Fermentative hydrogen production from macro-algae Laminaria japonica using anaerobic mixed bacteria

In this study, one macro-alga (Laminaria japonica) was used for fermentative hydrogen production by anaerobic mixed bacteria. The saccharification efficiency and hydrogen production by L. japonica with four different pretreatment methods, including heat, acid, alkaline and ultrasonic treatment, were investigated. The results showed that the saccharification efficiency from L. japonica that was pretreated with acid was the highest among the four methods. The saccharification efficiency for the total reducing sugars in the acid-pretreated L. japonica was 350.54 ± 19.89 mg/g (mean ± S.E.). The cumulative hydrogen production was 66.68 ± 5.68 mL/g from the heat-pretreated L. japonica, whereas that of L. japonica that was subjected to acid, alkaline, and ultrasonic pretreatment and the control was 43.65 ± 6.87 mL/g, 15.00 ± 3.89 mL/g, 23.56 ± 4.56 mL/g and 10.00 ± 1.21 mL/g, respectively. In addition, the effects of substrate concentration and initial pH on hydrogen production from heat-pretreated L. japonica were also analyzed. The results showed that the maximum hydrogen production was 83.45 ± 6.96 mL/g with a hydrogen concentration of approximately 28.4% from heat-pretreated L. japonica when the initial pH and substrate concentration were determined to be 6.0 and 2%, respectively. Heat pretreatment was the most effective method for increasing fermentative hydrogen production when L. japonica was used as the only substrate.     

Enhanced methane fermentation of municipal sewage sludge by microbial electrochemical systems integrated with anaerobic digestion

Sewage sludge from a municipal wastewater treatment plant was fed into a microbial electrochemical system, combined with an anaerobic digester (MES-AD), for enhanced methane production and sludge stabilization. The effect of thermally pretreating the sewage sludge on MES-AD performance was investigated. These results were compared to those obtained from control operations, in which the sludge was not pretreated or MES integration was absent. The soluble chemical oxygen demand (SCOD) in the raw sewage sludge after pretreatment was 31% higher than the SCOD in untreated sludge (5804.85 mg/L vs. 4441.46 mg/mL). The methane yield and proportion of methane in biogas generated by the MES-AD were higher than those of the control systems, regardless of the pretreatment process. The maximum methane yield (0.28 L CH₄/g COD) and methane production (1139 mL) were obtained with the MES inoculated with pretreated sewage sludge. Methane yield and production with this system using pretreated sewage were 47% and 56% higher, respectively, than those of the control (0.19 L CH₄/g COD, 730 mL). Additionally, the maximum SCOD removal (89%) and current generation were obtained with the MES inoculated with a pretreated substrate. These results suggested that sewage sludge could be efficiently stabilized with enhanced methane production by synergistic combination of MES-AD system with pretreatment process.     

Evaluation of pretreatment methods on harvesting hydrogen producing seeds from anaerobic digested organic fraction of municipal solid waste (OFMSW)

In order to harvest high-efficient hydrogen producing seeds, five pretreatment methods (including acid, heat, sonication, aeration and freeze/thawing) were performed on anaerobic digested sludge (AS) which was collected from a batch anaerobic reactor for treating organic fraction of municipal solid waste. The hydrogen production tests were conducted in serum bottles containing 20 gVS/L (24.8 g COD/L) mixture of rice and lettuce powder at 37 °C. The experimental results showed that the heat and acid pretreatment completely repressed the methanogenic activity of AS, but acid pretreatment also partially repressed hydrogen production. Sonication, freeze/thawing and aeration did not completely suppress the methanogen activity. The highest hydrogen yields were 119.7, 42.2, 26.0, 23.0, 22.7 and 22.1 mL/gVS for heated, acidified, freeze/thawed, aerated, sonicated and control AS respectively. A pH of about 4.9 was detected at the end of hydrogen producing fermentation for all tests. The selection of an initial pH can markedly affect the hydrogen producing ability for heated and acidified AS. The higher initial pH generated higher hydrogen yield and the highest hydrogen yield was obtained with initial pH 8.9 for heated AS.     

