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.     

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。     

Biohydrogen production from diluted-acid hydrolysate of rice straw in a continuous anaerobic packed bed biofilm reactor

Bio-hydrogen production in a continuously operated anaerobic packed bed biofilm reactor (APBR) using acid-hydrolysate of rice straw as feedstock and inoculated with an anaerobic mesophilic sludge from a municipal wastewater treatment plant was investigated at three different HRTs (17, 8.2 and 2 h). Fermentable sugars solution achieved from a two-stage diluted acid hydrolysis of rice straw was used as the feedstock. First, rice straw was treated with 1% w v^?1 sulfuric acid at 120 °C for 30 min with a yield of 58.5% xylose. Higher temperature of 180 °C for 10 min at 0.5% w v^?1 sulfuric acid was applied in the second stage in which cellulosic crystalline structure was partially depolymerized to glucose with a yield of 19.3% glucose. Hydrogen production rate and yield were enhanced as the hydraulic retention time was decreased with a maximum production rate of 252 mL L^?1 h^?1 and yield of 1 mol H₂ mol^?1 sugar consumed at 2 h HRT. Experimental results illustrated the increase of COD conversion from 44% to 47% by shortening the HRT from 17 to 2 h. Furthermore, acetic acid and butyric acid production were reduced slower than other soluble metabolites like ethanol.     

Hydrogen and methane production in extreme thermophilic conditions in two-stage (upflow anaerobic sludge bed) UASB reactor system

Two-stage hydrogen and methane production in extreme thermophilic (70 °C) conditions was demonstrated for the first time in UASB-reactor system. Inoculum used in hydrogen and methane reactors was granular sludge from mesophilic internal circulation reactor and was first acclimated for extreme thermophilic conditions. In hydrogen reactor, operated with hydraulic retention time (HRT) of 5 h and organic loading rate (OLR) of 25.1 kg COD/m³/d, hydrogen yield was 0.73 mol/mol glucose_added. Methane was produced in second stage from hydrogen reactor effluent. In methane reactor operated with HRT of 13 h and OLR of 7.8 kg COD/m³/d, methane yield was 117.5 ml/g COD_added. These results prove that hydrogen and methane can be produced in extreme thermophilic temperatures, but as batch experiments confirmed, for methane production lower temperature would be more efficient.     

Comparison of biohydrogen production in fluidized bed bioreactors at room temperature and 35 °C

The aim of this work was to compare the H₂ production in a lab scale anaerobic fluidized bed bioreactors (AFBRs) at two levels of operational temperature: ambient temperature (A) and 35 °C (M) and two organic volumetric loading rates B_v: 5 and 8 g sucrose/L.day, with a constant hydraulic residence time of 1 day.     

Start-up study of biohydrogen production from palm oil mill effluent in a lab-scale up-flow anaerobic sludge blanket fixed-film reactor

A start-up study of lab-scale up-flow anaerobic sludge blanket fixed-film reactor (UASFF) was conducted to produce biohydrogen from palm oil mill effluent (POME). The reactor was fed with POME at different hydraulic retention time (HRT) and organic loading rate (OLR) to obtain the optimum fermentation time for maximum hydrogen yield (HY). The results showed the HY, volumetric hydrogen production rate (VHPR), and COD removal of 0.5–1.1 L H₂/g COD_consumed, 1.98–4.1 L H₂ L^?1 day^?1, and 33.4–38.5%, respectively. The characteristic study on POME particles was analyzed by particle size distribution (PSD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX). The microbial Shannon and Simpson diversity indices and Principal Component Analysis assessed the alpha and beta diversity, respectively. The results indicated the change of bacterial community diversity over the operation, in which Clostridium sensu stricto 1 and Lactobacillus species were contributed to hydrogen fermentation.     

Hydrogen production in an upflow anaerobic packed bed reactor used to treat cheese whey

In this work, an upflow anaerobic packed bed reactor configuration to produce hydrogen using cheese whey as the substrate was tested. The microbiological composition was linked to the reactor operation.     

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.     

