Separation and concentration of L-phenylalanine using a supported liquid membrane

The separation and concentration of L-phenylalanine (L-Phe) using a supported liquid membrane (SLM) is investigated. A cation complex agent, di-2-ethylhexyl phosphoric acid (D₂EHPA), is used as a carrier in the SLM with n-Heptane as a solvent. The reaction order and equilibrium constant in the formation reaction of L-Phe-carrier complex are obtained from the extraction experment. A mathematical model for a carrier mediated counter transport process is proposed to estimate the diffusion coefficient of L-Phe-carrier complex in the liquid membrane. Permeation experiments of L-Phe using a SLM are performed under various operating conditions and optimum conditions for the transport of L-Phe are obtained. Concentration of L-Phe in the strip phase against its concentration is observed. Transport rate of glucose through liquid membrane is less than that of L-Phe in the competitive transport of L-Phe and glucose. And the existence of glucose reduced the transport rate of L-Phe. The performance of separation with continuous strip phase is increased due to the dilution effect in the strip phase.     

Urine sample preparation of tricyclic antidepressants by means of a supported liquid membrane technique for high-performance liquid chromatographic analysis

Supported liquid membrane (SLM) technique for sample work-up and enrichment was used for determination of tricyclic antidepressant drugs in urine by high-performance liquid chromatography (HPLC) with UV detection. The studied antidepressant drugs were amitriptyline, opipramol, noxiptyline and additionally diethazine was used as possible internal standard. Alkaline phosphoric buffer with urine sample, as the donor solution, was passed over the liquid membrane into which investigated substances were extracted. On the other side of the membrane, analyzed compounds were trapped due to creating non-extractable form in acidic acceptor solution. Enriched and cleaned up drugs were then injected into a HPLC system with ultraviolet detection to analyze of their concentration in acceptor solution. Optimum extraction efficiency was determined by changing acceptor and donor solutions pH, application of different flow rates of donor solution and by using different solvents in the membrane. Also, donor solution volume, extraction time and concentration of analytes were varied to check the linearity of extraction process. The highest extraction efficiency: 43% for opipramol, 56% for noxiptyline, 43% for amitriptyline and 42% for diethazine (R.S.D. values were <6% and n=3) was achieved when 0.05 M phosphate buffer pH 4.0 and 9.5 were used as donor and acceptor solutions, respectively, n-undecane with 5% tri-n-octylphosphine oxide (TOPO) was used as liquid membrane. Limit of quantification (LOQ) for tricyclic antidepressants after enrichment of 100ml of urine sample was about 1 ng/ml.     

A multiphasic hollow fiber reactor for the whole-cell bioconversion of 2-methyl-1,3-propanediol to (r)-beta-hydroxyisobutyric acid

This paper describes the bioconversion of 2-methyl-1,3-propanediol to (R)-beta-hydoxyisobutyric acid (HIBA) by Acetobacter ALEI in a hollow fiber membrane bioreaction system arrangement that allows the integration of three liquid phases: the aqueous bioconversion phase, the organic phase consisting of a solution of trioctyl phosphine oxide (TOPO) in isooctane, and the third phase consisting of a basic stripping solution that allows reextraction of HIBA from the organic phase. A comparison of HIBA mass transfer experiments was carried out in the membrane reactor with two and three phases for different pH and TOPO concentrations. The use of the three-phase arrangement allows the extraction of high quantities of HIBA from the aqueous medium (higher than 85%) independently of the pH, whereas in the two-phase system the percentage of HIBA extracted from the aqueous medium was lower, 42% in the best case, and strongly influenced by the pH. The percentage of the extractive agent TOPO in the organic phase influenced on the mass transfer rate in both bi- and triphasic arrangements. By simply integrating the re-extraction phase in the system it was possible to increase the extraction yield by 2-fold, reduce the amount of TOPO by 4-fold, and operate at the more favorable pH 4. A bioconversion experiment was done in these conditions (pH = 4, TOPO = 5%) to confirm the advantages of including the third stripping solution. Fed-batch operation of the triphasic membrane reactor was maintained for more than 20 h, reaching an HIBA concentration in the stripping solution of 29 g L(-)(1).     