Co-producing hydrogen and methane from higher-concentration of corn stalk by combining hydrogen fermentation and anaerobic digestion

In this paper, the high concentration of corn stalk (60 g/L) was employed as feedstock to produce bio-hydrogen and methane by combining hydrogen fermentation and anaerobic digestion. In the first stage of hydrogen fermentation, the effects of several key parameters, such as strain enhancement technique, cetyl trimethyl ammonium bromide (CTAB), NH₄HCO₃ on hydrogen production from cornstalk were investigated and optimized. The maximum hydrogen yield of 79.8 ± 1.5 ml H₂/g-TS and hydrogen production rate of 3.78 ml/g-cornstalk h was observed at fixed acidizing cornstalk of 60 g/L, strains Bacillus sp. FS2011 dosage of 10%(v/v), CTAB of 30 mg/L, NH₄HCO₃ of 1.2 g/L and initial pH of 7.5 ± 0.5 at 36 ± 1 °C, respectively. In the second stage of anaerobic digestion, the effluent from hydrogen production bio-reactor was further employed as the feedstock to produce methane by methanogenic bacteria, the maximum methane yield of 227 ± 2.5 ml CH₄/g-COD and COD removal rate of 95  ± 1% was recorded. The interesting observations were that the total amount of the organic wastewater produced in a higher substrate concentration (60 g/l) by hydrogen fermentation was reduced by about two-thirds compared with that of traditional low substrate concentration (≤20 g/l).     

Biohydrogen production from poplar leaves pretreated by different methods using anaerobic mixed bacteria

Leaves are one of the main by-products of forestry. In this study, batch experiments were carried out to convert poplar leaves pretreated by different methods into hydrogen using anaerobic mixed bacteria at 35 °C. The effects of acid (HCl), alkaline (NaOH) and enzymatic (Viscozyme L, a mixture of arabanase, cellulase, β-glucanase, hemicellulase and xylanase) pretreatments on the saccharification of poplar leaves were studied. Furthermore, the effects of acid and enzymatic pretreatment on hydrogen production, together with their corresponding degradation efficiencies for the total reducing sugar (TRS) and metabolites were compared. A maximum cumulative hydrogen yield of 44.92 mL/g-dry poplar leaves was achieved from substrate pretreated with 2% Vicozyme L, which was approximately 3-fold greater than that in raw substrate and 1.34-fold greater than that from substrate pretreated with 4% HCl. The results show that enzymatic pretreatment is an effective method for enhancing the hydrogen yield from poplar leaves.     

Effects of pretreatments of anaerobic sludge and culture conditions on hydrogen productivity in dark anaerobic fermentation

Effects of various pretreatments of the anaerobic sludge on hydrogen production were investigated for enhancing hydrogen production via dark anaerobic fermentation of organic substrates. The pretreatment methods included heat treatment, acid or base treatment, acid/heat treatment and base/heat treatment. After the pretreatment of the anaerobic sludge, productivity of H₂ by the pretreated sludge were evaluated when the culture were grown on glucose-based medium at ambient conditions. The detailed experimental investigation showed highest production of H₂ by the heat-treated culture followed by the heat and acid-treated culture and the heat and base-treated culture.     

Application of immobilized upflow anaerobic sludge blanket reactor using Clostridium LS2 for enhanced biohydrogen production and treatment efficiency of palm oil mill effluent

Polyethylene glycol (PEG) gel was used to immobilize hydrogen producing Clostridium LS2 bacteria for hydrogen production in an upflow anaerobic sludge blanket (UASB) reactor. The UASB reactor with a PEG-immobilized cell packing ratio of 10% weight to volume ratio (w/v) was optimal for dark hydrogen production. The performance of the UASB reactor fed with palm oil mill effluent (POME) as a carbon source was examined under various hydraulic retention time (HRT) and POME concentration. The best volumetric hydrogen production rate of 365 mL H₂/L/h (or 16.2 mmol/L/h) with a hydrogen yield of 0.38 L H₂/g COD_added was obtained at POME concentration of 30 g COD/L and HRT of 16 h. The average hydrogen content of biogas and COD reduction were 68% and 65%, respectively. The primary soluble metabolites were butyric acid and acetic acid with smaller quantities of other volatile fatty acid and alcohols formed during hydrogen fermentation. More importantly, the feasibility of PEG-immobilized cell UASB reactor for the enhancement of the dark-hydrogen production and treatment of wastewater is demonstrated.     

