Biochemical Engineering Journal (v.32, #2)
Editorial Board (CO2).
BEJ Keywords (IV).
Modelling and dynamic simulation of a moving bed bioreactor for the treatment of municipal wastewater by M. Plattes; E. Henry; P.M. Schosseler; A. Weidenhaupt (61-68).
A model for the dynamic simulation of a pilot scale moving bed bioreactor (MBBR) used for the treatment of municipal wastewater is proposed. The proposed MBBR model includes attachment of particulates to the biofilm and detachment of biofilm into the bulk liquid. The biofilm growth kinetics are modelled with the activated sludge model no. 1 (ASM1). Diffusional mass transport limitations are implemented implicitly by ASM1 and manifest by adapted half-saturation coefficients in the Monod expressions of the activated sludge model. The model layout incorporates completely mixed aeration tanks and flow splitters and can be implemented using the respective standard blocks available in wastewater treatment plant simulators. A calibration guideline is proposed. Attachment and detachment rates are adjusted during calibration in order to match the measured biofilm solids in the MBBR and effluent ammonium and nitrate data. The process dynamics of the MBBR were well reproduced using ASM1 with default parameter values. The biofilm age was calculated analogous to the sludge age in an activated sludge plant and it was found to be 2.6 d in the first and 2.1 d in the second compartment of the MBBR, which is small compared to typical sludge ages in nitrifying activated sludge plants.
Keywords: Attachment; Biofilms; Biofilm age; Detachment; Modelling; Moving bed bioreactors;
Novel operational strategy for partial nitrification to nitrite in a sequencing batch rotating disk reactor by C. Antileo; A. Werner; G. Ciudad; C. Muñoz; C. Bornhardt; D. Jeison; H. Urrutia (69-78).
Partial nitrification to nitrite has three practical advantages: lower oxygen consumption, lower need for organics and lower sludge production. In order to develop a stable partial nitrification a novel operational strategy was studied in a sequencing batch rotating disk reactor under oxygen concentrations lower than 1.0 mg/L throughout 270 days. The strategy was based on a supervisory pH control and an automatic interruption of aeration at the endpoint of ammonia oxidation. The supervisory control enabled the maintenance of a concentration of 3–4 mg NH3-N/L for optimal growing of ammonia oxidizing bacteria. For this reason on-line monitoring of sodium carbonate consumption was implemented during nitrification. The results showed that it is possible to reach a stable partial nitrification with high nitrite accumulations of 84–88% during long-term assays, and a relatively high ammonia conversion rate of 1.45–4.25 kg NH4 +-N/(m2 day). A high impact was observed by decreasing the oxygen concentration from 1.0 to 0.8 mg O2/L; the ammonium removal rate declined significantly from 4.25 to 1.62 kg/(m2 day). The molecular analyses by dot-blot hybridizations with 16S rRNA revealed the presence of more than 95% of Nitrosomonas sp., and only 5% of Nitrobacter sp. during the initial phase of the biofilm formation.
Keywords: Batch processing; Biofilms; Control; Immobilization; Nitrite accumulation; SBR;
Dynamic microwave-assisted extraction of flavonoids from Saussurea medusa Maxim cultured cells by Min Gao; Bao-Zhen Song; Chun-Zhao Liu (79-83).
An approach for automated, continuous and rapid extraction of flavonoids from Saussurea medusa Maxim dried cell cultures has been developed in a new-designed dynamic microwave-assisted extraction system. The main factors affecting the extraction process namely power of microwave irradiation, liquid/solid ratio, flow rate of solvent and irradiation time were optimized. The yield of flavonoids reached 4.97% in 60 min under the optimum microwave-assisted extraction conditions: 1200 W of radiation power, 50:1 (v/w) of the liquid/solid ratio, and 50 ml s−1 of solvent flow rate. The dynamic microwave-assisted extraction showed obvious advantages in short duration and high efficiency to extract flavonoids without causing degradation of target components from the S. medusa dried cell cultures in comparison with the dynamic solvent extraction without microwave assistance.
