermentations of rice

The gas environment is solid-substrate fermentations of rice significantly affected levels of biomass and enzyme formation by a fungal species screened for high amylase production. Constant oxygen and carbon dioxide partial pressures were maintained at various levels in fermentations by Aspergillus oryzae. Control of the gas phase was maintained by a “static” aeration system admitting oxygen on demand and stripping excess carbon dioxide during fermentation. Constant water vapor pressures were also maintained by means of saturated salt solutions. High Oxygen pressures stimulated amylase productivity significantly. On the other hand, amylase production was severely inhibited at high carbon dioxide pressures. While relatively insensitive to oxygen pressure, maximum biomass productivities were obtained at an intermediate carbon dioxide pressure. High oxygen transfer rates were obtained at elevated oxygen pressures, suggesting, in view of the stimulatory effect of oxygen on amylase production, a stringent oxygen requirement for enzyme synthesis. Solid-substrate fermentations were highly advantageous as compared with submerged cultures in similar gas environments. Not only were amylase productivities significantly higher, but the enzyme was highly concentration in the aqueous phase of the semisolid substrate particles and could be extracted in a small volume of liquid. Results of this work suggest that biomass and product formation in microbial processes may be amenable to control by the gas environment. This is believed to offer an interesting potential for optimizing selected industrial fermentation processes with respect to productivity and energy consumption.     

Development of a two-phase combination fermenter for the conversion of cellulose to methane

Cellulose degradation to methane under continuous fermentation conditions was compared using fully mixed, fully mixed with solids return, sludge-blanket, and fixed-film fermenters. In fully mixed fermenters, a decrease in hydraulic retention time (HRT) of two weeks or less caused the wash out of anaerobes capable of converting volatile fatty acids to methane, while at increased feeding rates over 1 g/L day the rapid growth of cellulolytic anaerobes upset the balance between acid formation and its conversion to CH(4). Circulation of cellulose and difficulty in settling of cellulose with attached bacteria imposed problems in the use of other types of fermenters. On the basis of information obtained from this study, a fermenter which combined a fully mixed phase for cellulose degradation and a fixed-film phase with pre-immobilized bacteria for converting fatty acids to CH(4) in one vessel, was devised. Using this fermenter, a mixed culture converted cellulose to CH(4) at 4.8 g/L day at a HRT of six days as compared to 0.7 g/L day at a HRT of 28 days in the fully mixed fermenter.     

The influence of pressure on the growth of methanotrophic bacteria

The growth rate and the maximum cell concentration of methanotrophic bacteria are limited by the transfer of methane and oxygen to the culture fluid. The operation under moderate pressure results in an increase in driving force for the mass transfer of both nutrients and, therefore, in a large increase in the attainable biomass concentration. Our laboratory pressure fermenter with a volume of 12 litres operates under a system pressure of up to 0.5 MPa. In this reactor a maximum productivity of 6 g biomass/lh is achieved. However, operating under moderate system pressure and exhaust gas recycling has also disadvantages because the concentrations of the gas phase components may inhibit the growth process. From the results of the laboratory fermenter we have developed kinetic models of the influence of dissolved oxygen and carbon dioxide on the specific growth rate of the methanotrophic strain GB 25. These models are the basis for processing under increased system pressure and exhaust gas recycling.     

Microbiological processes at the interface of aerobic and anaerobic waters in the deep-water zone of the Black Sea

Chemical and key microbiological processes (assimilation of carbon dioxide, oxidation and formation of methane, and sulfate reduction) occurring at the boundary between the aerobic-anaerobic interface in the deep-water zone of the Black Sea were investigated. Measurements were taken at depths from 90 to 300 m at intervals of 5-10 m. The integral rate of the dark assimilation of carbon dioxide varied from 120 to 207 mg C/(m2 day) with a maximum at the boundary of cyclonic currents. The organic matter (OM) formed from methane comprised less than 5% of the OM formed from carbon dioxide. A comparison between the rates of methane oxidation and methane production suggests that methane that is oxidized at depths from 100 to 300 m was formed in deeper water horizons. The maximum rate of sulfate reduction (1230 mg S/(m2 day)) was observed in the western halistatic region, and the minimum rate (490 mg S/(m2 day)), in the eastern halistatic region. The average rate of hydrogen sulfide production measured at three deep-sea stations amounted to 755 mg S/(m2 day), or 276 g S/(m2 year).     

