Han-Levenspiel Model Research Articles

Novel slow-release carbon source improves anodic denitrification and electricity generation efficiency in microbial fuel cells

MFC anodic denitrification is more suitable for the coexistence of organic matter and nitrate in actual sewage, but the traditional carbon source has some problems such as high cost and difficulty of dosage control in MFC. Herein, corncob and polycaprolactone (PCL) were mechanically pulverized and mixed in the system of polyvinyl alcohol and sodium alginate, and cross-linked to prepare slow-release carbon source fillers (CPSP), which were added to the MFC anolyte to realize the coupling of solid-phase denitrification and anodic denitrification. Results showed the start-up period of MFC experimental group (MFC-C) with CPSP was slightly longer than the control group (MFC-0), but MFC-C's maximum output voltage (648.4 mV) and power density (2738 mW/m3) could be increased by 5% and 15% higher than that of MFC-0 (P < 0.05). The degradation process of MFC substrate in unit cycle was mainly divided into nitrogen removal stage (0–8 h) and electricity generation stage (8–48 h). The NO3−-N and COD degradation and power generation kinetic processes of MFC conformed to the Han-Levenspiel model. Kinetics experiments showed CPSP can improve the affinity and tolerance of MFC to NO3−-N, also it can alleviate the pressure of electron competition in anolyte and improve coulombic efficiency. In addition, microbial communities were significantly changed under the effect of CPSP (P < 0.001). Meanwhile, CPSP can promote the synthesis of denitrification functional genes. This study provides a new strategy to improve the performance of MFC by the addition of novel denitrification carbon source.

Inhibitory Effect of Copper on the Growth Rate of Serratia marcescens strain DRY6 on SDS

The anionic surfactant known as sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS) is found in a wide variety of products designed for cleaning and personal hygiene. Because of the combination of its hydrocarbon tail and its polar "headgroup," the molecule possesses the amphiphilic qualities that make it suitable for use as a detergent. Due to this it is a major pollutant in aquatic bodies. One of the most researched types of cleanup is biodegradation by microorganisms, particularly bacteria. Copper has a profound effect in inhibiting the degradation of SDS by the bacteria Serratia marcescens strain DRY6. Under different copper concentrations, the SDS-degrading bacteria grew in a sigmoidal manner with lag times of 7 to 10 hours. Overall growth was decreased when the concentration of copper was raised, with 1.0 g/L virtually completely stopping bacterial growth. Rates of expansion at various copper concentrations were calculated using a modified Gompertz model. Following the modification of the Gompertz model, the growth rates were modeled using the modified Han-Levenspiel, Wang, Liu, modified Andrews, and the Amor models. Only three of the five models (Wang, modified Han-Levenspiel, and the Liu models) were able to match the curve; the modified Andrews and Amor models did not. As for model fit, the Wang and modified Han-Levenspiel models perform admirably, but the Liu model performs poorly. The Wang model performed best statistically, with the lowest RMSE and AICc values, the greatest adjusted correlation coefficient (adR2), and AF and BF values closest to unity. The Wang model yielded estimates of 0.216 (95% confidence interval: 0.193 to 0.239), 1.05 (95% confidence interval: 0.938 to 1.167), and 0.389 (95% confidence interval: 0.148 to 0.636) for the critical heavy metal ion concentration (g/l), maximum growth rate (g/l h), and empirical constant.

Biodegradation and power production kinetics in microbial fuel cell during rice mill wastewater treatment

