Feasibility of biohydrogen production by anaerobic co-digestion of food waste and sewage sludge

Anaerobic co-digestion of food waste and sewage sludge for hydrogen production was performed in serum bottles under various volatile solids (VS) concentrations (0.5–5.0%) and mixing ratios of two substrates (0:100–100:0, VS basis). Through response surface methodology, empirical equations for hydrogen evolution were obtained. The specific hydrogen production potential of food waste was higher than that of sewage sludge. However, hydrogen production potential increased as sewage sludge composition increased up to 13–19% at all the VS concentrations. The maximum specific hydrogen production potential of 122.9 ml/g carbohydrate-COD was found at the waste composition of 87:13 (food waste:sewage sludge) and the VS concentration of 3.0%. The relationship between carbohydrate concentration, protein concentration, and hydrogen production potential indicated that enriched protein by adding sewage sludge might enhance hydrogen production potential. The maximum specific hydrogen production rate was 111.2 ml H₂/g VSS/h. Food waste and sewage sludge were, therefore, considered as a suitable main substrate and a useful auxiliary substrate, respectively, for hydrogen production. The metabolic results indicated that the fermentation of organic matters was successfully achieved and the characteristics of the heat-treated seed sludge were similar to those of anaerobic spore-forming bacteria, Clostridium sp.     

Anaerobic co-digestion of sewage sludge,wine vinasse and poultry manure for bio-hydrogen production

The influence of the addition of poultry manure on the thermophilic acid co-fermentation of sewage sludge and wine vinasse was studied. For this, discontinuous tests were carried out to determine the potential for hydrogen production (BHP tests) of 50:50 mixtures of sludge and wine vinasse with different amounts of poultry manure (10  g/L, 20  g/L and 30  g/L). The hydrogen production performance was determined under the tested conditions. The experimental results revealed performance values of TCOD and SCOD, TS and VS, similar in all tests, with removal efficiencies lower than 25%. Likewise, an increase in the production of volatile fatty acids was observed. Regarding the yield, the best results were obtained for the mixture with 10 g/L of poultry manure (with a C/N ratio: 27). Thus, the H₂ production and the yield expressed as mL H₂/gVS_added was 18.20% and 27.57% higher in the test with 10  g/L of poultry manure compared to the test with 20  g/L. Furthermore, from 20 g/L of poultry manure, the mixtures showed poorer purification behavior and performance.     

基于响应面法对秸秆纤维素乙醇生产工艺参数的优化

文章在对里氏木霉T12菌株产纤维素酶的培养条件进行单因素优化的基础上,以滤纸酶活力(FPA)为响应值,通过Plackett-Burman设计法筛选出对产酶影响最显著的3个因素,依次为麦麸>温度>氯化钙。响应面优化结果为当麦麸、温度、氯化钙分别为6.27 g/L,31℃,0.709 g/L时,纤维素酶理论最大FPA酶活为62281.3 U/m L。在优化后的培养条件下纤维素酶粗酶液的实际FPA酶活为60 126.5±16.0 U/m L。将纤维素酶粗酶液以10%添加量加入秸秆一步转化乙醇的5 L发酵罐中,经过144 h的发酵,乙醇产量(v/v)可达到7.05%±0.18%。     

Process optimization for PHA production by activated sludge using response surface methodology

A five-level-three factor central composite rotary design was employed to find out the interactive effects of three variables, i.e. static magnetic field intensity, concentration of NH₃–N and initial pH on polyhydroxyalkanoates (PHA) production by activated sludge under the aerobic dynamic feeding (ADF) technique. Response surface methodology (RSM) was utilized for process optimization and a second-order polynomial equation was obtained by multiple regression analysis. A yield of 49.5% of dry cell weight (dcw) was achieved at optimized conditions, i.e. magnetic field 11 mT, NH₃–N 4.8 mg l^?1 (C:N = 60:1)and initial pH 9.0.     