Sample preparation,preservation, and storage for volatile fatty acid quantification in biogas plants

Volatile fatty acids (VFA) represent short‐chain fatty acids consisting of six or fewer carbon atoms that can be distilled at atmospheric pressure. In anaerobic digestion processes VFAs are of central importance for maintaining stable reactor performance and biogas production, are used as indicators for arising problems and are important process monitoring parameters. In the present study, sludge derived form a full‐scale anaerobic digester of a wastewater treatment plant was spiked with formate, acetate, propionate, and butyrate in order to evaluate various commonly used techniques for VFA extraction, preservation, and storage. It was shown that VFA extraction after centrifugation warranted the highest recovery rates for spiked VFAs. Moreover, experiments clearly indicated the importance of a fast sample handling, including the necessity of immediate cooling of the samples. Chemical sample preservation within a narrow time frame or deep freezing emerged as an alternative to instant VFA extraction. Short‐time storage of extracted VFA samples at + 4°C is an option for up to 7 days, for longer periods storage at –20°C was found to be applicable.     

Two-stage recovery of S-adenosylmethionine using supported liquid membranes with strip dispersion

We report the selective recovery of S-adenosylmethionine (SAM) from fermentation broths using a two-stage supported liquid membrane system with strip dispersion (SLM-SD). The system utilized two MiniModule^® hollow-fiber membrane modules as microporous supports and an organic membrane solution consisting of the extractants of sodium di-2-ethylhexyl sulfosuccinate (AOT), di-(2-ethylhexyl)phosphoric acid (DEHPA), and trioctylphosphine oxide (TOPO) in the solvent n-octanol. SAM was extracted in the first membrane module. Methionine (Met) was captured by the first stripping solution and further purified in the second membrane module. pH values in the feed phase and the first and second stripping solutions, extractant concentrations, NaCl concentration, and the SAM acceptor in the first stripping solution were optimized. Strip dispersion mixing speed, pressure differences across the membranes, and flow rates of the feed and strip dispersion phases were investigated experimentally. The optimal extractant concentrations were: AOT 2.78 wt%, DEHPA 27.0 wt%, and TOPO 1.61 wt%. The optimal pH values in the feed phase and the first and second stripping solution were 3.0, 2.5, and 1.0, respectively. SAM extraction efficiency of 98.7%, SAM recovery efficiency of 91.8% and Met removal efficiency of 85.4% were achieved within 5 h. Finally, the mass transfer analysis indicated that the mass transfer resistances from the extraction reaction and the membrane phase were predominant.     

On-line extraction of volatile fatty acids in acidogenic chemostat culture using a supported liquid membrane

An on-line extraction of volatile fatty acids (acetic and butyric acids) from acidogenic fermentation in chemostat cultures using a supported liquid membrane (SLM) was investigated in order to overcome end-product inhibition. By using SLM, the high-cell-density retaining dilution rate of the chemostat could be increased, thus enhancing the microbial acidogenesis. To further understand this phenomenon, the growth and extraction kinetics were studied. The effect of substrate concentration was found to obey the Haldane equation. Regarding the inhibition by volatile fatty acids, it turned out that undissociated butyric acid rather than acetic acid severely inhibited the growth, corresponding to non-competitive kinetics. The extraction rates of the acids were proportional to their undissociated concentration as well as to the SLM area/broth volume, and butyric acid extraction was easier than that of acetic acid.     

Exploring low-cost carbon sources for microbial lipids production by fed-batch cultivation of <Emphasis Type="Italic">Cryptococcus albidus</Emphasis>

Volatile fatty acids (VFAs), acetic acid, acetates, and ethanol were used as carbon sources for the production of microbial lipids using Cryptococcus albidus in batch cultures. C. albidus utilized organic acids less than glucose in the production of lipids, resulting in a lipid yield coefficient on VFAs of 0.125 g/g. In a two-stage batch culture, the lipid content increased to 43.8% (w/w) when VFAs were used as the sole carbon source in the second stage, which was two times higher than that of the batch culture. Furthermore, a 192 h, two-stage fed-batch cultivation of C. albidus produced a dry cell weight, lipid concentration, and lipid content of 26.4 g/L, 14.5 g/L, and 55.1% (w/w), respectively. The fed-batch culture model used in this study featured pure VFA solutions, with intermittent feeding, under oxygen-enriched air supply conditions. This study investigated several alternative carbon sources to reduce the cost of microbial lipids production and proved the feasibility of using VFAs as the carbon source for the provision of a high lipid content and productivity.     

