Biohydrogen production from dual digestion pretreatment of poultry slaughterhouse sludge by anaerobic self-fermentation

Poultry slaughterhouse sludge from chicken processing wastewater treatment plant was tested for their suitability as a substrate and inoculum source for fermentation hydrogen production. Dual digestion of poultry slaughterhouse sludge was employed to produce hydrogen by batch anaerobic self-fermentation without any extra-seeds. The sludge (5% TS) was dual digested by aerobic thermophilic digestion at 55 °C with the varying retention time before using as substrate in anaerobic self-fermentation. The best digestion time for enriching hydrogen-producing seeds was 48 h as it completely repressed methanogenic activity and gave the maximum hydrogen yield of 136.9 mL H₂/g TS with a hydrogen production rate of 2.56 mL H₂/L/h. The hydrogen production of treated sludge at 48 h (136.9 mL H₂/g TS) was 15 times higher than that of the raw sludge (8.83 mL H₂/g TS). With this fermentation process, tCOD value in the activated sludge could be reduced up to 30%.     

Effect of the initial total solids concentration and initial pH on the bio-hydrogen production from cafeteria food waste

In this paper, the influence of the initial pH and the total solids (TS) concentration on hydrogen production from the organic fraction of cafeteria food waste at mesophilic conditions in batch reactors was determined. It was found that the yield and specific hydrogen production rate were influenced by the initial pH and the initial total solids concentration. The highest hydrogen production rate, 2.90 mmolH₂/d, was obtained at 90 gTS/L and a pH of 5.5. Under this condition, the TS and chemical oxygen demand (COD) removal were the lowest (10% as TS and 14% as COD). However, considering the specific values, the highest specific degradation rate (192.2 mLH₂/gVS_removed/d) was obtained with the lowest TS concentration and an initial pH of 7.0. It was found that the influence of the TS concentration on hydrogen production was more significant than that of the initial pH for this type of residues.     

Biohydrogen production from paper industry wastes by SSF: A study of the influence of temperature/enzyme loading

The present work focused in assessing the hydrogen production from pretreated wastes of the paper industry (PIW) by simultaneous saccharification and fermentation (SSF) using anaerobic biofilms developed in natural fibers (ixtle) at different conditions. Anaerobic sludge from brewery wastewater treatment was used for biofilms and they were developed in plastic spheres covered with fiber cord from ixtle. The solid wastes of paper industry were previously pretreated with H₂SO₄ at 2.5% (v/v) at 120 °C by 30 min. The solids pretreated were hydrolyzed and fermented in batch reactors. All reactors were kept at an initial pH of 5.0 and three levels of enzyme loadings (10, 40 and 70 FPU/mL) and temperatures (35, 45, 55 °C) were assessed. The maximum hydrogen obtained (60.75 mmol/h*g volatile solids) was at 45 °C and 70 FPU/mL, moreover, no methane was detected in all cases.     

皇竹草厌氧发酵特性及稀土元素溶出研究

为探讨稀土尾矿区修复用皇竹草的厌氧发酵特性和发酵过程稀土元素溶出情况,开展不同发酵浓度（总固体浓度分别为2%、4%、6%、8%、10%）的中温（37±1℃）批式厌氧发酵实验。结果表明,总固体（TS）浓度为4%条件下皇竹草产甲烷性能最佳,日产甲烷率和累积产甲烷率分别为25.56 mL/g和197.33 mL/g。采用修正Gompertz方程能较好地模拟不同TS下皇竹草发酵累积产甲烷率的变化。分析发酵液中稀土元素浓度变化,结果表明,皇竹草内的稀土元素在厌氧发酵过程中只发生小部分溶出,主要包括La、Ce、Nd、Sc、Y等,各处理发酵液中稀土元素浓度并未超出文献报道的抑制浓度。相关性分析结果表明,稀土元素溶出率与发酵体系的TS浓度、化学需氧量（COD）呈负相关,与pH呈正相关。研究可为稀土矿区皇竹草沼气工程应用和发酵剩余物的肥料化利用提供指导。     