The influence of the initial substrate concentration of rice mill wastewater on substrate degradation rate and power production in a dual-chambered MFC was explored over a wide range of chemical oxygen demand (COD: 500–6000 mg/L) and lignin (77.5–930 mg/L) levels. Within a limited concentration range, increasing COD concentration increased degradation rates and electricity generation, but both processes were hindered at high substrate concentrations. A maximum power density of 4.3 W/m3 was attained in a MFC operated with an initial COD concentration of 2480 ± 17 mg/L which can be attributed to the low ohmic resistance (23.8 Ω) due to better solution conductivity. Different kinetic models were used to examine inhibition kinetics from an electrical perspective. The relationship between power density and COD concentration was best described by Han–Levenspiel model. The maximum power density, half-saturation constant, and critical inhibitory concentration were predicted to be 4.56 W/m3, 799.6 mg/L, and 7627 mg/L, respectively. A maximum lignin degradation rate of 0.063 ± 0.007 kg/m3∙d was achieved at a lignin concentration of 387.5 ± 2.8 mg/L which accounts for 83.17 ± 0.26 % removal efficiency, suggesting the possibility of lignin degradation in MFC even at higher concentrations. The detection of low molecular weight degradation by-products of lignin in the effluent sample further confirmed the ability of exoelectrogens to degrade lignin.

Optimized cell growth and poly(3-hydroxybutyrate) synthesis from saponified spent coffee grounds oil

Spent coffee ground (SCG) oil is an ideal substrate for the biosynthesis of polyhydroxyalkanoates (PHAs) by Cupriavidus necator. The immiscibility of lipids with water limits their bioavailability, but this can be resolved by saponifying the oil with potassium hydroxide to form water-soluble fatty acid potassium salts and glycerol. Total saponification was achieved with 0.5 mol/L of KOH at 50 °C for 90 min. The relationship between the initial carbon substrate concentration (C0) and the specific growth rate (µ) of C. necator DSM 545 was evaluated in shake flask cultivations; crude and saponified SCG oils were supplied at matching initial carbon concentrations (C0 = 2.9–23.0 g/L). The Han-Levenspiel model provided the closest fit to the experimental data and accurately described complete growth inhibition at 32.9 g/L (C0 = 19.1 g/L) saponified SCG oil. Peak µ-values of 0.139 h−1 and 0.145 h−1 were obtained with 11.99 g/L crude and 17.40 g/L saponified SCG oil, respectively. Further improvement to biomass production was achieved by mixing the crude and saponified substrates together in a carbon ratio of 75:25% (w/w), respectively. In bioreactors, C. necator initially grew faster on the mixed substrates (µ = 0.35 h−1) than on the crude SCG oil (µ = 0.23 h−1). After harvesting, cells grown on crude SCG oil obtained a total biomass concentration of 7.8 g/L and contained 77.8% (w/w) PHA, whereas cells grown on the mixed substrates produced 8.5 g/L of total biomass and accumulated 84.4% (w/w) of PHA.Key points• The bioavailability of plant oil substrates can be improved via saponification.• Cell growth and inhibition were accurately described by the Han-Levenpsiel model.• Mixing crude and saponified oils enable variation of free fatty acid content.

Effect of Nitrate Concentration on the Coupling Process of Electricity Generation and Nitrate Removal in Biocathode Microbial Fuel Cells

The effect of nitrate (NO3−-N) concentration in catholyte on electricity generation and pollutant removal was investigated in biocathode microbial fuel cells (BMFCs). Results indicated that the NO3−-N removal rate and output voltage could be promoted with increasing NO3−-N concentrations, but both of them would be inhibited when the NO3−-N concentrations was more than 100.0 mg/L. The maximum NO3−-N removal rate and the maximum output voltage was 0.833 mg/(L/h) and 406 mV, respectively, when the initial NO3−-N concentration was 100.0 mg/L. Based on the Han–Levenspiel model, the kinetics of NO3−-N removal and output voltage were established in which the maximum NO3−-N removal rate was 1.06 mg/(L/h), and the maximum output voltage was 478 mV. Moreover, NO3−-N concentrations had a great impact on the coupling of electricity generation and NO3−-N removal, which indicated that electricity generation was closely related to the NO3−-N removal. In addition, it was found that the community structure in the cathode biofilm by high-throughput sequencing changed at different NO3−-N biofilm as measured by the main functional microbial genus responsible for removing NO3−-N, which remained as denitrifying Proteobacteria.

