Effect of coagulation on palm oil mill effluent and subsequent treatment of coagulated sludge by anaerobic digestion

A new effluent treatment scheme is proposed for treating palm oil mill effluent based on coagulation and anaerobic digestion of coagulated sludge. The effectiveness of anionic (N9901) and cationic (N9907) polyelectrolytes manufactured by NALCO (Malaysia) was evaluated both as coagulant and coagulant aid. The results showed that the anionic and cationic polyelectrolytes were best suited as a coagulant aid, and the cationic polyelectrolyte showed better performance than the anionic polyelectrolyte. For an influent chemical oxygen demand (COD) concentration of 59 700 mg L^?1 at an alum dosage of 1700 mg L^?1, the residual COD, suspended solid removal, sludge volume and pH were found to be 39 665 mg L^?1, 87%, 260 mL L^?1 and 6.3, respectively. For the above influent COD and alum dosage with the addition of 2 mg L^?1 of cationic polyelectrolyte as coagulant aid, the results were 30 870 mg L^?1, 90%, 240 mL L^?1 and 6.2, respectively. The sludge resulting from the coagulation process using alum as coagulant and cationic polyelectrolyte as coagulant aid was tested for its digestibility in an anaerobic digester. The quantity of biogas generated per gram of volatile solids (VS) destroyed at a loading rate of 26.7 ± 0.5 and 35.2 ± 0.4 g VS L^?1 d^?1 was found to be 0.68 and 0.72 L g^?1 VS destroyed. The anaerobic biomass when subjected to varying alum dosage in the coagulated palm oil sludge did not exhibit inhibition as the digester performance was in conformity with the regular treatment process Copyright © 2006 Society of Chemical Industry     

Pre‐treatment and utilization of raw glycerol from sunflower oil biodiesel for growth and 1,3‐propanediol production by Clostridium butyricum

BACKGROUND: The objective of the present work is to report an efficient pre‐treatment process for sunflower oil biodiesel raw glycerol (SOB‐RG) and its fermentation to 1,3‐propanediol. RESULTS: The growth inhibition percentages of Clostridium butyricum DSM 5431 on grade A (pH 4.0) and grade B (pH 5.0) phosphoric acid‐treated SOB‐RG were similar to those of pure glycerol at 20 g glycerol L^?1; i.e., 18.5 ± 0.707% to 20.5 ± 0.7% inhibition. In grade A, growth inhibition was reduced from 85.25 ± 0.35% to 32 ± 1.4% (a 53.25% reduction) at 40 g glycerol L^?1 by washing grade A raw glycerol twice with n‐hexanol (grade A‐2). The kinetic parameters for product formation and substrate consumption in anaerobic batch cultures gave almost similar values at 20 g glycerol L^?1, while at 50 g glycerol L^?1 volumetric productivity (Q_p) and specific rate of 1,3‐propanediol formation (q_p) were improved from 1.13 to 1.85 g L^?1 h^?1 and 1.60 to 2.65 g g^?1 h^?1, respectively, by employing grade A‐2 raw glycerol, while the yields were similar (0.5–0.52 g g^?1). CONCLUSION: The results are important as the pre‐treatment of SOB‐RG is necessary to develop bioprocess technologies for conversion of SOB‐RG to 1,3‐propanediol. Copyright © 2008 Society of Chemical Industry     

Modeling Kinetics of Anaerobic Co-Digestion of Poultry Litter and Wheat Straw Mixed with Municipal Wastewater in a Continuously Mixed Digester with Biological Solid Recycle Using Batch Experimental Data