Biomass purge strategies to control the bacterial community and reactor stability for biohydrogen production from winery wastewater

Hydrogen production is a viable alternative for the valorization of agro-industrial effluents, such as winery wastewater (WW). One limitation of using new substrates is system stability, where high organic loading rates favor high productivities. Using a new reactor configuration of packed bed reactors, different biomass purge strategies were evaluated in parallel reactors to maintain the stability in the long-term feeding WW, along with a community evaluation. A frequently programmed purge of biofilm and suspended biomass (every 7–8 days) resulted in the most stable hydrogen productivity, 930 mL H₂ L^?1d^?1, unlike only purging biofilm or not programing the purge (<650H₂ L^?1d^?1). The long-term stability is explained by a proper balance of the microbial genera in the reactor, Lactobacillus, Pectinatus, and Clostridium. This work proposes an innovative reactor configuration and operation strategy using WW, where a programmed biomass purge helps control the lactate and hydrogen-producing microbial groups.     

Evaluation of hidden H2-consuming pathways using metabolic flux-based analysis for a fermentative side-stream dynamic membrane bioreactor using untreated seed sludge

This study investigates the performance and hidden hydrogen consuming metabolic pathways of a fermentative side stream dynamic membrane (DM) bioreactor using flux balance analysis (FBA). The bioreactor was inoculated with untreated methanogenic seed sludge. It was found that fouling rate aggravated with increasing COD concentration (10–30 g/L) and was positively correlated to it rather than to the applied solid flux on the DM module. Due to increased fouling rate the hydraulic retention time (HRT) could not be reduced less than 0.82 ± 0.02 d. An increase in the organic loading rate (OLR) led to an increase in H₂ yield from 0.01 to 0.76 mol H₂/mol of sucrose. FBA revealed that homoacetogenesis was the main H₂-consuming pathway at lower OLRs (corresponding to 10 and 15 g COD/L), while for the OLR corresponding to 30 g COD/L, homoacetogens were suppressed. More importantly, caproic acid production pathway was identified for the first time as another H₂-consuming pathway at high OLR which was not significant at lower OLRs during fermentative dynamic membrane bioreactor operations.     

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.     

Anaerobic fluidized bed reactor with expanded clay as support for hydrogen production through dark fermentation of glucose

This study evaluated hydrogen production in an anaerobic fluidized bed reactor (AFBR) fed with glucose-based synthetic wastewater. Particles of expanded clay (2.8–3.35 mm) were used as a support material for biomass immobilization. The reactor was operated with hydraulic retention times (HRT) ranging from 8 to 1 h. The hydrogen yield production increased from 1.41 to 2.49 mol H₂ mol⁻¹ glucose as HRT decreased from 8 to 2 h. However, when HRT was 1 h, there was a slight decrease to 2.41 mol H₂ mol⁻¹ glucose. The biogas produced was composed of H₂ and CO₂, and the H₂ content increased from 8% to 35% as HRT decreased. The major soluble metabolites during H₂ fermentation were acetic acid (HAc) and butyric acid (HBu), accounting for 36.1–53.3% and 37.7–44.9% of total soluble metabolites, respectively. Overall, the results demonstrate the potential of using expanded clay as support material for hydrogen production in AFBRs.     

Energy balance of dark anaerobic fermentation as a tool for sustainability analysis

A process aimed at producing energy needs to produce more energy than the energy necessary to run the process itself in order to be energetically sustainable. In this paper, an energy balance of a batch anaerobic bioreactor has been defined and calculated, both for different operative conditions and for different reactor scales, in order to analyze the sustainability of hydrogen production through dark anaerobic fermentation. Energy production in the form of hydrogen and methane, energy to warm up the fermentation broth, energy loss during fermentation and energy for mixing and pumping have been considered in the energy balance. Experimental data and literature data for mesophilic microorganism consortia have been used to calculate the energy balance. The energy production of a mesophilic microorganism consortium in a batch reactor has been studied in the 16–50 °C temperature range. The hydrogen batch dark fermentation resulted to only have a positive net production of energy over a minimal reactor dimension in summer conditions with an energy recovery strategy. The best working temperature resulted to be 20 °C with 20% of available energy. Hydrogen batch dark fermentation may be coupled with other processes to obtain a positive net energy by recovering energy from the end products of hydrogen dark fermentation. As an example, methane fermentation has been considered to energetically valorize the end products of hydrogen fermentation. The combined process resulted in a positive net energy over the whole range of tested reactor dimension with 45–90% of available energy.     