Keywords: Dynamic microwave-assisted extraction; Flavonoids; Dynamic solvent extraction; Saussurea medusa Maxim; Plant cell cultures;
Long-term operation of a compost-based biofilter for biological removal of n-butyl acetate, p-xylene and ammonia gas from an air stream by Dan Wu; Xie Quan; Yaobin Zhang; Yazhi Zhao (84-92).
An experimental study on the removal of the mixtures of n-butyl acetate (n-BA), p-xylene (p-XY) and ammonia gas (NH3) from an air stream was performed in a laboratory scale three-segment biofilter over a period of 4 months. The biofilter was packed with the mixture of mature pig compost, forest soil and a packing material made of polyethylene (PE) which was used in the moving bed biological reactor (MBBR) for treating wastewater. n-BA elimination capacities of 157 and 150 g m−3 h−1 were obtained at empty bed residence time (EBRT) of 60 and 30 s, respectively, corresponding to removal efficiency of approximate 100 and 96%. An approximate 100% removal of NH3 could be achieved with inlet concentration varying from 0.043 to 0.15 g m−3 at EBRT of 30 and 90 s. For p-XY, the maximal inlet concentration (0.51 g m−3) with removal efficiency of 100% at EBRT of 60 s was a little higher than 0.4 g m−3 at EBRT of 90 s due to NH3 feeding. The pH of the packing media varied in the neutral range (6.5–7.9) during the operation period. The results indicated that the mixtures of n-BA, p-XY and NH3 were successfully eliminated simultaneously in this biofilter.
Keywords: Biofilters; Biofilms; Biodegradation; Microbial growth; VOCs; Biofiltration;
Microbial production of 1,3-propanediol from glycerol by encapsulated Klebsiella pneumoniae by Ya-Nan Zhao; Guo Chen; Shan-Jing Yao (93-99).
Klebsiella pneumoniae was encapsulated in the NaCS/PDMDAAC (sodium cellulose sulfate/poly-dimethyl-diallyl-ammonium chloride) microcapsule to produce 1,3-propanediol (PDO) from glycerol. Fermentations including batch culture, fed-batch culture and continuous culture were carried out in shake flasks and a fixed-bed bioreactor. Results showed that the NaCS/PDMDAAC microcapsule has desirable properties – such as biomass enrichment in the microcapsule (6.84 g/L capsule, 2.6-fold higher than that of free cell culture), enhanced substrate tolerance and stable activity of cells, operation convenience for continuous culture – for the microbial production of 1,3-propanediol. A 1,3-propanediol concentration of 63.1 g/L with a yield of 0.65 mol PDO/mol glycerol was obtained in the batch culture. The encapsulated cells remained its activity for 67 h in the fed-batch culture and produced 1,3-propanediol at a concentration of 51.86 g/L. In the continuous culture, 1,3-propanediol was provided at a productivity of 4.49 g/L h, a concentration of 13.6 g/L, and a yield of 0.43 mol PDO/mol glycerol at a dilution rate of 0.33 h−1.
Keywords: 1,3-Propanediol; Bioconversion; Immobilized cells; NaCS/PDMDAAC (sodium cellulose sulfate/poly-dimethyl-diallyl-ammonium chloride) microcapsules; Fixed-bed bioreactor; Glycerol;
Enhancement of sonocatalytic cell lysis of Escherichia coli in the presence of TiO2 by Chiaki Ogino; Mahmoud Farshbaf Dadjour; Keiko Takaki; Nobuaki Shimizu (100-105).
An ultrasonic system with TiO2 particles was utilized for disinfection of Escherichia coli (E. coli) under condition of darkness. The mechanism of disinfection was studied by investigating the cell lysis and degradation of DNA leaked through the cell membrane. The degradation of DNA was enhanced remarkably in the presence of TiO2 particles. The effects of Al2O3 particles on the degradation of DNA were also examined, and these particles were found to be less effective than TiO2 particles at enhancing degradation. Compared with TiO2 addition case, the ultrasonic irradiation with no particles afforded 5% degradation, while the addition of Al2O3 induced approximately 54% degradation under the conditions used. The role of hydroxyl radicals in this process was also investigated by examining the effects of a hydroxyl radical scavenger, glutathione. A significant suppression of DNA leakage through the cell membrane was observed in the solutions containing glutathione, and the suppressive effects were dose-dependent. These results indicate that hydroxyl radicals may play a primary role in the degradation of DNA as well as cell lysis.
