Influence of growth medium composition on the lipolytic enzyme activity of Ophiostoma piliferum (CartapipTM)

Production of esterases (carboxyl esterase EC 3.1.1.1) and lipases (glycerol ester hydrolase EC 3.1.1.3) by Ophiostoma piliferum (Cartapip^TM), a fungus commercialized to decrease fatty acyl esters in wood, is described. The influence of various combinations of carbon and nitrogen sources, in the growth medium, was examined. Medium containing yeast extract as a nitrogen source and olive oil as a carbon source was found to be optimal for extracellular esterase (221 U dm⁻³) and lipase (152 U dm ⁻³) activities. Further increases in those enzyme activities were achieved by decreasing medium pH from 6.5 to 5.5 (esterase 508 U dm⁻³; lipase 415 U dm ⁻³) and increasing medium calcium content from 8 m mol dm⁻³ to 160 m mol dm⁻³ (esterase 4084 U dm⁻³; lipase 508 U dm ⁻³) © 1999 Society of Chemical Industry     

Mn‐peroxidase production by Panus tigrinus CBS 577.79: response surface optimisation and bioreactor comparison

This study reports the statistical optimisation through response surface methodology of the growth medium for Panus tigrinus manganese‐dependent peroxidase (MnP) production in shaken culture. Three crucial variables, including carbon source, malonic acid and Mn²⁺, were optimised in a nitrogen‐limited medium. Sucrose was the best carbon source for MnP production. Mn²⁺ ions and malonic acid significantly stimulated MnP production at an optimal concentration of 53 mg dm^?3 and 8.2 mmol dm^?3, respectively, resulting in 0.83 U cm^?3. Further experiments were performed in lab‐scale stirred tank (STR) and bubble‐column (BCR) reactors using the previously optimised liquid medium. BCR proved to be more adequate than STR in supporting MnP production, leading to 3700 U dm^?3 after 144 h with a productivity of 25.7 U dm^?3 h^?1. On a comparative basis with other production data in lab‐scale reactors, these results appear to be compatible with scale transfer. Copyright © 2006 Society of Chemical Industry     

Pilot‐scale demonstration of pre‐fermentation for enhancement of food‐processing wastewater biodegradability

A pilot‐scale anaerobic/aerobic ultrafiltration system was tested to treat high‐strength tomato‐processing wastewater, to achieve stringent dry‐ditch discharge criteria of soluble biochemical oxygen demand (SBOD) <10 mg dm^?3, total suspended solids <10 mg dm^?3, ammonia nitrogen <3 mg dm^?3 and soluble phosphorus <0.5 mg dm^?3. The anaerobic/aerobic system achieved 99.4% SBOD removal, 91.9% NH₃ N removal and 100% phosphorus removal at an overall hydraulic retention time of 1.5 days and solids retention time of 5 days during the tomato canning season. Respirometric studies confirmed that the pretreatment of tomato‐processing wastewater in the anaerobic reactor increased the readily biodegradable fraction, improved kinetics, and eliminated nutrient deficiency problem. Copyright © 2006 Society of Chemical Industry     

Production of Lipase from Geotrichum candidum Using Corn Steep Liquor in Different Bioreactors

The production of an extracellular lipase using corn steep liquor (CSL) as the nitrogen source in the cultivation of Geotrichum candidum NRRLY‐552 was evaluated. The optimized conditions in shake flasks were CSL, 8.0 % w/v, soybean oil, 0.6 % w/v, pH 7.0, 30 °C, 250 rpm, and 48 h, resulting in a maximum lipase productivity of 0.438 U mL^?1 h^?1(U = the amount of enzyme required to liberate 1 μmol of fatty acid per minute). Scale‐up was evaluated with airlift and stirred tank reactors; the best conditions, respectively, were 1 vvm(volume of gas per volume of medium per minute) of aeration which resulted in 0.535 U mL^?1 h^?1 (32 h) and 1 vvm and 300 rpm resulting in 0.563 U mL^?1 h^?1 (16 h). To facilitate downstream processes, lipase production was also evaluated using CSL previously clarified with activated charcoal resulting in 0.275 U mL^?1 h^?1 (24 h) using 12 % (w/v) of clarified CSL in shake flasks. The obtained results showed that CSL leads to similar productivity compared to peptone using the same microorganism under similar conditions. In addition the cost of fermentation medium using CSL is much lower because it is a very inexpensive by‐product from corn processing.     

