Recycle Membrane Research Articles

Ethanol production in a membrane bioreactor: pilot-scale trials in a corn wet mill.

Pilot plant trials were conducted in a corn wet mill with a 7000-L membrane recycle bioreactor (MRB) that integrated ceramic microfiltration membranes in a semi-closed loop configuration with a stirred-tank reactor. Residence times of 7.5-10 h with ethanol outputs of 10-11.5% (v/v) were obtained when the cell concentration was 60-100 g/L dry wt of yeast, equivalent to about 10(9)-10(10) cells/mL. The performance of the membrane was dependent on the startup mode and pressure management techniques. A steady flux of 70 L/(m2 x h) could be maintained for several days before cleaning was necessary. The benefits of the MRB include better productivity; a clear product stream containing no particulates or yeast cells, which should improve subsequent stripping and distillation operations; and substantially reduced stillage handling. The capital cost of the MRB is $21-$34/(m3 x yr) ($0.08-$0.13/[gal x yr]) of ethanol capacity. Operating cost, including depreciation, energy, membrane replacement, maintenance, labor, and cleaning, is $4.5-9/m3 ($0.017-$0.034/gal) of ethanol.

Production of poly(3-hydroxybutyrate) from whey by cell recycle fed-batch culture of recombinant Escherichia coli

A new fermentation strategy using cell recycle membrane system was developed for the efficient production of poly(3-hydroxybutyrate) (PHB) from whey by recombinant Escherichia coli strain CGSC 4401 harboring the Alcaligenes latus polyhydroxyalkanoate (PHA) biosynthesis genes. By cell recycle, fed-batch cultivation employing an external membrane module, the working volume of fermentation could be constantly maintained at 2.3 l. The final cell concentration, PHB concentration and PHB content of 194 g l−1, 168 g l−1 and 87%, respectively, were obtained in 36.5 h by the pH-stat cell recycle fed-batch culture using whey solution concentrated to contain 280 g lactose l−1 as a feeding solution, resulting in a high productivity of 4.6 g PHB l−1 h−1.

Kinetics of continuous starch hydrolysis in a membrane reactor

Following a previous study on kinetics of enzymatic starch hydrolysis with Termamyl 120 l (Novo Nordisk) in batch reactor, this paper deals with kinetics in a continuous recycled membrane reactor (CRMR). Starting from results obtained in various working conditions, an equation relating the production rates of small oligosaccharides (DP ranging from 1 to 5) to the sum of concentrations of oligosaccharides with a higher degree of polymerisation is proposed. This equation looks like the one already reported for a batch system, with the exception that in the CRMR the enzyme activity varies: an exponential decay of activity as a function of time must be introduced to smooth carefully data points.

The effect of enzyme concentration and space time on the performance of a continuous recycle membrane reactor for one-step starch hydrolysis

In spite of minor limitations due to membrane fouling and catalyst inactivation, one-step hydrolysis of starch with termamyl enzyme in a continuous recycle membrane reactor appears to be a promising way to produce high DE sugar syrups. In addition to the main advantage over batch process to correctly integrating reaction and separation, this type of system opens up to process engineer tunable performance in terms of conversion, capacity and productivity. In this paper the effects of enzyme concentration and space time have been examined. As a whole it appears that by increasing these two parameters the conversion is improved; but the capacity and productivity are reduced leading to higher processing costs. Optimisation of enzyme concentration and space time needs that economic criteria are very carefully taken into account.

Alternative tests for evaluating NF fouling

Two alternative batch tests use a smaller sample and simpler experimental setup.The batch recycle membrane test (BaReMT) and batch internal recycle membrane test (BaIReMT) were developed as simpler alternatives to the rapid bench‐scale membrane test (RBSMT) currently recommended by the Information Collection Rule for evaluating membrane treatment. All three methods were tested on a small (155‐cm2 [26‐sq‐in.]) flat sheet of membrane. Both the BaReMT and BaIReMT require a far smaller batch volume of water sample than does the RBSMT. The patterns of flux decline and recovery were similar in the BaReMT and RBSMT that used water treatment plant samples from Durham and Fayetteville, N.C. The fouling tendencies of water treatment plant samples from Durham, Fayetteville, and Raleigh, N.C. were similar. Although the mass of natural organic matter on the membrane was small, its estimated concentration in the foulant layer was large. Scanning electron and atomic force micrographs showed that not all foulants were removed from the membrane surface despite extensive cleaning. Only repeated cycles of cleaning can demonstrate the long‐term effect of the remaining foulants on flux recovery.

99/01792 Coal conversion. Membrane separation, recovery and recycle of gases in coal upgrading: Sakellaropoulos, P. Comm. Eur. Communities, [Rep.] EUR, 1998, (EUR 17929), 1–199

99/01792 Coal conversion. Membrane separation, recovery and recycle of gases in coal upgrading: Sakellaropoulos, P. Comm. Eur. Communities, [Rep.] EUR, 1998, (EUR 17929), 1–199

Stage extent of separation in ideal countercurrent recycle membrane cascades

Rony's extent of separation ξ is useful to characterize the quality of separation of a binary feed that occurs in membrane stages, membrane modules and cascades. The stage extent of separation, ξ i , has a maximum value for a specified stage separation factor, α i . The ideal cascade design requires a minimum total interstage flow compressor duty, and membrane area to make a specified overall separation. It is shown that ξ i has the maximum value at each stage in an ideal membrane cascade composed of ideal perfect-mix stages. This is also true in a “properly designed” no-mix cascade composed of crossflow stages. This suggests that ξ is a basic separation index.

