Influence of thermal and chemical pretreatment on structural stability of granular sludge for high-rate hydrogen production in an UASB bioreactor

Fermentation of organic waste materials presents an alternate route instead of photosynthetic and chemical routes for hydrogen production. Low yield of biohydrogen production is the major challenge in the fermentative hydrogen-producing technology. Improvement of fermentation process by various sludge pretreatment methods is one of the ways that have been applied to boost hydrogen productivity. This study sheds new light on the impact of thermal and chemical pretreatments on the hydrogen-producing granular sludge morphology and strength as well as up-flow anaerobic sludge blanket (UASB) reactor performance treating palm oil mill effluent (POME). Thermal pretreatment showed devastating effects on the morphological and structural characteristics of the granules. However, the chemically pretreated granules remained structurally stable and relatively undamaged. The thermal pretreatment increased the cumulative hydrogen production by 40% and 76% over chemical pretreatment and control test (untreated), respectively.     

Enhanced hydrogen production in a UASB reactor by retaining microbial consortium onto carbon nanotubes (CNTs)

Biohydrogen and subsequent biomethane generation from biomass is a promising strategy for renewable energy supply, because this combination can lead to higher energy recovery efficiency and faster fermentation than single methane fermentation. Microbial consortium control by retaining hydrogen-producers through the addition of microbial carriers is an alternative to constructing hydrogen-producing reactors. Here we report the use of carbon nanotubes (CNTs) as microbial carriers to enhance microbial retention and the production of biohydrogen. Laboratory-scale upflow anaerobic sludge blanket (UASB) reactors with CNTs at 100 mg/L achieved a maximal hydrogen production rate of 5.55 L/L/d and a maximal hydrogen yield of 2.45 mol/mol glucose. Compared to frequently used activated carbon (AC) particles, CNTs resulted in quicker startup and better performance of hydrogen fermentation in UASB reactors. Scanning electron microscopy (SEM) and pyrosequencing results revealed that the reactor with CNTs led to a high proportion of hydrogen-producing bacteria among the microbial consortium, which endowed the microbes with strong flocculation capacity and hydrogen productivity.     

Decreasing methane production in hydrogenogenic UASB reactors fed with cheese whey

One of the problems in fermentative hydrogen producing reactors, inoculated with pre-treated anaerobic granular sludge, is the eventual methane production by hydrogen-consuming methanogens. In this study, strategies such as reduction of pH and HRT, organic shock loads and repeated biomass heat treatment were applied to hydrogenogenic UASB reactors fed with cheese whey, that showed methane production after certain time of continuous operation (between 10 and 60 days). The reduction of pH to 4.5 not only decreased methane production but also hydrogen production. Organic shock load (from 20 to 30 g COD/L-d) was the more effective strategy to decrease the methane production rate (75%) and to increase the hydrogen production rate (172%), without stopping reactor operation. Repeated heat treatment of the granular sludge was the only strategy that inhibited completely methane production, leading to high volumetric hydrogen production rates (1.67 L H₂/L-d), however this strategy required stopping reactor operation; in addition homoacetogenesis, another hydrogen-consuming pathway, was not completely inhibited. This work demonstrated that it was possible to control the methane activity in hydrogen producing reactors using operational strategies.     

Effect of hydraulic retention time on a continuous biohydrogen production in a packed bed biofilm reactor with recirculation flow of the liquid phase

The present paper reports on results obtained from experiments carried out in a laboratory-scale anaerobic packed bed biofilm reactor (APBR), with recirculation of the liquid phase, for continuously biohydrogen production via dark fermentation. The reactor was filled with Kaldnes^® biofilm carrier and inoculated with an anaerobic mesophilic sludge from a urban wastewater treatment plant (WWTP). The APBR was operated at a temperature of 37 °C, without pH buffering. The effect of theoretical hydraulic retention time (HRT) from 1 to 5 h on hydrogen yield (HY), hydrogen production rate (HPR), substrate conversion and metabolic pathways was investigated. This study indicates the possibility of enhancing hydrogen production by using APBR with recirculation flow. Among respondents values of HRT the highest average values of HY (2.35 mol H₂/mol substrate) and HPR (0.085 L h^?1L^?1) have been obtained at HRT equal to 2 h.     