Using enriched cultures for elevation of anaerobic syntrophic interactions between acetogens and methanogens in a high-load continuous digester

Volatile fatty acids (VFAs) are key intermediates in anaerobic digestion. Enriched acetogenic and methanogenic cultures were used for syntrophic anaerobic digestion of VFAs in a high-load continuous reactor fed with acetic (HAc), propionic (HPr) and butyric (HBu) acids at maximum concentrations of 5, 3 and 4 g/L, respectively. Interactive effects of HPr, HBu and HAc were analyzed. Furthermore, hydraulic retention time (HRT) and methanogen to acetogen population ratio (M/A) were investigated as key microbiological and operating variables of VFA anaerobic degradations. Optimum conditions were found to be HPr = 1125.0 mg/L, HBu = 1833.4 mg/L, HAc = 1727.4 mg/L, HRT = 21 h and M/A = 2.5 (corresponding to maximum VFA removal and biogas production rate (BPR)). Results of verification experiments and predicted values from fitted correlations were in close agreement at 95% confidence interval. HRT and M/A had positive effects on VFA removal and BPR. M/A was the most important factor that affected BPR. All VFAs inhibited VFA removals.     

Extractive separation of penicillin G by facilitated transport via carrier supported liquid membranes

The facilitated transport of penicillin G (Pen G), through a supported liquid membrane with Amberlite LA-2 dissolved in 1-decanol, supported on a microporous polypropylene membrane, were studied. The distribution coefficient was obtained from a batch extraction experiment. The effects of flow rate, carrier concentration, initial concentration of Pen G, and the pH of feed and stripping phases on the transport rate of Pen G through the supported liquid membrane were also investigated. The results are in agreement with theoretical predictions, and it is demonstrated that the transport of Pen G through the supported liquid membrane is controlled simultaneously by mass transfer across both aqueous and liquid membranes. (c) 1993 John Wiley & Sons, Inc.     

Medium chain length polyhydroxyalkanoate (mcl-PHA) production from volatile fatty acids derived from the anaerobic digestion of grass

A two step biological process for the conversion of grass biomass to the biodegradable polymer medium chain length polyhydroxyalkanoate (mcl-PHA) was achieved through the use of anaerobic and aerobic microbial processes. Anaerobic digestion (mixed culture) of ensiled grass was achieved with a recirculated leach bed bioreactor resulting in the production of a leachate, containing 15.3 g/l of volatile fatty acids (VFAs) ranging from acetic to valeric acid with butyric acid predominating (12.8 g/l). The VFA mixture was concentrated to 732.5 g/l with a 93.3 % yield of butyric acid (643.9 g/l). Three individual Pseudomonas putida strains, KT2440, CA-3 and GO16 (single pure cultures), differed in their ability to grow and accumulate PHA from VFAs. P. putida CA-3 achieved the highest biomass and PHA on average with individual fatty acids, exhibited the greatest tolerance to higher concentrations of butyric acid (up to 40 mM) compared to the other strains and exhibited a maximum growth rate (μ_MAX?=?0.45 h^?1). Based on these observations P. putida CA-3 was chosen as the test strain with the concentrated VFA mixture derived from the AD leachate. P. putida CA-3 achieved 1.56 g of biomass/l and accumulated 39 % of the cell dry weight as PHA (nitrogen limitation) in shake flasks. The PHA was composed predominantly of 3-hydroxydecanoic acid (>65 mol%).     

Dynamics of the anaerobic process: effects of volatile fatty acids

A complex and fast dynamic response of the anaerobic biogas system was observed when the system was subjected to pulses of volatile fatty acids (VFAs). It was shown that a pulse of specific VFAs into a well-functioning continuous stirred tank reactor (CSTR) system operating on cow manure affected both CH(4) yield, pH, and gas production and that a unique reaction pattern was seen for the higher VFAs as a result of these pulses. In this study, two thermophilic laboratory reactors were equipped with a novel VFA-sensor for monitoring specific VFAs online. Pulses of VFAs were shown to have a positive effect on process yield and the levels of all VFA were shown to stabilize at a lower level after the biomass had been subjected to several pulses. The response to pulses of propionate or acetate was different from the response to butyrate, iso-butyrate, valerate, or iso-valerate. High concentrations of propionate affected the degradation of all VFAs, while a pulse of acetate affected primarily the degradation of iso-valerate or 2-methylbutyrate. Pulses of n-butyrate, iso-butyrate, and iso-valerate yielded only acetate, while degradation of n-valerate gave both propionate and acetate. Product sensitivity or inhibition was shown for the degradation of all VFAs tested. Based on the results, it was concluded that measurements of all specific VFAs are important for control purposes and increase and decrease in a specific VFA should always be evaluated in close relationship to the conversion of other VFAs and the history of the reactor process. It should be pointed out that the observed dynamics of VFA responses were based on hourly measurements, meaning that the response duration was much lower than the hydraulic retention time, which exceeds several days in anaerobic CSTR systems.     

