Fermentative H2 production using a switchgrass steam exploded liquor fed to mixed anaerobic cultures: Effect of hydraulic retention time,linoleic acid and nitrogen sparging

Fermentative hydrogen (H₂) production from a steam exploded switchgrass liquor using inhibited mixed anaerobic microbial communities was studied in upflow anaerobic sludge blanket reactors (UASBRs). Increasing the H₂ yield was accomplished by treating the inoculum with linoleic acid (LA), varying the hydraulic retention time (HRT) and sparging liquid phase with nitrogen (N₂). A maximum H₂ yield of 2.56 ± 0.10 mol mol⁻¹ hexose, was obtained at a 6 h HRT in LA treated cultures sparged with N₂. Sparging or LA treatment alone was able to enhance the H₂ yield by 46 ± 5% and 38 ± 3%, respectively, in comparison to control cultures operating at a 6 h HRT. Of the different methods employed, N₂ sparging in combination with LA treatment proved to be more effective in enriching the H₂ producing bacteria belonging to Clostridium sp. Species belonging to Propionibacterium, Bacteroides and Eubacterium, which were associated with H₂ consumption and reduced byproducts formation, were observed in addition to Clostridium sp. in unsparged control cultures.     

Simultaneous hydrogen and ethanol production from a mixture of glucose and xylose using extreme thermophiles II: Effect of hydraulic retention time

In this study, biofuels (hydrogen and ethanol) fermentation from glucose and xylose by extreme thermophiles in an Up-flow Anaerobic Sludge Bed (UASB) reactor was successfully demonstrated. Autoclaved methanogenic granules were used as carriers for the extreme thermophiles. High yields of hydrogen and ethanol were achieved at various HRTs from 24 h to 6 h. The highest hydrogen production rate of 121 ± 23 mL/(L h) and highest ethanol production rate of 6.7 ± 1.2 mmol/(L h) were observed at HRT = 12 h. The highest simultaneous hydrogen and ethanol yields were 0.58 ± 0.11 mol H₂/(mol hexose) and 0.72 ± 0.13 mol ethanol/(mol hexose), reaching a total energy yield of 1151 kJ/mol hexose. The substrate conversion efficiency was maintained over 90% at three HRTs (24, 18, and 12 h).     

Enhanced anaerobic digestion of sewage sludge by thermal or alkaline-thermal pretreatments: Influence of hydraulic retention time reduction

The influence of hydraulic retention times (HRTs) reduction from 25 days to 15 days on the enhancement effects of two pretreatments (thermal pretreatment and alkaline-thermal pretreatment) on the continuous anaerobic digestion (AD) of sewage sludge was studied in a long-term experiment (196 days). The operation of the semi-continuous AD fed with raw sludge or pretreated sludge was stable at the three HRTs. The methane production increased from 70.6 to 165.8 ml/L·d to 75.2–172.6 ml/L·d and the methane yield decreased from 98.9 to 234.9 ml/g added volatile solid to 65.6–144.9 ml/g added volatile solid when the HRT reduced from 25 days to 15 days. The two pretreatments reduced the HRT of raw sludge AD by over 40%, and the effects of the alkaline-thermal pretreatment were greater than those of the thermal pretreatment. The reduction of HRT from 25 days to 15 days increased the enhancement effects of the two pretreatments on the removal of organic matter (4.7–15.9% for volatile solid), average hydrolysis ratio (36.9–116.4%), and specific hydrolysis rate (44.1–155.6%) but decreased the enhancement effects of the pretreatments on the methane production (0.9–4.6%) and yield (4.0–15.8%), average reaction ratios (0.4–8.2%), and specific rates of the last three AD steps (0.1–13.9%). The influence of HRT reduction on the enhancement effects of the alkaline-thermal pretreatment for sludge AD was slightly greater than on the enhancement effects of the thermal pretreatment.     

Influence of the temperature and hydraulic retention time in bioelectrochemical anaerobic digestion of sewage sludge

At ambient temperature (25 °C), bioelectrochemical anaerobic digestion of sewage sludge was investigated with a hydraulic retention time (HRT) of 10 days and compared to that at a mesophilic condition (35 °C). The methane production and methane content in the biogas at ambient temperature were 612.8 mL/L·d and 73.3%, respectively, which were not significantly lower than that of the mesophilic condition. Additionally, the VS removal was 54.5% which was similar for both temperature conditions. However, for a HRT of 20 days, the bioelectrochemical anaerobic digestion at ambient temperature became more stable, and the VS removal improved up to 65.0%. For the HRT of 10 days, the net energy production at ambient temperature was about 168 kJ/L·d, which was similar to the mesophilic condition; however, the apparent energy efficiency at ambient temperature was 249.2% which was significantly higher than 197.7% at the mesophilic condition. The bioelectrochemical anaerobic digestion that can save the thermal energy input at ambient temperature is recommended for the treatment of organic waste including sewage sludge in moderate and cold climate regions.     