Formation and impact of granules in fostering clean energy production and wastewater treatment in upflow anaerobic sludge blanket (UASB) reactors

Anaerobic reactors have acquired a new relevance in recent years due to their ability to generate methane from biodegradable wastewaters—thereby producing clean energy. Methane capture in this manner also prevents the escape of the greenhouse gas to the atmosphere which otherwise occurs when anaerobic conditions develop in drains and outfalls carrying wastewater. Of all the different types of anaerobic reactors in vogue - anaerobic filter, downflow fixed-film reactor, expanded fluidized-bed anaerobic reactor, etc. - the upflow anaerobic sludge blanket (UASB) reactor is arguably the most widely used. Nearly 80% of the world's anaerobic wastewater treatment systems are estimated to be based on the UASB technology. The functioning of a UASB reactor revolves round its sludge bed which gets expanded as the wastewater is made to flow vertically upwards through it. It is the microflora attached to the sludge particles which acts upon the wastewater. Hence the quality of biofilms sported by the sludge particles, and the intimacy of the sludge-wastewater contact are the factors which, principally, govern the success of a UASB reactor. Very early in the development of UASB technology it was realized that granular sludge of appropriate particle size, particle density, and microfilm characteristics enhances the reactor efficiency in terms of the rate as well as the extent of wastewater treatment. From then onwards efforts have been made by scientists across the world to understand the factors which shape the granules and the manner in which the granules contribute to wastewater treatment. The state-of-the-art is presented in this paper.     

Anaerobic digestion of skim latex serum (SLS) for hydrogen and methane production using a two-stage process in a series of up-flow anaerobic sludge blanket (UASB) reactor

A series of up-flow anaerobic sludge blanket (UASB) reactors operated under thermophilic conditions was used to investigate the two-stage anaerobic process for continuous hydrogen and methane production from skim latex serum (SLS). The first reactor for producing hydrogen was operated by feeding 38 g-VS/L-SLS at various hydraulic retention times (HRTs) of 60, 48, 36, and 24 h. The optimum hydrogen production yield of 2.25 ± 0.09 L-H₂/L-SLS was achieved at a 36 h HRT. Meanwhile, the effluents containing mainly with acetate was fed to the second UASB reactor for methane production at 9-day HRT and could be converted to methane with the production yield of 6.41 ± 0.52 L-CH₄/L-SLS. The efficiency of organic matters removal obtained from this two-stage process was 62%. The present study shows high value fuel gases in a form of hydrogen and methane can be potentially generated by using a continuous two-stage anaerobic process, in which available organic matters is simultaneously degraded.     

Photohydrogen production using purple nonsulfur bacteria with hydrogen fermentation reactor effluent

Hydrogen production from waste using photosynthetic bacteria is an attractive methodology. A combination of purple nonsulfur photosynthetic bacteria and anaerobic bacteria is ideal for the efficient conversion of wastewater into hydrogen. In this paper, photohydrogen production using effluent from different hydrogen fermentation reactors was carried out using two strains of photosynthetic purple nonsulfur bacteria. The results indicated that the effluent from the hydrogen fermentation reactors could be used directly for photohydrogen production without aeration or dilution pretreatment. Effluent from the carbohydrate fed hydrogen fermentation reactors is more suitable for photohydrogen production than effluent from a peptone fed reactor. Among the initial dark hydrogen fermentation stage effluents from the three carbohydrate fed reactors (CSTR, ASBR, UASB), CSTR effluent was the most suitable for photohydrogen production.     

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.     

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.     