Why on Earth Can People Need Continuous Recycle Membrane Reactors for Starch Hydrolysis?

Why on Earth Can People Need Continuous Recycle Membrane Reactors for Starch Hydrolysis?

Why on Earth Can People Need Continuous Recycle Membrane Reactors for Starch Hydrolysis?

Classically enzymatic hydrolysis of starch is conducted in batch reactor in a two-step process including liquefaction and saccharification. This paper presents some ideas to simplify this process and decrease its cost. Because today, either saccharifying enzymes able to attack native starch or strong liquefying catalysts leading to sufficient low-molecular weight hydrolysates may be easily found on the market, one can imagine to develop a one-step process just involving a unique species of enzymes. The process can also be improved by operating in a continuous way and reusing enzymes. Among the various reactors, the continuous recycle membrane reactor, briefly CRMR, seems to be the most attractive since it allows to perform hydrolysis while separating at the same time syrups from enzymes and non-hydrolyzed starch. (Resume d'auteur)

Gas‐separation membrane cascades utilizing limited numbers of compressors

AbstractA systematic procedure is presented to drawn n‐compressor membrane cascades for gas‐separation applications with n ≥ 1. In this method, a parent cascade structure is created that contains the n‐compressor cascades as substructures. These substructures are then revealed by systematically eliminating unwanted membrane stages and recycle compressors from the parent cascade. The procedure is illustrated by generating arrays of one‐ and two‐compressor cascade schemes. It is found that these arrays contain the cascade schemes known from the literature and also lead to some new schemes. This procedure increases the likelihood of finding an economically viable membrane cascade for a given separation application.

A Comparison of Countercurrent Recycle Membrane Cascades with Some “One-Compressor” Recycle Permeators for Gas Separations in Terms of Ideal Crossflow Stages

Abstract A comparison is made of counter-current recycle membrane cascades (5-stage constant recycle and 6-stage no-mix) with continuous membrane columns, two-unit series, and one-unit recycle membrane modules for the enrichment of O2 from air, assuming ideal crossflow stages. The crossflow stage equations permit easy comparisons and give insight into the inefficiencies associated with the “one compressor” module designs. For the separation specified (production of O2 enriched up to y P = 0.983, at a rate P = 17.6, from a feed x F = 0.21, rate F = 100), the one compressor designs require from about 90 to 16 times more total compressor duty, and from about 50 to 10 times more membrane area than the no-mix cascade design, depending on module design, to make the same separation. The one unit recycle module is least efficient, followed by the continuous membrane column, and the two unit series module. The basic reasons for the inefficiencies associated with the one compressor modules relative to the recycle cascades are explored.

Continuous hydrolysis of whey proteins in a membrane recycle reactor

Whey proteins were hydrolyzed in a membrane recycle reactor (MRR) in the presence of Alcalase 0.6L under varying enzyme to substrate ratios and residence times. Substrate conversion was directly dependent on these two parameters, and at a fixed enzyme-substrate ratio of 10%, conversion levels could be controlled through residence time, resulting in peptide permeates with homogeneous molecular and functional properties. In addition, recycling of the enzyme and elimination of peptide products resulted in much improved enzyme yields and process productivity levels. However, the process was only operational for 7 h, given membrane fouling and enzyme inactivation phenomena whose contribution occurred in a time-dependent manner. Changes in process design leading to increased reactor stability were examined, and the system is considered to provide a suitable basis for the production of peptides with specific functional and nutritional properties at the industrial level in the future.

?-Amylase production by Bacillus amyloliquefaciens in a membrane recycle bioreactor

A strain of Bacillus amyloliquefaciens was cultivated in a membrane recycle bioreactor for the production of an extracellular α-amylase. Continuous cultivations of B. amyloliquefaciens in the recycle fermentor led to higher cell mass and volumetric productivities than the ones obtained in batch or chemostat cultivations; the α-amylase activities were lower than in the batch mode but significantly higher than in the chemostat mode. The operation of the membrane recycle bioreactor was sometimes disturbed by high broth viscosity leading to a stronger fouling of the membrane.

Lactic acid from cheese whey permeate. Productivity and economics of a continuous membrane bioreactor

The economics of incorporating membrane modules in several steps in the conversion of whey permeate to lactic acid was studied. Membrane recycle fermenters operating at a cell concentration of 40 g l−1 resulted in a productivity of 22.5 g l−1h−1 with a lactate concentration of 89 g l−1 and a yield of 0.89. The membrane units (reverse osmosis for preconcentrating whey permeate, hollow-fiber ultrafiltration for clarification and for cell recycling) contribute about 28% of the total fixed capital costs and less than 5% of the operating cost. The two largest costs are whey transportation and yeast extract, contributing about 35% and 38% to the total product cost of US $ 0.98/kg 85% lactate. Without these two costs, unpurified lactate could be produced for $ 0.27/kg.