Volatile fatty acid production from lignocellulosic biomass by lime pretreatment and its applications to industrial biotechnology

Lignocellulosic biomass was pretreated with lime, and used for the production of VFA (volatile fatty acid) through batch anaerobic digestion. About 0.34 g VFA yield was obtained using 10 g/L reed, after 3 days of fermentation with lime treatment; however, a higher VFA yield (more than 0.5 g/g biomass) was achieved with a modified lime treatment. Overall, our study showed that that the modified lime treatment is better suited for VFA production. VFAs can be widely used in platforms for fuels and chemicals from biomass.     

Extraction of organic acids from kiwifruit juice using a supported liquid membrane process

In order to extract or remove organic acids from kiwifruit juice, we evaluated their separation and transport rates through supported liquid membranes (SLMs). The liquid membrane consisted of an organic solution composed of a carrier (Aliquat 336/Alamine 336) and a linear alcohol (oleyl alcohol) and was loaded on a microporous polypropylene support (commercial grade Celgard 2500/2400). These SLMs were evaluated (i) in a batch cell to determine the permeability and (ii) in a continuous spiral membrane module to study the effects of various process parameters – flow of feed and strip solutions, membrane composition, recycling mode of operation and kiwifruit juice at natural pH. It was observed that there exists an optimum for each system: pH?2.5–?3.0 for Alamine 336/oleyl alcohol and pH?4.5 for Aliquat 336/oleyl alcohol. At this pH?the flux rates of citric acid and malic acid was greater (6–8 times) than that of quinic acid. The flux rates decreased (greatly for citric acid) with the flow rate of feed and strip solutions and increased (considerably for citric acid) with the SLM composition . The recycling of feed and strip solutions significantly improved the removal efficiency. The SLM system retained its performance over a period of a few days. The SLM process allowed extraction of the above three organic acids (ascorbic acid was removed in trace amounts) from kiwifruit juice at a rate of a few percent (5%) in a single-pass processing.     

A novel membrane bioreactor for detoxifying industrial wastewater: II. Biodegradation of 3-chloronitrobenzene in an industrially produced wastewater

A novel membrane bioreactor has been used for the treatment of an industrially produced wastewater arising in the manufacture of 3-chloronitrobenzene. This wastewater is not amenable to direct biological treatment without some form pretreatment or dilution, due to the inorganic composition (pH <1, salt concentration 4% w/w) of the wastewater. In the membrane bioreactor, the organic pollutants are first separated from the wastewater by selective membrane permeation, and then biodegraded in the biological growth compartment of the bioreactor. At a wastewater flow rate of 64 mL h(-1) (corresponding to a contact time of approximately 1.7 hours) over 99% of the 3-chloronitrobenzene and over 99% of the nitrobenzene in the wastewater were degraded. Degradation of 3-chloronitrobenzene was accompanied by evolution of chloride ions in a stoichiometric ratio. Both 3-chloronitrobenzene and nitrobenzene degradation were accompanied by the evolution of carbon dioxide; approximately 80% of the carbon entering the system was oxidized to CO(2) carbon. Analysis of mass transport across the membrane revealed that 3-chloronitrobenzene and nitrobenzene are transported more rapidly than phenol. This is explained in terms of a resistances-in-series model, which shows phenol transfer to be rate limited by the membrane diffusion step, whereas the chloronitrobenzene and nitrobenzene transfer are rate limited by the liquid film mass transfer. (c) 1993 Wiley & Sons, Inc.     