Rapid formation of hydrogen-producing granules in an up-flow anaerobic sludge blanket reactor coupled with high-rate recirculation

Application of an up-flow anaerobic sludge blanket (UASB) reactor to dark fermentative H₂ production greatly improves H₂ productivity due to the maintenance of high biomass concentration. However, a long start-up HRT and start-up period are required to develop the H₂-producing granules (HPGs) and to avoid washing out the suspended sludge at the start of the process. In the present work, a novel strategy to rapidly form HPGs was developed in UASB reactor. To induce highly active mass transfer in the UASB reactor, a high recirculation rate (15 times the influent) was adopted over 10 days, then recirculation was stopped. As the operation progressed, self-flocculation took place and HPGs developed after 90 h of operation. A stable production of H₂ was observed after 20 days of operation. The thickness of the HPGs layer in the sole UASB reactor increased progressively, and consequently the average HPG diameter and concentration were 1.86 mm (0.1–3.9 mm) and 52 g/L, respectively, after 60 days of operation. These findings seem to suggest that high-rate recirculation plays a crucial role in accelerating the formation of HPGs in such UASB reactors through high up-flow velocity, providing active mass transfer.     

Optimization of hydrogen production in a granule-based UASB reactor

Hydrogen production from sucrose in a granule-based upflow anaerobic sludge blanket (UASB) reactor was optimized through employing response surface methodology (RSM) with a central composite design in this study. The individual and interactive effects of influent sucrose concentration (S_in) and hydraulic retention time (HRT) on anaerobic hydrogen production were elucidated. Experimental results show that a maximum hydrogen yield of 1.62 mol-H₂/mol-hexose was obtained under the optimum conditions of S_in 14.5 g/L and an HRT 16.4 h. The hydrogen yield was individually dependent on S_in and HRT, while their interactive effect on the hydrogen yield was not significant. Throughout the experiments the hydrogen content fluctuated between 25.9% and 50.0%, but free of methane. Ethanol, acetate and butyrate were the main aqueous products and their yields all correlated well with S_in and HRT, indicating a mixed-type fermentation in this UASB reactor.     

Comparative analysis of thermophilic immobilized biohydrogen production using packed materials of ceramic ring and pumice stone

Ceramic ring and pumice stone were used as a support matrix for the enhancement of biohydrogen production in immobilized cell culture systems. The reactors were continuously operated for the hydrogen fermentation using sucrose as the major carbon source at varying hydraulic retention times (HRT) as an important operational factor. In terms of volumetric hydrogen production, the best value was obtained with ceramic ring at 1.5 h HRT (2.98 l H₂/l/d), on the other hand, the pumice stone packed reactor resulted in 30% less volumetric hydrogen production (2.28 l H₂/l/d) at two fold longer retention time (HRT 3 h). It was demonstrated that volumetric hydrogen production with the immobilized bioreactor configurations was 6 fold better than the suspended culture bioreactor configuration (CSTR). Furthermore, up to 4 mol and 5 mol hydrogen yields per mole of sucrose used (which are 62.5% and 50% of the theoretical values) were achieved by pumice stone and ceramic ring packed reactors, respectively, whereas suspended culture system yielded only 0.5 mol H₂/mol sucrose.     

The effect of hydraulic retention time on thermophilic dark fermentative biohydrogen production in the continuously operated packed bed bioreactor

The main objective of the study is to investigate the effect of hydraulic retention times on continuous dark fermentative biohydrogen production in an up-flow packed bed reactor (UPBR) containing a novel microorganism immobilization material namely polyester fiber beads. The hydrogen producing dark fermentative microorganisms were obtained by heat-pretreatment of anaerobic sludge from the acidogenic phase of an anaerobic wastewater treatment plant. Glucose was the sole carbon source and the initial concentration was 15 ± 1 g/L throughout the continuous feeding. UPBR was operated under the thermophilic condition at T = 48 ± 2 °C and at varying HRTs between 2 h and 6 h. The hydrogen productivity of continuously operated UPBR increased with increasing HRT. Hydrogen production volume varied between 4331 and 6624 ml/d, volumetric hydrogen production rates (VHPR) were obtained as 3.09–4.73 L H₂/L day, and hydrogen production yields (HY) were 0.49 mol/mol glucose-0.89 mol/mol glucose depending on HRT. Maximum daily hydrogen volume (6624 ml/d), the yield (0.89 mol/mol glucose) and VHPR (4.73 L H₂/L day) were obtained at HRT = 6 h. The production rate and the yield decreased with increasing organic loading rate due to substrate inhibition.     