An experimental approach to produce hydrogen and methane from food waste using catalyst

Anaerobic co-digestion of food waste, cow dung, and sludge solution is experimented in the presence of calcium peroxide (CaO₂) as the catalyst to produce hydrogen and methane as a source of renewable energy. The substrate to inoculum ratios (v/v) of 1:1(S1), 1:2(S2), 1:3(S3), 1:4(S4) and 1:5(S5) are investigated in separate fermentative and methanogenic reactors. The result from the fermentative reactors indicate maximum hydrogen concentration of 26.34% with cumulative yield of 114.1 mL/g total solid (TS) in S3 compared to the other samples. Methanogenic reaction shows the highest methane concentration of 54.13% in S3. The highest daily (average) and cumulative biogas yield of 5.36 mL/g TS and 201.9 mL/g TS respectively are identified in S3. A maximum carbon dioxide concentration of 63.11% is found in S1. Overall, the substrate to inoculum ratio of 1:3 is spotted to be optimal for effective hydrogen and methane production during the anaerobic co-digestion process.     

Thermophilic dark fermentation of untreated rice straw using mixed cultures for hydrogen production

Biohydrogen production from untreated rice straw using different heat-treated sludge, initial cultivation pH, substrate concentration and particle size was evaluated at 55 °C. The peak hydrogen production yield of 24.8 mL/g TS was obtained with rice straw concentration 90 g TS/L, particle size <0.297 mm and heat-treated sludge S1 at pH 6.5 and 55 °C in batch test. Hydrogen production using sludge S1 resulted from acetate-type fermentation and was pH dependent. The maximum hydrogen production (P), production rate (R_m) and lag (λ) were 733 mL, 18 mL/h and 45 h respectively. Repeated-batch operation showed decreasing trend in hydrogen production probably due to overloading of substrate and its non-utilization. PCR-DGGE showed both hydrolytic and fermentative bacteria (Clostridium pasteurianum, Clostridium stercorarium and Thermoanaerobacterium saccharolyticum) in the repeated-batch reactor, which perhaps in association led to the microbial hydrolysis and fermentation of raw rice straw avoiding the pretreatment step.     

Dark fermentation of starch factory wastewater with acid- and base-treated mixed microorganisms for biohydrogen production

Biohydrogen (Bio-H₂) can be produced from starch factory wastewater and mixed microorganisms using dark fermentation. Acidic and basic chemicals were used to treat the microorganisms to select the hydrogen (H₂)-producing culture. The experiment used a 120 mL bioreactor at 35 °C and the operation commenced with the initial pH level of wastewater in the pH range 4–7 in batch mode. The bacteria:chemical oxygen demand (COD) ratio was 0.2. The initial pH level of the wastewater in the fermentation process affected the H₂ yield and the specific hydrogen production rate (SHPR). For acid-treated bacteria, the maximum H₂ yield and SHPR were produced at an initial pH of 6.5. The maximum H₂ yield and SHPR were 138 mL/g COD degraded and 7.42 mL/g cells?h, respectively. For the base-treated bacteria, the maximum H₂ yield and SHPR were produced at initial pH of 6.5 and pH 7, respectively. The maximum H₂ yield and SHPR were 182 mL/g COD degraded and 25.60 mL/g cells?h, respectively. The COD degradation efficiency levels were 16 and 20% for acid- and base-treated bacteria, respectively. The digested wastewater remained acidic at pH 4.79–4.83. Throughout the study, no methane gas was observed in the gas mixture produced.     