Bioprocess scale‐up: quest for the parameters to be used as criterion to move from microreactors to lab‐scale

Advances in high‐throughput process development and optimization involve the rational use of miniaturized stirred bioreactors, instrumented shaken flasks and microtiter plates. As expected, each one provides different levels of control and monitoring, requiring a compromise between data quantity and quality. Despite recent advances, traditional shaken flasks with nominal volumes below 250 mL and microtiter plates are still widely used to assemble wide arrays of biotransformation/bioconversion data, because of their simplicity and low cost. These tools are key assets for faster process development and optimization, provided data are representative. Nonetheless, the design, development and implementation of bioprocesses can present variations depending on intrinsic characteristics of the overall process. For each particular process, an adequate and comprehensive approach has to be established, which includes pinpointing key issues required to ensure proper scale‐up. Recently, focus has been given to engineering characterization of systems in terms of mass transfer and hydrodynamics (through gaining insight into parameters such as k_La and P/V at shaken and microreactor scale), due to the widespread use of small‐scale reactors in the early developmental stages of bioconversion/biotransfomation processes. Within this review, engineering parameters used as criteria for scaling‐up fermentation/bioconversion processes are discussed. Particular focus is on the feasibility of the application of such parameters to small‐scale devices and concomitant use for scale‐up. Illustrative case studies are presented. Copyright © 2010 Society of Chemical Industry     

A comprehensive study of lipase production by Yarrowia lipolytica CECT 1240 (ATCC 18942): from shake flask to continuous bioreactor

BACKGROUND: Lipases are commercially important enzymes, and the development and optimization of their production processes are of great interest. The diversity of behaviours between strains stresses the need for research on this topic, especially when bioreactor culture is considered. The study of a continuous operating mode is especially attractive, since very scarce information is available on its application to microbial lipases production. RESULTS: Lipase production in submerged cultures of Yarrowia lipolytica CECT 1240 (ATCC 18 942) has been investigated. Significant lipolytic activity (over 700 U dm^?3), mostly extracellular and membrane‐bound, was obtained in shake flasks using medium supplemented with olive oil. The culture was carried out in air‐lift and stirred tank bench‐scale bioreactors and the latter was selected. The influence of aeration and agitation rates was assessed in batch cultures, and agitation from 400–700 rpm and low aeration rates (i.e. 0.2 vvm) are recommended. Batch, fed‐batch and continuous operation were investigated, and regular enzyme production (up to 600 U dm^?3) was achieved with the latter. CONCLUSION: Lipase production by the selected strain was successfully carried out in shake flasks and bench‐scale bioreactors. After studying batch, fed‐batch and continuous processes, continuous culture in a stirred tank bioreactor was found best in terms of regular enzyme production, exceptionally good operational stability and good fitting of the results to mathematical models. Copyright © 2009 Society of Chemical Industry     

Scale-Up studies of non-aerated fed-batch fermentation of dextransucrase and the industrial synthesis of dextran using the enzymatic route

High activities of the enzyme dextransucrase were repeatedly produced using slowly agitated non-aerated fed-batch fermentations of Leuconostoc mesenteroides B-512(F). Activities in excess of 24.0 U cm^?3 were obtained consistently in a 16 dm³ laboratory fermenter using a 6 dm³ initial work volume. Yeast extract type was identified to be one of the important factors influencing the enzyme yield. Studies on aerating the medium with different gases indicated that the presence of carbon dioxide in the medium favoured high enzyme production. Agitation rates did not appear to have significant effects on either cell growth or enzyme production. One type of antifoam (silicone antifoam) was observed to affect enzyme production but not the cell growth. Scale-up of the non-aerated process was carried out up to a 1000 dm³ scale with enzyme broths containing up to 21.0 U cm^?3 being produced. Two batches of the enzyme that were produced at the large scale were used for the first time to synthesize dextran at a 50000 dm³ industrial scale. The dextran yields were up to 95.5% of the conventional industrial yields and were achieved in much shorter reaction time intervals.     

