Enhancement of bioenergy production from organic wastes by two-stage anaerobic hydrogen and methane production process

The present study investigated a two-stage anaerobic hydrogen and methane process for increasing bioenergy production from organic wastes. A two-stage process with hydraulic retention time (HRT) 3 d for hydrogen reactor and 12 d for methane reactor, obtained 11% higher energy compared to a single-stage methanogenic process (HRT 15 d) under organic loading rate (OLR) 3 gVS/(L d). The two-stage process was still stable when the OLR was increased to 4.5 gVS/(L d), while the single-stage process failed. The study further revealed that by changing the HRT_hydrogen:HRT_methane ratio of the two-stage process from 3:12 to 1:14, 6.7%, more energy could be obtained. Microbial community analysis indicated that the dominant bacterial species were different in the hydrogen reactors (Thermoanaerobacterium thermosaccharolyticum-like species) and methane reactors (Clostridiumthermocellum-like species). The changes of substrates and HRT did not change the dominant species. The archaeal community structures in methane reactors were similar both in single- and two- stage reactors, with acetoclastic methanogens Methanosarcina acetivorans-like organisms as the dominant species.     

Eliminating methanogenic activity in hydrogen reactor to improve biogas production in a two-stage anaerobic digestion process co-digesting municipal food waste and sewage sludge

Laboratory scale two-stage anaerobic digestion process model was operated for 280 days to investigate the feasibility to produce both hydrogen and methane from a mixture feedstock (1:1 (v/v)) of municipal food waste and sewage sludge. The maximum hydrogen and methane yields obtained in the two stages were 0.93 and 9.5 mL/mL feedstock. To eliminate methanogenic activity and obtain substantial hydrogen production in the hydrogen reactor, both feedstock and mixed liquor required treatment. The heat treatment (100 °C, 10 min) for feedstock and a periodical treatment (every 2-5 weeks, either heating, removal of biomass particles or flushing with air) for mixed liquor were effective in different extent. The methane production in the second stage was significantly improved by the hydrogen production in the first stage. The maximum methane production obtained in the period of high hydrogen production was more than 2-fold of that observed in the low hydrogen production period.     

Performance and microbial community analysis of two-stage process with extreme thermophilic hydrogen and thermophilic methane production from hydrolysate in UASB reactors

The two-stage process for extreme thermophilic hydrogen and thermophilic methane production from wheat straw hydrolysate was investigated in up-flow anaerobic sludge bed (UASB) reactors. Specific hydrogen and methane yields of 89 ml-H₂/g-VS (190 ml-H₂/g-sugars) and 307 ml-CH₄/g-VS, respectively were achieved simultaneously with the overall VS removal efficiency of 81% by operating with total hydraulic retention time (HRT) of 4 days . The energy conversion efficiency was dramatically increased from only 7.5% in the hydrogen stage to 87.5% of the potential energy from hydrolysate, corresponding to total energy of 13.4 kJ/g-VS. Dominant hydrogen-producing bacteria in the H₂-UASB reactor were Thermoanaerobacter wiegelii, Caldanaerobacter subteraneus, and Caloramator fervidus. Meanwhile, the CH₄-UASB reactor was dominated with methanogens of Methanosarcina mazei and Methanothermobacter defluvii. The results from this study suggest the two stage anaerobic process can be effectively used for energy recovery and for stabilization of hydrolysate at anaerobic conditions.     

Hydrogen and methane production from desugared molasses using a two‐stage thermophilic anaerobic process

Hydrogen and methane production from desugared molasses by a two‐stage thermophilic anaerobic process was investigated in a series of two up‐flow anaerobic sludge blanket (UASB) reactors. The first reactor that was dominated with hydrogen‐producing bacteria of Thermoanaerobacterium thermosaccharolyticum and Thermoanaerobacterium aciditolerans could generate a high hydrogen production rate of 5600 mL H₂/day/L, corresponding to a yield of 132 mL H₂/g volatile solid (VS). The effluent from the hydrogen reactor was further converted to methane in the second reactor with the optimal production rate of 3380 mL CH₄/day/L, corresponding to a yield of 239 mL CH₄/g VS. Aceticlastic Methanosarcina mazei was the dominant methanogen in the methanogenesis stage. This work demonstrates that biohydrogen production can be very efficiently coupled with a subsequent step of methane production using desugared molasses. Furthermore, the mixed gas with a volumetric content of 16.5% H_2, 38.7% CO₂, and 44.8% CH₄, containing approximately 15% energy by hydrogen is viable to be bio‐hythane.     