响应面法优化沼液预处理玉米秸秆条件的研究

为了确定沼液预处理玉米秸秆最优反应条件,选取沼液处理前后纤维素相对结晶度为评价指标,根据Box-Behnken试验设计原理,建立了纤维素相对结晶度与沼液用量、温度和时间之间的数学模型,并采用扫描电镜、X射线衍射法对处理前后玉米秸秆的结构特性进行分析。试验结果表明:回归方程决定系数R2为0.989 5;3个因素影响主次顺序为时间沼液用量温度,三者存在显著的交互作用;最佳处理条件为沼液用量48 m L,温度27℃,时间13 d,该条件下纤维素相对结晶度预测值为22.50%,实测值为21.88%,即沼液处理后玉米秸秆纤维素结晶度由60.82%降至47.51%,预测值与实测值相对误差为3%。沼液预处理后玉米秸秆表层被破坏,孔洞增加,有利于纤维素酶水解作用的进行。     

Optimization of process parameters for preparation of powdered activated coke to achieve maximum SO2 adsorption using response surface methodology

Powdered activated coke (PAC) is a good adsorbent of SO₂, but its adsorption capacity is affected by many factors in the preparation process. To prepare the PAC with a high SO₂ adsorption capacity using JJ-coal under flue gas atmosphere, six parameters (oxygen-coal equivalent ratio, reaction temperature, reaction time, O₂ concentration, CO₂ concentration, and H₂O concentration) were screened and optimized using the response surface methodology (RSM). The results of factor screening experiment show that reaction temperature, O₂ concentration, and H₂O (g) concentration are the significant factors. Then, a quadratic polynomial regression model between the significant factors and SO₂ adsorption capacity was established using the central composite design (CCD). The model optimization results indicate that when reaction temperature is 904.74°C, O₂ concentration is 4.67%, H₂O concentration is 27.98%, the PAC (PAC-OP) prepared had a higher SO₂ adsorption capacity of 68.15 mg/g while its SO₂ adsorption capacity from a validation experiment is 68.82 mg/g, and the error with the optimal value is 0.98%. Compared to two typical commercial activated cokes (ACs), PAC-OP has relatively more developed pore structures, and its S_BET and V_tot are 349 m²/g and 0.1475 cm³/g, significantly higher than the 186 m²/g and 0.1041 cm³/g of AC1, and the 132 m²/g and 0.0768 cm³/g of AC2. Besides, it also has abundant oxygen-containing functional groups, its surface O content being 12.09%, higher than the 10.42% of AC1 and 10.49% of AC2. Inevitably, the SO₂ adsorption capacity of PAC-OP is also significantly higher than that of both AC1 and AC2, which is 68.82 mg/g versus 32.53 mg/g and 24.79 mg/g, respectively.     

Green biohydrogen production in a Co-digestion process from mixture of high carbohydrate food waste and cattle/chicken manure digestate

This study was investigated biohydrogen production on the effects of different ratio of food waste to seed digestate and pH value from co-digestion process in anaerobic reactor. The seed digestate was mixture of cattle manure 45%, corn silage 25%, chicken manure 15%, and olive pomace 15% which was collected from the biogas plant in central Italy. It was found that the peaks of total biogas and the biohydrogen productions were 1355 ± 26 and 436 ± 10 mL whereas the biohydrogen yield was 50.4 mL/g-VS (45.8 mL/g-COD) with 43.33% COD removal rate, the bacteria to substrate volatile solids (VS) ratio was 2:1 where seed digestate to food waste was 6:4 under pH 6.5. As a consequence, food waste with a high COD concentration can be adapted C/N ratio by the cattle manure and chicken manure in the seed digestate which resulted in a high biohydrogen production. The food waste co-digestion system mixed with biogas plant digestate is one of approach to increase total biogas production.     

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.     

Determining optimum conditions for hydrogen production from glucose by an anaerobic culture using response surface methodology (RSM)

Hydrogen fermentation is a very complex process and is greatly influenced by many factors. Previous studies have demonstrated that temperature, pH and substrate are important factors controlling biological H₂ production. Response surface methodology with central composite design was used in this study to optimize H₂ production from glucose by an anaerobic culture. The individual and interactive effects of pH, temperature and glucose concentration on H₂ production were also evaluated. The optimum conditions for maximum H₂ yield of 1.75 mol-H₂ mol-glucose⁻¹ were found as temperature 38.8 °C, pH 5.7 and glucose concentration 9.7 g L⁻¹. The linear effects of temperature and pH as well as their quadratic effects on H₂ yield were significant, while the interactive effects of three parameters were minor.     