Hydrogen and methane production from untreated rice straw and raw sewage sludge under thermophilic anaerobic conditions

Bioenergy produced from co-digestion of sewage sludge (SS) and rice straw (RS) as raw materials, without pretreatment and additional nutrients, was compared for the one-stage system for producing methane (CH₄) and the two-stage system for combined production of hydrogen (H₂) and CH₄ in batch experiments under thermophilic conditions. In the first stage H₂ fermentation process using untreated RS with raw SS, we obtained a high H₂ yield (21 ml/g-VS) and stable H₂ content (60.9%). Direct utilization of post-H₂ fermentation residues readily produced biogas, and significantly enhanced the CH₄ yield (266 ml/g-VS) with stable CH₄ content (75–80%) during the second stage CH₄ fermentation process. Overall, volatile solids removal (60.4%) and total bioenergy yield (8804 J/g-VS) for the two-stage system were 37.9% and 59.6% higher, respectively, than the one-stage system. The efficient production of bioenergy is believed to be due to a synergistically improved second stage process exploiting the well-digested post-H₂ generation residues over the one-stage system.     

Advances in economically driven optimization of processing of biosolids from sewage sludge

Management of biosolids from sewage sludge is a problem of global importance with comprehensive environmental and economic impacts. A wide portfolio of various processing techniques was investigated during last decades, however, most of them failed from the economic point of view. This study initially mentions some inhibition mechanisms in the steam-explosion pretreatment followed by anaerobic fermentation and assesses them in a commercial scale from the technological–economic point of view. Several synergies have been observed that improve the management of biosolids (increased CH₄ production, deeper removal of the organic matter, and easier dewatering). Nevertheless, other results indicate that the full technological–economic potential is far from being achieved.     

Biohydrogen from molasses with ethanol-type fermentation: Effect of hydraulic retention time

Though ethanol-type fermentation has many advantages for improving hydrogen production rate (HPR) in continuously mode hydrogen producing system, information on this fermentation is very deficient. The effect of hydraulic retention time (HRT) on biohydrogen production and operational stability of ethanol-type fermentation was investigated in a continuous stirred tank reactor (CSTR) using molasses as substrate. Five HRTs were examined, ranging from 4 to 10 h. At HRT 5 h, the highest HPR of 12.27 mmol L⁻¹ h⁻¹ was obtained from ethanol-type fermentation in the pH range of 4.3–4.4. During the whole operation process, ethanol, butyrate and acetate were the predominant metabolites. A total COD concentration of ethanol and acetate accounted for above 73.3% of total soluble microbial products. Linear regression showed that HPR and ethanol production rate were proportionately correlated at all HRTs which could be expressed as y = 0.9821x − 3.5151 (r² = 0.9498). It is meaningful that the proposed recovery of both hydrogen and ethanol from fermentation process can improve energy production rate and economic profit. Results demonstrated that the best energy production rate was 15.50 kJ L⁻¹ h⁻¹, occurred at HRT = 5 h.     

Effect of wastewater treatment processes on the pyrolysis properties of the pyrolysis tars from sewage sludges

The pyrolysis properties of five different pyrolysis tars, which the tars from 1# to 5# are obtained by pyrolyzing the sewage sludges of anaerobic digestion and indigestion from the A2/O wastewater treatment process, those from the activated sludge process and the indigested sludge from the continuous SBR process respectively, were studied by thermal gravimetric analysis at a heating rate of 10 ℃/min in the nitrogen atmosphere. The results show that the pyrolysis processes of the pyrolysis tars of 1#, 2#, 3# and 5# all can be divided into four stages: the stages of light organic compounds releasing, heavy polar organic compounds decomposition, heavy organic compounds decomposition and the residual organic compounds decomposition. However, the process of 4# pyrolysis tar is only divided into three stages: the stages of light organic compounds releasing, decomposition of heavy polar organic compounds and the residual heavy organic compounds respectively. Both the sludge anaerobic digestion and the "anaerobic" process in wastewater treatment processes make the content of light organic compounds in tars decrease, but make that of heavy organic compounds with complex structure increase. Besides, both make the pyrolysis properties of the tars become worse. The pyrolysis reaction mechanisms of the five pyrolysis tars have been studied with Coats-Redfern equation. It shows that there are the same mechanism functions in the first stage for the five tars and in the second and third stage for the tars of 1#, 2#, 3# and 5#, which is different with the function in the second stage for 4# tar. The five tars are easy to volatile.     