Biodegradation potential of sodium dodecyl sulphate (SDS) by mixed cells in domestic and non-domestic actual wastewaters: Experimental and kinetic studies

This study aimed to assess and compare the potential of sodium dodecyl sulfate (SDS) biodegradation in four types of real-field effluents including domestic wastewater (DWW), laundry wastewater (LWW), carwash garage wastewater (CWW), and wastewater from household detergent industry wastewater (HWW) using non adapted mixed cells having Pseudomonas medocina and Bacillus as the dominant types of bacterial cells. Examining and comparing various types of actual wastewaters supported the originality of this study by considering different levels of SDS concentrations, meanwhile, taking into account implicitly the effect of different species associated with SDS based on the origin of wastewater. The effect of inoculum size including 1%, 3%, 5%, 7%, and 10% (v/v) as well as the SDS initial concentrations of10, 20, 50, 100, 300, 500, and 1000 mg/L were explored. The results demonstrated that the removal efficiency of SDS in the DWW, LWW, CWW, and HWW were 99.63%, 92.31%, 98.78%, and 85.77%, respectively after 48 h. The outcomes of this study revealed the potential and significance of SDS removal in actual effluents by aerobic biodegradation regardless of its concentration. Haldane kinetics model fitted the experimental data very well compared to Monod and Han-Levenspiel models with determination coefficient (R2), sum square error (SSE), and P-value of 0.96, 1.65 × 10−14, and 1.57×10−5, respectively indicating the inhibitory action of SDS at high concentrations.

Surfactants-induced photo-fermentative biohydrogen production from corncob

Surfactants could improve the mass transfer capacity by avoiding agglomeration and sedimentation of substrate. This study evaluated the effects of diverse Tween series surfactants on hydrogen production performance of photo-fermentative biohydrogen production (PFHP) process. Tween 80 was found to be the most suitable surfactant. The maximum cumulative hydrogen yield (CHY) reached 49.38 ± 1.90 mL/g TS under 0.20% (v/v) Tween 80 addition. Highest energy recovery efficiency of 3.41 ± 0.13% and substrate conversion efficiency of 94.93 ± 0.44% were obtained, which was 50.37% and 1.7% higher than that of the control group, respectively. The effect of diverse Tween series surfactants on photosynthetic bacteria (PSB) was further studied. Results showed that Tween 80 significantly improved the growth and activity of PSB. The modified Han-Levenspiel model was adopted to analyze the effects of Tween 80 addition on PFHP. Results indicated that the reaction system was non-competitive inhibition, the predicted critical concentration of Tween 80 was 0.42% (v/v). This study provides a way to increase the CHY of corncob by the PFHP process.

Enhancing photo-fermentative biohydrogen production using different zinc salt additives

The kinetic properties of the hydrogen yield of photosynthetic bacteria were investigated using Han–Levenspiel and modified Gompertz models to determine the effects of different zinc salts on the growth and hydrogen production of the photosynthetic bacterium HAU-M1. Inorganic zinc salts (zinc standard solution and zinc sulfate) inhibited bacterial growth by 1–4-fold higher than organic zinc salts (zinc lactate and zinc gluconate). Among these four zinc salts, 5 mg/L zinc lactate displayed the weakest inhibition performance. This compound increased cumulative hydrogen production by approximately 57.81% (80.44 mL/g) and maximum hydrogen production rate by 58.27% (3.43 mL/[g·h]). The Han–Levenspiel model with parameters m > n > 0 indicated that the addition of zinc salts influenced the hydrogen production process of the bacterium in a noncompetitive manner. Compared with the inorganic zinc, the organic zinc salts were more suitable as exogenous zinc supplements to promote bacterial growth and its hydrogen production.

Role of L-cysteine and iron oxide nanoparticle in affecting hydrogen yield potential and electronic distribution in biohydrogen production from dark fermentation effluents by photo-fermentation

