Extreme-thermophilic biohydrogen production by an anaerobic heat treated digested sewage sludge culture

Biohydrogen production process from glucose using extreme-thermophilic H₂-producing bacteria enriched from digested sewage sludge was investigated for five cycles of repeated batch experiment at 70 °C. Heat shock pretreatment was used for preparation of hydrogen-producing bacteria comparing to an untreated anaerobic digested sludge for their hydrogen production performance and responsible microbial community structures. The results showed that the heat shock pretreatment completely repressed methanogenic activity and gave the maximum hydrogen production yield of 355-488 ml H₂/g COD in the second cycle of repeated batch cultivation with more stable gas production during the cultivation when compared with control. Hydrogen production was accompanied by production of acetic acid. The average specific hydrogen in five cycles experiment ranged from 150 to 200 ml H₂/g VSS. PCR-DGGE profiling showed that the extreme-thermophilic culture predominant species were closely affiliated to Thermoanaerobacter pseudethanolicus.     

Optimizing hydrogen production from a switchgrass steam exploded liquor using a mixed anaerobic culture in an upflow anaerobic sludge blanket reactor

In this study, the operation of an upflow anaerobic sludge blanket reactor (UASBR) producing hydrogen (H₂) from a steam-exploded switchgrass (SWG) liquor was statistically optimized. The factors consider included pH, hydraulic retention time (HRT) and linoleic acid (LA) concentration. Under optimal operational conditions (pH 5.0, 10 h HRT and 1.75 g L⁻¹ LA), which were close to the predicted conditions using the D-optimality index, the maximum H₂ and methane yield observed were 99.86 ± 5.6 mL g⁻¹ TVS and 0.5 ± 0.1 mL g⁻¹ TVS, respectively. Under maximum H₂-producing conditions, high levels of acetate plus butyrate were observed with low levels of ethanol and lactate. A principal component analysis revealed that clustering of the samples was based on the operating conditions and fermentation metabolites. The microbial profiles revealed that by lowering the HRT from 16 to 8 h or decreasing the pH from 7.0 to 5.0 in the controls caused a 50% reduction in the relative abundance of the terminal restriction fragments belonging to the methanogenic population (Methanobacteria, Methanomicrobia, Methanococci). With LA treatment, H₂ producers (Ruminococcaceae and Clostridiaceae) were dominant and methanogens were inhibited and/or washed-out from the UASBR.     

Semi-continuous hydrogen production from catalytic methane decomposition using a fluidized-bed reactor

Non-oxidative, catalytic decomposition of hydrocarbons is an alternative, one-step process to produce pure hydrogen with no production of carbon oxides or higher hydrocarbons. Carbon produced from the decomposition reaction, in the form of potentially valuable carbon nanotubes, remains anchored to the active catalyst sites in a fixed bed. To facilitate periodical removal of this carbon from the reactor and to make hydrogen production continuous, a fluidized-bed reactor was envisioned. The hypothesis that the tumbling and inter-particle collisions of bed material would efficiently separate nanotubes anchored to the active catalyst sites of the bed particles was tested and shown to be invalid. However, a switching mode reaction system for the semi-continuous production of hydrogen and carbon nanotubes by periodic removal and replenishment of the catalytic bed material has been successfully demonstrated.     

热处理对污泥厌氧发酵产氢的影响

通过对污泥进行热处理来提高污泥厌氧发酵产氢的能力.结果表明:热处理是一种有效的污泥融胞方法,热处理对糖和蛋白质的水解效果好,热处理后污泥中可溶蛋白质浓度为原污泥的6.4～8.9倍,可溶糖浓度为原污泥的1.6～7.9倍.75℃热处理10 min效果最好,最大累积产氢量可达20.3 ml,较原污泥提高了19倍;VS最大比产氢率为152.2 ml·(kg·h)-1.并用SGompertz方程对实验数据进行拟合,定量说明在不同的热处理温度和时间下,厌氧发酵的累积产氢量(y)和时间(x)的关系.污泥厌氧发酵产氢前后各指标都发生明显变化,NH4 -N和总挥发性脂肪酸(TVFA)的浓度都增加了,而可溶糖和可溶蛋白质的浓度都降低了.热处理后的污泥在厌氧发酵产氢过程中,主要降解的有机物为蛋白质,发酵后蛋白质可降解20%～41%.     