Optimization of two-phase thermophilic anaerobic digestion of biowaste for hydrogen and methane production through reject water recirculation

The optimization of a two-phase thermophilic anaerobic process treating biowaste for hydrogen and methane production was carried out at pilot scale using two stirred reactors (CSTRs) and without any physical/chemical pre-treatment of inoculum. During the experiment the hydrogen production at low hydraulic retention time (3d) was tested, both with and without reject water recirculation and at two organic loading rate (16 and 21 kgTVS/m³d). The better yields were obtained with recirculation where the pH reached an optimal value (5.5) thanks to the buffering capacity of the recycle stream. The specific gas production of the first reactor was 51 l/kgVS_fed and H₂ content in biogas 37%. The mixture of gas obtained from the two reactors met the standards for the biohythane mix only when lower loading rate were applied to the first reactor, with a composition of 6.7% H₂, 40.1% CO₂ and 52.3% CH₄ the overall SGP being 0.78 m³/kgVS_fed.     

In situ ammonia production as a sanitation agent during anaerobic digestion at mesophilic temperature

Aim: To measure the sanitizing effect of mesophilic (37°C) anaerobic digestion in high ammonia concentrations produced in situ. Methods and Results: Indicator organisms and salmonella were transferred to small‐scale anaerobic batch cultures and D‐values were calculated. Batch cultures were started with material from two biogas processes operating at high (46 mmol l^?1) and low (1·6 mmol l^?1) ammonia concentration. D‐values were shortened from c. 3 days to <1 day for the bacteria. MS2 had the same D‐value (1·3 days) independent of ammonia concentration whereas ΦX174 and 28B were faster inactivated in the control (1·1 and 7·9 days) than in the high ammonia (8·9 and 39 days) batch cultures. Conclusion: Running biogas processes at high levels of ammonia shortens the time to meet EU regulation concerning reduction of salmonella and enterococci (5 log). Unless a minimum retention time of 2 days, post‐treatment digestion is needed to achieve sufficient sanitation in continuous biogas processes. Significance and Impact of the Study: Running mesophilic biogas processes at high ammonia level produces residue with a high fertilizer value. With some stipulations concerning management parameters, such processes provide a method of bacterial sanitation without preceding pasteurization of the incoming organic waste.     

Thermal and enzymatic pretreatment of sludge containing phthalate esters prior to mesophilic anaerobic digestion

The present study aimed at investigating the effect of thermal pretreatment of sludge at 70 degrees C on the anaerobic degradation of three commonly found phthalic acid esters (PAE): di-ethyl phthalate (DEP), di-butyl phthalate (DBP), and di-ethylhexyl phthalate (DEHP). Also, the enzymatic treatment at 28 degrees C with a commercial lipase was studied as a way to enhance PAE removal. Pretreatment at 70 degrees C of the sludge containing PAE negatively influenced the anaerobic biodegradability of phthalate esters at 37 degrees C. The observed reduction of PAE biodegradation rates after the thermal pretreatment was found to be proportional to the PAE solubility in water: the higher the solubility, the higher the percentage of the reduction (DEP > DBP > DEHP). PAE were slowly degraded during the pretreatment at 70 degrees C, yet this was probably due to physicochemical reactions than to microbial/biological activity. Therefore, thermal pretreatment of sludge containing PAE should be either avoided or combined with a treatment step focusing on PAE reduction. On the other hand, enzymatic treatment was very efficient in the removal of PAE. The enzymatic degradation of DBP, DEP, and DEHP could be one to two orders of magnitude faster than under normal mesophilic anaerobic conditions. Moreover, the enzymatic treatment resulted in the shortest half-life of DEHP in sludge reported so far. Our study further showed that enzymatic treatment with lipases can be applied to raw sludge and its efficiency does not depend on the solids concentration.     