Dark fermentation effluent is a potential substrate for hydrogen production by photosynthetic bacteria(PSB). Influences of adding L-cysteine and Fe3O4 nanoparticles (NPs) on hydrogen production performance and electronic distribution from dark fermentation effluents (DFEs) during photo fermentation hydrogen production(PFHP) process were experimentally studied, as well as the critical kinetic analysis. L-cysteine addition can promote flocculability and cell growth rates of PSB HAU-M1 while addition of 300 mg/L L-cysteine and 100 mg/L Fe3O4 NPs can peak H2 yield from the DFEs, resulting in 29.94% and 29.23% substrate electrons were diverted to H2, respectively. Controlling the adding time interval of L-cysteine and Fe3O4 NPs can improve the activity of nitrogenase without weakening flocculation and increase the hydrogen production, the maximum hydrogen yield of 234.55 ± 7.5 mL was obtained at 12 h interval time, 35.94% substrate electrons diverted towards bio-hydrogen generation, and the corresponding nitrogenase activity increased by 2.12 times as comparing to the control. The modified Gompertz and Han-Levenspiel models were employed to model the effect of the L-cysteine and Fe3O4 NPs on hydrogen production, the predicted critical L-cysteine and Fe3O4 NPs concentrations were 4630.87 and 1969.18 mg/L, respectively.

The short- and long-term inhibitory effects of Fe (II) on anaerobic ammonium oxidizing (anammox) process.

The application of the anammox process has great potential in treating nitrogen-rich wastewater. The presence of Fe (II) is expected to affect the growth and activity of anammox bacteria. Short-term (acute) and long-term effects (chronic) of Fe (II) on anammox activity were investigated. In the short-term study, results demonstrated that the optimum concentration of Fe (II) that could be added to anammox is 0.08 mM, at which specific anammox activity (SAA) improved by 60% compared to the control assay, 0.00 mM. The inhibition concentration, IC50, of Fe (II) was found to be 0.192 mM. Kinetics of anammox specific growth rate were estimated based on results of the batch test and evaluated with Han-Levenspiel's substrate inhibition kinetics model. The optimum concentration and IC50 of Fe (II) predicted by the Han-Levenspiel model was similar to the batch test, with values of 0.07 mM and 0.20 mM, respectively. The long-term effect of Fe (II) on the performance of a sequencing batch reactor (SBR) was evaluated. Results showed that an appropriate Fe (II) addition enhanced anammox activity, achieving 85% NH4 +-N and 96% NO2 --N removal efficiency when 0.08 mM of Fe (II) was added. Quantitative polymerase chain reaction (qPCR) was adopted to detect and identify the anammox bacteria.

Operating control for enrichment of hydrogen-producing bacteria from anaerobic sludge and kinetic analysis for vinasse inhibition

This study was aimed to evaluate bio-hydrogen production from sugarcane vinasse by the mixed culture enriched through controlling operational parameters in an Anaerobic Sequencing Batch Reactor (AnSBR), as well as determining the effect of the sugarcane vinasse concentration on hydrogen production and the critical kinetic analysis. The Volumetric Hydrogen Production Rate (VHPR) of 28.1 mL H2/L h at the substrate concentration of 10 g COD/L was obtained in biomass enriching step. In batch tests, the increase in substrate concentration ranging from 1.70 to 11.60 g COD/L caused an increase in Hydrogen Yield (HY); however, it had a negative effect on HY at the substrate concentrations of higher than 11.60 g COD/L. The maximum HY in terms of initial Chemical Oxygen Demand (CODi) of 58.41 mL H2/g CODi was obtained at the substrate concentration of 11.60 g COD/L. Additionally, Andrew and Han-Levenspiel models were employed to model the hydrogen production rate (R) in case of different chemical oxygen demand (COD) concentrations of vinasse. According to the comparison made between the correlation coefficient values of the fittings using the aforementioned models, the Han-Levenspiel model could be considered as a better model to describe the substrate inhibition effect. The carbohydrate removal efficiency was superior to 90% at substrate concentrations less than 16.80 g COD/L.

Understanding the NaCl-dependent behavior of hydrogen production of a marine bacterium, Vibrio tritonius.