Geometric parameters and response surface methodology on cooling performance of vortex tubes

This research has investigated the effect of certain geometric parameters on cooling performance of three vortex tubes. The influencing parameters include three length/diameter ratios L/D?=?10, 25, 40, three nozzle cases and each case with number n?=?2, 4, 6 nozzles, three cold orifice/diameter ratios β?=?0.389, 0.5, 0.611 and three inlet pressures P_i?=?2, 2.5 and 3?bar. The experiments are conducted based on three factors, two-level and central composite face-centred design with full factorial. The results are analysed according to the principle of response surface methodology. The goodness of fit of the regression model is inspected using the analysis of variance and F-ratio test. The values of R² and R²-adjusted are close to 100% which show a very good correlation between the observed and predicted values. The results show that the effect of number of nozzles on the energy separation depends on the L/D values.     

Optimization of biohydrogen production by Clostridium butyricum EB6 from palm oil mill effluent using response surface methodology

Clostridium butyricum EB6 successfully produced hydrogen gas from palm oil mill effluent (POME). In this study, central composite design and response surface methodology were applied to determine the optimum conditions for hydrogen production (P_c) and maximum hydrogen production rate (R_max) from POME. Experimental results showed that the pH, temperature and chemical oxygen demand (COD) of POME affected both the hydrogen production and production rate, both individually and interactively. The optimum conditions for hydrogen production (P_c) were pH 5.69, 36 °C, and 92 g COD/l; with an estimated P_c value of 306 ml H₂/g carbohydrate. The optimum conditions for maximum hydrogen production rate (R_max) were pH 6.52, 41 °C and 60 g COD/l; with an estimated R_max value of 914 ml H₂/h. An overlay study was performed to obtain an overall model optimization. The optimized conditions for the overall model were pH 6.05, 36 °C and 94 g COD/l. The hydrogen content in the biogas produced ranged from 60% to 75%.     

Feasibility of bio-hythane production by co-digesting skim latex serum (SLS) with palm oil mill effluent (POME) through two-phase anaerobic process

Hydrogenogenic batch fermentation without nutrients addition was investigated at different SLS: POME mixing ratios of 100:0, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45,50:50, and 0:100 (Volatile Solid, VS basis) at initial organic concentrations of 21 and 7 g-VS/L. Satisfactory hydrogen yield of 84.5 ± 0.7 mL H₂/g-VS_added was achieved from 7 g-VS/L batch having SLS: POME-VS mixing ratio of 55:45. Adding NaHCO₃ 3 g/L or 0.43 g-NaHCO₃/g-VS) in the two-stage anaerobic system at 7 g-VS/L could provide sufficient buffering capacity. Hydrogenogenic effluent from 7 g-VS/L batch at SLS: POME mixing ratio of 55:45 (VS basis) could further generate rather high methane yield of 311.2 ± 8.0 mL- CH₄/g-VS_added in themethanogenic stage.According to the experimental results, bio-hythane approximately 55.5 × 10⁶ m³/year with 21% (V/V) of hydrogen, equivalent to51.0 × 10⁶ l-gasoline could be produced potentially from 3.88 × 10⁶ m³ of mixed SLS and POME through the two-stage anaerobic co-digestion.     

Methanogenic activity optimization using the response surface methodology,during the anaerobic co-digestion of agriculture and industrial wastes. Microbial community diversity

The anaerobic co-digestion of manure, agriculture and industrial wastes for methane production depends on the nutritional condition to develop the microbial community. The effect of each substrate concentrations, as well as their interactive effects on specific methanogenic activity and microbial community diversity were investigated in this work. A central composite design and the response surface methodology were applied for designing the anaerobic co-digestion batch test at 35 and 55 °C. It was analyzed the anaerobic sludge by specific methanogenic activity (SMA) and using molecular techniques (terminal restriction fragment length polymorphism, TRFLP). The results showed a significant interaction among the substrates and an enhancement of the methane production and SMA response caused by the three components. Rice straw had lower influence on SMA than clay residues, due to the mineral content and the beneficial ammonia nitrogen adsorbent properties of the latter. The optimum condition for mesophilic and thermophilic anaerobic co-digestion of pig manure, rice straw and clay mixture allowed SMA values of 1.31 and 1.38 gCH₄-COD/gVSSd⁻¹, respectively. The TRFLP analysis showed the effect of rice straw and clay addition on microbial community diversity at both temperatures. The acetotrophic methanogens belonging to the order Methanosarcinales (genera Methanosarcina and Methanosaeta) dominated in mesophilic condition, whereas at thermophilic conditions dominated Methanomicrobiales and Methanobacteriales order. The optimization allowed identifying the substrate interaction effects in a concentration range with a reduced number of experiments. Besides, the model validation proved to be useful for defining optimal combination of wastes in anaerobic system.     