Energy valorization of crude glycerol and sanitary sewage in hydrogen generation by biological processes

Biohydrogen production was studied with increased concentrations of crude glycerol (CG) co-digested with sanitary sewage by anaerobic consortium bacteria in anaerobic batch reactors, at 30 °C and initial pH 7.0. The CG was obtained during the biodiesel production from waste cooking oils (WCO). The anaerobic consortium was from a granular sludge of UASB reactor used in the treatment of poultry wastes heat treated to inhibit methanogenic activity previously. The higher H₂ generation was observed with 240.0 g COD L⁻¹ (35.82 mmol L⁻¹), being consumed 63.9% of CG. The co-digestion associated with sanitary sewage facilitated the CG consumption with the increase of organic load, favoring the acetic acid and 1,3-propanediol production in a liquid phase of the reactors. These results are promising, contributing effectively to the treatment of both wastes with concomitant generation of bioenergy.     

Biodesulfurization of Cayirhan Lignites

In this study, the lignite was improved oxidizing sulfur compounds by Thiobacillus thiooxidans and Thiobacillus ferrooxidans bacteria. Experiments in the batch reactors have been carried out 20% aqueous suspension of coal samples. Sugar beet molasses was used as the bacterial substrate. The maximum removal of combustible sulfur was obtained as 78.2% under the following conditions; addition 5% of T. thiooxidans and 5% T. ferrooxidans into coal suspension, 0.2 g molasses/g coal change, pH value of 3, at shaking rate of 70 rpm and at 40°C for 5 days.     

勿忘我花杆发酵产沼气潜力的实验研究

为研究勿忘我花杆的产沼气潜力和特性,实验设计对照组（120 mL接种物）和实验组（120 mL接种物 + 27 g勿忘我花杆）,在30℃恒温条件下,采用全混合批量式发酵工艺,进行厌氧发酵产沼气的实验。结果表明,实验组沼气发酵历时36 d,净产气量为1 650 mL,计算得出勿忘我花杆的产气潜力为359 mL/(g•TS),393 mL/(g•VS)。     

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.     

Co-digestion of waste glycerol and glucose to enhance biogas production

Co-digestion in anaerobic fermentation has been widely used to improve biogas production. The biogas production from co-digestion of glucose and glycerol was studied in laboratory-scale batch reactors under mesophilic temperatures, pH 7. The batch experiments involved a variation of glycerol/glucose ratios with initial chemical oxygen demand (COD) for all conditions was fixed at 5,200 mg L⁻¹. The highest yield of biogas production was obtained from glycerol/glucose with 5:5 ratio. The cumulative biogas production was 298.2 mL, and the maximum production rate was 8 mL hr⁻¹. The findings suggested that co-digestion is a potential method to achieve glycerol waste treatment and energy recovery at the same time.     

Enhanced bio-hydrogen production by anaerobic fermentation of apple pomace with enzyme hydrolysis

A series of batch experiments were conducted to investigate the effects of the HCl-pretreated concentrations, enzyme hydrolysis time and temperature, the cellulase dosage, the ultrasonic time and the fermentation substrate concentration on hydrogen (H₂) production from the anaerobic fermentation of apple pomace (AP). The natural mixed microorganisms from river sludge was used as the seed after being boiled for 15 min. A maximum cumulative H₂ yield (CHYm) of 134.04 ml/g total solid (TS) and an average H₂ production rate (AHPR) of 12.00 ml/g TS/h were obtained from the fermentation of the enzyme-hydrolyzed AAP (a AP soaked with 6% ammonia liquor for 24 h) at the substrate concentration of 15 g/L. The optimal enzyme hydrolysis conditions were proposed as follows: AAP with a cellulase dosage of 12.5 mg/g TS at the hydrolysis substrate concentration of 20 g/L after the ultrasonic irradiation for 20 min was hydrolyzed by the enzyme catalysis at 45 °C and initial pH 5.0 for 48 h.     

