Heat-treated Anaerobic Sludge Research Articles

Enhancing biohydrogen production from xylose through natural FeS2 ore: Mechanistic insights

In this study, we investigated the advantages of utilizing natural FeS2 ore in the context of dark fermentative hydrogen production within a fermentation system employing heat-treated anaerobic granular sludge with xylose as the carbon source. The results demonstrated a significant improvement in both hydrogen production and the maximum rate, with increases of 2.58 and 4.2 times, respectively. Moreover, the presence of FeS2 ore led to a reduction in lag time by more than 2–3 h. The enhanced biohydrogen production performance was attributed to factors such as the intracellular NADH/NAD+ ratio, redox-active components of extracellular polymeric substances, secreted flavins, as well as the presence of hydrogenase and nitrogenase. Furthermore, the FeS2 ore served as a direct electron donor and acceptor during biohydrogen production. This study shed light on the underlying mechanisms contributing to the improved performance of biohydrogen production from xylose during dark fermentation through the supplementation of natural FeS2 ore.

Dark Fermentation of Sweet Sorghum Stalks, Cheese Whey and Cow Manure Mixture: Effect of pH, Pretreatment and Organic Load

The aim of this study was to determine the optimal conditions for dark fermentation using agro-industrial liquid wastewaters mixed with sweet sorghum stalks (i.e., 55% sorghum, 40% cheese whey, and 5% liquid cow manure). Batch experiments were performed to investigate the effect of controlled pH (5.0, 5.5, 6.0, 6.5) on the production of bio-hydrogen and volatile fatty acids. According to the obtained results, the maximum hydrogen yield of 0.52 mol H2/mol eq. glucose was measured at pH 5.5 accompanied by the highest volatile fatty acids production, whereas similar hydrogen productivity was also observed at pH 6.0 and 6.5. The use of heat-treated anaerobic sludge as inoculum had a positive impact on bio-hydrogen production, exhibiting an increased yield of 1.09 mol H2/mol eq. glucose. On the other hand, the pretreated (ensiled) sorghum, instead of a fresh one, led to a lower hydrogen production, while the organic load decrease did not affect the process performance. In all experiments, the main fermentation end-products were volatile fatty acids (i.e., acetic, propionic, butyric), ethanol and lactic acid.

Enrichment Versus Bioaugmentation-Microbiological Production of Caproate from Mixed Carbon Sources by Mixed Bacterial Culture and Clostridium kluyveri.

Chain elongation is a process that produces medium chain fatty acids such as caproic acid, which is one of the promising products of the carboxylate platform. This study analyzed the impact of bioaugmentation of heat-treated anaerobic digester sludge with Clostridium kluyveri (AS + Ck) on caproic acid production from a mixed substrate (lactose, lactate, acetate, and ethanol). It was compared with processes initiated with non-augmented heat-treated anaerobic digester sludge (AS) and mono-culture of C. kluyveri (Ck). Moreover, stability of the chain elongation process was evaluated by performing repeated batch experiments. All bacterial cultures demonstrated efficient caproate production in the first batch cycle. After 18 days, caproate concentration reached 9.06 ± 0.43, 7.86 ± 0.38, and 7.67 ± 0.37 g/L for AS, Ck, and AS + Ck cultures, respectively. In the second cycle, AS microbiome was enriched toward caproate production and showed the highest caproate concentration of 11.44 ± 0.47 g/L. On the other hand, bioaugmented culture showed the lowest caproate production in the second cycle (4.10 ± 0.30 g/L). Microbiome analysis in both AS and AS + Ck culture samples indicated strong enrichment toward the anaerobic order of Clostridia. Strains belonging to genera Sporanaerobacter, Paraclostridium, Haloimpatiens, Clostridium, and Bacillus were dominating in the bioreactors.

Addition of electron shuttling compounds and different pH conditions for hydrogen production by a heat-treated sludge

Abstract In the present work, the effect of anthraquinone-2-sulfonate (AQS) and its reduced form anthrahydroxyquinone-2-sulfonate (AH2QS), and different pH values were evaluated during a dark fermentation process using heat-treated anaerobic granular sludge for hydrogen production. The highest maximum hydrogen production (1.99 mmol) was obtained by adding the reduced electron shuttling compound (AH2QS) at pH 6. This experimental condition also reflected the highest substrate consumption efficiency and the lowest lag phase in relation to the AQS and the control (only sludge). In contrast, the lag phase and maximum hydrogen production were not impacted by AH2QS addition at initial pH of 6.4 and 7.8. Regardless of the initial pH value, the hydrogen production rate was increased after the addition of the electron shuttling compounds, which could be attributable to the performance of either the oxidized and reduced form of the electron shuttling compound. These findings demonstrate the feasibility of AH2QS addition during dark fermentation at pH 6.4 for improving the hydrogen production rate. Exoelectrogenic microorganisms identified in the inoculum could be responsible to improve the dark fermentation process in assays with electron shuttling compounds.