Anaerobic treatment of wastewater using an upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket (UASB) reactor of volume 0.03 m³ was designed and fabricated to treat wastewater. The initial organic loading rate (OLR) of the wastewater estimated to be 4.8 gVS/l.d was later reduced to 0.96 gVS/l.d to control the observed acidity in the medium while the reactor was operated continuously for 64 days. The percent biological oxygen demand (BOD) and volatile solid (VS) removal were calculated over a period of 5 weeks to measure the efficiency of the reactor. The mean VS, total solid (TS), and BOD for the influent substrate were 0.43 g/kg, 0.84 g/kg, and 0.020 mg/m³, respectively, while for the treated wastewater, the VS, TS, and BOD were 0.30 g/kg, 0.59 g/kg, and 0.013 mg/m³, respectively. The estimated energy produced by the biogas was 5.8 kWh and 0.001 m³ of the biogas raised the temperature of 20 ml of water by 11.8°C in 40 s. The study concluded that the UASB reactor designed could treat the wastewater and the biogas generated could also serve as a source of renewable energy for cooking. However, the start-up OLR should be monitored in the course of operation to prevent souring of the digester and to achieve optimum performance of the reactor.     

Effect of acid,heat and combined acid-heat pretreatments of anaerobic sludge on hydrogen production by anaerobic mixed cultures

Activated sludge (AS) from wastewater treatment plant of brewery industry was used as substrate for hydrogen production by anaerobic mixed cultures in batch fermentation process. The AS (10% TS) was pretreated by acid, heat and combined acid and heat. Combined acid- heat treatment (0.5% (w/v) HCl, 110 °C, 60 min) gave the highest soluble COD (sCOD) of 1785.6 ± 27.1 mg/L with the highest soluble protein and carbohydrate of 8.1 ± 0.1 and 38.5 ± 0.8 mg/L, respectively. After the pretreatment, the pretreated sludge was used to produce hydrogen by heat treated upflow anaerobic sludge blanket (UASB) granules. A maximum hydrogen production potential of 481 mL H₂/L was achieved from the AS pretreated with acid (0.5% (w/v) HCl) for 6 h.     

Enhancement of hydrogen production in a novel fluidized-bed membrane reactor for naphtha reforming

In this work, a novel fluidized-bed membrane reactor (FBMR) for naphtha reforming in the presence of catalyst deactivation has been proposed. In this reactor configuration, a fluidized-bed reactor with perm-selective Pd–Ag (23 wt% Ag) wall to hydrogen has been used. The reactants are flowing through the tube side which is a fluidized-bed membrane reactor while hydrogen is flowing through the shell side which contains carrier gas. Hydrogen penetrates from fluidized-bed side into the carrier gas due to the hydrogen partial pressure driving force. Hydrogen permeation through membrane leads to shift the reaction toward the product according to the thermodynamic equilibrium. This membrane-assisted fluidized-bed reactor configuration solves some drawbacks of conventional naphtha reforming reactors such as pressure drop, internal mass transfer limitations and radial gradient of concentration and temperature. In FBMR the hydrogen which is produced in shell side is a valuable gas and can be used for different purposes. The two-phase theory of fluidization is used to model and simulate the FBMR. Industrial packed bed reactor (PBR) for naphtha reforming is used as a basis for comparison. This comparison shows enhancement in the yield of aromatic production in FBMR for naphtha reforming. Although using FBMR reduces hydrogen mole fraction in reaction side and enhances catalyst deactivation due to coking, but this effect can be compensated using advantages of FBMR such as suitable hydrogen to hydrocarbon molar ratio, lowering deactivation rate due to lower temperature, control of permeation rate by adjusting shell side pressure and shifting the equilibrium reactions. The impacts of hydrogen to hydrocarbon molar ratio, pressure, membrane thickness, flow rate and temperature have been investigated in this work.     