Production of methanol from methane by methanotrophic bacteria

Methanotrophs can oxidize methane to carbon dioxide through sequential reactions catalyzed by a series of enzymes including methane monooxygenase, methanol dehydrogenase, formaldehyde dehydrogenase, and formate dehydrogenase. When suspensions of methanotrophic bacteria of Methylosinus trichosporium IMV 3011 were incubated at 32°C with methane and oxygen, there was an extracellular accumulation of methanol from methane oxidation in response to carbon dioxide addition. Maximal accumulation of methanol was achieved with 40% carbon dioxide in the mixed reaction gases. A continuous experiment was performed in a continuous ultrafiltration reactor. The optimum gas mixture containing 20% (v v^?1) methane, 20% oxygen, 20% nitrogen and 40% carbon dioxide was used to provide substrates and to maintain the transmembrane pressure. The product (methanol) was removed in the eluate buffer. The initial methanol concentration in the eluate buffer was 8.22 μmol L^?1. The bioreactor was operated continuously for 198 h without obvious loss of productivity.     

Biofixation of carbon dioxide by Spirulina sp. and Scenedesmus obliquus cultivated in a three-stage serial tubular photobioreactor

The increase in the concentration of atmospheric carbon dioxide is considered to be one of the main causes of global warming. As estimated by the Intergovernmental Panel on Climate Change (IPCC) criteria, about 10-15% of the gases emitted from the combustion coal being in the form of carbon dioxide. Microalgae and cyanobacteria can contribute to the reduction of atmospheric carbon dioxide by using this gas as carbon source. We cultivated the Scenedesmus obliquus and Spirulina sp. at 30 degrees C in a temperature-controlled three-stage serial tubular photobioreactor and determined the resistance of these organisms to limitation and excess of carbon dioxide and the capacity of the system to fix this greenhouse gas. After 5 days of cultivation under conditions of carbon limitation both organisms showed cell death. Spirulina sp. presenting better results for all parameters than S. obliquus. For Spirulina sp. the maximum specific growth rate and maximum productivity was 0.44 d(-1), 0.22 g L(-1)d(-1), both with 6% (v/v) carbon dioxide and maximum cellular concentration was 3.50 g L(-1) with 12% (v/v) carbon dioxide. Maximum daily carbon dioxide biofixation was 53.29% for 6% (v/v) carbon dioxide and 45.61% for 12% carbon dioxide to Spirulina sp. corresponding values for S. obliquus being 28.08% for 6% (v/v) carbon dioxide and 13.56% for 12% (v/v) carbon dioxide. The highest mean carbon dioxide fixation rates value was 37.9% to Spirulina sp. in the 6% carbon dioxide runs.     

Production of methanol from methane by methanotrophic bacteria

Methanotrophs can oxidize methane to carbon dioxide through sequential reactions catalyzed by a series of enzymes including methane monooxygenase, methanol dehydrogenase, formaldehyde dehydrogenase, and formate dehydrogenase. When suspensions of methanotrophic bacteria of Methylosinus trichosporium IMV 3011 were incubated at 32°C with methane and oxygen, there was an extracellular accumulation of methanol from methane oxidation in response to carbon dioxide addition. Maximal accumulation of methanol was achieved with 40% carbon dioxide in the mixed reaction gases. A continuous experiment was performed in a continuous ultrafiltration reactor. The optimum gas mixture containing 20% (v v^-1) methane, 20% oxygen, 20% nitrogen and 40% carbon dioxide was used to provide substrates and to maintain the transmembrane pressure. The product (methanol) was removed in the eluate buffer. The initial methanol concentration in the eluate buffer was 8.22 μmol L^-1. The bioreactor was operated continuously for 198 h without obvious loss of productivity.     