Rhamnolipid induced deagglomeration of anaerobic granular biosolids for energetically feasible ultrasonic homogenization and profitable biohydrogen

The present study exposes the effect of deagglomeration using rhamnolipid on anaerobic granular biosolids (AGB) followed by ultrasonic homogenization for effective biohydrogen production. Rhamnolipid was used to remove the extracellular polymeric substance bound over the surface of AGB to increase the rate of biogranular lysis during ultrasonic homogenization. Extracellular polymeric substance (EPS) removal was achieved at an optimum rhamnolipid dosage of 0.04 g Rh/g SS. Ultrasonic homogenization (UH) of AGB demands 27016 kJ/kg TS of specific energy to achieve 16.8% and 13.9% of biogranular lysis and biosolids reduction, respectively. However, rhamnolipid-alkaline pH induced ultrasonic homogenization (RAUH) demand lesser (12607 kJ/kg TS) and achieves greater biogranular lysis (25.4%) and biosolids reduction (20.7%). RAUH significantly saves the net energy. Exponential first order kinetic analysis was done to evaluate and compare the biohydrogen production potential of RAUH with that of UH. The biohydrogen production was found to be 55.1 mL H₂/g COD and 36.7 mL H₂/g COD for RAUH and UH respectively. A higher positive net energy of 2.62 kWh/kg AGB was achieved by RAUH when compared to UH (−3.49 kWh/kg anaerobic granular biosolids).     

Optimization of key factors affecting hydrogen production from coffee waste using factorial design and metagenomic analysis of the microbial community

The objective of this study was to evaluate the fermentation conditions that led to the optimization of H₂ production from coffee waste (wastewater, pulp and husk) and the taxonomic and functional characterization of autochthonous microorganisms. Assays in batch reactors with microbial consortium bioaugmentation (bacteria and fungi) evaluated the pH (4.82–8.18), pulp and husk concentration (6.95–17.05 g/L) and headspace factor (33.18–66.82%) by means of rotational central composite design and response surface. Operating conditions in the reactor optimized for 3.04 LH₂/Ld were at pH 7.0, 7 g/L pulp and husk and 30% headspace. The main metabolites observed were butyric acid (3838 mg/L), isobutyric acid (506 mg/L), methanol (226 mg/L) and butanol (156 mg/L). Clostridium sp. (87.9%), Lactobacillus sp. (1.7%), Kazachstania sp. (18.6%) and Saccharomyces sp. (16.3%) were the main genera identified in the optimized reactor, which had functional gene diversity for H₂ production, alcoholic fermentation, cellulose degradation, lignin, hemicellulose and phenol.     

Application of nano-scale transition metal carbides as accelerants in anaerobic digestion

Four types of nano-scale transition metal carbides (HfC, SiC, TiC, and WC), used as accelerants in anaerobic digestion (AD) with cattle manure, were investigated through batch experiments under mesophilic conditions (37 ± 1 °C). The AD system with four carbide accelerants showed a higher biogas yield (463–499 mL/g TS), chemical oxygen demand (COD) degradation rate (58.62–78.90%) and total Kjeldahl nitrogen (TKN) concentrations (905.0–1077.0 mg/L) as compared with control check (CK, 294 mL/g TS, 46.99%, 290 mg/L). All of the digestate samples from the AD systems using four carbide accelerants showed not only higher degradation of organic compounds during thermal analysis, but also stronger fertilizer values. The use of transition metal compounds (TMCs) as accelerants in AD can efficiently improve the conversion of waste resources into biogas and fertilizers, which can potentially open new avenues for the use of TMCs in upcoming research on biomass energy.     

Biological hydrogen production: Simultaneous saccharification and fermentation with nitrogen and phosphorus removal from wastewater effluent

