Potentials of bio-hydrogen and bio-methane production from diseased swines

Diseased swines can be utilized as substrate for anaerobic fermentation after proper pretreatment. The cumulative bio-hydrogen and bio-methane production yields were taken as targets, the effects of different initial pH values and enzyme concentration on bio-hydrogen and bio-methane production characteristics by anaerobic fermentation from diseased swines were investigated. Results showed that the highest cumulative hydrogen yield reached up to 175.84 mL/L when pH value and enzyme concentration are of 8.0 and 2.5% respectively. While the maximum cumulative bio-methane-production yield of 104.59 mL/L was obtained when the enzyme concentration and pH value are of 1.0% and 8.0 respectively. The effects of enzyme on cumulative bio-hydrogen yield was greater than that of the initial pH while it is opposite for cumulative bio-methane yield. The potential of bio-hydrogen production from diseased swines is higher than that of bio-methane production.     

Two-stage thermophilic bio-hydrogen and methane production from lime-pretreated oil palm trunk by simultaneous saccharification and fermentation

A simultaneous saccharification and fermentation (SSF) process was applied for thermophilic bio-hydrogen production from lime-pretreated oil palm trunk (OPT) by Thermoanaerobacterium thermosaccharolyticum KKU19. The SSF hydrogen fermentation conditions were optimized to maximize hydrogen yield (HY). Based on Plackett-Burman design, substrate loading and initial pH had significant effects on HY. The substrate loading and initial pH were further optimized using response surface methodology with a central composite design. The optimum conditions were a substrate loading, enzyme loading, inoculum concentration, initial pH and temperature of 4.6%, 10 filter paper unit (FPU)/g-OPT, 10% (v/v), 6.3 and 50 °C, respectively, which yielded the highest HY of 60.22 mL H₂/g-OPT. Structural analysis showed that lime pretreatment and SSF decreased the crystallinity of OPT. Methane production was carried out following the hydrogen production to improve the energy yield from OPT. The results showed that methane production increased total energy yield from 0.65 to 11.79 kJ/g-OPT under the optimal conditions.     

Calcium silicate-based catalytic filters for partial oxidation of methane and biogas mixtures: Preliminary results

Development and testing of catalytic filters for partial oxidation of methane to increase hydrogen production in a biomass gasification process constitute the subject of the present study. Nickel, iron and lanthanum were coated on calcium silicate filters via co-impregnation technique, and catalytic filters were characterized by ICP-MS, XPS, XRD, TEM, TGA, TPR and BET techniques. The influences of varying reaction temperature and addition of Fe or La to Ni-based catalytic filters on methane conversion, and hydrogen selectivity have been investigated in view of preliminary results obtained from reactions with 6% methane-nitrogen mixture, and catalytic filters were tested with model biogas mixtures at optimum reaction temperature of each filter which were 750 °C or 850 °C. Approximately 93% methane conversion was observed with nearly 6% methane-nitrogen mixture, and 97.5% methane conversion was obtained with model biogas containing CH₄ which is 6%, CO₂, CO, and N₂ at 750 °C. These results indicate that calcium silicate provides a suitable base material for catalytic filters for partial oxidation of methane and biogas containing methane.     

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

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

Sustainable biohythane production from algal bloom biomass through two-stage fermentation: Impacts of the physicochemical characteristics and fermentation performance

Algal bloom biomass, sourced from a freshwater lake in Chongqing, was pre-treated by hydrothermal pre-treatments with or without acid/alkali catalysts, and subsequently used as a substrate for sustainable biohythane production via fermentation. Fourier transform infrared (FTIR) spectroscopy analyses suggested hydrothermal acid/alkali pre-treatments significantly changed peak intensities of chemical compositions in algal bloom biomass. Derivative thermogravimetric (DTG) analyses showed more macromolecular substances hydrolysed after hydrothermal acid/alkali pre-treatments. When bloom algae were pre-treated with 1% HCl at 140 °C for 10 min, an optimal specific hydrogen yield (SHY) of 39.4 mL/g volatile solid (VS) was obtained, which is 38.2% higher than raw biomass. However, a 34.4% decrease in SHY occurred under hydrothermal pre-treatment with 1% NaOH due to the enhancement of Maillard reaction. When using the effluents in methane fermentation, specific methane yields (SMYs) were 177.1–276.8 mL/g VS. Two-stage process effectively reduced the total fermentation time by 22.7% compared with single-stage fermentation.     