Microbial processes at the aerobic-anaerobic interface in the deep-water zone of the black sea

Chemical and key microbiological processes (assimilation of carbon dioxide, oxidation and formation of methane, and sulfate reduction) occurring at the aerobic-anaerobic interface in the deep-water zone of the Black Sea were investigated. Measurements were taken at depths from 90 to 300 m at intervals of 5–10 m. The integral rate of the dark assimilation of carbon dioxide varied from 120 to 207 mg C/(m² day) with a maximum at the boundary of cyclonic currents. The organic matter (OM) formed from methane comprised less than 5% of the OM formed from carbon dioxide. A comparison between the rates of methane oxidation and methane production suggests that methane that is oxidized at depths from 100 to 300 m was formed in deeper water horizons. The maximum rate of sulfate reduction (1230 mg S/(m₂ day)) was observed in the western halistatic region, and the minimum rate (490 mg S/(m₂ day)), in the eastern halistatic region. The average rate of hydrogen sulfide production measured at three deep-sea stations amounted to 755 mg S/(m₂ day), or 276 g S/(m₂ year).     

Application of the IWA ADM1 model to simulate anaerobic co-digestion of organic waste with waste activated sludge in mesophilic condition

Anaerobic digestion model no. 1 model of international water association was applied to a full scale anaerobic co-digestion process for the treatment of the organic fraction of municipal solid wastes along with activated sludge wastes originating from a municipal wastewater treatment plant. This operation was carried out in a digester of 2000 m(3) in volume. It is operates at an average hydraulic retention time of 26.9 days with an average organic loading rate of 1.01 kg TVS/m(3) day, at a temperature of 37 degrees C with an average gas production rate of 0.296 m(3)/m(3) day. The aim of the present study is to compare the results obtained from the simulation with the experimental values. The simulated results showed a good fit for pH, methane and carbon dioxide percentages, biogas volume, chemical oxygen demand, total volatile fatty acids, inorganic nitrogen and inorganic carbon.     

Two-phase anaerobic fermentation of liquid swine waste to methane

Two-phase anaerobic digestion of liquid swine manure has been developed with options for single-cell protein (SCP) or methane production. In the acidogenic phase at two to four days retention time, and 2.5-7.0% dry matter (DM) concentration, 8-46% of the volatile solids was solubilized. Maximum reactor capacity was 3.86 g/L at 7.0% DM concentration, but optimal operation was achieved at 4.5% DM concentration at four days retention time. The second methanogenic phase was operated continuously and had a maximum specific methane production rate of 0.70 L/L day at 12 days retention time. With recirculation, the rate was 1.16 L/L day at 8.5 days retention time with 52.7% conversion of organic matter. Maximum digestibility was 66% of the lignin free organic matter.     

The potential of biological methane generation from chicken manure

The potential for biological methane generating from the manure of laying hens was investigated in the laboratory. Fresh manure was collected, analyzed, and used to prepare medium for bacterial growth. At 55°C and under anaerobic conditions, methanogenic cultures were initiated by incubating the medium with different inoculations from various natural environments. Since there were no significant differences in gas production among these initiated cultures after 40 days of acclimation, they were mixed to maintain a genetic pool. The mixed culture was then challenged with different retention times (RT) and different volatile solid (VS) concentrations for the selection of optimal conditions and cultures. The conditions were finally selected to be 4-day RT and 6% VS for the maximal rate of gas production. The optimal pH and temperature were determined to be 7.5 and 50°C, respectively. Under such conditions the selected culture produced total gas at a rate 4.5 L/L day and methane (70% of total gas) 3.2 L/L day. The chicken manure therefore was able to support the methane yield at 270 L/kg of VS, a value comparably higher than other kinds of livestock wastes.     

Anaerobic Biodegradation of Eleven Aromatic Compounds to Methane

A range of 11 simple aromatic lignin derivatives are biodegradable to methane and carbon dioxide under strict anaerobic conditions. A serum-bottle modification of the Hungate technique for growing anaerobes was used for methanogenic enrichments on vanillin, vanillic acid, ferulic acid, cinnamic acid, benzoic acid, catechol, protocatechuic acid, phenol, p-hydroxybenzoic acid, syringic acid, and syringaldehyde. Microbial populations acclimated to a particular aromatic substrate can be simultaneously acclimated to other selected aromatic substrates. Carbon balance measurements made on vanillic and ferulic acids indicate that the aromatic ring was cleaved and that the amount of methane produced from these substrates closely agrees with calculated stoichiometric values. These data suggest that more than half of the organic carbon of these aromatic compounds potentially can be converted to methane gas and that this type of methanogenic conversion of simple aromatics may not be uncommon.     