Biohydrogen is one of the most suitable clean energy sources for sustaining a fossil fuel independent society. The use of both land and ocean bioresources as feedstocks show great potential in maximizing biohydrogen production, but sodium ion is one of the main obstacles in efficient bacterial biohydrogen production. Vibrio tritonius strain AM2 can perform efficient hydrogen production with a molar yield of 1.7 mol H2/mol mannitol, which corresponds to 85% theoretical molar yield of H2 production, under saline conditions. With a view to maximizing the hydrogen production using marine biomass, it is important to accumulate knowledge on the effects of salts on the hydrogen production kinetics. Here, we show the kinetics in batch hydrogen production of V. tritonius strain AM2 to investigate the response to various NaCl concentrations. The modified Han–Levenspiel model reveals that salt inhibition in hydrogen production using V. tritonius starts precisely at the point where 10.2 g/L of NaCl is added, and is critically inhibited at 46 g/L. NaCl concentration greatly affects the substrate consumption which in turn affects both growth and hydrogen production. The NaCl-dependent behavior of fermentative hydrogen production of V. tritonius compared to that of Escherichia coli JCM 1649 reveals the marine-adapted fermentative hydrogen production system in V. tritonius. V. tritonius AM2 is capable of producing hydrogen from seaweed carbohydrate under a wide range of NaCl concentrations (5 to 46 g/L). The optimal salt concentration producing the highest levels of hydrogen, optimal substrate consumption and highest molar hydrogen yield is at 10 g/L NaCl (1.0% (w/v)).

Sustainable biohydrogen production by dark fermentation using carbon monoxide as the sole carbon and energy source

Abstract This study evaluated the kinetics of biomass growth, biohydrogen production and substrate utilization using carbon monoxide as the sole carbon and energy source. Experiments were conducted at different initial CO concentration in the range 1.8–5.12 mmol/L over a period of 144 h in order to assess the effect of CO concentration on biomass growth, substrate utilization and H2 production. Complete utilization (100%) of CO was achieved up to an initial concentration of 3.8 mmol/L and it gradually decreased to 84.5% for 4.4 mmol/L and 83.7% for 5.12 mmol/L. The experimental results of CO utilization were fitted to substrate utilization kinetic models reported in the literature, and it followed a modified Gompertz model. A maximum yield of H2 on CO was found to be 70.8% and a maximum H2 production of 29.9 mmol/L was obtained for an initial CO concentration of 5.12 mmol/L. The experimental results on biohydrogen production matched well with the values predicted using the modified Gompertz model. Furthermore, the experimental data on specific growth rate of the ananerobic biomass at different H2 concentration was fitted to different product inhibition models and the best fit was obtained with Aiba model. This study showed product inhibition on both specific growth rate of biomass and H2 production due to H2 accumulation in the gas phase. A very good correlation between the experimental specific growth rate and the Han-Levenspiel model predicted values were obtained with a high determination coefficient (R2) value of more than 0.96.

Modelling the Effect of Heavy Metals on the Growth Rate of Enterobacter sp. Strain Neni-13 on SDS

The SDS-degrading bacterium Enterobacter sp. strain Neni-13 was strongly inhibited by mercury. Growth of the SDS-degrading bacterium at various concentrations of mercury shows a sigmoidal pattern with lag periods ranging from 7 to 10 h. As the concentration of mercury was increased, the overall growth was inhibited with 1.0 g/L causing an almost cessation of bacterial growth. The growth rates obtained from the modified Gompertz model was then modelled according to the modified Han-Levenspiel, Wang, Liu, modified Andrews and the Amor models. Out of the five models, only Wang, modified Han-Levenspiel and the Liu models were able to fit the curve, whilst the modified Andrews and Amor models were unable to fit the curves. Both the Wang and modified Han-Levenspiel models show acceptable fitting while the Liu model shows poor fitting. Results of the statistical analysis showed that the Wang model was the best model based on the lowest values for RMSE and AICc, highest adjusted correlation coefficient (adR2) and values of AF and BF closest to unity. The parameters obtained from the Wang model, which are Ccrit, max and m which represent critical heavy metal ion concentration (g/l), maximum growth rate (g/l h) and empirical constant values were 0.216 (95%, confidence interval f 0.193 to 0.239), 1.05 (95%, confidence interval of 0.938 to 1.167) and 0.389 (95%, confidence interval of 0.148 to 0.636) respectively.