The half-saturation rate coefficient and maximum rate constant in the Monod model, yield coefficient defined as the ratio of microbial mass to substrate mass, and endogenous decay coefficient are important kinetic parameters for design of anaerobic digestion. These parameters are usually determined from a continuous stable operation of anaerobic digestion, which is more difficult and complex than batch operation in laboratory scale. In this study, a novel method has been developed to determine those parameters from data of batch experiments. To verify this method, kinetics of batch anaerobic co-digestion of poultry litter and wheat straw mixed with municipal wastewater at three total solid (TS) levels (2, 4, and 8% TS) and 50% volatile solid (VS) of wheat straw (VSWS) were investigated. The results showed that the maximum specific methane volume (209?mL (initial g?VS)^?1)) was reached at 4% TS of 50% VSWS. Using the developed method, the kinetic parameters of endogenous decay coefficient, yield coefficient, maximum rate constant, and half-saturation coefficient were determined to be between 0.57?×?10^?3 and 1.2?×?10^?3?d^?1, 0.00938 and 0.0644?g volatile suspended solid (VSS) (VS)^?1, 1.394 and 13,797?d^?1, and 1.6?×?10^?8 and 99,996?g. The kinetic parameters obtained were used to simulate kinetic behaviors of a continuous mixed digester with biological solid recycle. The simulated results showed that the dilution rate was very significant for methane volume produced, VS and VSS concentrations in digestion operation. The maximum methane volume could be predicted to be 3071 and 4152?mL for 2 and 4% TS, respectively.     

Volatile fatty acid production during anaerobic mesophilic digestion of solid potato waste

The production of volatile fatty acids by anaerobic digestion of solid potato waste was investigated using a batch solid waste reactor with a working capacity of 2 dm^?3 at 37°C. Solid potato waste was packed into the digester and the organic content of the waste was released by microbial activity by circulating water over the bed, using batch loads of 500 g or 1000 g potato waste. The sequence of appearance of the volatile fatty acids was (acetic, propionic); (n‐butyric); (n‐valeric, iso‐valeric, caproic); (iso‐butyric). After 300 h digestion of potato waste on a small scale, the fermentation products were chiefly (mg g^?1 total VFAs): acetic acid (420), butyric acid (310), propionic acid (140) and caproic acid (90), with insignificant amounts of iso‐butyric acid, n‐valeric and iso‐valeric acids. When the load of potato solids was increased, the volatile fatty acid content was similar, but butyric acid constituted 110 mg g^?1 and lactic acid 400 mg g^?1 of the total volatile fatty acids. The maximum soluble chemical oxygen demand (COD) achieved under the experimental conditions used was 27 and 37 g COD dm^?3 at low and high loadings of potato solids, respectively. The total volatile fatty acids reached 19 g dm^?3 of leachate at both loads of potato solid waste. Gas production was negligible, indicating that methanogenic activity was effectively inhibited. Copyright © 2004 Society of Chemical Industry     

Ultrasonic pre‐treatment of biological sludge: consequences for disintegration,anaerobic biodegradability,and filterability

BACKGROUND: Disintegration was developed as a pretreatment process for sludge to accelerate the digestion processes. Ultrasonic treatment may be a good alternative for sludge disintegration. In this study, different specific energy inputs ranged between 0 and 15 880 kJ kg^?1 and very low ultrasonic densities ranged between 0.04 and 0.1 W mL^?1 were applied to biological sludge for disintegration purposes. The potential for improving anaerobic digestion through ultrasonic pre‐treatment and the effect of ultrasonic pre‐treatment on the filterability characteristics of sludge were also investigated. RESULTS: 9690 kJ kg^?1 TS of supplied energy and very low power density of 0.09 Wm L^?1 are efficient for floc disintegration. For 9690 kJ kg^?1 TS, 44% higher methane production was achieved than with raw sludge as a result of biochemical methane potential assay. The supernatant characteristics of the sludge were also affected by the ultrasonic pre‐treatment. For 9690 kJ kg^?1 TS, the soluble chemical oxygen demand (SCOD), dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) in the sludge supernatant increased by 340%, 860%, 716%, and 207.5%, respectively. CONCLUSION: Ultrasonic pre‐treatment is an effective method for biological sludge disintegration even at very low ultrasonic density levels. It leads to increased anaerobic biodegradability but deteriorates the filterability characteristics of biological sludge. Copyright © 2009 Society of Chemical Industry     