Vegetable waste as substrate and source of suitable microflora for bio-hydrogen production

Self-fermentation of cellulosic substrates to produce biohydrogen without inoculum addition nor pretreatments was investigated. Dark fermentation of two different substrates made of leaf-shaped vegetable refuses (V) and leaf-shaped vegetable refuses plus potato peels (VP), was taken in consideration. Batch experiments were carried out, under two mesophilic anaerobic conditions (28 and 37 °C), in order to isolate and to identify potential H₂-producing bacterial strains contained in the vegetable extracts. The effect of initial glucose concentration (at 1, 5 and 10 g/L) on fermentative H₂ production by the isolates was also evaluated.H₂ production from self-fermentation of both biomasses was found to be feasible, without methane evolution, showing the highest yield for V biomass at 28 °C (24 L/kg VS). The pH control of the culture medium proved to be a critical parameter. The isolates had sequence similarities ≥98% with already known strains, belonging to the family Enterobacteriaceae (γ-proteobacteria) and Streptococcaceae (Firmicutes). Four genera found in the samples, namely Pectobacterium, Raoultella, Rahnella and Lactococcus have not been previously described for H₂ production from glucose. The isolates showed higher yield (1.6–2.2 mol H₂/mol glucose_added) at low glucose concentration (1 g/L), while the maximum H₂ production ranged from 410 to 1016 mL/L and was obtained at a substrate concentration of 10 g/L. The results suggested that vegetable waste can be effectively used as both, substrate and source of suitable microflora for bio-hydrogen production.     

Two-stage anaerobic process for bio-hydrogen and bio-methane combined production from biodegradable solid wastes

A two-stage anaerobic digestion process intended for biohydrogen and bio-methane combined production from organic fraction of municipal solid wastes was investigated. In thermophilic conditions blocking of methanogenesis at the first stage of the anaerobic fermentation was achieved at pH 9.0. Cumulative hydrogen production made 82.5 l/kg volatile solids. Pretreatment of organic fraction of municipal solid wastes and exploitation of mixed cultures of anaerobic thermophilic cellulolytic and saccharolytic bacteria of Clostridia sp resulted in the increase of hydrogen cumulative production up to 104 l/kg volatile solids. Content of methane in biohydrogen didn’t exceed 0.1%. Cumulative bio-methane production made 520 l/kg volatile solids. Methane percentage in produced biogas was 78.6%. Comparison of energy data for two-stage anaerobic digestion with those for solely methane production shows the increase in energy recovery from biodegradable fraction of municipal solid wastes. Results obtained make a foolproof basis for the development of cost-effective technological process providing hydrogen and methane combined production from solid organic wastes. Technology can be implemented at large scale biogas plants improving economical and ecological characteristics of the overall process.     

Enhanced hydrogen production from sewage sludge by cofermentation with wine vinasse

The cofermentation of sewage sludge and wine vinasse at different mixing ratios to enhance hydrogen production was investigated. Batch experiments were carried out under thermophilic conditions with thermophilic sludge inoculum obtained from an acidogenic anaerobic reactor. The results showed that the addition of wine vinasse enhances the hydrogen production of sewage sludge fermentation. The highest hydrogen yields, 41.16 ± 3.57 and 43.25 ± 1.52 mL H₂/g VS_added, were obtained at sludge:vinasse ratios of 50:50 and 25:75, respectively. These yields were 13 and 14 times higher than that obtained in the monofermentation of sludge (3.17 ± 1.28 mL H₂/g VS_added). The highest VS removal (37%) was obtained at a mixing ratio of 25:75. Cofermentation had a synergistic effect the hydrogen yield obtained at a sludge:vinasse ratio of 50:50 was 40% higher, comparing to the sum of each waste. Furthermore, kinetic analysis showed that Cone and first-order kinetic models fitted hydrogen production better than the modified Gompertz model.     