Design of different bioreactor configurations: application to ligninolytic enzyme production in semi‐solid‐state cultivation

The production of ligninolytic enzymes by Phanerochaete chrysosporium BKM‐F‐1767 (ATCC 24725) in laboratory‐scale bioreactors was studied. The cultivations were carried out in semi‐solid‐state conditions, employing corncob as carrier, which functioned both as a place of attachment and as a source of nutrients. Several bioreactor configurations were investigated in order to determine the most suitable one for ligninolytic enzyme production: a 1‐dm³‐static‐bed bioreactor, a 1‐dm³‐static‐bed bioreactor with air diffusers into the bed, a 0.5‐dm³‐static‐bed bioreactor with air diffusers into the bed and a tray bioreactor. Although the static‐bed configurations produced maximum individual lignin peroxidase (LiP) activities about 400 U dm⁻³ (1.0‐dm³ bioreactor) and about 700 U dm⁻³ (0.5‐dm³ bioreactor), manganese‐dependent peroxidase (MnP) was not detected throughout the cultures. Nevertheless, the tray configuration led to maximum individual MnP and LiP activities of about 200 U dm⁻³ and 300 U dm⁻³, respectively. Therefore, this configuration is the most adequate of the different bioreactor configurations tested in the present work, since the ligninolytic complex formed by MnP and LiP is more efficient for its application to bio‐processing systems. In addition, the results indicated the influence of the oxygen in ligninolytic enzyme production. © 2001 Society of Chemical Industry     

Production of the enzyme dihydrofolate reductase by methotrexate-resistant bacteria isolated from soil

Six bacterial cultures isolated from soil were capable of growing in the presence of methotrexate (MTX). Two strains, PFR-1 and 3, developed resistance to 500 μg cm^?3 MTX in the medium and produced elevated levels of the enzyme dihydrofolate reductase (EC 1.5.1.3): 2580 and 2702 U dm^?3 compared to the sensitive parent strains (28 and 35 U dm^?3). Isolate PFR-3 showed maximum enzyme production (4950 U dm^?3, specific activity 12.56 U mg^?1 in flasks and 5737 U dm^?3, specific activity 14.80 U mg^?1 in 5-dm³ fermenter) during exponential phase of growth (6 h) at 37°C and pH 7.0.     

Production of fructose and ethanol from media with high sucrose concentrations by a mutant of Saccharomyces cerevisiae

The production of enriched fructose syrups and ethanol from a synthetic medium with high sucrose concentrations was studied in a batch process using Saccharomyces cerevisiae ATCC 36858. The results showed that the fructose yield was above 92% of theoretical values in synthetic media with sucrose concentrations between 180 g dm^?3 and 726 g dm^?3. Ethanol yield was about 82% in media with sucrose concentrations up to 451 g dm^?3. A product containing 178 g dm^?3 fructose, which represents 97% of the total sugar content, and 79 g dm^?3 ethanol was obtained using a medium with 360 g dm^?3 sucrose. The fructose fraction in the carbohydrates content in the produced syrups decreased with increases in the initial sucrose concentration. In a medium with initial sucrose concentration of 574 g dm^?3, the fructose content in the produced broth was 59% of the total carbohydrates. Glycerol and fructo‐oligosaccharides were also produced in this process. The produced fructo‐oligosaccharides started to be consumed when the concentration of sucrose in the media was less than 30% of its initial value. Complete hydrolysis of these sugars was noticed in media with sucrose concentrations below 451 g dm^?3. These findings will be useful in the production of ethanol and high fructose syrups using sucrose‐based raw materials with high concentrations of this carbohydrate. © 2001 Society of Chemical Industry     

Comparison of lipase production by Geotrichum candidum in stirring and airlift fermenters

The production of lipase by Geotrichum candidum in both, stirred tank and airlift bioreactors were compared. G candidum an imperfect filamentous fungus, grows well in liquid medium, and produces a lipase with specific affinity for long‐chain fatty acids with cis‐9 double bonds but, lipase production is generally not efficient because the optimum medium composition and fermentation conditions are not known. Response surface methodology was used to optimize the agitation speed (100–500 rpm) and aeration (0.2–1.8 vvm) for production of lipase by G candidum in a bench‐scale stirred fermenter. A Central Composite Rotatable Design (CCRD) was used to optimize lipase activity and productivity. Lipase production in an airlift fermenter was also studied with aeration ranging from 1 to 3 vvm. A previously optimized culture medium containing 3.58% of peptone, 0.64% of soy oil and an initial pH of 7.0, was used in the experiments, incubating at 30°C. In the stirred reactor the optimum conditions of agitation and aeration for lipase production and productivity were 300 rpm and 1 vvm, leading to an activity of 20 U cm^?3 in 54 h of fermentation and 0.3900 (U cm^?3 h^?1) of productivity. The best aeration condition in the airlift fermenter was 2.5 vvm, which yielded similar lipase activity after 30 h of fermentation, resulting in a productivity of 0.6423 (U cm^?3 h^?1). In the absence of mechanical agitation similar lipase yields were achieved but in less time, resulting in productivity, about 60% greater than in a stirred fermenter; the lower energy demand for the same lipase yield offers economic advantages. Copyright © 2004 Society of Chemical Industry     