Anaerobic biodegradation of phenol in sulfide‐rich media

In the refinery industry, the washing processes of middle‐distillates using caustic solutions generate phenol‐ and sulfide‐containing waste streams. The spent caustic liquors generated contain phenols at concentrations higher than 60 g dm^?3(638.3 mmol dm^?3). For sulfur compounds, the average sulfide concentration was 48 g dm^?3(1500 mmol dm^?3) in these streams. The goal of this study was to evaluate the specific impact of phenol and sulfide concentrations towards the phenol‐biodegradation activity of a phenol‐acclimated anaerobic granular sludge. An inhibition model was used to calculate the phenol and sulfide inhibitory concentrations that completely stopped the phenol‐biodegradation activity (IC100). A maximum phenol‐biodegradation activity of 83 µmol g^?1 VSS h^?1 was assessed and the IC100 values were 21.8 mmol dm^?3 and 13.4 mmol dm^?3 for phenol and sulfide respectively. The limitation of the phenol biodegradation flow by phenol inhibition seemed to be related to the more important sensitivity of phenol‐degrading bacteria. The up‐flow anaerobic sludge bed reactor operating in a non‐phenol‐dependent inhibition condition did not present any sensitivity to sulfide concentrations below 9.6 mmol dm^?3. At this residual concentration, the pH and bisulfide ions' concentration might be responsible for the general collapsing of the reactor activity. Copyright © 2004 Society of Chemical Industry     

钠盐浓度对厌氧产氢颗粒污泥从蔗糖中产氢的影响

This work evaluated the effects of sodium ion concentration, ranging from 0 to 16000mg·L-1(Na ), on the conversion of sucrose to hydrogen by a high-activity anaerobic hydrogen-producing granular sludge. At the optimum sodium ion concentration [1000-2000mg·L-1(Na )] for hydrogen production at 37℃, the maximum sucrose degradation rate, the specific hydrogen production yield and the specific hydrogen production rate were 393.6-413.1mg·L-1·h-1, 28.04-28.97ml·g-1, 7.52-7.83ml·g-1·h-1, respectively. The specific production yields of propionate, butyrate and valerate decreased, with increasing sodium ion concentration, whereas the specific acetate production yield increased, meanwhile the specific production yields of ethanol and caproate were less than 55.3 and 12.6mg·g-1, respectively. The hybrid fermentation composition gradually developed from acetate, propionate and butyrate to acetate with the increase in sodium ion concentration.     

Assessment of solid retention time of a temperature phased anaerobic digestion system on performance and final sludge characteristics

BACKGROUND: This paper describes the results obtained during the thermophilic/mesophilic temperature phased anaerobic digestion (TPAD) of sewage sludge on a pilot scale. The aim of this research study was not only to optimize the anaerobic digestion process, but also to obtain a digested sludge suitable for agricultural applications according to the legal requirements. RESULTS: Four TPAD assays were carried out: 5/15, 3/15, 3/12 and 3/9 (days/days of solid retention time) with a specific methane production (expressed as LCH₄ g^?1 VS_destroyed) of 0.77, 0.83, 0.66 and 0.20, respectively. TPAD 3/15 and 3/12 reached pathogen concentrations of less than 1000 MPN g^?1 TS (faecal colifoms) and 3 MPN per 4 g TS (Salmonella spp.); therefore, these digested sludges can be considered Class A biosolids, according to the US Environmental Protection Agency. Concentrations of heavy metals rose after the anaerobic digestion of mixed sludge, but the final values were always below the limits required by legal regulations. CONCLUSION: TPAD 3/15 is the best option in terms of organic matter removal, CH₄ generation, and process stability. TPAD 3/12 obtained the best final dewaterability and pathogen reduction and in general, showed much better results than those obtained by anaerobic mesophilic control (15 days of SRT). Copyright © 2012 Society of Chemical Industry     

Batch treatment of saline wastewater by Halanaerobium lacusrosei in an anaerobic packed bed reactor