Green biohydrogen production in a Co-digestion process from mixture of high carbohydrate food waste and cattle/chicken manure digestate

This study was investigated biohydrogen production on the effects of different ratio of food waste to seed digestate and pH value from co-digestion process in anaerobic reactor. The seed digestate was mixture of cattle manure 45%, corn silage 25%, chicken manure 15%, and olive pomace 15% which was collected from the biogas plant in central Italy. It was found that the peaks of total biogas and the biohydrogen productions were 1355 ± 26 and 436 ± 10 mL whereas the biohydrogen yield was 50.4 mL/g-VS (45.8 mL/g-COD) with 43.33% COD removal rate, the bacteria to substrate volatile solids (VS) ratio was 2:1 where seed digestate to food waste was 6:4 under pH 6.5. As a consequence, food waste with a high COD concentration can be adapted C/N ratio by the cattle manure and chicken manure in the seed digestate which resulted in a high biohydrogen production. The food waste co-digestion system mixed with biogas plant digestate is one of approach to increase total biogas production.     

Enhanced bio-methane and bio-hydrogen production using banana plant waste and sewage sludge through anaerobic co-digestion

The yield of bio-methane and bio-hydrogen was enhanced by co-digesting banana plant waste (BPW) and sewage sludge (SS). In stage 1, acclimatisation of the inoculum SS is performed in a continuous stirred tank reactor (CSTR), and its various parameters are analyzed daily. In stage 2, six different BPW to SS ratios is optimized and incubated in manual methane potential test setup (MMPTS) for 40 days. The highest bio-methane and bio-hydrogen yields were observed from R4 (60% BPW and 40% SS). In stage 3, the best-achieved ratio of BPW and SS are then treated with different doses of NaOH as an alkaline pre-treatment. The highest bio-methane was achieved from dose 2 (0.75 mol NaOH) as 620.8 NmL/day. The study shows that the co-digestion of the BWP with SS has promising potential for enhanced bio-methane and bio-hydrogen production.     

Effects of anaerobic pre-treatment on the degradation of dewatered-sewage sludge

Effects of anaerobic pre-treatment were evaluated on the dewatered-sewage sludge from a municipal wastewater treatment plant in order to improve its biodegradability through anaerobic digestion. The pre-treatment was conducted in laboratory scale at 25, 50 and 70 °C for an incubation time of two days. As a reference, sludge sample was also autoclaved at 121 °C for 20 min to determine the thermal effect to the subsequent sludge digestion. Characteristics of dewatered-sludge such as viscosity, pH and soluble chemical oxygen demand (SCOD) were affected by the pre-treatment. A higher SCOD after the pre-treatment did not necessarily imply an increase in methane yield, although initial biodegradability rate was improved. In fact, a ‘great’ improvement in SCOD concentration (up to 27%) was translated in only 8% increase in the methane yield (298 ± 9 and 276 ± 6 Nml CH₄ gVS_added^?1 for pre-treated and untreated samples, respectively). Increasing the anaerobic pre-treatment time from 12 h to 2 days at 50 °C led to an 11% improvement in methane yield. Methane content in biogas increased from an average of 65–69% for the pre-treated and untreated substrates, respectively. Volatile solids (VS) reduction increased from 42% to 51%. The overall digestion time was not affected by the pre-treatment but 90% of methane was produced in the first 12 days of incubation for 50 °C pre-treated samples whereas it took 2–5 days more for 25, 70 °C pre-treated and untreated sludge samples. In this study, thermophilic digestion was also found to be a better option in terms of faster digestion and higher VS-reduction, but it showed lower methane yield as compared to mesophilic digestion, i.e. 9% and 11% increment in methane yields for thermophilic and mesophilic digestions, respectively.     

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

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

Fermentative hydrogen production by a new mesophilic bacterium Clostridium sp. 6A-5 isolated from the sludge of a sugar mill

The fermentative hydrogen production capability of the newly isolated Clostridium sp. 6A-5 bacterium was studied in a batch cultivation experiment. Various culture conditions (temperature, initial pH, and glucose concentration) were evaluated for their effects on cell growth and hydrogen production (including the yield and rate) of Clostridium sp. 6A-5. Optimal cell growth was observed at 40 °C, initial pH 7.5–8, and glucose concentration 16–26 g/L. The optimal hydrogen yield was obtained at 43 °C, initial pH 8, and glucose concentration 10–16 g/L. Hydrogen began to evolve when cell growth entered the mid-exponential phase and reached the maximum production rate at the late exponential and stationary phases. The maximum hydrogen yield, and rate were 2727 mL/L, and 269.3 mL H₂/L h, respectively. These results indicate that Clostridium sp. 6A-5 is a good candidate for mesophilic fermentative hydrogen production.     