木糖厌氧发酵产氢特性研究

以木糖作为厌氧发酵产氢底物,热预处理(100℃,处理20 min)的厌氧颗粒污泥作为接种物,研究了中温条件(37℃)下厌氧发酵产氢特性.结果表明,当反应进行至50 h时,累积产氢量最大,为81.11 mL;乙酸、丁酸和乙醇是液相末端产物中的主要物质,其中乙酸和丁酸的浓度分别为1290 mg/L和1225 mg/L,发酵类型是典型的丁酸型发酵;反应体系的pH值开始降低,最后稳定在4.40左右,形成一个稳定的缓冲体系.     

Photocatalytic pretreatment for the redox conversion of waste activated sludge to enhance biohydrogen production

Photocatalytic pretreatment of waste activated sludge (WAS) using a flat photocatalytic reactor was undertaken. Photocatalytic pretreatment enhanced the release of soluble substances from WAS, in which the soluble protein and soluble carbohydrate concentration increased by about 50% and 80%, respectively. Significant removal of heavy metal ions from the liquid phase of WAS was also achieved after photocatalytic pretreatment. In addition, the highest hydrogen yield and the highest concentration of volatile fatty acids (VFAs) were achieved from the photocatalysis pretreated WAS by batch anaerobic digestion (55 °C). The cumulative hydrogen yield from photocatalysis pretreated WAS was 211.0 ml/l-sludge, much higher than those from UV pretreated WAS (111.0 ml/l-sludge) and from raw WAS (93.0 ml/l-sludge). The results indicate that photocatalysis is a promising WAS pretreatment method for the enhancement of biohydrogen production, probably due to the photo-oxidation of organics and simultaneous photo-reduction of heavy metal ions in WAS.     

A pilot study of biohythane production from cornstalk via two-stage anaerobic fermentation

This study aimed to study the feasibility and stability of biohythane production from cornstalk via two-stage anaerobic fermentation without hydrolysis step in a semi-continuous pilot scale system. The present study applied a 1 m³ continuous stirred tank reactor for biohydrogen production and a 0.5 m³ up-flow anaerobic sludge bed for biomethane production. During the entire operation, a hydrogen production yield of 25.02 L/kg TS and hydrogen production rate of 0.46 L/L/d was achieved in first-stage. In addition, a methane yield of 95.38 L/kg TS and methane production rate of 4.06 L/L/d was achieved in second-stage by using the liquid effluent after first-stage. The percentage of hydrogen in the biohythane gas was 18.47% which suitable for vehicle fuel. Moreover, it was feasible to use the solid residue as a growth medium in seedlings to improve energy and carbon recovery. The results suggest that biohythane production from cornstalk could be a promising biofuel avenue.     

Effects of pretreatment in a vortex layer apparatus on the properties of confectionery wastewater and its dark fermentation