BACKGROUND: This study considers batch treatment of saline wastewater in an upflow anaerobic packed bed reactor by salt tolerant anaerobic organisms Halanaerobium lacusrosei . RESULTS: The effects of initial chemical oxygen demand (COD) concentration (COD₀ = 1880–9570 mg L^?1), salt concentration ([NaCl] = 30–100 g L^?1) and liquid upflow velocity (V_up = 1.0–8.5 m h^?1) on COD removal from salt (NaCl)‐containing synthetic wastewater were investigated. The results indicated that initial COD concentration significantly affects the effluent COD concentration and removal efficiency. COD removal was around 87% at about COD₀ = 1880 mg L^?1, and efficiency decreased to 43% on increasing COD₀ to 9570 mg L^?1 at 20 g L^?1 salt concentration. COD removal was in the range 50–60% for [NaCl] = 30–60 g L^?1 at COD₀ = 5200 ± .100 mg L^?1. However, removal efficiency dropped to 10% when salt concentration was increased to 100 g L^?1. Increasing liquid upflow velocity from V_up = 1.0 m h^?1 to 8.5 m h^?1 provided a substantial improvement in COD removal. COD concentration decreased from 4343 mg L^?1 to 321 mg L^?1 at V_up = 8.5 m h^?1, resulting in over 92% COD removal at 30 g L^?1 salt‐containing synthetic wastewater. CONCLUSION: The experimental results showed that anaerobic treatment of saline wastewater is possible and could result in efficient COD removal by the utilization of halophilic anaerobic bacteria. Copyright © 2008 Society of Chemical Industry     

Effect of Ferric Chloride on the Properties of Biological Sludge in Co-precipitation Phosphorus Removal Process

This paper studied the effect of ferric chloride on waste sludge digestion, dewatering and sedimentation under the optimized doses in co-precipitation phosphorus removal process. The experimental results showed that the concentration of mixed liquid suspended solid (MLSS) was 2436 mg稬^-1 and 2385 mg稬^-1 in co-precipitation phosphorus removal process (CPR) and biological phosphorous removal process (BPR), respectively. The sludge reduction ratio for each process was 22.6% and 24.6% in aerobic digestion, and 27.6% and 29.9% in anaerobic digestion, respectively. Due to the addition of chemical to the end of aeration tank, the sludge content of CPR was slightly higher than that of BPR, but the sludge reduction rate for both processes had no distinct difference. The sludge volume index (SVI) and sludge specific resistance of BPR were 126 ml穏^-1 and 11.7?10¹² m穔g^-1, respectively, while those of CPR were only 98 ml穏^-1 and 7.1?10¹² m穔g^-1, indicating that CPR chemical could improve sludge settling and dewatering.     

Fermentative production of L(+)‐lactic acid from starch hydrolyzate and corn steep liquor as inexpensive nutrients by batch culture of Enterococcus faecalis RKY1

BACKGROUND: Attempts were made to determine the lactic acid production efficiency of novel isolate, Enterococcus faecalis RKY1 using four different starches (corn, tapioca, potato, and wheat starch) with different concentrations (50, 75, 100, and 125 g L^?1) and corn steep liquor as an inexpensive nitrogen source. RESULTS: The yield of lactic acid from each starch was higher than 95% based on initial starch concentrations. High lactic acid concentration (129.9 g L^?1) and yield (1.04 g‐lactic acid g^?1‐starch) were achieved faster (84 h) from 125 g L^?1 of corn starch. Among the starches used, tapioca starch fermentation usually completed in a shorter incubation period. The final dry cell weight was highest (7.0 g L^?1) for the medium containing 75 g L^?1 of corn starch, which resulted in maximum volumetric productivity of lactic acid (3.6 g L^?1 h^?1). The addition of 30 g L^?1 corn steep liquor supplemented with a minimal amount of yeast extract supported both cell growth and lactic acid fermentation. CONCLUSION: Enterococcus faecalis RKY1 was found to be capable of growing well on inexpensive nutrients and producing maximum lactic acid from starches and corn steep liquor as lower‐cost raw materials than conventionally‐used refined sugars such as glucose, and yeast extract as an organic nitrogen source in laboratory‐scale studies. These fermentation characteristics are prerequisites for the industrial scale production of lactic acid. Copyright © 2008 Society of Chemical Industry     