Methane production from glucose in vitro by mixed rumen bacteria

1. Methane was produced in vitro by incubating cell suspensions of rumen bacteria with glucose, under nitrogen. The amount of methane produced varied considerably and was lowered by high glucose concentrations. Carbon dioxide, acetic acid, propionic acid, butyric acid and lactic acid were also produced. An oxidation–reduction balance of near unity could be calculated, although carbon recovery was low. Under the experimental conditions, rumen bacteria used most of the metabolic hydrogen produced during the oxidation of glucose to form lactic acid. 2. Lower methane production at high glucose concentrations was balanced by higher lactic acid production. Low pH values due to a high production rate of lactic acid might explain the inhibition of methane production. 3. No lactic acid, less methane, but considerably more propionic acid were formed when nitrogen was replaced by carbon dioxide in the incubation system.     

Oxidation of methane in the absence of oxygen in lake water samples.

Methane was oxidized to carbon dioxide in the absence of oxygen by water samples from Lake Mendota, Madison, Wis. The anaerobic oxidation of methane did not result in the assimilation of carbon from methane into material precipitable by cold 10% trichloracetic acid. Only samples taken at the suface of the sediment of Lake Mendota were capable of catalyzine the anaerobic oxidation of methane. The rate of methane oxidation in the presence of oxygen was highest in samples taken from near the thermocline. Of the radioactive methane oxidized, 30 to 60% was assimilated into material precipitable by cold 10% trichloroacetic acid during aerobic incubation of the samples. These data support the conclusion that two distinct groups of methane-oxidizing organisms occur in stratifield lakes. Enrichments with acetate and methane as the sole sources of carbon and energy and sulfate as the electron acceptor resulted in the growth of bacteria that oxidize methane. Sulfate, acetate, and methane were all required for growth of enrichments. Acetate was not oxidized to carbon dioxide but was assimilated by cells. Methane was not assimilated but was oxidized to carbon dioxide in the absence of air.     

Oxidation of methane in the absence of oxygen in lake water samples.

Methane was oxidized to carbon dioxide in the absence of oxygen by water samples from Lake Mendota, Madison, Wis. The anaerobic oxidation of methane did not result in the assimilation of carbon from methane into material precipitable by cold 10% trichloracetic acid. Only samples taken at the suface of the sediment of Lake Mendota were capable of catalyzine the anaerobic oxidation of methane. The rate of methane oxidation in the presence of oxygen was highest in samples taken from near the thermocline. Of the radioactive methane oxidized, 30 to 60% was assimilated into material precipitable by cold 10% trichloroacetic acid during aerobic incubation of the samples. These data support the conclusion that two distinct groups of methane-oxidizing organisms occur in stratifield lakes. Enrichments with acetate and methane as the sole sources of carbon and energy and sulfate as the electron acceptor resulted in the growth of bacteria that oxidize methane. Sulfate, acetate, and methane were all required for growth of enrichments. Acetate was not oxidized to carbon dioxide but was assimilated by cells. Methane was not assimilated but was oxidized to carbon dioxide in the absence of air.     

Formation and Degradation Pathways of Intermediate Products Formed during the Hydropyrolysis of Glucose as a Model Substance for Wet Biomass in a Tubular Reactor

In this study, glucose as a model substance for cellulose is pyrolyzed in supercritical water. The experiments are conducted in a continuously operated tubular reactor. From the usage of model substances, key information on the degradation pathway of biomass in supercritical water can be obtained. With this knowledge, it is tried to optimize a new method for gasification of wet biomass considering high yields of hydrogen and methane and also the suppressing of tar and char formation. The gaseous products mainly contain hydrogen, carbon dioxide, methane and a small amount of carbon monoxide. The effect of experimental conditions, such as pressure, temperature and reaction time, on the degradation of glucose is investigated in the experiments. The qualitative and quantitative composition of the gas and liquid phases formed are determined. The results show that only the amount of phenols increases with increasing temperature in the liquid phase. No complete gasification of glucose is achieved in the studied temperature range between 400 °C and 500 °C. The addition of alkali salts leads to a higher gas generation and to a decrease in carbon monoxide concentration via water‐gas‐shift reaction. A lower furfural concentration is obtained in the presence of KHCO₃. Furthermore, this study shows that there is a wide conformity between the results of real and model biomass. A simplified scheme for glucose degradation is also presented with the help of the results found.