Keywords: Cell lysis; Ultrasonic irradiation; Titanium dioxide; E. coli; Disinfection; Hydroxyl radical;
Production and partial characterization of endoxylanase by Bacillus pumilus using agro industrial residues by C. Asha Poorna; P. Prema (106-112).
Agro industrial residues, cheap sources of energy have high potential in the area of fermentation for the production of lignocellulases. Different agro industrial waste products were evaluated as substrates in submerged and solid-state fermentation for xylanolytic enzyme production by Bacillus pumilus and the enzyme titers were compared. Higher titer of endoxylanase was obtained with solid state than with liquid fermentation with feeble amount of cellulase. High proteolytic activity was observed in submerged fermentation where as in solid state the proteolytic activity was lower in all cases except in media supplemented with soy meal due to its high protein content. The endoxylanase produced by solid-state fermentation was stable over a wide range of pH and temperatures. The highest enzyme activity was obtained at pH 6.5–7 and at 50 °C. The enzyme could retain 30% of its activity even after 1 h at 60 °C. Considering the conditions under which Kraft pulps are bleached during the manufacture of paper, xylanase from B. pumilus exhibit favorable potential for application in the paper processing industries.
Keywords: Submerged fermentation; Solid-state fermentation; Bacillus pumilus; Endoxylanase; Cellulase; Proteases;
Age-related responses of suspension cultured Taxus cuspidata to hydrodynamic shear stress by Yan-Wen Gong; Shu-Ying Li; Rong-Bin Han; Ying-Jin Yuan (113-118).
Hydrodynamic shear sensitivity is considered one of the obstacles for large-scale plant cell culture. Understanding the mechanism of shear sensitivity might assist the industrial application of plant cell culture. Here we investigated the responses of suspension cultured Taxus cuspidata in different culture phases under shear stress using a Couette reactor. It was found that the pH in medium and peroxide hydrogen (H2O2) in cells increased more rapidly in the exponential phase than that in lag phase under shear stress. The pH and H2O2 concentration in the exponential phase were also higher than those in the lag phase. Inhibition studies showed that there existed a 30–45 min delay in the action time of G-protein, Ca2+ channel and phospholipase C of T. cuspidata cells in the lag phase than that in the exponential phase. Age-related different membrane fluidity and H+-ATPase activity may partially contribute to the observed responses. These early responses might be indicators for selecting shear-resistant cell lines and for cell damage caused by shear stress.
Keywords: Hydrodynamic stress; Plant cell culture; Bioreactors; Large-scale cultivation; Physiology; Membrane fluidity;
Neural-network rate-function modeling of submerged cultivation of Monascus anka by Jyh-Shyong Chang; Jinn-Tsair Lee; Audrey-Chingzu Chang (119-126).
An experimental verification and validation of the neural-network rate-function (NNRF) approach to modeling dynamic systems is provided. The NNRF modeling scheme utilizes the designed experimental data to build the interested states of the dynamic system as a function of the related recurrent states and the external inputs by feedforward artificial neural networks (FANNs). Once these FANNs are trained, they can be put back into the original differential equations, thereby turning out this combined NNRF-differential-equation model. The experimental system for demonstrating the applicability of the NNRF modeling approach is the liquid phase cultivation of Monascus anka. In a 5 l batch reactor system, the controlled inputs are the cultivating temperature and the dissolved oxygen; the desired outputs are the glucoamylase activity and the concentration of red pigment. Based on the developed sequential pseudo-uniform design (SPUD) method, 11 batches are adequate to provide the identified NNRF model with sufficient information. Facing the noisy inputs and outputs, the identified NNRF demonstrates its predictive capability and could be applied to determine the optimal operating conditions for the submerged cultivation of M. anka.
Keywords: Neural networks; Bioprocess; Batch reactor; Monascus anka;