High cell density fermentation via a metabolically engineered Escherichia coli for the enhanced production of succinic acid

BACKGROUND: Succinic acid is a valuable four‐carbon organic chemical with applications in many fields. It was found that cell mass was an important factor in succinic acid production by metabolically engineered Escherichia coli strains. In this work, high cell density fermentation was investigated for succinic acid production by a metabolically engineered strain SD121 with ldhA, pflB, ptsG mutation and heterogenous cyanobacterial ppc overexpression. RESULTS: Under two‐stage cultivation, the controlled DO feeding strategy during the aerobic growth phase facilitated biomass up to a dry cell weight of 19.6 g L^?1, and enhanced succinic acid production in the following anaerobic fermentation phase to a concentration of 116.2 g L^?1. A near theoretical maximum succinic acid yield of 1.73 mol mol^?1 glucose was achieved with an average productivity of 1.55 g L^?1 h^?1. CONCLUSION: The results indicated the potential advantage of high cell density fermentation for improvement of succinic acid production by E. coli. Copyright © 2010 Society of Chemical Industry     

苯酚对污水生物脱氮系统亚硝积累及污泥性能的影响

采用SBR缺氧/好氧反应工艺,研究了不同苯酚浓度对脱氮过程中亚硝积累与污泥性能的影响。结果表明,苯酚浓度在0~90 mg·L^-1变化时系统出现2次明显亚硝酸盐积累,最终稳定维持在70%±5%,低浓度(0~30 mg·L^-1)系统亚硝酸盐积累恢复是微生物改变自身结构及分泌胞外聚合物导致;高浓度(60~90 mg·L^-1)苯酚条件下亚硝积累是由于苯酚对AOB(ammonia-oxidizing bacteria,氨氮氧化细菌)和NOB(nitrite-oxidizing bacteria,亚硝酸氧化细菌)抑制作用引起的微生物种群改变形成。氨氮氧化速率和氮氧化物生成速率由10.85 mg N·(g MLSS)^-1·h^-1和10.12 mg N·(g MLSS)^-1·h^-1降低至2.79 mg N·(g MLSS)^-1·h^-1和2.32 mg N·(g MLSS)^-1·h^-1,亚硝酸盐积累率和氮氧化物生成速率呈现负相关性,与苯酚浓度呈正相关;荧光原位杂交表明苯酚的抑制使得硝化菌群结构发生了变化,AOB 相对数量由2.80%增加为9.30%。苯酚的可降解性使得系统污泥浓度由2500 mg·L^-1左右上升至5870 mg·L^-1。当EPS(extracellular polymeric substances,胞外聚合物)总量由67.20 mg·(g VSS)^-1减少至32.10 mg·(g VSS)^-1时,SVI从165 ml·g^-1降到50 ml·g^-1。亚硝酸盐积累、丝状菌和胞外聚合物是引起活性污泥系统SVI变化的原因,其中NAR影响最大,丝状菌次之。     

Study of a newly isolated thermophilic bacterium capable of Kuhemond heavy crude oil and dibenzothiophene biodesulfurization following 4S pathway at 60 °C