Anaerobic digestion of secondary residuals from an anaerobic bioreactor at a brewery to enhance bioenergy generation

Many beer breweries use high-rate anaerobic digestion (AD) systems to treat their soluble high-strength wastewater. Biogas from these AD systems is used to offset nonrenewable energy utilization in the brewery. With increasing nonrenewable energy costs, interest has mounted to also digest secondary residuals from the high-rate digester effluent, which consists of yeast cells, bacteria, methanogens, and small (hemi)cellulosic particles. Mesophilic (37 °C) and thermophilic (55 °C) lab-scale, low-rate continuously-stirred anaerobic digestion (CSAD) bioreactors were operated for 258 days by feeding secondary residuals at a volatile solids (VS) concentration of ∼40 g l⁻¹. At a hydraulic retention time (HRT) of 15 days and a VS loading rate of 2.7 g VS l⁻¹ day⁻¹, the mesophilic bioreactor showed an average specific volumetric biogas production rate of 0.88 l CH₄ l⁻¹ day⁻¹ and an effluent VS concentration of 22.2 g VS l⁻¹ (43.0% VS removal efficiency) while the thermophilic bioreactor displayed similar performances. The overall methane yield for both systems was 0.21 l CH₄ g⁻¹ VS fed and 0.47–0.48 l CH₄ g⁻¹ VS removed. A primary limitation of thermophilic digestion of this protein-rich waste is the inhibition of methanogens due to higher nondissociated (free) ammonia (NH₃) concentrations under similar total ammonium (NH₄ ⁺) concentrations at equilibrium. Since thermophilic AD did not result in advantageous methane production rates or yields, mesophilic AD was, therefore, superior in treating secondary residuals from high-rate AD effluent. An additional digester to convert secondary residuals to methane may increase the total biogas generation at the brewery by 8% compared to just conventional high-rate digestion of brewery wastewater alone. JIMB-2008: BioEnergy—Special issue.     

Influence of surfactants on anaerobic digestion of waste activated sludge: acid and methane production and pollution removal

The objective of this study is to summarize the effects of surfactants on anaerobic digestion (AD) of waste activated sludge (WAS). The increasing amount of WAS has caused serious environmental problems. Anaerobic digestion, as the main treatment for WAS containing three stages (i.e. hydrolysis, acidogenesis, and methanogenesis), has been widely investigated. Surfactant addition has been demonstrated to improve the efficiency of AD. Surfactant, as an amphipathic substance, can enhance the efficiency of hydrolysis by separating large sludge and releasing the encapsulated hydrolase, providing more substance for subsequent acidogenesis. Afterwards, the short chain fatty acids (SCFAs), as the major product, have been produced. Previous investigations revealed that surfactant could affect the transformation of SCFA. They changed the types of acidification products by promoting changes in microbial activity and in the ratio of carbon to nitrogen (C/N), especially the ratio of acetic and propionic acid, which were applied for either the removal of nutrient or the production of polyhydroxyalkanoate (PHA). In addition, the activity of microorganisms can be affected by surfactant, which mainly leads to the activity changes of methanogens. Besides, the solubilization of surfactant will promote the solubility of contaminants in sludge, such as organic contaminants and heavy metals, by increasing the bioavailability or desorbing of the sludge.     

Analysis and application of ADM1 for anaerobic methane production

An anaerobic model for the serum bottle test was developed and analyzed with sensitivities of stoichiometric and kinetic parameters to the components in order to establish a basis for appropriate application of the model. Anaerobic glucose degradation in a serum bottle was selected as an example. The anaerobic model was developed based on the anaerobic digestion model no. 1 (ADM1), which had five processes with 17 kinetic and stoichiometric parameters. Sensitivity analysis showed that the yield of product on the substrate (f) has high sensitivities to model components, and that the methane concentration was the most sensitive component. Important parameters including yield of product on the substrate (f), yield of biomass on the substrate (Y), and half-saturation values (K) were estimated using genetic algorithms, which optimized the parameters with experimental results. The Monod maximum specific uptake rate (k) was, however, so strongly associated with the concentration of biomass, that values could not be estimated individually. Simulation with estimated parameters showed good agreement with experimental results in the case of methane production. However, there were some differences in acetate and propionate concentrations.     