Effect of inoculum pre-treatment on mesophilic hydrogen and methane production from food waste using two-stage anaerobic digestion

Two-stage anaerobic digestion of food waste was performed using four different inoculum pre-treatment methods to enrich hydrogen (H₂) producing bacteria from sludge. The pretreatments used in this study included heat shock, alkaline treatment, aeration, and a novel pretreatment using waste frying oil (WFO). Alkaline pretreatment and aeration did not completely inhibit methanogens in the first stage while no methane (CH₄) was detected in the reactors cultivated either with heat shock or WFO-pretreated inocula. The highest H₂ and CH₄ yields (76.1 and 598.2 mL/gVS, respectively) were obtained using the inoculum pretreated with WFO. The highest total energy yield (21.96 kJ/gVS) and total organic carbon (TOC) removal efficiencies (95.77%) were obtained using inoculum pretreatment with WFO. The total energy yield trend obtained using the different pretreatments was as follows: WFO > alkaline > heat > aeration > control.     

基于UASB反应器的厨余厌氧发酵产氢研究

针对目前厨余连续流发酵产氢处理负荷不高、产氢率较低的难题,采用UASB反应器进行厨余发酵产氢研究。在温度为30℃,进水COD浓度为2 000~10 000 mg/L,水力停留时间为2~6 h条件下,产氢速率最大达到17.04 L/(L.d)。反应器内有颗粒污泥的形成,平均生物量达到6.17 g/L,为氢气的产生提供了有利保障。当出水pH为4.2~4.4,碱度为260~340 mg/L的条件下,乙醇和乙酸占挥发酸总量的89.2%,形成稳定的乙醇型发酵类型,反应器最高处理负荷COD达到60 kg/(m3.d)。试验结果表明,UASB反应器具有更高的产氢效能和更加稳定的产氢效果,能够为厨余发酵产氢提供有利的保障。     

Biological hydrogen production in suspended and attached growth anaerobic reactor systems

Biological production of hydrogen gas has received increasing interest from the international community during the last decade. Most studies on biological fermentative hydrogen production from carbohydrates using mixed cultures have been conducted in conventional continuous stirred tank reactors (CSTR) under mesophilic conditions. Investigations on hydrogen production in reactor systems with attached microbial growth have recently come up as well as investigations on hydrogen production in the thermophilic temperature range. The present study examines and compares the biological fermentative production of hydrogen from glucose in a continuous stirred tank type bioreactor (CSTR) and an upflow anaerobic sludge blanket bioreactor (UASB) at various hydraulic retention times (2–12 h HRT) under mesophilic conditions (35 °C). Also the biohydrogen production from glucose in the CSTR at mesophilic and thermophilic (55 °C) temperature range was studied and compared. From the CSTR experiments it was found that thermophilic conditions combine high hydrogen production rate with low production of microbial mass, thus giving a specific hydrogen production rate as high as 104 mmole _H2/h/l/g${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}/\mathrm{g}$ VSS at 6 h retention time compared to a specific hydrogen production rate of 12 mmole _H2/h/l/g${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}/\mathrm{g}$ VSS under mesophilic conditions. On the other hand, the UASB reactor configuration is more stable than the CSTR regarding hydrogen production, pH, glucose consumption and microbial by-products (e.g. volatile fatty acids, alcohols etc.) at the HRTs tested. Moreover, the hydrogen production rate in the UASB reactor was significantly higher compared to that of the CSTR at low retention times (19.05 and 8.42 mmole _H2/h/l${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}$, respectively at 2 h HRT) while hydrogen yield (mmole _H2/mmole${\mathrm{H}}_2/\mathrm{mmole}$ glucose consumed) was higher in the CSTR reactor at all HRT tested. This implies that there is a trade-off between technical efficiency (based on hydrogen yield) and economic efficiency (based on hydrogen production rate) when the attached (UASB) and suspended (CSTR) growth configurations are compared.     