Effect of hydraulic retention time on the hydrogen production in a horizontal and vertical continuous stirred-tank reactor

Hydraulic retention time (HRT) is the main process parameter for biohydrogen production by anaerobic fermentation. This paper investigated the effect of the different HRT on the hydrogen production of the ethanol-type fermentation process in two kinds of CSTR reactors (horizontal continuous stirred-tank reactor and vertical continuous stirred-tank reactor) with molasses as a substrate. Two kinds of CSTR reactors operated with the organic loading rates (OLR) of 12kgCOD/m3•d under the initial HRT of the 8 h condition, and then OLR was adjusted as 6kgCOD/m3•d when the pH drops rapidly. The VCSTR and HCSTR have reached the stable ethanol-type fermentation process within 21 days and 24 days respectively. Among the five HRTs settled in the range of 2–8 h, the maximum hydrogen production rate of 3.7LH₂/Ld and 5.1LH₂/Ld were investigated respectively in the VCSTR and HCSTR. At that time the COD concentration and HRT were 8000 mg/L and 5 h for VCSTR, while 10000 mg/L and 4 h for HCSTR respectively.Through the analysis on the composition of the liquid fermentation product and biomass under the different HRT condition in the two kinds of CSTR, it can found that the ethanol-type fermentation process in the HCSTR is more stable than VCSTR due to enhancing biomass retention of HCSTR at the short HTR.     

Waste activated sludge treatment in an anaerobic dynamic membrane bioreactor at varying hydraulic retention time: Performance monitoring and microbial community analysis

In this study, the variations in system performance and microbial community composition when treating waste activated sludge without prior chemical or physical pretreatment in anaerobic systems is examined. Two lab-scale digesters, namely anaerobic dynamic membrane bioreactor (AnDMBR) and continuously stirred tank reactor (CSTR), were operated and maintained under mesophilic conditions at varying hydraulic retention times (10-25 days). Decreasing the hydraulic retention time (HRT) affected the methane yield (MY) and methane production rate (MPR) proportionally in both systems. The AnDMBR's maximum MY of 252 mL CH₄/g-VS and MPR of 0.73 L/L/d were 25% and 34% higher than those obtained using the CSTR, respectively. Moreover, a decrease in HRT was accompanied by accumulation of butyric acid in the CSTR, which caused further performance deterioration. In both systems, AnDMBR's dynamic membrane acted as an added layer preventing methanogen wash-out and retaining the essential microorganisms for stable sludge treatment. Dominance in the microbial composition shifted from a strict acetoclastic to a mixed acetoclastic and hydrogenotrophic methanogenic community and that a decrease in the ration of Bacteroidetes to Firmicutes was associated with the increased MY.     

Effect of hydraulic retention time on hydrogen production from sewage sludge and wine vinasse in a thermophilic acidogenic CSTR: A promising approach for hydrogen production within the biorefinery concept

The aim of the present study was to investigate the effect of hydraulic retention time (HRT) on hydrogen production from sewage sludge:wine vinasse (50:50 v/v) in a laboratory-scale continuously stirred tank reactor under thermophilic conditions. For this purpose, nine HRT ranging from 5.0 to 0.25 days were tested. Maximum hydrogen production and specific hydrogen production of 0.90 LH₂/L_reactor/d and 35.19 mLH₂/g VS_added were respectively obtained at a HRT of 0.5 days. Eubacteria was the main group (65–79%) for all the tested HRT. Decreasing HRT was inversely correlated with hydrogen production and microbial population. HRT of 0.5 days is optimal for the growth of the acidogenic population and therefore this population is more active and maximum microbial activity (15.28·10^?10 LH₂/cells) was also achieved at this HRT.     

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.     

Effects of substrate concentration and hydraulic retention time on hydrogen production from common reed by enriched mixed culture in continuous anaerobic bioreactor

This study aims to investigate the effect of substrate concentration and hydraulic retention time (HRT) on hydrogen production in a continuous anaerobic bioreactor from unhydrolyzed common reed (Phragmites australis) an invasive wetland and perennial grass. The bioreactor has capacity of 1 L and working volume of 600 mL. It was operated at pH 5.5, temperature at 37 °C, hydraulic retention time (HRT) 12 h, and variation of substrate concentration from 40, 50, and 60 g COD/L, respectively. Afterward, the HRT was then varied from 12, 8, to 4 h for checking the optimal biohydrogen production. Each condition was run until reach steady state on hydrogen production rate (HPR) which based on hydrogen percentage and daily volume. The results were obtained the peak of substrate concentration was at the 50 g COD/L with HRT 12 h, average HPR and H₂ concentration were 28.71 mL/L/h and 36.29%, respectively. The hydrogen yield was achieved at 106.23 mL H₂/g CODre. The substrate concentration was controlled at 50 g COD/L for the optimal HRT experiments. It was found that the maximum of average HPR and H₂ concentration were 43.28 mL/L/h and 36.96%, respectively peak at HRT 8 h with the corresponding hydrogen yield of 144.35 mL H₂/g CODre. Finally, this study successful produce hydrogen from unhydrolyzed common reed by enriched mixed culture in continuous anaerobic bioreactor.     