Effects of alginate immobilization on dynamic membrane formation and H2 fermentation from galactose

A dynamic membrane (DM) is a biofilm that forms on a support material, acting as a filter to retain high-density biomass. This study aims to explain the effects of alginate immobilization on DM formation during dark-H2 fermentation. Galactose is used as a model substrate. Heat-treated anaerobic sludge, with and without immobilization, is used for an inoculum for two identical lab-scale DM bioreactors (DMBR). The DMBRs are continuously operated for more than 40 days by changing the hydraulic retention time (HRT) from 12 to 3 h. Biomass retention and H2 production performance are significantly improved at an HRT of 3 h with immobilization. The alginate-added bioreactor shows higher extracellular polymeric substance content both in the mixed liquor and the DM. At an HRT of 3 h with immobilization, the fraction of Sporolactobacillus spp. and Lactobacillus spp. increases, possibly contributing to DM formation. However, lactic-acid concentration does not increase, implying it can be further consumed by the dominant bacteria, Clostridium butyricum.

Formation of a dynamic membrane altered the microbial community and metabolic flux in fermentative hydrogen production

This study aimed to investigate the relationship among dynamic membrane (DM) formation, metabolic flux, and microbial community population in dark fermentative hydrogen production. A continuously stirred tank reactor was equipped with an external submerged polyester screen mesh and inoculated with heat-treated anaerobic sludge without immobilization. DM was successfully developed on the polyester mesh and provided high-rate hydrogen production at 60.5 L H2/L.d and 2.39 mol H2/mol glucoseadded. DM formation was along with tightly bound extracellular polymeric substances. Flux balance analysis revealed that formation of DM altered the metabolic pathways for acetic acid production from homoacetogenesis to hydrogenesis. Bacterial community analysis suggested that Sporolactobacillaceae would contributed to this metabolic pathway shift. Nevertheless, lactic acid was not accumulated and assumed to be consumed by hydrogen producers including Clostridia.

Biohydrogen production from hydrolyzed waste wheat by dark fermentation in a continuously operated packed bed reactor: The effect of hydraulic retention time

Abstract The aim of the study is biohydrogen production from hydrolyzed waste wheat by dark fermentation in a continuously operated up-flow packed bed reactor. For this purpose, the effect of hydraulic retention time (HRT) on the rate (RH2) and yield (YH2) of hydrogen gas formation were investigated. In order to determine the most suitable hydraulic retention time yielding the highest hydrogen formation, the reactor was operated between HRT = 1 h and 8 h. The substrate was the acid hydrolyzed wheat powder (AHWP). Waste wheat was sieved down to 70 μm size (less than 200 mesh) and acid hydrolyzed at pH = 2 and 90 °C in an autoclave for 15 min. The sugar solution obtained from hydrolysis of waste wheat was used as substrate at the constant concentration of 15 g/L after neutralization and nutrient addition for biohydrogen production by dark fermentation. The microbial growth support particle was aquarium biological sponge (ABS). Heat-treated anaerobic sludge was used as inoculum. Total gas volume and hydrogen percentage in total gas, hydrogen gas volume, total sugar and total volatile fatty acid concentrations in the feed and in the effluent of the system were monitored daily throughout the experiments. The highest yield and rate of productions were obtained as YH2 = 645.7 mL/g TS and RH2 = 2.51 L H2/L d at HRT = 3 h, respectively.

Biohydrogen Productions from Hydrolysate of Water Hyacinth Stem (Eichhornia crassipes) Using Anaerobic Mixed Cultures

Response surface methodology (RSM) with central composite design (CCD) was applied to optimize key factors affecting hydrogen production (HP) from diluted acid hydrolysate of water-hyacinth stem (WHS) by heat-treated anaerobic sludge in a batch fermentation process. Key factors affecting namely substrate concentration and initial pH was investigated. The results indicated that substrate concentration and initial pH had significantly effects on HP (p<0.05). A maximum HP hydrogen production rate and hydrogen yield of 182.7 mmol H2/L, 2.81 mmol H2/L h and 0.84 mol H2/mol hexose were obtained under the optimum conditions i.e. substrate concentration of 4.06 g/L and initial pH of 5.81. The total energy production from the fermentative of WHS hydrolysate was 1.97 kJ.