Effect of lipids and surfactants on extracellular lipase production by Yarrowia lipolytica

The production of extracellular lipase in submerged cultures of Yarrowia lipolytica CECT 1240 has been investigated. Several compounds have been added to the culture medium, in order to assess their efficiency as inducers of lipase production. First, the effect of triglycerides (olive oil, sunflower oil, tributyrin) and fatty acids (oleic acid) has been studied. The highest activity level was obtained with sunflower oil (58 U cm^?3), followed by olive oil (49 U cm^?3). The cultures with tributyrin and oleic acid attained similar activities (33 U cm^?3). Then, several surfactants (Tween 80, Triton X‐100, gum arabic, polyethylene glycol 200) were added to the cultures with sunflower oil, in an attempt to increase the levels of extracellular lipase activity. The obtained activities were slightly lower than those achieved without surfactants. The assay of a wide range of surfactant concentrations in the case of PEG‐200 (with which the highest activity levels had been attained) did not improve the results. This strain secreted lipase concentrations two‐fold higher and showed significantly different behaviour towards the presence of surfactants in the culture medium, compared with other wild‐type Yarrowia lipolytica strains. Copyright © 2003 Society of Chemical Industry     

Electrolytic removal of ammonia from brine wastewater: scale‐up,operation and pilot‐scale evaluation

Brine wastewater with a high ammonia content from an iodine processing plant (commonly called kansui in Japan) was treated by electrolysis. The system, which can be considered as an indirect electrolytic treatment process, generates chlorine at the anodes and initiates the formation of mixed oxidants like hypochlorous acid. The oxidants then act as agents for ammonia destruction. Laboratory‐scale experiments showed that high ammonia concentrations (as much as 200 mg dm^?3) could be completely removed within a few minutes, and could be considered a good alternative for efficient ammonia removal from saline wastewaters. From laboratory‐scale experiments in the batch and continuous modes, the charge dose was analyzed and used as the operating and scale‐up factor. The value of the charge dose was not severely affected by changes in operating conditions such as electrode spacing and temperature. The charge dose from batch and continuous runs was found to be in the range of 23 C (mg NH₄‐N removed)^?1 to 29 C (mg NH₄‐N removed)^?1. Using the charge dose obtained from laboratory‐scale continuous electrolysis experiments as the scale‐up factor, a pilot‐scale reactor was designed, and the operating conditions were calculated. In the pilot‐scale reactor tests at different flow rates, the effluent ammonia concentrations were reasonably close to the calculated values predicted from the charge dose equation. Copyright © 2004 Society of Chemical Industry     

Inoculum strategies for Penicillium simplicissimum lipase production by solid‐state fermentation using a residue from the babassu oil industry

Two alternative inoculation strategies for lipase production by the fungus Penicillium simplicissimum were tested in solid‐state fermentation using a residue from the babassu oil industry (babassu cake). Conventional spore inoculation was compared with fungal pellets grown in liquid medium and with inocula consisting of fermented cake. Fungal pellets delayed lipase production whereas fermented cake accelerated enzyme synthesis, yielding a productivity of 0.45 U g^?1 h^?1, which is equivalent to the highest values obtained with conventional inocula. Therefore, a 2² factorial design was used to determine the best conditions for lipase production with fermented cake as inoculum strategy, varying the inoculum propagation time and inoculum concentration. Lipase activity and productivity reached 30 U g^?1 and 0.63 U g^?1 h^?1, respectively, with 10% inoculum and 36 h. Thus, fermented cake inocula increased production 1.5‐fold with 10 times fewer spores than in conventional inoculation, indicating that fermented solids are an interesting alternative for inoculum development in solid‐state fermentation, mainly for large‐scale processes. Copyright © 2007 Society of Chemical Industry     

Lipolytic enzyme production in batch and fed‐batch cultures of Ophiostoma piceae and Fusarium oxysporum