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％。     

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%.     

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.     

Influence of AlCl3 and oxidant catalysts on hydrogen production from the supercritical water gasification of dewatered sewage sludge and model compounds

Hydrogen has attracted significant attention as a clean energy source. Supercritical water gasification (SCWG) technology can produce hydrogen-rich gas while also disposing of sludge. The hydrogen yield from the SCWG of sludge is greatly increased when catalyzed by AlCl₃. In this paper, a combined catalyst based on AlCl₃ was proposed to further increase the hydrogen yield of SCWG of dewatered sewage sludge (DSS). Analysis of the products from catalytic gasified of DSS and its model compounds were used to propose a catalytic mechanism and reaction pathway of the catalytic SCWG of DSS. Among the combined catalysts used for the SCWG of DSS, 10 wt% AlCl₃–H₂O₂ (mass ratio 8:2) had the best hydrogen production effect, and the hydrogen yield reached 8.88 mol/kg organic matter. This was 14% higher than when catalyzed by 10 wt% AlCl₃. During catalysis with AlCl₃, Al³⁺ reacted with OH⁻ in water and precipitated as Al(OH)₃, which produced an acidic environment in the liquid product. Al(OH)₃ dehydrated to form an AlO(OH) and deposited in the solid product. A small amount of H₂O₂ promoted the steam reforming reaction of organic matter in DSS, which increased the hydrogen yield. H₂O₂ further promoted the hydrogen yield in an acidic environment. The catalytic effect of AlCl₃ was unaffected by H₂O₂. The H⁺ generated by AlCl₃ during catalysis promoted H₂O₂ to further depolymerized organic matter (such as humic substances) in DSS, so that AlCl₃–H₂O₂ catalyzed the SCWG of DSS to further increase the hydrogen yield. The order of hydrogen yield catalyzed by AlCl₃–H₂O₂ was guaiacol > humic acid > glycerol > alanine > glucose. Compared with AlCl₃, AlCl₃–H₂O₂ reduced the hydrogen yield of glucose by nearly 20% and increased the hydrogen yield of humic acid by about 17% (25.81 mol/kg feed).     

Determination of hydraulic retention time using a Piecewise linear regression analysis in the anaerobic digestion process

Hydraulic retention time (HRT) determination in the anaerobic digestion process is an important factor for reactor design. This study aims to investigate the optimal HRT determination method for beef manure and sawdust mixture in the anaerobic digestion (AD). The Piecewise linear regression (PLR) analysis method was applied to compare the HRT with MGT_P95 determined by the Modified Gompertz model analysis, cumulative methane yield (Cum.CH₄), cumulative biomass removal (Cum.BMR) and biodegraded volatile solids (PLT_BVS). Lab-scale (6 cases of lab-scale in the anaerobic digestion) experiments were performed and analyzed by Modified Gompertz model and Piecewise linear regression analysis. The parameters selected for Piecewise linear regression analysis: Cumulative methane yield (PLTCUM.CH4), cumulative biomass removal (PLTCUM.BMR), biodegradable volatile solids (PLTBVS) and time to produce 95% of methane yield potential from Modified Gompertz model (MGTP95). The HRT determined from PLTCum.CH4 varied in between 26.4~34.9 days, and which were 0.4~3.9 days, 8.3~16.0 days, and 9.4~22.2 days shorter than PLTCum.BMR, MGTP95, and PLTBVS, respectively. The daily maximum methane yield rate in the HRT from PLTCum.CH4 showing the highest daily methane yields rate which was less than 2.1%. Therefore, reactor utilization rate and organic loading rate for PLTCum. BMR, MGTP95, and PLTBVS were 94.4~99.4%, 78.0~84.4%, and 70.9~83.9%, respectively, lower than PLTCum.CH4. Conclusively, the HRT from PLTCum.CH4 is the most appropriate method to maximize the organic loading rate relative to other determination methods.     

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

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 (R_H2) and yield (Y_H2) 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 Y_H2 = 645.7 mL/g TS and R_H2 = 2.51 L H₂/L d at HRT = 3 h, respectively.