Biological hydrogen production in an anaerobic sequencing batch reactor: pH and cyclic duration effects

An anaerobic sequencing batch reactor (ASBR) was used to evaluate biological hydrogen production from carbohydrate-rich organic wastes. The goal of the proposed project was to investigate the effects of pH (4.9, 5.5, 6.1, and 6.7), and cyclic duration (4, 6, and 8 h) on hydrogen production. With the ASBR operated at 16-h HRT, 25 g COD/L, and 4-h cyclic duration, the results showed that the maximum hydrogen yield of 2.53 mol H₂/mol sucrose_consumed appeared at pH 4.9. The carbohydrate removal efficiency declined to 56% at pH 4.9, which indirectly resulted in the reduction of total volatile fatty acid production. Acetate fermentation was the dominant metabolic pathway at pH 4.9. The concentration of mixed liquor volatile suspended solid (MLVSS) also showed a decrease from nearly 15,000 mg/L between pHs 6.1 and 6.7 to 6000 mg/L at pH 4.9. Investigation of the effect of cyclic duration found that hydrogen yield reached the maximum of 1.86 mol H₂/mol sucrose_consumed at 4-h cyclic duration while ASBR was operating at 16-h HRT, 15 g COD/L, and pH 4.9. The experimental results showed that MLVSS concentration increased from 6200 mg/L at 4-h cyclic duration to 8500 mg/L at 8-h cyclic duration. However, there was no significant change in effluent volatile suspended solid concentration. The results of butyrate to acetate ratio showed that using this ratio to correlate the performance of hydrogen production is not appropriate due to the growth of homoacetogens. In ASBR, the operation is subject to four different phases of each cycle, and only the complete mix condition can be achieved at react phase. The pH and cyclic duration under the unique operations profoundly impact fermentative hydrogen production.     

The influence of the degree of back-mixing on hydrogen production in an anaerobic fixed-bed reactor

This paper reports on results obtained from experiments carried out in an acidogenic anaerobic reactor aiming at the optimization of hydrogen production by altering the degree of back-mixing. It was hypothesized that there is an optimum operating point that maximizes the hydrogen yield. Experiments were performed in a packed-bed bioreactor by covering a broad range of recycle ratios (R) and the optimum point was obtained for an R value of 0.6. In this operating condition the reactor behaved as 8 continuous stirred-tank reactors in series and the maximum yield was 4.22 mol H₂ mol sucrose⁻¹. Such optimum point was estimated by deriving a polynomial function fitted to experimental data and it was obtained as the conjugation of three factors related to the various degrees of back-mixing applied to the reactor: mass transfer from the bulk liquid to the biocatalyst, liquid-to-gas mass transfer and the kinetic behavior of irreversible reactions in series.     

Magnetite nanoparticles enhanced glucose anaerobic fermentation for bio-hydrogen production using an expanded granular sludge bed (EGSB) reactor

The feasibility and efficiency of magnetite nanoparticles (Fe₃O₄NPs) enhanced bio-hydrogen production from glucose anaerobic fermentation were evaluated in this study. The results demonstrated that the maximum hydrogen yield (HY) of 12.97 mL H₂/g-VSS was obtained with 50 mg/L and 40–60 nm of Fe₃O₄NPs in batch experiments. Moreover, the optimum dosage of Fe₃O₄NPs produced hydrogen production (HP) of 4.95 L H₂/d in an expanded granular sludge bed (EGSB) reactor. Fe₃O₄NPs involved could promote ethanol and acetic acid accumulation. Fe²⁺ as by-product of iron corrosion could effectively promote the activity of key coenzymes and soluble microbial products (SMPs). Importantly, Fe₃O₄NPs addition resulted in the formation of electronic conductor chains to enhance the electron transport efficiency in the granular sludge. Microbial community analysis revealed that the relative abundance of butyrate-hydrogen-producing bacteria (Clostridium) decreased from 40.55% to 11.45%, while the relative abundance of ethanol-hydrogen-producing bacteria (Acetanaerobacterium and Ethanoligenens) increased from 19.62% to 35.35% with Fe₃O₄NPs involved, confirming that the fermentation type was transformed from butyrate-type to ethanol-type, which finally facilitated more hydrogen production.     