A sustainable pathway of cellulosic ethanol production integrating anaerobic digestion with biorefining

Anaerobic digestion (AD) of animal manure is traditionally classified as a treatment to reduce the environmental impacts of odor, pathogens, and excess nutrients associated with animal manure. This report shows that AD also changes the composition of manure fiber and makes it suitable as a cellulosic feedstock for ethanol production. Anaerobically digested manure fiber (AD fiber) contains less hemicellulose (11%) and more cellulose (32%) than raw manure, and has better enzymatic digestibility than switchgrass. Using the optimal dilute alkaline pretreatment (2% sodium hydroxide, 130°C, and 2 h), enzymatic hydrolysis of 10% (dry basis) pretreated AD fiber produces 51 g/L glucose at a conversion rate of 90%. The ethanol fermentation on the hydrolysate has a 72% ethanol yield. The results indicate that 120 million dry tons of cattle manure available annually in the U.S. can generate 63 million dry tons of AD fiber that can produce more than 1.67 billion gallons of ethanol. Integrating AD with biorefining will make significant contribution to the cellulosic ethanol production. Biotechnol. Bioeng. 2010;105: 1031–1039. © 2009 Wiley Periodicals, Inc.     

Using cheese whey for hydrogen and methane generation in a two-stage continuous process with alternative pH controlling approaches

This study focuses on the exploitation of cheese whey as a source for hydrogen and methane, in a two-stage continuous process. Mesophilic fermentative hydrogen production from undiluted cheese whey was investigated at a hydraulic retention time (HRT) of 24 h. Alkalinity addition (NaHCO₃) or an automatic pH controller were used, to maintain the pH culture at a constant value of 5.2. The hydrogen production rate was 2.9 ± 0.2 L/Lreactor/d, while the yield of hydrogen produced was approximately 0.78 ± 0.05 mol H₂/mol glucose consumed, with alkalinity addition, while the respective values when using pH control were 1.9 ± 0.1 L/Lreactor/d and 0.61 ± 0.04 mol H₂/mol glucose consumed. The corresponding yields of hydrogen produced were 2.9 L of H₂/L cheese whey and 1.9 L of H₂/L cheese whey, respectively. The effluent from the hydrogenogenic reactor was further digested to biogas in a continuous mesophilic anaerobic bioreactor. The anaerobic digester was operated at an HRT of 20d and produced approximately 1 L CH₄/d, corresponding to a yield of 6.7 L CH₄/L of influent. The chemical oxygen demand (COD) elimination reached 95.3% demonstrating that cheese whey could be efficiently used for hydrogen and methane production, in a two-stage process.     

Volatile fatty acid production during anaerobic mesophilic digestion of tea and vegetable market wastes

Extraction of the organic content from vegetable market waste and tea waste was carried out in a packed digester for 24 and 300 h respectively. The sequence of appearance of volatile fatty acids during digestion of both the substrates was found to be different. The sequence was (Acetic, Propionic) > (Isobutyric, Butyric) > Valeric for digestion of vegetable market waste while it was Isovaleric > (Isobutyric, Acetic) > Propionic during digestion of tea waste. During the course of digestion, the early appearance of an acid did not relate to its high concentration. The rate of production of acetic acid and propionic acid was found to be higher than other volatile acids during digestion of both the substrates, although it was approximately ten times higher for vegetable market waste compared to tea waste. The acids can be arranged in four groups according to their rate of production as Acetic > Propionic > Butyric > (Valeric, Isobutyric) for vegetable market waste and Acetic > Isobutyric > Isovaleric > Propionic for tea waste.     

Bioaugmentation of a two-stage thermophilic (68 degrees C/55 degrees C) anaerobic digestion concept for improvement of the methane yield from cattle manure

The possibility of improving a two-stage (68 degrees C/55 degrees C) anaerobic digestion concept for treatment of cattle manure was studied. In batch experiments, a 10-24% increase of the specific methane yield from cattle manure and its fractions was obtained, when the substrates were inoculated with bacteria of the genus Caldicellusiruptor and Dictyoglomus. In a reactor experiment inoculation of a 68 degrees C pretreatment reactor with Caldicellusiruptor resulted in a 93% increase in the methane yield of the pretreatment reactor for a period of 18 days, but gave only a slight increase in the overall methane yield of the two-stage setup.     