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.     

Selection of natural bacterial communities for the biological production of hydrogen

Current processes used for the production of hydrogen consume a great part of the energy they produce and/or depend on fossil fuel consumption, making them inefficient and harmful to the environment. Obtaining hydrogen from living systems by fermentation of organic matter considered waste is a promising alternative for the future. Especially when you take into account that the biological production of hydrogen is intrinsically linked to the degradation of said organic matter. In this paper, we explore the efficiency of different bacterial communities (also called consortia) for anaerobic fermentation of carbohydrates. The evaluated consortia were obtained from soil, commercial compost and sludge from a sewage treatment plant. The cultures that produced the highest amounts of hydrogen were those in which the inoculums used came from sludge and compost. Both reached a maximum accumulated concentration of approximately 30% of biological hydrogen in the gas mixture on day 8 of the fermentation process, as estimated by gas chromatography.     

The effect of HRT on biohydrogen production from acid hydrolyzed waste wheat in a continuously operated packed bed reactor

Biohydrogen production in a continuously operated up flow packed bed reactor was investigated at different hydraulic retention time (HRT) varying between 2 h and 13 h scouring sponge pad. The substrate was sugar solution obtained from hydrolysis of waste wheat at pH = 2 and 90 °C in an autoclave for 15 min. Experimental results indicated that hydrogen production volume and yield increases with decreasing HRT. The highest volumetric hydrogen production rate and yield were obtained as VHPR = 1.75 L H₂/L d and Y_H2 = 1.6 moL H₂/mol TS, respectively, at HRT = 2 h. Yields and rates at HRT = 2 h were almost two times of that obtained at HRT = 13 h. It can be concluded that metal mesh covered plastic scouring sponge pad is a suitable microorganism support particle to obtain high hydrogen yield and rate at short HRTs by dark fermentation.     

Optimization of particle number,substrate concentration and temperature of batch immobilized reactor system for biohydrogen production by dark fermentation

Immobilized cell bioreactor was operated in batch mode for biohydrogen generation by dark fermentation from acid hydrolyzed waste wheat powder. It was aimed to optimize the fermentation conditions with the purpose of obtaining the highest hydrogen yield (Y_H2) and production rate (HPR) by applying Box–Wilson statistical experimental design method. Particle number (PN = 120–240; X₁), initial total sugar concentration (TS₀ = 10–30 g/l; X₂) and fermentation temperature (T = 35–55 °C; X₃) were selected as independent variables. Polyester fibers with particle diameter “Dp” = 0.5 cm were used as support material to immobilize microorganisms with heat-pretreated sludge. Quadratic equations for production yield and rate were developed by using experimental results. The maximum Y_H2 (3.21 mol H₂/mol glucose) and HPR (73.3 ml H₂/h) were predicted at the optimum conditions of PN = 240, TS₀ = 10 g/l and T = 44.9 °C. Also, analysis of variance, as well as sum of ranking difference test results demonstrated that fitting models were statistically significant.     

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.     

Numerical studies of sorption-enhanced glycerol steam reforming in a fluidized bed membrane reactor at low temperature

In order to improve the hydrogen production efficiency by glycerol steam reforming, a membrane-assisted fluidized bed reactor with carbon dioxide sorption is developed to enhance the reforming process. Low-temperature operation in a membrane reactor is necessary considering the thermal stability of membrane. In this work, the sorption-enhanced glycerol steam reforming process in a fluidized bed membrane reactor under the condition of low temperature is numerically investigated, where the hydrotalcite is employed as CO₂ sorbents. The impact of operating pressure on the reforming performance is further evaluated. The results demonstrate that the integration of membrane hydrogen separation and CO₂ sorption can effectively enhance the low-temperature glycerol reforming performance. The fuel conversion above 95% can be achieved under an elevated pressure.