Optimization of fermentative hydrogen production process using genetic algorithm based on neural network and response surface methodology

A central composite design was carried out to investigate the effect of temperature, initial pH and glucose concentration on fermentative hydrogen production by mixed cultures in batch test. The modeling abilities of the response surface methodology model and neural network model, as well as the optimizing abilities of response surface methodology and the genetic algorithm based on a neural network model were compared. The results showed that the root mean square error and the standard error of prediction for the neural network model were much smaller than those for the response surface methodology model, indicting that the neural network model had a much higher modeling ability than the response surface methodology model. The maximum hydrogen yield of 289.8 mL/g glucose identified by response surface methodology was a little lower than that of 360.5 mL/g glucose identified by the genetic algorithm based on a neural network model, indicating that the genetic algorithm based on a neural network model had a much higher optimizing ability than the response surface methodology. Thus, the genetic algorithm based on a neural network model is a better optimization method than response surface methodology and is recommended to be used during the optimization of fermentative hydrogen production process.     

Modeling,optimization, and control of microbial electrolysis cells in a fed‐batch reactor for production of renewable biohydrogen gas

An integrated modeling, optimization, and control approach for the design of a microbial electrolysis cell (MEC) was studied in this paper. Initially, this study describes the improvement of the mathematical MEC model for hydrogen production from wastewater in a fed‐batch reactor. The model, which was modified from an already existing model, is based on material balance with the integration of bioelectrochemical reactions describing the steady‐state behavior of biomass growth, consumption of substrates, hydrogen production, and the effect of applied voltage on the performance of the MEC fed‐batch reactor. Another goal of this work is to implement a suitable control strategy to optimize the production of biohydrogen gas by selecting the optimal current and applied voltage to the MEC. Various simulation tests involving multiple set‐point changes, disturbance rejection, and noise effects were performed to evaluate the performance where the proposed proportional–integral–derivative control system was tuned with an adaptive gain technique and compared with the Ziegler–Nichols method. The simulation results show that optimal tuning can provide better control effect on the MEC system, where optimal H₂ gas production for the system was achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of process,operational and environmental variables on biohydrogen production using palm oil mill effluent (POME)

A batch study for biohydrogen production was conducted using raw palm oil mill effluent (POME) and POME sludge as a feed and inoculum respectively. Response Surface Methodology (RSM) was used to design the experiments. Experiments were conducted at different reaction temperatures (30–50 °C), inoculum size to substrate ratios (I:S) and reaction times (8–24 h). An optimum condition of biohydrogen production was achieved with COD removal efficiency of 21.95% with hydrogen yield of 28.47 ml H₂ g^?1 COD removed. The I:S ratio was 40:60, with reaction temperature of 50 °C at 8 h of reaction time. The study showed that a lower substrate concentration (less than 20 g L^?1) for biohydrogen production using pre-settled POME was achievable, with optimum HRT of 8 h under thermophilic condition (50 °C). This study also found that pre-settled POME is feasible to be used as a substrate for biohydrogen production under thermophilic condition.     

Spatially explicit assessment of local biomass availability for distributed biogas production via anaerobic co-digestion - Mediterranean case study

Renewable energies, especially energy from biomass, contribute to the sustainable development of the territory. Simultaneously, by using biomass to produce bioenergy, bioreproductive land is devoted to supply energy. As the bioreproductive land area on the European level is decreasing, bioenergy competes against other demands like the production of food, industrial resources or cultural goods and services, among others, thus the correct assessment of the available local potential is important for local and regional planning. Moreover, bioenergy system being a socio-ecological system requires integrated approaches for the evaluation of the factors, components and interactions of such a system, considering that agriculture presents one of the major drivers of the land use change and biodiversity loss. Therefore, this work was focused on the development of the approach for and on the assessment of biogas potentials to provide a support for decision-makers and bioenergy industry at a local scale. The approach exploits the spatial relations among territorial units (i.e., a contiguity analysis), and integrates time series of continuous and discrete data. It is based on the analytic hierarchy process (AHP) combined with GIS-based analysis, and permitted to develop a territorial information system in support for biogas planning, perform analysis of feedstock for biogas from different sources potential and produce plausible scenarios for identification of biogas suitable territorial clusters; the analysis of the tradeoffs between the use of different local sources of the feedstock for biogas production are discussed as well.     