Lipase and esterase production by Ophiostoma piceae and Fusarium oxysporum were enhanced and extended by developing a fed‐batch process in stirred tank reactors. Fed‐batch strategy improved lipolytic enzyme production from Ophiostoma piceae in both 2 and 20 dm³ stirred tank reactors. However, fed‐batch fermentation of Fusarium oxysporum in the 2 dm³ reactor was more effective than both batch and fed‐batch fermentations in the 20 dm³ reactor. When a medium composed of only carbon and nitrogen source was intermittently fed to the cultures, the maximum specific lipase activity was improved by more than 80% and 35% in Ophiostoma piceae and Fusarium oxysporum cultures respectively. The maximum specific esterase activity was improved by 20% and 15% in Ophiostoma piceae and Fusarium oxysporum cultures respectively. The duration of production for both fungi extended from 144 to 216 h compared with a batch culture under the same condition. © 2000 Society of Chemical Industry     

Lecithin‐enhanced biotransformation of cholesterol to androsta‐1,4‐diene‐3,17‐dione and androsta‐4‐ene‐3,17‐dione

A biotransformation process using Mycobacterium sp was studied for androsta‐1, 4‐diene‐3,17‐dione (ADD) and androsta‐4‐ene‐3,17‐dione (AD) production from cholesterol. Cholesterol has a poor solubility in water (～1.8 mg dm^?3 at 25 °C), which makes it difficult to use as the substrate for biotransformation. Lecithin is a mixture of phospholipids of phosphatidylcholine (PC) and phosphatidylethanolamine (PE), which behave like surfactants and can form planar bi‐layer structures in an aqueous medium. Therefore, a small amount of lecithin (<1 g dm^?3) can be used to form stable colloids with cholesterol at a relatively high concentration (20 g dm^?3) in water. In this work, an energy density of 1000 J cm^?3 from sonication was provided to overcome the self‐association of cholesterol and to generate a stable lecithin–cholesterol suspension that could be used for enhanced biotransformation. The lecithin–cholesterol suspension was stable and could withstand typical autoclaving conditions (121 °C, 15 psig, 20 min). In contrast to conventional surfactants, such as Tween 80, that are commonly used to help solubilize cholesterol, lecithin did not change the surface tension of the aqueous solution nor cause any significant foaming problem. Lecithin was also biocompatible and showed no adverse effect on cell growth. Compared with the medium with Tween 80 as the cholesterol‐solubilizing agent, lecithin greatly improved the biotransformation process in regard to its final product yield (～59% w/w), productivity (0.127–0.346 g dm^?3 day^?1), ADD/AD ratio (6.7–8), as well as the long‐term process stability. Cells can be reused in repeated batch fermentations for up to seven consecutive batches, but then lose their bioactivity due to aging problems, possibly caused by product inhibition and nutrient depletion. © 2002 Society of Chemical Industry     

Optimum culture medium composition for rhamnolipid production by pseudomonas aeruginosa AT10 using a novel multi‐objective optimization method

BACKGROUND: Rhamnolipid is a biosurfactant that finds wide applications in pharmaceuticals and beauty products. Pseudomonas aeruginosa is a producer of rhamnolipids, and the process can be implemented under laboratory‐scale conditions. Rhamnolipid concentration depends on medium composition namely, carbon source concentration, nitrogen source concentration, phosphate content and iron content. In this work, existing data⁷ were used to develop an artificial neural network‐based response surface model (ANN RSM) for rhamnolipid production by pseudomonas aeruginosa AT10. This ANN RSM model is integrated with non‐dominated sorting differential evolution (DE) to identify the optimum medium composition for this process. RESULTS: Different strategies for optimization of culture medium composition for this process were evaluated, and the best determined to be an ANN model combined with DE involving a combination of Naïve and Slow and ε‐constrained techniques. The optimal culture medium is determined to have carbon source concentration of 49.86 g dm^?3, nitrogen source concentration of 4.99 g dm^?3, phosphate content of 1.42 g dm^?3, and iron content of 17.12 g dm^?3. The maximum rhamnolipid activity was found to be 18.07 g dm^?3, which compares favorably with that previously reported (18.66 g dm^?3), and is in fact closer to the experimentally determined value of 16.50 g dm^?3. CONCLUSION: This method has distinct advantages over methods using statistical regression models, and can be used for optimization of other multi‐objective biosurfactant production processes. © 2012 Society of Chemical Industry     

One pot synthesis of xanthan gum‐g‐N‐vinyl‐2‐pyrrolidone and study of their metal ion sorption behavior and water swelling property