Elevated methane emissions from a paddy field in southeast China occur after applying anaerobic digestion slurry

One hundred million tons of farm stalk waste and livestock and poultry excrement are used every year in China for the production of clean energy (biogas) by anaerobic digestion. Consequently, a large amount of fermented liquid is produced, and if disposed of improperly, it will result in secondary pollution. Agricultural application of this anaerobic slurry as a liquid fertilizer would reduce possible eutrophication of water sources from random slurry discharge and supply a superior organic fertilizer for farming. This study investigated the effect of applying anaerobic digestion slurry as a liquid fertilizer on the methane emitted from a paddy field. A two‐year (2008–2009) field experiment replacing chemical fertilizer with liquid fertilizer from anaerobically digested pig manure slurry was conducted in a paddy field in Yixing, Jiangsu, China. A static closed chamber method was used to measure methane fluxes over the period from June 2008 to October 2009. All fertilizer treatments increased methane emissions relative to untreated controls, with increases in methane ranging from 40–70% in 2008 to 48–84% in 2009. Paddy fields treated with anaerobically digested pig manure slurry had greater methane emissions (8–84% in 2008 and 3–26% in 2009) than those treated with chemical fertilizer. This suggests that the anaerobic digestion slurry would increase methane emission and so is unsuitable as a liquid fertilizer in paddy fields without development of cultivation practices to limit these emissions.     

Enhanced methane production in a two-phase anaerobic digestion plant, after CO2 capture and addition to organic wastes

Cost-effective technologies are needed to reach the international greenhouse gas (GHG) reduction targets in many fields, including waste and biomass treatment. This work reports the effects of CO₂ capture from a combustion flue gas and its use in a newly-patented, two-phase anaerobic digestion (TPAD) process, to improve energy recovery and to reduce CO₂ emissions. A TPAD process, fed with urban wastewater sludge, was successfully established and maintained for several months at pilot scale. The TPAD process with injection of CO₂ exhibits efficient biomass degradation (58% VSS reduction), increased VFA production during the acidogenic phase (leading to VFA concentration of 8.4 g/L) and high biomethane production (0.350 Sm³/kg_SSV; 0.363 Sm³/m³_react·d). Moreover, CO₂ intake in the acid phase has a positive impact on the overall GHG balance associated to biomethane production, and suggests an improved solution for both emission reduction and biomass conversion into biomethane.     

Effects of thermo-chemical pre-treatment of grass silage on methane production by anaerobic digestion

Dried grass silage (GS) was pre-treated at different NaOH loading rates (1%, 2.5%, 5% and 7.5% by volatile solids (VS) mass in grass silage) and temperatures (20 °C, 60 °C, 100 °C and 150 °C) to determine effects on its bio-degradability in terms of the hydrolysis yield and degradation of ligno-cellulosic materials for biogas production. At 100 °C and the four NaOH loadings, up to 45% of the total COD was solubilised and up to 65.6%, 36.1% and 21.2% of lignin, hemicellulose and cellulose were removed, respectively; biological methane production potentials obtained were 359.5, 401.8, 449.5 and 452.5 ml CH?/g VS added, respectively, being improved by 10-38.9% in comparison with untreated GS. VS removals following anaerobic digestion were 67.6%, 76.9%, 85.3%, 95.2% and 96.7% for untreated GS and GS treated at the four NaOH loadings, respectively. 100 °C and the NaOH loading rate of 5% is recommended as a proper GS pre-treatment condition.     

Model-based predictions of anaerobic digestion of agricultural substrates for biogas production

A modified Anaerobic Digestion Model No. 1 (ADM1), calibrated on a laboratory digester with a feeding mix of 30% weight of cow manure and 70% weight of corn silage, was implemented, showing its performances of simulation as a decision-making and planning-supporting tool for the anaerobic digestion of agricultural substrates. The virtual fermenter obtained was used to conduct simulations with different feeding compositions and loading rates of cow manure, corn silage, grass silage and rape oil. All simulations were started at the same initial state which was represented by a steady state with an organic loading rate of 2.5 kg ODM/(). The effects of the different feeding combinations on biogas composition and biogas yield were predicted reasonably, and partly verified with the available literature data. Results demonstrated that the simulations could be helpful for taking decisions on agricultural biogas plant operation or experimental set-ups, if used advisedly.     

The Survival of antibiotic resistant and sensitiveEscherichia coli strains during anaerobic digestion

Summary Total counts ofEscherichia coli were followed during anaerobic digestion of pig slurry laboratory scale digesters at 37° C. Counts decreased rapidly during anaerobic digestion. Antibiotic resistant strains in most cases appeared to be more persistent in anaerobic digesters than sensitiveE. coli strains as calculated from the decimal decay rates.