Auto-selection of microorganisms of sewage sludge used as an inoculum for fermentative hydrogen production from different substrates

When mixed organic waste is used for hydrogen production by dark fermentation, the microbial community which is most adapted to the actual biopolymer composition of the substrate is auto-selected. In this research, six substrates simulating different biopolymers (proteins, fats, carbohydrates) and their mixtures were used to enrich hydrogen-producing bacteria adapted to these substrates from non-pretreated sewage sludge. Phylum Firmicutes dominated in the microbial community (67–100%) regardless of the substrate used, as was shown by high-throughput sequencing. Microbial diversity was low when using carbohydrate-rich substrates and the microbial community was mainly represented by Ruminococcus (26–90%) and Thermoanaerobacterium (6–67%). Dark fermentation of fats and proteins was characterized by higher microbial diversity. Thermoanaerobacterium (21%), Thermobrachium (19%), Tepidiphilus (16%) and Acetomicrobium (14%) dominated when using fats, while Thermobrachium (34%), Acetomicrobium (16%) and Clostridium sensu stricto 7 (12%) dominated when using proteins, as substrate. Different microbial communities and substrates resulted in diverse process performance and metabolic pathways. Dark fermentation of starch achieved the maximum hydrogen yield of 138 mL/g volatile solids with 60.4% hydrogen content in biogas. The dominance of genus Ruminococcus was thought to be responsible for the highest hydrogen production. Minor quantities of methane from proteins and fats were produced by Methanothermobacter and Methanosarcina. Based upon the stable ¹³C isotope analysis, the hydrogenotrophic pathway was a slightly more predominant methane formation route than the others considered.     

Hydrogen production from rice winery wastewater in an upflow anaerobic reactor by using mixed anaerobic cultures

Continuous production of hydrogen from the anaerobic acidogenesis of a high-strength rice winery wastewater by a mixed bacterial flora was demonstrated. The experiment was conducted in a 3.0-l upflow reactor to investigate individual effects of hydraulic retention time (HRT) (2–24 h), chemical oxygen demand (COD) concentration in wastewater (14–36 g COD/l), pH (4.5–6.0) and temperature (20–55°C) on bio-hydrogen production from the wastewater. The biogas produced under all test conditions was composed of mostly hydrogen (53–61%) and carbon dioxide (37–45%), but contained no detectable methane. Specific hydrogen production rate increased with wastewater concentration and temperature, but with a decrease in HRT. An optimum hydrogen production rate of 9.33 lH₂/gVSSd was achieved at an HRT of 2 h, COD of 34 g/l, pH 5.5 and 55°C. The hydrogen yield was in the range of 1.37–2.14 mol/mol-hexose. In addition to acetate, propionate and butyrate, ethanol was also present in the effluent as an aqueous product. The distribution of these compounds in the effluent was more sensitive to wastewater concentration, pH and temperature, but was less sensitive to HRT. This upflow reactor was shown to be a promising biosystem for hydrogen production from high-strength wastewaters by mixed anaerobic cultures.     

替硝唑片对污泥厌氧发酵产氢作用的研究

研究表明，在污泥中添加替硝唑片可使污泥中的有机物质含量明显增加，特别是可溶的有机物质；替硝唑片对提高污泥产氢效果显著，替硝唑片添加量为1．40g时，污泥的产氢效果最佳，其累积产氢量和产氢潜能分别为580．64mL和98．41mL／gVS；厌氧发酵属于典型的乙醇型发酵；发酵代谢过程主要降解的有机物质为糖类物质，总糖降解率高达70．32％，蛋白质降解率只有26.25％。