Dark fermentative hydrogen production by anaerobic sludge growing on glucose and ammonium resulting from nitrate electroreduction

The main objective of this work was to study the feasibility of biohydrogen production by heat-treated anaerobic sludge with glucose as carbon substrate and ammonium as nitrogen source, obtained from the electrochemical reduction of concentrated nitrate solutions (3 g L−1NO3−), namely model solutions simulating those obtained after physicochemical denitrification of industrial wastewaters. Experiments were realized in bacth systems involving 125 mL (without pH control) and 3 L (with pH control) reactor, respectively.In order to find the optimal conditions for H2 production, the first set of experiments were conducted without pH control at various initial pH (pH 5.5, 6.5 and 7.5) and glucose concentrations (5–30 g L−1); and the highest H2 yield (1.1 mol H2mol−1glucoseconsumed) was reached for a glucose concentration of 25 g L−1 and at pH 6.5. These optimal conditions were then considered to examine the effect of pH control on biohydrogen production, in a 3 L bioreactor. The pH control allowed a considerable improvement of the hydrogen gas conversion efficiency, which reached 2.02 mol H2mol−1glucoseconsumed.

Enhancement of biohydrogen production from brewers’ spent grain by calcined-red mud pretreatment

This paper investigated the utilization of calcined-red mud (CRM) pretreatment to enhance fermentative hydrogen yields from brewers’ spent grain (BSG). The BSG samples were treated with different concentrations (0.0–20g/L) of CRM at 55°C for 48h, before the biohydrogen process with heat-treated anaerobic sludge inoculum. The highest specific hydrogen production of 198.62ml/g-VS was obtained from the BSG treated with 10g/L CRM, with the corresponding lag time of 10.60h. Hydrogen yield increments increased by 67.74%, compared to the control tests without CRM. The results demonstrated that the CRM could hydrolyze more cellulose and further provided adequate broth and suitable pH value for efficient fermentative hydrogen. The model-based analysis showed that the modified Gompertz model presented a better fit for the experimental data than the first-order model.

Ni-Mg-Al Hydrotalcite for Improvement of Dark Fermentative Hydrogen Production

Ni-Mg-Al hydrotalcite (HT) was employed to test its potential to enhance biohydrogen production with various doses, from 83 to 417mg/L. Experiments were carried out at 37 oC using heat-treated anaerobic sludge as inoculum and sucrose as synthetic wastewater in batch tests. X-ray diffraction (XRD) pattern and Fourier transform infrared (FTIR) spectrum were recorded to determine structure and functional groups of HT. As a result, addition of 250mg/L Ni-Mg-Al HT showed the highest hydrogen yield of 3.37 ± 0.17mol H2/mol sucrose, which improved the biohydrogen production by 80%. At the end of fermentation process, concentrations of metabolites, including lactic acid, acetic acid, and butyric acid were 160mg/L, 4661mg/L, and 5625mg/L, respectively. Enhancement of biohydrogen production by addition of 250mg/L Ni-Mg-Al HT can be attributed to basic property of HT, facilitation of magnesium in electron transfer process and suitable concentration of nickel as well.

Optimization of Factors Affecting Acid Hydrolysis of Water Hyacinth Stem (Eichhornia Crassipes) for Bio-Hydrogen Production

Response surface methodology (RSM) with central composite design (CCD) was applied to optimize hydrolysis conditions of water-hyacinth stem (WHS). Firstly, the effects of reaction time (h), % diluted H2SO4 concentration (v/v) and shaking speed (rpm) for hydrolyze WHS were investigated. The optimum condition for WHS hydrolysis was reaction time of 7.73h, H2SO4 concentration of 1.31% (v/v) and stirring speed of 264.41rpm in which a maximum total sugar of 13g/L was obtained. Secondly, the hydrolysate WHS obtained from the optimum hydrolysis condition was further used as the substrate for hydrogen production by heat-treated anaerobic sludge. Results showed that the maximum HP of 127. 6 mmol H2/L was obtained.