Pretreatment prior to anaerobic digestion is an effective option for increasing the biodegradability of organic waste. Vortex layer apparatus (VLA) is considered one of the promising types of equipment for pretreatment. In this work, confectionery wastewater (CW) was pretreated in VLA for 1 and 3 min before dark fermentative hydrogen production in anaerobic upflow biofilters. The pretreatment resulted in a slight increase in soluble chemical oxygen demand (COD), soluble sugars and acetic acid, and a decrease in the concentration of propionic, butyric and caproic acids. Due to the abrasion of steel needles in VLA, the concentration of iron in the pretreated CW increased by 2.57 times. Hydraulic retention time in anaerobic upflow biofilters was gradually reduced from 5.6 to 1.8 and 1.3 days, which corresponded to organic loading rate of 2.0, 6.3 and 8.8 kg COD/(m³ day). Although the highest hydrogen yield (96.2 ± 8.1 ml/g COD) was obtained for non-pretreated CW, the pretreatment contributed to a significant increase in methane yield (39.2 ± 2.5 ml/g COD), possibly due to higher iron content (1.8 ± 0.3 mg/L). The highest energy production rate (4407 J/(L day)) was achieved after 3 min CW pretreatment. Thus, pretreatment in VLA can be a promising method for improving the biohythane production process.     

Effects of pretreatment methods on cassava wastewater for biohydrogen production optimization

Batch production of biohydrogen from cassava wastewater pretreated with (i) sonication, (ii) OPTIMASH BG^® (enzyme), and (iii) α-amylase (enzyme) were investigated using anaerobic seed sludge subjected to heat pretreatment at 105 °C for 90 min. Hydrogen yield at pH 7.0 for cassava wastewater pretreated with sonication for 45 min using anaerobic seed sludge was 0.913 mol H₂/g COD. Results from pretreatment with OPTIMASH BG^® at 0.20% and pH 7 showed a hydrogen yield of 4.24 mol H₂/g COD. Superior results were obtained when the wastewater was pretreated with α-amylase at 0.20% at pH 7 with a hydrogen yield of 5.02 mol H₂/g COD. In all cases, no methane production was observed when using heat-treated sludge as seed inoculum. Percentage COD removal was found to be highest (60%) using α-amylase as pretreatment followed by OPTIMASH BG^® at 54% and sonication (40% reduction rate). Results further suggested that cassava wastewater is one of the potential sources of renewable biomass to produce hydrogen.     

Dilute-acid pretreatment of barley straw for biological hydrogen production using Caldicellulosiruptor saccharolyticus

The main objective of this study was to use the fermentability test to investigate the feasibility of applying various dilute acids in the pretreatment of barley straw for biological hydrogen production. At a fixed acid loading of 1% (w/w dry matter) 28–32% of barley straw was converted to soluble monomeric sugars, while at a fixed combined severity of −0.8 30–32% of the straw was converted to soluble monomeric sugars. With fermentability tests at sugar concentrations 10 and 20 g/L the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus showed good hydrogen production on hydrolysates of straw pretreated with H₃PO₄ and H₂SO₄, and to a lesser extent, HNO₃. The fermentability of the hydrolysate of straw pretreated with HCl was lower compared to the other acids but equally high as that of pure sugars. At sugar concentration 30 g/L the fermentability of all hydrolysates was low.     

Biohydrogen production from immobilized cells and suspended sludge systems with condensed molasses fermentation solubles

The anaerobic fermentation using the condensed molasses fermentation solubles (CMS) as substrate in a continuously stirred anaerobic bioreactor (CSABR) was carried out for optimal hydrogen production performance of biohydrogen production rate and yield, where as two kinds of bioreactors used. One is a suspended sludge bioreactor (SSB) which used suspended seed sludge. The other bioreactor is an immobilized cell bioreactor (ICB) which used immobilized cells and mix the same seed sludge in the SSB as the source of the bacteria. It was found that the hydrogen production rate increased with a decrease in the hydraulic retention time (HRT), when substrate concentration was 40 g COD/L in an SSB as well as maximum hydrogen production rate of 14.04 ± 2.08 L/d/L obtained at HRT 0.5 h (ca. 5.78 times value of HRT 4 h) in the SSB system. The hydrogen production rate at low dilution rate (HRT > 4 h), in the ICB is better than SSB, meanwhile at a high dilution rate (HRT < 4 h), due to the presence of enriched granules in the SSB (12.30 g VSS/L), absent in the ICB (9.89 g VSS/L), the hydrogen production rate was 7.60 ± 1.05 L/d/L (ca. 1.23 times higher than HRT 4 h), which was lower than the rate in the SSB. Eventually, the hydrogen production rate increased by increasing the substrate concentrations from 40 to 60 g COD/L within the HRT range of 2–4 h in both the SSB as well as in ICB systems.     