Modelling the Effect of Copper on the Mo-reduction Rate of the Antarctic Bacterium Pseudomonas sp. strain DRY1

Molybdenum reduction by the Antarctic bacterium Pseudomonas sp. strain DRY1 is strongly inhibited by copper. Mo reduction by this bacterium at 10 mM sodium molybdate shows a sigmoidal pattern with lag periods ranging from 7 to 10 h at various concentrations of copper. As the concentration of copper was increased, the overall Mo reduction rate was inhibited with 1.2 mg/L causing the cessation of Mo reduction rate. The modified Gompertz model was utilized to obtain Mo reduction rates at different concentrations of copper. The Mo reduction rates obtained from the modified Gompertz model was then modelled according to the modified Han-Levenspiel, Wang, Liu, modified Andrews and the Amor models. Out of the five models, only Wang, modified Han-Levenspiel and the Liu models were able to fit the curve, whilst the modified Andrews and Amor models were unable to fit the curves. Both the Wang and modified Han-Levenspiel models show acceptable fitting while the Liu model shows poor fitting. Results of the statistical analysis showed that the modified Han-Levenspiel model was the best model based on the lowest values for RMSE and AICc, highest adjusted correlation coefficient (adR2) and values of AF and BF closest to unity. The parameters obtained from the modified Han Levenspiel model, which were Ccrit, max and m which represent critical heavy metal ion concentration (mg/l), maximum reduction rate (nmole Mo blue/h) and empirical constant values were 0.225 (95%, confidence interval from 0.198 to 0.251), 1.200 (95%, confidence interval from 1.180 to 1.220) and 0.443 (95%, confidence interval from 0.261 to 0.626). The modified Han-Levenspiel accurately predicted the critical copper concentration that completely inhibited molybdenum reduction rate in this bacterium.

Cu(II) removal by Nostoc muscorum and its effect on biomass growth and nitrate uptake: A photobioreactor study

This study investigated the Cu(II) removal by Nostoc muscorum, a cyanobacterium isolated from a toxic metal polluted site in Meghalaya, using a batch photobioreactor with an aim to elucidate the removal mechanism and its effect on nitrate uptake by the cyanobacterium. Experiments were carried out using a batch photobioreactor by varying the initial Cu(II) concentration in the range of 5–30 mg L−1. Results obtained in this study showed that a maximum of 5.628 ± 0.05 g L−1 of biomass concentration could be obtained in the absence of Cu(II), whereas this value of biomass reduces to 4.3 ± 0.0057 g L−1 in presence of 5 mg L−1 of initial Cu(II) concentration, which further reduces to 2.51 ± 0.01 g L−1 for an initial Cu(II) concentration of 30 mg L−1. Besides, an increase in the initial Cu(II) concentration delayed the uptake of nitrate by the cyanobacterium. However, complete removal of Cu(II) was observed for all the four different initial Cu(II) concentration. The estimated value of nitrate uptake rate in the absence of Cu(II) was found to be 0.115 mg L−1 d−1, which was reduced to 0.029 mg L−1 d−1 due to 30 mg L−1 initial Cu(II) concentration in the medium. The experimental nitrate uptake rate values were fitted to three unstructured kinetic models reported in the literature for estimating the biokinetic constants. Among the three models, Han-levenspiel and Andrew models fitted the experimental data closely with a determination coefficient (R2) value of 0.942 and 0.921, respectively. The critical Cu(II) concentration obtained as per the Han-levenspiel model was found to be 0.0325 g L−1.