Application of rice rhizosphere microflora for hydrogen production from apple pomace

The combination of substrate materials and bacteria is an important factor affecting conversion technology for biological hydrogen production. We performed anaerobic hydrogen fermentation of apple pomace wastes using rhizosphere bacterial microflora of rice as the parent inoculum. In the vial test, the optimal condition for hydrogen fermentation was initial pH 6.0, 35 °C, and 73.4 g pomace per liter of medium (equivalent to 10 g-hexose/L). In the batch experiment (pH 6.0, temperature 35 °C) the hydrogen yield reached 2.3 mol-H₂/mol-hexose. The time course of biogas production and PCR-DGGE analysis suggest that Clostridium spp. decomposed degradable carbohydrates rapidly and a part of the refractory carbohydrate (e.g. pectin) gradually in the apple pomace slurry. In addition to hydrogen, volatile fatty acids (VFAs) were produced in the anaerobic fermentation of apple pomace, which can be a substrate for methane fermentation. The rice rhizosphere can be a promising source of inoculum bacteria for hydrogen fermentation in combination with plant material waste like apple pomace.     

Enhancement of batch biohydrogen production from prehydrolysate of acid treated oil palm empty fruit bunch

Carbohydrates from hydrolyzed biomass has been a potential feedstock for fermentative hydrogen production. In this study, oil palm empty fruit bunch (OPEFB) was treated by sulfuric acid in different concentrations at 120 °C for 15 min in the autoclave. The optimal condition for pretreatment was obtained when OPEFB was hydrolyzing at 6% (w/v) sulfuric acid concentration, which gave the highest total sugar of 26.89 g/L and 78.51% of sugar production yield. However, the best conversion efficiency of OPEFB pretreatment was 39.47 at sulfuric acid concentration of 4%. A series of batch fermentation were performed to determine the effect of pH in fermentation media and the potential of this prehydrolysate was used as a substrate for fermentative hydrogen production under optimum pretreatment conditions. The prehydrolysate of OPEFB was efficiently converted to hydrogen via fermentation by acclimatized mixed consortia. The maximum hydrogen production was 690 mL H₂ L⁻¹ medium, which corresponded to the yield of 1.98 molH₂/mol_xylose achieved at pH 5.5 with initial total sugar concentration of 5 g/L. Therefore, the results implied that OPEFB prehydrolysate is prospective substrate for efficient fermentative hydrogen conducted at low controlled pH. No methane gas was detected throughout the fermentation.     

Dark fermentation of starch factory wastewater with acid- and base-treated mixed microorganisms for biohydrogen production

Biohydrogen (Bio-H₂) can be produced from starch factory wastewater and mixed microorganisms using dark fermentation. Acidic and basic chemicals were used to treat the microorganisms to select the hydrogen (H₂)-producing culture. The experiment used a 120 mL bioreactor at 35 °C and the operation commenced with the initial pH level of wastewater in the pH range 4–7 in batch mode. The bacteria:chemical oxygen demand (COD) ratio was 0.2. The initial pH level of the wastewater in the fermentation process affected the H₂ yield and the specific hydrogen production rate (SHPR). For acid-treated bacteria, the maximum H₂ yield and SHPR were produced at an initial pH of 6.5. The maximum H₂ yield and SHPR were 138 mL/g COD degraded and 7.42 mL/g cells?h, respectively. For the base-treated bacteria, the maximum H₂ yield and SHPR were produced at initial pH of 6.5 and pH 7, respectively. The maximum H₂ yield and SHPR were 182 mL/g COD degraded and 25.60 mL/g cells?h, respectively. The COD degradation efficiency levels were 16 and 20% for acid- and base-treated bacteria, respectively. The digested wastewater remained acidic at pH 4.79–4.83. Throughout the study, no methane gas was observed in the gas mixture produced.     