Hydrogen bioproduction with anaerobic bacteria consortium from brewery wastewater

Biohydrogen production is a cheap and clean way to obtain hydrogen gas. In subtropical countries such as Brazil the average temperatures of 27 °C can favor the hydrogen producing bacteria growth. A mixed culture was obtained from a subtropical sludge treating brewery wastewater and anaerobic batch reactors were fed with glucose, sucrose, fructose and xylose in low concentrations (2.0, 5.0 and 10.0 g L⁻¹) at 37 °C, initial pH 5.5 and headspace with N₂ (99%) to maintain the anaerobic conditions. The inoculum was a subtropical granulated sludge from UASB (Upflow Anaerobic Sludge Blanket) reactor treating brewery wastewater. The higher H₂ yields were obtained in reactors operated with 2 and 5 g L⁻¹ of fructose and they were 1.5 mol H₂ mol⁻¹ of fructose and 1.3 mol H₂ mol⁻¹ of sucrose, respectively. The volatile fatty acids (VFA) generated at the end of operation were, predominantly, butyric and acetic acid, indicating the favoring of the metabolic route of hydrogen generation by the consortium of anaerobic bacteria from the brewery wastewater. Biomolecular analyses revealed the predominance of hydrogen producing bacteria from Firmicutes phylum distributed in the families Streptococcaceae, Veillonellaceae and uncultured bacteria. These results confirm future applications of subtropical sludges with agroindustrial wastewaters containing low concentrations of sugars on hydrogen generation.     

The effects of seed sludge and hydraulic retention time on the production of hydrogen from a cassava processing wastewater and glucose mixture in an anaerobic fluidized bed reactor

The potential for co-fermentation of a cassava processing wastewater and glucose mixture was studied in anaerobic fluidized bed reactors. The effects of different hydraulic retention times (HRTs) (10–2 h) and varying sources of inoculum are reported. The sludge from a UASB reactor that had been used to treat poultry slaughterhouse wastewater (SP) resulted in the highest yields of hydrogen (HY) and ethanol (EtOHY) of 1.0 mmol H₂ g⁻¹ COD (10 h) and 3.0 mmol EtOH g⁻¹ COD (6 h). The sludge from a UASB reactor used for the treatment of swine wastewater (SW) resulted in a maximum HY of 0.65 mmol H₂ g⁻¹ COD (6 h) and EtOHY of 2.1 mmol g⁻¹ COD (10 and 8 h). Methane was produced with a maximum production of 9.68 L CH₄ d⁻¹ L⁻¹. Based on phylogenetic analysis of 16S rRNA, bacteria and methanogenic archaea similar to Lactobacillus and Methanobacterium, respectively, were identified.     

Critical assessment of anaerobic processes for continuous biohydrogen production from organic wastewater

Production of biohydrogen using dark fermentation has received much attention owing to the fact that hydrogen can be generated from renewable organics including waste materials. The key to successful application of anaerobic fermentation is to uncouple the liquid retention time and the biomass retention time in the reactor system. Various reactor designs based on biomass retention within the reactor system have been developed. This paper presents our research work on bioreactor designs and operation for biohydrogen production. Comparisons between immobilized-cell systems and suspended-cell systems based on biomass growth in the forms of granule, biofilm and flocs were made. Reactor configurations including column- and tank-based reactors were also assessed. Experimental results indicated that formation of granules or biofilms substantially enhanced biomass retention which was found to be proportional to the hydrogen production rate. Rapid hydrogen-producing culture growth and high organic loading rate might limit the application of biofilm biohydrogen production, since excessive growth of fermentative biomass would result in washout of support carrier. It follows that column-based granular sludge process is a preferred choice of process for continuous biohydrogen production from organic wastewater, indicating maximum hydrogen yield of 1.7 mol-H₂/mol-glucose and hydrogen production rate of 6.8 L-H₂/L-reactor h.     