BIODEGRADATION KINETICS OF MIXED MICROBIAL CULTURE UTILIZING 1,1-DCE AS THE SOLE CARBON SOURCE

The mixed microbial culture, isolated from the aerobic sludge was used to study biodegradation of 1,1-DCE as the sole carbon source in batch flasks. 1,1-DCE initial concentration in the medium was varied from 100 g/L to 1000 g/L. The maximum removal rate of 1,1-DCE was 89.2% obtained at 400 g/L 1,1-DCE concentration in the medium. The biodegradation kinetics of 1,1-DCE was found to follow three-half-order model at all initial 1,1-DCE concentrations with regression values greater than 0.95. The maximum specific degradation rate of 1.1 10-2 ( g DCE/(mg.VSS.h)) was observed at 400 g/L 1,1-DCE concentration in the medium. In the range of 1,1-DCE concentrations used in the experiment, the specific degradation rates were observed to follow substrate inhibition kinetics. The specific degradation rate was fitted to kinetic model of Haldane, Luong, Edward and Han-levenspiel that are used to explain substrate inhibition on degradation of 1,1-DCE. Out of these models Luong and Han-Levenspiel model fitted the experimental data better with lower root mean square error values. In addition, the degradation pathway of 1,1-DCE by the mixed microbial culture was discussed in this study. Key words: 1,1-DCE, biodegradation kinetics, mixed microbial culture, specific substrate degradation rate, substrate inhibition

Characteristics and kinetics of biohydrogen production with Ni2+ using hydrogen-producing bacteria

The characteristics and kinetics of biohydrogen production with Ni2+ using hydrogen-producing bacteria (HPB) obtained from cow dung were investigated in batch tests. The results indicated that cumulative biohydrogen production and hydrogen yield were enhanced with an increase of 0.3–6 mg/L in the Ni2+ concentration at 35 °C and an initial pH of 6.0. The maximum cumulative biohydrogen production was 442.52 mL, and the maximum hydrogen yield was 2.05 mol H2/mol sucrose at 0.6 mg/L Ni2+. Compared with the control, the cumulative biohydrogen production with 0.6 mg/L Ni2+ was doubled. The major soluble metabolites produced in this study were ethanol, acetate, and butyrate. In addition, the final pH was lower than the initial pH after the production of biohydrogen, and the substrate degradation efficiency was slightly enhanced with an increase in the Ni2+ concentration from 0.3 to 9 mg/L. Modified Gompertz and Han–Levenspiel models were used to describe the effects of Ni2+ on biohydrogen production, and the model predicted data fit the experimental results well. The mathematical constants n and m of these models were 103.59 and 2.69, respectively, suggesting that the reaction was uninhibited. The predicted critical Ni2+ concentration was 15.58 mg/L, which completely suppressed biohydrogen production. This study contributes to the improvement of organic waste utilisation by HPB.

Effect of Sulfate Concentration on Biohydrogen Production by Enriched Anaerobic Sludge

The effect of SO2-4 concentration ranging from 0 to 10 g/L on fermentative hydrogen production by enriched anaerobic sludge was investigated using glucose as substrate at 35°C and initial pH 7.0. The experimental results showed that the hydrogen yield increased with increasing SO2-4 concentration from 0 to 0.05 g/L. The maximum maximum hydrogen yield of 272.2 mL/g glucose were obtained at the SO2-4 concentration of 0.05 g/L. The average hydrogen production rate increased with increasing SO2-4 concentration from 0 to 0.1 g/L and the maximum average hydrogen production rate of 8.4 mL/h was obtained at the SO2-4 concentration of 0.1 g/L. The Han-Levenspiel model could describe the effect of SO2-4 concentration on average hydrogen production rate successfully.

Kinetics of substrate degradation and electricity generation in anodic denitrification microbial fuel cell (AD-MFC)

Effect of substrate concentration on substrate degradation and electricity generation in anodic denitrification microbial fuel cell (AD-MFC) was investigated over a broad range of substrate concentrations. Substrate degradation rates and power generation could be promoted with increasing substrate concentration in a certain range, but both of them would be inhibited at high substrate concentrations. Maximum denitrification rate of 1.26 ± 0.01 kg NO(-)-N/m(3)d and maximum output voltage of 1016.75 ± 4.74 mV could be achieved when initial NO3(-)-N concentration was 1999.95 ± 2.86 mg/L. Based on Han-Levenspiel model, kinetics of substrate degradation and power generation in the AD-MFC were established. According to the kinetic model, the half-saturation coefficient and the critical inhibitory concentration for nitrate were more than 200 and 4300 mg/L, respectively. The results demonstrated that AD-MFC was capable of treating nitrate-containing wastewater and generating electricity simultaneously, and tolerant to high strength nitrate-containing wastewater.