Process modelling considerations for the production of lactate from whey using membrane recycle bioreactors operated in continuous and cyclic batch modes

Using a membrane recycle bioreactor (MRB) to produce lactate from whey is potentially more cost effective than a traditional batch fermentation. Membrane recycle bioreactors can be operated in two modes: (1) cyclic batch; (2) continuous. Mathematical modelling of these two modes along with a batch fermentation is used to compare cost and reactor productivity and to examine the effects of selected process and kinetic parameters. Both modes have an optimum operating cell concentration, because there exists an economic trade-off between reactor vessel cost and membrane filtration cost with cell concentration as an optimization variable. The continuous mode is much more sensitive than the cyclic batch to the value of desired residual lactose concentration leaving the reactor, such that, for given kinetic parameters, there exists a value of residual lactose concentration below which the cyclic batch mode becomes more cost effective than the continuous mode. The big disadvantage of cyclic batch is that it is highly sensitive to any cell growth lag time between cycles.

Bioconversion of starches into maltotetraose using Pseudomonas stutzeri maltotetraohydrolase in a membrane recycle bioreactor: Effect of multiple enzyme systems and mass balance study

A simplified single-step method involving simultaneous production and purification of maltotetraose (G 4) by employing ultrafiltration (UF) membranes was previously proposed. The addition of a pretreatment step using pullulanase and then the G 4-amylase was expected to increase the yield of G 4. The single-enzyme system, however, showed 0.42 g higher total product output than the successive dual-enzyme system throughout 6 h reaction. The G 4 yield using the successive dual-enzyme system could be improved after removing the unwanted side product with UF. Experiments were conducted with membranes of larger pore size, but this did not significantly increase the total product output. The membrane unit with a molecular weight cutoff of 1,000 was the most appropriate membrane pore size for the G 4-exo-α-amylase membrane recycle bioreactor system. The total amount of substrate fouled in the membrane during a 6-h reaction was estimated as 69 mg glucose equivalent when substrate concentration was 0.25% (w/v). The mass balance equation indicated that the percent conversion of soluble starch to G 4 at steady state was 65%.

Starch to lactic acid in a continuous membrane bioreactor

Fermentation production of lactic acid directly from starch was studied in a membrane recycle bioreactor (MRB) using Lactobacillus amylovorus. With 50 g litre −1 liquefied starch as feed, essentially complete conversion to lactic acid was obtained up to a dilution rate of 0·2h −1; maximum productivity of 25 g litre −1 h −1 was obtained at 0·5 h −1. A higher starch concentration in the feed caused lower conversions, resulting in rapid accumulation of unconverted starch in the fermenter. The MRB was operated continuously for 10 days without significant problems. Media components were responsible for fouling the membrane module.

Bioconversion of unmodified native starches by Pseudomonas stutzeri maltotetraohydrolase: effect of starch type

Maltooligosaccharides including maltotetraose (G4) have unique uses in biochemical, clinical, pharmaceutical, and food applications. G4 productivity utilizing a G4-producing amylase from Pseudomonas stutzeri in a membrane recycle bioreactor (MRB) was compared using four kinds of unmodified starches differing in the ration of amylose to amylopectin and the amylopectin chain lengths, and also one modified soluble starch. The specific activity of the enzyme used for the MRB system was 21.5 units/mg protein. The product purity using a native corn starch was 20.0% higher than that using a modified soluble starch in an MRB of bench-top scale. Four kinds of unmodified native corn starches were shown to be better substrates than the modified soluble starch considering all the criteria of product purity, production rate, and total product output.

Process engineering for a membrane recycle fermentor

Membrane recycle fermentors are used successfully on laboratory scale to increase the efficiency of fermentation processes. The design of a process on larger scale however is obstructed by the lack of relevant data in literature. Compared to a stand-alone fermentor a membrane recycle fermentor presents new features which must be considered in the design. These features include the use of high density cultures, the additional volume in the membrane section and the circulation of the broth. In this theoretical study these aspects are analyzed with the characteristic time concept, in case of an ethanol fermentation integrated with microfiltration. The analysis shows that depending on the reactor configuration used concentration gradients can be expected. These gradients may decrease the efficiency of the fermentation, or can be advantageous, for example by letting the substrate conversion approach completion in the membrane section.

Ethanol production from whey in a membrane recycle bioreactor

Ethanol production from sulphuric acid whey permeate by Kluyveromyces marxianus Y-113 was examined in a membrane recycle bioreactor. The system was operated with 100% cell recycle and at a steady-state with 10 g litre −1 biomass. At D = 0·44 h −1 almost complete utilization of 53 g litre −1 lactose was achieved with an ethanol productivity of 8·6 g litre −1 h −1. Increasing the inlet lactose concentration or dilution rate increased the ethanol productivity but at the expense of lactose utilization. Elevated biomass or ethanol concentrations markedly decreased the specific growth rate and specific ethanol production rate.