BACKGROUND: To meet stringent emission standards stipulated by regulatory agencies, the oil industry is required to bring down the sulfur content in fuels. As some compounds cannot be desulfurized by existing desulfurizing processes (such as hydrodesulfurization, HDS) biodesulfurization has become an interesting topic for researchers. Most of the isolated biodesulfurizing microorganisms are capable of desulfurization of refined products whose predominant sulfur species are dibenzothiophenes so biocatalyst development is still needed to desulfurize the spectrum of sulfur‐bearing compounds present in whole crude. RESULTS: The first desulfurizing bacterium active at 60 °C has been isolated, which reduces DBT concentration from 2 mmol L^?1 to 0.1 mmol L^?1 after 95 h, following the 4S pathway. Its DBT desulfurization pattern was represented by the Michaelis‐Menten equation. Various parameters such as V_max, K_m, µ_m, K_s and maximum specific DBT desulfurization rate were calculated which are 0.092 mmol L^?1 h^?1, 3.554 mmol L^?1, 0.157 h^?1, 3.722 mmol L^?1 and 0.192 mmol L^?1 DBT g^?1 DCW (dry cell weight) h^?1, respectively. It can desulfurize 50% of the sulfur content of Kuhemond heavy crude oil (KHC oil) with an initial sulfur content of 7.6%wt in 6 days. Its maximum specific desulfurization rate for KHC oil is equivalent to 0.005 g sulfur g^?1 DCW h^?1. The bacterium was isolated during a heavy crude oil biodesulfurization project initiated by PEDEC, a subsidiary of National Iranian Oil Company. CONCLUSION: The KHC oil sulfur removal efficiency of the bacterium is approximately five times that of BBRC‐9016 bacterium. It removes sulfur selectively without using sulfur‐containing compounds as its carbon source. By applying various media during its isolation, the probability of screening the correct microorganism is increased. Copyright © 2008 Society of Chemical Industry     

Effect of acetic acid on lipid accumulation by glucose‐fed activated sludge cultures

BACKGROUND: The effect of acetic acid, a lignocellulose hydrolysis by‐product, on lipid accumulation by activated sludge cultures grown on glucose was investigated. This was done to assess the possible application of lignocellulose as low‐cost and renewable fermentation substrates for biofuel feedstock production. RESULTS: Biomass yield was reduced by around 54% at a 2 g L^?1 acetic acid dosage but was increased by around 18% at 10 g L^?1 acetic acid dosage relative to the control run. The final gravimetric lipid contents at 2 and 10 g L^?1 acetic acid levels were 12.5 ± 0.7% and 8.8 ± 3.2% w/w, respectively, which were lower than the control (17.8 ± 2.8% w/w). However, biodiesel yields from activated sludge grown with acetic acid (5.6 ± 0.6% w/w for 2 g L^?1 acetic acid and 4.2 ± 3.0% w/w for 10 g L^?1 acetic acid) were higher than in raw activated sludge (1–2% w/w). The fatty acid profiles of the accumulated lipids were similar with conventional plant oil biodiesel feedstocks. CONCLUSIONS: Acetic acid enhanced biomass production by activated sludge at high levels but reduced lipid production. Further studies are needed to enhance acetic acid utilization by activated sludge microorganisms for lipid biosynthesis. Copyright © 2011 Society of Chemical Industry     

不同预处理温度对厌氧颗粒污泥发酵产氢的影响

为消除发酵生物制氢系统接种污泥中的耗氢菌,加速系统的启动进程并提高产氢效能,以啤酒厂废水处理车间的厌氧颗粒污泥为对象,通过间歇发酵试验,探讨了经65、80、95、110、121℃处理后的污泥的产氢特性.葡萄糖间歇发酵试验证明,在初始pH 7.0,葡萄糖浓度10000 mg·L-1、污泥接种量2 g MLVSS·L-1等...     

Mesophilic anaerobic digestion of corn thin stillage: a technical and energetic assessment of the corn‐to‐ethanol industry integrated with anaerobic digestion

BACKGROUND: The purpose of this study was to reduce the VS (volatile solid) and recover energy (methane) from thin stillage through mesophilic anaerobic digestion in corn–ethanol plants. The performance of a continuously stirred tank reactor (CSTR) with different hydraulic retention times (HRTs) was evaluated in this study. RESULTS: The results show no differences in volatile solid (VS) destruction (82–83%) in the reactor with HRTs ranging from 25 to 40 days. The maximum volumetric methane production rate of 1.41 L L^?1 day^?1 was produced at 25‐day HRT, whereas the maximum methane yield of approximately 0.63 L CH₄ g^?1 VS_fed (0.77 L g^?1 VS_removed) was achieved with HRTs between 30 and 40 days. Simulation results using a kinetic model indicate that the reactor needs to be operated for longer than 23 days in order to achieve 80% of maximum methane yield. The techno‐economic potential of a corn–ethanol facility to produce an estimated 57% energy recovery using mesophilic anaerobic digestion has long been overlooked. A corn–ethanol plant integrated with mesophilic anaerobic digestion increases the net energy balance ratio from 1.26 to 1.80. CONCLUSION: Mesophilic anaerobic digestion complements the corn–ethanol business so that the sustainable energy obtained from corn recovery is made more lucrative and renewable. Copyright © 2011 Society of Chemical Industry     