Continuous hydrogen production from tofu processing waste using anaerobic mixed microflora under thermophilic conditions

We carried out continuous fermentative H₂ production from tofu (soybean curd)-processing waste (TPW) using anaerobic mixed microflora under thermophilic (60 °C) conditions and compared the rates and yields of H₂ production in a continuous stirred-tank reactor (CSTR) and a membrane bioreactor (MBR), wherein the membrane filtration unit was coupled to the CSTR. The TPW was diluted with tap water and then hydrolyzed by blending for 5 min in the presence of 0.5% HCl, and it was found that this protocol significantly increased the amount of soluble material in the mixture. The soluble chemical oxygen demand (SCOD)-to-total COD (TCOD) ratio jumped from 14% to 60%, and the soluble carbohydrate concentration was increased threefold, from 2.4 g/L to 7.2 g/L. Accordingly, H₂ production potential was increased 2.8-fold. In a CSTR operation using pretreated TPW as the substrate, a stable volumetric H₂ production rate (VHPR) of 8.17 ± 0.32 L H₂/L/d and a H₂ yield of 1.20 ± 0.05 mol H₂/mol hexose_added at 8-h HRT were achieved. Substantial increases in the VHPR and H₂ yield over those obtained with the CSTR were observed in the MBR operation. The role of the MBR was to increase the retention time of the solid substrate and the concentration of microorganisms, thereby enhancing the substrate utilization rate for H₂ production. Acetic and butyric acids were the main liquid-state metabolites produced during the fermentation process, thus indicating that the thermophilic operation provided favorable conditions for H₂ production from TPW. A maximum H₂ yield of 1.87 mol H₂/mol hexose_added was achieved at 8-h HRT and then gradually decreased to 1.00 mol H₂/mol hexose-equivalent at 2-h HRT. Meanwhile, the VHPR continuously increased to a maximum of 19.86 L H₂/L/d at 4-h HRT and then decreased with a high dilution rate as the HRT was lowered to 2 h (minimum). At 2-h HRT, the degradation of soluble carbohydrate was limited.     

Hydrogen and methane production in a bio-electrochemical system assisted anaerobic baffled reactor

In this study, a new process was proposed to enhance the stability and efficiency of an anaerobic baffled reactor (ABR). The process was examined in a four equal compartments ABR with total volume of 3.46 L. The first compartment was operated for fermentative hydrogen production and the last three compartments were used as continuous singer chamber microbial electrolysis cells (MECs) for methanogenesis. The system was operated at 35 ± 1 °C and hydraulic retention time (HRT) of 24 h with influent chemical oxygen demand (COD) concentration of 3500 mg/L–4000 mg/L. The results indicated that the proportion of hydrogen in the first compartment was 20.7% and proportions of methane in the last three compartments were 98.0%, 93.6% and 70.1%, respectively. A total of 98.0% of COD removal rate was achieved as well. Hence, this new system has following advantages: hydrogen production with cleaner effluent, high COD removal rate, and net methane production for practical use.     

Performance of anaerobic bioreactor treating fish-processing plant wastewater pre-hydrolyzed with a solid enzyme pool

The effect of a lipase-rich enzyme preparation produced by the fungus Penicillium simplicissimum on solid-state fermentation was evaluated in a 4.9 L up-flow anaerobic sludge blanket bioreactor (UASB) treating fish-processing plant wastewater containing 1500 mg oil and grease (O&G)/L. The oil and grease hydrolysis step was carried out with 0.5% or 0.2% (w/v) of the solid enzyme preparation (SEP) at 30 °C for 8 h. The bioreactor operated at 30 °C with a hydraulic retention time of 10 h for a period of over 100 days, showed high total COD removal efficiencies (85.3% for 0.5% SEP and 90.9% for 0.2% SEP), when fed with pre-hydrolyzed wastewater, compared to a Control bioreactor fed with raw wastewater (79.9%). The Control bioreactor also showed high oil and grease accumulation in the biomass throughout the operational period (the O&G content reached 1.7 times that found in the inoculum of the UASB bioreactor), intensive scum formation, and several episodes of cessation of treatment to clean the three-phase separator. Thus it can be concluded that the enzyme pre-hydrolysis step together with anaerobic treatment of the fish-processing plant wastewater improved the quality of the treated effluent and reduced operational problems.     