A simple anaerobic biodegradation process using wastewater treatment plant (WWTP) effluent, shredded paper, and a purge of nitrogen gas was used to produce hydrogen and simultaneously capture nitrogen and phosphorus. Two reactor configurations, a sequencing batch reactor (SBR) and a classic batch reactor (CBR) were tested as simultaneous saccharification and fermentation reactors (enzymatic hydrolysis and fermentation in one tank). The CBR demonstrated greater stability of hydrogen production and simplicity of operation, while the SBR provided better nitrogen and phosphorus removal efficiencies. Nuclear magnetic resonance analyses showed acetic acid to be the main product from both reactors. Optimal CBR conditions were found to be pH 5, 4 g/L loading, 0.45 ml/g Accellerase 1500, and 38 °C. Experiments with an argon purge in place of nitrogen and with ammonium chloride spiking suggested that hydrogenase and nitrogenase enzymes contributed similarly to hydrogen production in the cultures. Analysis of a single fermentation showed that hydrogen production occurred relatively early in the course of TOC removal, and that follow-on treatments might extract more energy from the products.     

Optimization of fermentative hydrogen production process by response surface methodology

The effect of temperature, initial pH and glucose concentration on fermentative hydrogen production by mixed cultures was investigated in batch tests, and the optimization of fermentative hydrogen production process was conducted by response surface methodology with a central composite design. Experimental results showed that temperatures, initial pH and glucose concentrations had impact on fermentative hydrogen production individually and interactively. The maximum hydrogen yield of 289.8 mL/g glucose was estimated at the temperature of 38.6 °C, the initial pH of 7.2 and the glucose concentration of 23.9 g/L. The maximum hydrogen production rate of 28.2 mL/h was estimated at the temperature of 37.8 °C, the initial pH of 7.2 and the glucose concentration of 27.6 g/L. The maximum substrate degradation efficiency of 96.9% was estimated at the temperature of 39.3 °C, the initial pH of 7.0 and the glucose concentration of 26.8 g/L. Response surface methodology was a better method to optimize the fermentative hydrogen production process. Modified logistic model could describe the progress of cumulative hydrogen production in the batch tests of this study successfully.     

Solar chemical reactor technology for industrial production of lime

We developed the solar chemical reactor technology to effect the endothermic calcination reaction CaCO₃(s) → CaO(s) + CO₂(g) at 1200–1400 K. The indirect heating 10 kW_th multi-tube rotary kiln prototype processed 1–5 mm limestone particles, producing high purity lime that is not contaminated with combustion by-products. The quality of the solar produced quicklime meets highest industrial standards in terms of reactivity (low, medium, and high) and degree of calcination (exceeding 98%). The reactor’s efficiency, defined as the enthalpy of the calcination reaction at ambient temperature (3184 kJ kg⁻¹) divided by the solar energy input, reached 30–35% for quicklime production rates up to 4 kg h⁻¹. The solar lime reactor prototype operated reliably for more than 100 h at solar flux inputs of about 2000 kW m⁻², withstanding the thermal shocks that occur in solar high temperature applications. By substituting concentrated solar energy for fossil fuels as the source of process heat, one can reduce by 20% the CO₂ emissions in a state-of-the-art lime plant and by 40% in a conventional cement plant. The cost of solar lime produced in a 20 MW_th industrial solar calcination plant is estimated in the range 131–158 $/t, i.e. about 2–3 times the current selling price of conventional lime.     

Evaluation of hydrogen fermentation by a newly isolated alkaline tolerant Clostridium felsineum strain CUEA03

A new alkaline tolerant Clostridium felsineum strain (CUEA03) was isolated from a mangrove sediment in Thailand. Genomics revealed that this strain contained a 5,081,113 bp genome sequence with 4797 predicted protein coding sequences, comprised of a large number of genes that are linked to several processes of carbon utilization, hydrogen (H₂), and butanol production. Chemical tests revealed that the bacteria have a high potential for utilization of a wide range of carbon sources. After optimization by batch fermentation, a maximum cumulative H₂ production (CHP) of 5425 mL/L in 72 h was obtained at pH 9, 30 °C, 0.9 g/L NaCl, and 35 g/L glucose. Moreover, this strain was compatible with agro-industrial waste, giving a CHP of 5187 mL/L (893 mL/g COD_consumed). This demonstrates that environmentally isolated organisms have the potential to be used as robust high H₂ producers from various complex organic substrates.