New sustainable bioconversion concept of date by-products (Phoenix dactylifera L.) to biohydrogen,biogas and date-syrup

The dates production is usually accompanied by considerable loss of fruit byproducts. The chemical analysis showed that ‘Deglet Nour’ discarded flesh is rich in soluble sugars (79.8% ± 0.8%) and fibers (12.3% ± 0.4%). A processing approach was implemented to permit the production of biohydrogen from the flesh and biogas from the crude fiber fraction after soluble sugars extraction. This approach showed interesting results since the obtained biochemical hydrogen potential and the maximum methane yield were 292 mL H₂/gVS _initial and 235 mL CH₄/gVS _fibers respectively. Parallelly, the “hot water” soluble sugar fraction (date syrup) was of interest for agro-alimentary applications and showed a high sucrose, glucose and fructose content of 33.5%, 11.8% and 13.17% respectively. This study presents a proof of concept allowing an efficient sustainable energetic conversion of the date by-products biomass to biohydrogen via dark fermentation or to soluble sugars fraction and biogas via a biorefinery approach.     

Production of hydrogen by catalytic methane decomposition using biochar and activated char produced from biosolids pyrolysis

Catalytic methane decomposition (CMD) was studied by employing biochar and activated char of biosolids’ origin under different reaction temperatures and methane concentrations. Higher reaction temperatures and lower inlet methane concentrations were found to be favourable for achieving higher methane conversion. A maximum initial methane conversion of 71.0 ± 2.5 and 65.2 ± 2.3% was observed for activated char and biochar, respectively at 900 °C and for 10% CH₄ in N₂ within the first 0.5 h of experiment. Active sites from oxygen containing carboxylic acid functional groups and smaller pore volume and pore diameter were attributed to assist in higher initial methane conversion for biochar and activated char respectively. However, rapid blockages of active sites and surfaces of biochar and activated char due to carbon formation have caused a rapid decline in methane conversion values in the first 0.5 h. Later on, crystalline nature of the newly formed carbon deposits due to their higher catalytic activity have stabilised methane conversion values for an extended experimental period of 6 h for both biochar and activated char. The final conversion values at the end of 6 h experiment with biochar and activated char at 900 °C and for 10% CH₄ in N₂, were found to be 40 ± 1.9 and 35 ± 1.6% respectively. Analysing carbon deposits in detail revealed that carbon nanofiber type structures were observed at 700 °C while nanospheres of carbon were found at 900 °C.     

Isolation and characterization of a new hydrogen-producing strain Bacillus sp. FS2011

A new fermentative hydrogen-producing strain FS2011 was isolated from an effluent of bio-hydrogen production reactor, and identified as Bacillus amyloliquefaciens on the basis of 16S rDNA gene sequence. The strain could utilize various carbon and nitrogen sources to produce hydrogen in a broad range of initial pH (5.29–7.38). Phosphate buffer concentration and fermentation temperature significantly affected hydrogen production and cell growth. The maximum hydrogen yield of 2.26 mol/mol was observed at glucose concentration of 10 g/l, beef extract concentration of 2 g/l, initial pH 6.98, phosphate buffer of 20 mmol/l, and 35 °C, indicating FS2011 was a high-efficiency hydrogen-producing bacterium.     

A sequential process of anaerobic solid-state fermentation followed by dark fermentation for bio-hydrogen production from Chlorella sp.

Microalgal biomass has recently been one of the most widely studied feedstocks for bio-hydrogen production, owing to its richness in fermentable components, e.g. polysaccharides and proteins, and high biomass productivity. In this study, biomass of microalga Chlorella sp. TISTR 8411 was converted to hydrogen through a sequential process consisting of an anaerobic solid-state fermentation (ASSF) followed by a dark fermentation. The microalga was grown photoautothrophically in 80-L rectangular glass tanks and then scaled-up to a 240-L open pond for the production of biomass. The highest biomass concentration attained was 4.45 g L⁻¹. The biomass was harvested with over 90% flocculation efficiency at pH 11.5 and a biomass concentration of 2.6 g/L. The sequential process gave a total hydrogen yield (HY) of 16.2 mL/g-volatile-solid (VS), of which 11.6 mL/g-VS was from ASSF. The high HY obtained from the ASSF indicated that it was effective and could be integrated with a conventional hydrogen production process to improve energy recovery from biomass.