Fermentative hydrogen production by conventionally and unconventionally heat pretreated seed cultures: A comparative assessment

In this study, the effects of pretreatment temperature and time during conventional and unconventional, microwave-assisted heat shock on the hydrogen producing capability of anaerobic seed sludge from soluble starch was focused. It was found that the different heat transfer techniques resulted in seed cultures with comparable hydrogen production potentials, with the highest obtainable values of approximately 0.9 L H₂/L-d. A comprehensive, statistical analysis revealed that both treatment temperature and time could be designated as significant process variables, however, in distinguishable extents for the two alternative methods. The results indicated that microwave-based sludge pretreatment needed remarkably shorter curing times (2 min) to eliminate H₂-consuming, methanogenic activity in comparison to the conventional heat shock method (30 min). It was also demonstrated that microwave irradiation increased the soluble organic matter content in the seed sludge.     

Hydrogen and methane production via a two-stage processes (H2-SBR + CH4-UASB) using tequila vinasses

The feasibility of producing hydrogen and methane via a two-stage fermentation of tequila vinasses was evaluated in sequencing batch (SBR) and up-flow anaerobic sludge blanket (UASB) reactors. Different vinasses concentrations ranging from 500 mg COD/L to 16 g COD/L were studied in SBR by using thermally pre-treated anaerobic sludge as inoculum for hydrogen production. Peak volumetric hydrogen production rate and specific hydrogen production were attained as 57.4 ± 4.0 mL H₂/L-h and 918 ± 63 mL H₂/gVSS-d, at the substrate concentration of 16 g COD/L and 6 h of hydraulic retention time (HRT). Increasing substrate concentration has no effect on the specific hydrogen production rate. The fermentation effluent was used for methane production in an UASB reactor. The higher methane composition in the biogas was achieved as 68% at an influent concentration of 1636 mg COD/L. Peak methane volumetric, specific production rates and yield were attained as 11.7 ± 0.7 mL CH₄/L-h, 7.2 ± 0.4 mL CH₄/g COD-h and 257.9 ± 13.8 mL CH₄/g COD at 24 h-HRT and a substrate concentration of 1636 mg COD/L. An overall organic matter removal (SBR + UASB) in this two-stage process of 73–75% was achieved.     

Bio-hydrogen production from thin stillage using conventional and acclimatized anaerobic digester sludge

To assess the viability of biohydrogen production from thin stillage, a comparative evaluation of anaerobic digester sludge (ADS) and acclimatized anaerobic digester sludge (AADS) for biohydrogen production over a wide range of S⁰/X⁰ ratio (0.5-8 gCOD/gVSS) was performed. A maximum hydrogen yield of 19.5 L H₂/L thin stillage was achieved for the AADS while tests with ADS achieved a maximum yield of only 7.5 L H₂/L thin stillage. The optimum range of S⁰/X⁰ ratio for hydrogen production was found to be 1 to 2 gCOD/gVSS using conventional ADS and 3 to 6 gCOD/gVSS using AADS. The biomass specific hydrogen production rate for the AADS was 3.5 times higher than rate for the ADS throughout the range of S⁰/X⁰ ratio examined in this study. The DGGE profiles of the 16S rDNA gene fragments confirmed the superior performance of the AADS over the ADS, showing that the widely known hydrogen producers Clostridium acetobutyricum, Klebsiella pneumonia, Clostridium butyricum and Clostridium pasteurianum were the predominant species.