Enzymatic characterization of acid tolerance response (ATR) during the enhanced biohydrogen production process from Taihu cyanobacteria via anaerobic digestion

Enhancement of biohydrogen production via anaerobic digestion from Taihu cyanobacteria (blue algae) after acid stress on anaerobic sludge, and the enzymatic characterization of the acid tolerance response (ATR) during the enhanced biohydrogen production process were investigated in this study. Comparing to those of the control, biohydrogen accumulation and hydrogen content increased by 1.9 and 1.7 times, when 12.5 and 7.5 g/L of acid stress on anaerobic sludge were performed respectively. Other than that, activities of hydrolytic enzymes, such as β-glucosidase, BAA-proteolytic enzyme and phosphatase were all improved during the enhanced biohydrogen process after appropriate acid stress. Significantly, activity of glutamate decarboxylase (GAD), the main microbial ATR stimulated by excessive acids, was increased consistently with the biohydrogen accumulation. Therefore, acid stress might be a practical approach to improving the biochemical traits of the anaerobic sludge. In turn, improved hydrolysis of organic substances would help the anaerobic sludge better survive excessive organic acids, and then enhance biohydrogen production from Taihu cyanobacteria.     

Optimization of furfural production from millet husk using response surface methodology

Biomass has been recognized as a viable source for energy and bio-based chemicals. This study reported furfural production from millet husk via simultaneous hydrolysis and dehydration processes. Effect of reaction variables such as temperature (120–200°C), resident time (15–45 min), and acid concentration (5–10%) was studied using central composite design. Furfural yield (71.55%) was achieved at 184°C, 39 min, and 9% acid concentration. FT-IR spectrum of the produced furfural showed absorption at 1,697 and 2,880 cm^?1 indicating a conjugated carbonyl functional group and aldehydic hydrogen. The results revealed that millet husk could be a potential substrate for furfural production.     

Optimization and microbial community analysis for production of biohydrogen from palm oil mill effluent by thermophilic fermentative process

The optimum values of hydraulic retention time (HRT) and organic loading rate (OLR) of an anaerobic sequencing batch reactor (ASBR) for biohydrogen production from palm oil mill effluent (POME) under thermophilic conditions (60 °C) were investigated in order to achieve the maximum process stability. Microbial community structure dynamics in the ASBR was studied by denaturing gradient gel electrophoresis (DGGE) aiming at improved insight into the hydrogen fermentation microorganisms. The optimum values of 2-d HRT with an OLR of 60 gCOD l⁻¹ d⁻¹ gave a maximum hydrogen yield of 0.27 l H₂ g COD⁻¹ with a volumetric hydrogen production rate of 9.1 l H₂ l⁻¹ d⁻¹ (16.9 mmol l⁻¹ h⁻¹). The hydrogen content, total carbohydrate consumption, COD (chemical oxygen demand) removal and suspended solids removal were 55 ± 3.5%, 92 ± 3%, 57 ± 2.5% and 78 ± 2%, respectively. Acetic acid and butyric acid were the major soluble end-products. The microbial community structure was strongly dependent on the HRT and OLR. DGGE profiling illustrated that Thermoanaerobacterium spp., such as Thermoanaerobacterium thermosaccharolyticum and Thermoanaerobacterium bryantii, were dominant and probably played an important role in hydrogen production under the optimum conditions. The shift in the microbial community from a dominance of T. thermosaccharolyticum to a community where also Caloramator proteoclasticus constituted a major component occurred at suboptimal HRT (1 d) and OLR (80 gCOD l⁻¹ d⁻¹) conditions. The results showed that the hydrogen production performance was closely correlated with the bacterial community structure. This is the first report of a successful ASBR operation achieving a high hydrogen production rate from real wastewater (POME).