In this article, graft copolymerization of N‐vinyl‐2‐pyrrolidone onto xanthan gum initiated by potassium peroxydiphosphate/Ag⁺ system in an aqueous medium has been studied under oxygen free nitrogen atmosphere. Grafting ratio, grafting efficiency, and add on increase on increasing the concentration of potassium peroxydiphosphate (2.0 × 10^?3 to 12 × 10^?3 mol dm^?3), Ag⁺(0.4 × 10^?3 to 2.8 × 10^?3 mol dm^?3), and hydrogen ion concentration from 2 × 10^?3 to 14.0 × 10^?3 mol dm^?3. Maximum grafting has been obtained when xanthan gum and monomer concentration were 0.4 g dm^?3 and 16 × 10^?2 mol dm^?3, respectively, at 35°C and 120 min. Water swelling capacity, swelling ratio, metal ion uptake, and metal retention capacity have also been studied, and it has been found that graft copolymer shows enhancement in these properties than pure xanthan gum. The graft copolymer has been characterized by FTIR and thermal analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Utilization of response surface methodology to optimize the culture media for the production of rhamnolipids by Pseudomonas aeruginosa AT10

Pseudomonas aeruginosa AT10 produced a mixture of surface‐active rhamnolipids when cultivated on mineral medium with waste free fatty acids as carbon source. The development of the production process to an industrial scale included the design of the culture medium. A 2⁴ full factorial, central composite rotational design and response surface modelling method (RSM) was used to enhance rhamnolipid production by Pseudomonas aeruginosa AT10. The components that are critical for the process medium were the carbon source, the nitrogen source (NaNO₃), the phosphate content (K₂ HPO₄/KH₂PO₄ 2:1) and the iron content (FeSO₄·7H₂O). Two responses were measured, biomass and rhamnolipid production. The maximum biomass obtained was 12.06 g dm^?3 DCW, when the medium contained 50 g dm^?3 carbon source, 9 g dm^?3 NaNO₃, 7 g dm^?3 phosphate and 13.7 mg dm^?3 FeSO₄·7H₂O. The maximum concentration of rhamnolipid, 18.7 g dm^?3, was attained in medium that contained 50 g dm^?3 carbon source, 4.6 g dm^?3 NaNO₃, 1 g dm^?3 phosphate and 7.4 mg dm^?3 FeSO₄·7H₂O. © 2002 Society of Chemical Industry     

Effects of cationic polymer on start‐up and granulation in upflow anaerobic sludge blanket reactors

The upflow anaerobic sludge blanket (UASB) has been used successfully to treat a variety of industrial wastewaters. It offers a high degree of organics removal, low sludge production and low energy consumption, along with energy production in the form of biogas. However, two major drawbacks are its long start‐up period and deficiency of active biogranules for proper functioning of the process. In this study, the influence of a coagulant polymer on start‐up, sludge granulation and the associated reactor performance was evaluated in four laboratory‐scale UASB reactors. A control reactor (R1) was operated without added polymer, while the other three reactors, designated R2, R3 and R4, were operated with polymer concentrations of 5 mg dm^?3, 10 mg dm^?3 and 20 mg dm^?3, respectively. Adding the polymer at a concentration of 20 mg dm^?3 markedly reduced the start‐up time. The time required to reach stable treatment at an organic loading rate (OLR) of 4.8 g COD dm^?3 d^?1 was reduced by more than 36% (R4) as compared with both R1 and R3, and by 46% as compared with R2. R4 was able to handle an OLR of 16 g COD dm^?3 d^?1 after 93 days of operation, while R1, R2 and R3 achieved the same loading rate only after 116, 116 and 109 days respectively. Compared with the control reactor, the start‐up time of R4 was shortened by about 20% at this OLR. Granule characterization indicated that the granules developed in R4 with 20 mg dm^?3 polymer exhibited the best settleability and methanogenic activity at all OLRs. The organic loading capacities of the reactors were also increased by the addition of polymer. The maximum organic loading of the control reactor (R1) without added polymer was 19.2 g COD dm^?3 d^?1, while the three polymer‐assisted reactors attained a marked increase in organic loading of 25.6 g COD dm^?3 d^?1. Adding the cationic polymer could result in shortening of start‐up time and enhancement of granulation, which may in turn lead to improvement in the efficiency of organics removal and loading capacity of the UASB system. Copyright © 2004 Society of Chemical Industry