Kinetic study on ethanol production using Saccharomyces cerevisiae ITV‐01 yeast isolated from sugar cane molasses

BACKGROUND: Bio‐ethanol production from renewable sources, such as sugar cane, makes it a biofuel that is both renewable and environmentally friendly. One of the strategies to reduce production costs and to make ethanol fuel economically competitive with fossil fuels could be the use of wild yeast with osmotolerance, ethanol resistance and low nutritional requirements. The aim of this work was to investigate the kinetics of ethanol fermentation using Saccharomyces cerevisiae ITV‐01 yeast strain in a batch system at different glucose and ethanol concentrations, pH values and temperature in order to determine the optimum fermentation conditions. RESULTS: This strain showed osmotolerance (its specific growth rate (µ_max) remained unchanged at glucose concentrations between 100 and 200 g L^?1) as well as ethanol resistance (it was able to grow at 10% v/v ethanol). Activation energy (Ea) and Q₁₀ values calculated at temperatures between 27 and 39 °C, pH 3.5, was 15.6 kcal mol^?1 (with a pre‐exponential factor of 3.8 × 10¹² h^?1 (R² = 0.94)) and 3.93 respectively, indicating that this system is biologically limited. CONCLUSIONS: The optimal conditions for ethanol production were pH 3.5, 30 °C and initial glucose concentration 150 g L^?1. In this case, a maximum ethanol concentration of 58.4 g L^?1, ethanol productivity of 1.8 g L^?1 h^?1 and ethanol yield of 0.41 g g^?1 were obtained. Copyright © 2010 Society of Chemical Industry     

Batch cooling crystallization of xylitol produced by biotechnological route

BACKGROUND: This work deals with the xylitol production by biotechnological routes emphasizing the purification process using crystallization. RESULTS: Xylitol volumetric productivity of 0.665 g L^?1 h^?1 and yield of 0.7024 g g^?1 were obtained after 92 h fermentation. The fermented broth (61.3 g L^?1 xylitol) was centrifuged, treated and concentrated obtain a syrup (745.3 g L^?1 xylitol) which was crystallized twice, xylitol crystals with 98.5–99.2% purity being obtained. CONCLUSION: The hypothetical distribution obtained permits the determination of modeling parameters, which make possible the estimation of crystal dominant size from different initial experimental conditions. Copyright © 2008 Society of Chemical Industry     

High power generation with simultaneous COD removal using a circulating column microbial fuel cell

BACKGROUND: A circulating column microbial fuel cell (MFC) with Cu anode and Au? Cu air cathode was used for power generation and chemical oxygen demand (COD) removal from synthetic wastewater. The column was operated in repeated‐fed batch mode using acclimated anaerobic sludge. The contents of the column MFC were circulated while the feed wastewater was fed to the reactor in fed‐batch mode. Effects of feed COD concentration and COD loading rate on voltage difference, power density and percentage COD removal were investigated. RESULTS: The highest voltage difference (650 mV), power density (40 W m^?2) were obtained with a feed COD of 6400 mg L^?1, yielding 45% COD removal with a COD loading rate of nearly 90 mg h^?1. Low COD loadings (<90 mg h^?1) caused substrate limitations, and high loadings (>90 mg h^?1) resulted in inhibition of COD removal and power generation. The highest percentage COD removal (50%) was obtained with feed COD content of 10.35 g L^?1 or a COD loading rate of 145 mg h^?1. CONCLUSION: The power densities obtained with the circulating column MFC were considerably higher than those reported in the literature due to elimination of mass transfer limitations by the high circulation rates, proximity of electrodes and small anode surface area used in this study. Further improvements may be possible with optimization of the operating parameters. Copyright © 2009 Society of Chemical Industry