Biohydrogen production by dark fermentation: Experiences of continuous operation in large lab scale

Hydrogen is a clean energy carrier which can be used as fuel in fuel cells. Today, hydrogen is produced mainly by steam reforming of fossil fuels like natural gas or oil. But only hydrogen produced by renewable sources can be called clean energy production. One possibility for hydrogen production is the biological fermentation of biogenous wastes by hydrogen producing bacteria. For the experimental setup four 30-L-working-volume reactors were constructed for continuous biohydrogen production. As inoculum, heat-treated sludge of a wastewater treatment plant was used. Different hydraulic retention times (HRT) were tested and an organic loading rate (OLR) of 2–14 kg VS/m³*d. As starting substrate, waste sugar medium was used. The pH and other parameters were observed to find boundary conditions for a stable continuous process with a minimum of online-control measurements. The high concentration of organic acids in the reactor led to a very low pH, which was controlled manually and online > 4 up to 5.5, otherwise the biohydrogen production decreased rapidly. The gas amount varied with the different OLRs, but could be stabilised on a high level as well as the hydrogen concentration in the gas with 44–52%. No methane was detected in the gas. It turned out, that continuous biohydrogen production with stable gas amounts and qualities could be achieved at different operation conditions. The results showed, that the operation of a continuous biohydrogen reactor has to be observed very carefully to ensure a constant gas production, and that pH-control is necessary to ensure stable operation conditions.     

Biohydrogen production from crude glycerol by immobilized Klebsiella sp. TR17 in a UASB reactor and bacterial quantification under non-sterile conditions

Biohydrogen production from crude glycerol by immobilized Klebsiella sp. TR17 was investigated in an up-flow anaerobic sludge blanket (UASB) reactor. The reactor was operated under non-sterile conditions at 40^○C and initial pH 8.0 at different hydraulic retention times (HRTs) (2–12 h) and glycerol concentrations (10–30 g/L). Decreasing the HRT led to an increase in hydrogen production rate (HPR) and hydrogen yield (HY). The highest HPR of 242.15 mmol H₂/L/d and HY of 44.27 mmol H₂/g glycerol consumed were achieved at 4 h HRT and glycerol concentrations of 30 and 10 g/L, respectively. The main soluble metabolite was 1,3-propanediol, which implies that Klebsiella sp. was dominant among other microorganisms. Fluorescence in situ hybridization (FISH) revealed that the microbial community was dominated by Klebsiella sp. with 56.96, 59.45, and 63.47% of total DAPI binding cells, at glycerol concentrations of 10, 20, and 30 g/L, respectively.     

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.     

Biohydrogen production in anaerobic fluidized bed reactors: Effect of support material and hydraulic retention time

This study evaluated two different support materials (polystyrene and expanded clay) for biohydrogen production in an anaerobic fluidized bed reactor (AFBR) treating synthetic wastewater containing glucose (4000 mg L⁻¹). The AFBRs contained either polystyrene (R1) or expanded clay (R2) as support materials were inoculated with thermally pre-treated anaerobic sludge and operated at a temperature of 30 °C and a pH of approximately 5.5. The AFBRs were operated with a range of hydraulic retention times (HRTs) between 1 and 8 h. For R1 with an HRT of 2 h, the maximum hydrogen yield (HY) was 1.90 mol H₂ mol⁻¹ glucose, with 0.805 mg of biomass (as total volatile solids, or TVS) attached to each g of polystyrene. For R2 operated at an HRT of 2 h, the maximum HY was 2.59 mol H₂ mol⁻¹ glucose, with 1.100 mg of attached biomass (as TVS) g⁻¹ expanded clay. The highest hydrogen production rates (HPR) were 0.95 and 1.21 L h⁻¹ L⁻¹ for R1 and R2, respectively, using an HRT of 1 h. The H₂ content increased from 16–47% for R1 and from 22–51% for R2. No methane was detected in the biogas produced throughout the period of AFBR operation. These results show that the values of HY, HPR, H₂ content, and g of attached biomass g⁻¹ support material were all higher for AFBRs containing expanded clay than for reactors containing polystyrene.