Thermophilic bio-hydrogen production from corn-bran residue pretreated by calcined-lime mud from papermaking process

This study investigated the use of calcined-lime mud from papermaking process (CLMP) pretreatment to improve fermentative hydrogen yields from corn-bran residue (CBR). CBR samples were pretreated with different concentrations (0–15g/L) of CLMP at 55°C for 48h, prior to the thermophilic fermentation with heat-treated anaerobic sludge inoculum. The maximum hydrogen yield (MHY) of 338.91ml/g-VS was produced from the CBR pretreated with 10g/L CLMP, with the corresponding lag-phase time of 8.24h. Hydrogen yield increments increased from 27.76% to 48.07%, compared to the control. The CLMP hydrolyzed more cellulose, which provided adequate substrates for hydrogen production.

Modified hydrotalcites for enhancement of biohydrogen production

Different hydrotalcites (HTs), namely Mg–Al HT, Ni–Mg–Al HT, magnetic Mg–Al HT, and magnetic Ni–Mg–Al HT, synthesized by a co-precipitation method were tested for their capacity to improve biohydrogen production with a wide range of doses, from 83 to 833 mg/L. Batch experiments were conducted at 37 °C using heat-treated anaerobic sludge as inoculum and sucrose as synthetic wastewater. The highest hydrogen yield was obtained around 3.37 ± 0.17 mol H2/mol sucrose added for an optimum dose of 250 mg/L Ni–Mg–Al HT. This was equivalent to 80% yield increment in relation to control. At the end of the fermentation process, sucrose was converted completely. Lactic acid (160 mg/L), acetic acid (4661 mg/L), and butyric acid (5625 mg/L) were produced as metabolites. A good performance with addition of HTs may be due to the basic property of HT and metals leaching from HTs, which may cause metabolic changes. For magnetic HTs, at optimum dose, they could be recycled three times. However, the magnetic property of such HTs was lost gradually and hydrogen yield was reduced with each run. At the third cycle, as compared to control, the obtained hydrogen yield increased 40% and 22% for magnetic Ni–Mg–Al HT and magnetic Mg–Al HT, respectively.

Effect of hydrogen producing mixed culture on performance of microbial fuel cells

This study examined the influence of H2-producing mixed cultures on improving power generation using air-cathode microbial fuel cells (MFCs) inoculated with heat-treated anaerobic sludge. The MFCs installed with graphite brush anode generated higher power than the MFCs with carbon cloth anode, regardless heat treatment of anaerobic sludge. When the graphite brush anode-MFCs were inoculated selectively with H2-producing bacteria by heat treatment, power production was not improved (about 490 mW/m2) in batch mode operation, but for slightly increased in carbon cloth anode-MFCs (from 0.16 to 2.0 mW/m2). Although H+/H2 produced from H2-producing bacteria can contribute to the performance of MFCs, suspended biomass did not affect the power density or potential, but the Coulombic efficiency (CE) increased. A batch test shows that propionate and acetate were used effectively for electricity generation, whereas butyrate made a minor contribution. H2-producing mixed cultures do not affect the improvement in power generation and seed sludge, regardless of the pretreatment, can be used directly for the MFC performance.

Characteristics of biohydrogen fermentation from various substrates

The characteristics of biohydrogen production from sucrose, slurry-type piggery waste and food waste under the effects of the reactor configurations and operational pHs (6 and 9) were examined by using heat-treated anaerobic sludge as a seed biomass. When sucrose was used in the batch test, the maximum hydrogen yield was 0.12–0.13 g COD (as H2)/g COD (1.41–1.43 mol/mol hexose) at pH 6. In contrast, 0.10–0.11 g COD (as H2)/g COD (1.12–1.21 mol/mol hexose) hydrogen yield was achieved from the reactor at pH 9. On the other hand, hydrogen production was not observed in the continuous sequencing batch mode fermenters fed with sucrose. Profile analysis at each cycle revealed hydrogen production at the initial operation periods but eventually only methane at 36 days. When slurry-type piggery waste was used as the substrate, the upflow elutriation-type fermenters produced methane but not hydrogen after 30 days operation. The fermentation intermediate profile showed that the hydrogen produced might have been consumed by homoacetogenic or propionate producing reactions, and eventually converted into methane by acetoclastic methanogens. The downflow leaching bed fermenters using food waste produced 0.013 L H2/g volatile solids (VS) (0.0061 g COD (as H2)/g COD) at pH 6 with 54% VS reduction whereas 0.0041 L H2/g VS (0.0020 g COD (as H2)/g COD) was produced at pH 9 with 86% VS reduction. The results show that the hydrogen produced should be released rapidly from the reactor before it can be consumed in other biochemical reactions, and substrates with high pH level (>9.0) can be used directly to produce hydrogen without needing to adjust the pH.

Combination of dark- and photo-fermentation to improve hydrogen production from Arthrospira platensis wet biomass with ammonium removal by zeolite

Arthrospira platensis wet biomass was subjected to microwave-assisted dilute H2SO4 pretreatment to improve saccharification by hydrolysis with glucoamylase and hydrogen production from dark-fermentation. When the hydrolyzed biomass from A. platensis was inoculated with hydrogenogens (heat-treated anaerobic sludge) to produce hydrogen during dark-fermentation, the maximum hydrogen yield of 96.6 ml H2/g DW was obtained. Because high concentration of NH4+ (31.6–56.5 mM) in the residual solution (also containing acetate and butyrate) obtained from dark-fermentation can significantly inhibit the activities of photosynthetic bacteria in sequential photo-fermentation, a modified zeolite was used to extract NH4+ by ion exchange to reduce the NH4+ content to 2.2–2.7 mM (91.8%–95.8% of NH4+ removal efficiency). The treated residual solution was reused for hydrogen production in sequential photo-fermentation. The maximum hydrogen yield from A. platensis wet biomass was significantly enhanced from 96.6 to 337.0 ml H2/g DW using a combination of dark- and photo-fermentation.

Fermentative hydrogen production from lipid-extracted microalgal biomass residues

The conversion of lipid-extracted microalgal biomass residues (LMBRs) into hydrogen plays the dual role in renewable energy production and sustainable development of microalgal biodiesel industry. An anaerobic fermentation process to covert LMBRs into hydrogen was investigated in this work. Using batch experiments, the effects of pretreatment of inoculum (by acid, base, heat, and chloroform, respectively), initial pH (5.0–7.0), inoculum concentrations at 0.59–2.94 g VSS/l (volatile suspended solids, VSS) and substrate concentrations at 4.5–45 g VS/l (volatile solids, VS) were investigated, respectively. The results showed that the most effective hydrogen production was obtained from fermentation of LMBRs with a concentration of 36 g VS/l at the initial pH 6.0–6.5 using the heat-treated anaerobic digested sludge as inoculum. Acetate, propionate and butyrate were the main fermentation byproducts in the conversion of LMBRs into hydrogen.

Comparison of bio-hydrogen production from hydrolyzed wheat starch by mesophilic and thermophilic dark fermentation

Hydrogen gas production potentials of acid-hydrolyzed and boiled ground wheat were compared in batch dark fermentations under mesophilic (37 °C) and thermophilic (55 °C) conditions. Heat-treated anaerobic sludge was used as the inoculum and the hydrolyzed ground wheat was supplemented by other nutrients. The highest cumulative hydrogen gas production (752 ml) was obtained from the acid-hydrolyzed ground wheat starch at 55 °C and the lowest (112 ml) was with the boiled wheat starch within 10 days. The highest rate of hydrogen gas formation (7.42 ml H 2 h −1) was obtained with the acid-hydrolyzed and the lowest (1.12 ml H 2 h −1) with the boiled wheat at 55 °C. The highest hydrogen gas yield (333 ml H 2 g −1 total sugar or 2.40 mol H 2 mol −1 glucose) and final total volatile fatty acid (TVFA) concentration (10.08 g L −1) were also obtained with the acid-hydrolyzed wheat under thermophilic conditions (55 °C). Dark fermentation of acid-hydrolyzed ground wheat under thermophilic conditions (55 °C) was proven to be more beneficial as compared to mesophilic or thermophilic fermentation of boiled (partially hydrolyzed) wheat starch.

Effects of dark/light bacteria ratio on bio-hydrogen production by combined fed-batch fermentation of ground wheat starch

Abstract Bio-hydrogen production by combined dark and light fermentation of ground wheat starch was investigated using fed-batch operation. Serum bottles containing heat-treated anaerobic sludge and a mixture of Rhodobacter sp. was fed with a medium containing 20 g dm −3 wheat powder (WP) at a constant flow rate. The system was operated at different initial dark/light biomass ratios (D/L). The optimum D/L ratio was 1/2 yielding the highest cumulative hydrogen (1548 cm 3 ), yield (65.2 cm 3 g −1 starch), and specific hydrogen production rate (5.18 cm 3 g −1 h −1 ). Light fermentation alone yielded higher hydrogen production than dark fermentation due to fermentation of volatile fatty acids (VFAs) to H 2 and CO 2 . The lowest hydrogen formation was obtained with D/L ratio of 1/1 due to accumulation of VFAs in the medium.