Effect of temperature and hydraulic retention time on volatile fatty acid production based on bacterial community structure in anaerobic acidogenesis using swine wastewater

To investigate the effect of hydraulic retention time (HRT) and temperature (T) on bacterial community structure and volatile fatty acids (VFAs) production of an acidogenic process, and VFA production and changes in the bacterial community in three identical automated anaerobic continuously-stirred tank reactors were analyzed using response surface analysis (RSA) and nonmetric multidimensional scaling (NMDS). For RSA, 11 trials were conducted to find the combination of T and HRT under which VFA production was greatest; VFA production was affected more by HRT than by T. To identify the bacterial community structure in each trial, DNA from each experimental point of the RSA was analyzed using denaturating gradient gel electrophoresis (DGGE), and eight bacteria species were detected. NMDS was conducted on band intensities obtained using DGGE, and bacterial community structure was affected more by T than by HRT. Taken together, these results suggest that VFA production during acidogenesis was more dependent on the physicochemical properties of acidogens, such as their specific growth rate or contact time with of substrates, than on changes in the microbial community.     

Performance of microbial fuel cell with volatile fatty acids from food wastes

Food wastes were used as feedstock for the direct production of electricity in a microbial fuel cell (MFC). MFC operations with volatile fatty acids (VFA) produced 533 mV with a maximum power density of 240 mW/m². Short-chain VFAs, such as acetate, were degraded more rapidly and thus supported higher power generation than longer chain ones. In general, the co-existence of other, different VFAs slowed the removal of each VFA, which indicated that anodic microbes were competing for different substrates. 16S rRNA gene analysis using PCR-DGGE indicated that the MFC operation with VFAs had enriched unique microbial species.     

A novel membrane bioreactor for detoxifying industrial wastewater: I. Biodegradation of phenol in a synthetically concocted wastewater

A novel process has been used to biodegrade phenol present in an acidic (1 M HCI) and salty (5% w/w NaCl) synthetically bioreactor, in which the phenol present in the wastewater is separated from the inorganic components by means of a silicone rubber membrane. Transfer of the phenol from the wastewater and into a biological growth medium allows biodegradation to proceed under controlled conditions which are unaffected by the hostile inorganic composition of the wastewater. At a wastewater flow rate of 18 mL h(-1) (contact time 6 h), 98.5% of the phenol present in the wastewater at an inlet concentration of 1000 mg ( (-1) ) was degraded; at a contact time of 1.9 h, 65% of the phenol was degraded. Phenol degradation was accompanied by growth of a biofilm on the membrane tubes and by conversion of approximately 80% of the carbon entering the system to CO(2) carbon. Analysis of the transport of phenol across the membrane revealed that the major resistance to mass transfer arose in the diffusion of phenol across the silicone rubber membrane. A mathematical model was used to describe the transfer of phenol across the membrane and the subsequent diffusion and reaction of phenol in the biofilm attached to the membrane tube. This analysis showed that (a) the attached biofilm significantly lowers the mass transfer driving force for phenol across the membrane, and (b) oxygen concentration limits the phenol degradation rate in the biofilm. These conclusions from the model are consistent with the experimental results. (c) 1993 Wiley & Sons, Inc.     

Separation and recovery of radioactive and non-radioactive toxic trace elements from aqueous industrial effluents

An update is presented on liquid membrane-based processes as viable and relevant alternatives to conventional approaches such as precipitation, solvent extraction, ion exchange processes and electrochemical techniques for the removal and recovery of some toxic and/or valuable trace metal ions including some actinides and fission products e.g. U, Am, Y etc and As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Zn etc from radioactive as well as non-radioactive aqueous waste solutions respectively. In particular, results of experiments aimed at developing supported liquid membrane(SLM)-based process using commercially available porous membranes and indigenously prepared track--etch membranes (TEMs) have been critically examined in laboratory studies to generate basic data needed to evaluate their utility for continuous operation without regeneration. These include effect of pore size, porosity, optimum pore size and their reusability. It is clearly demonstrated that indigenously prepared 10 microm thick TEMs with a porosity in the range of 2-5% give comparable transport rates for metal ions-matching with that of commercial membranes of much higher thickness (160 microm) and higher porosity of 60-85%. The smaller thickness of TEMs more than compensates for their lower porosity. It is shown that because of their well defined pore characteristics TEMs could serve as model supports in SLM studies. By comparing the values of permeability coefficient (P) for TEM and polytetraflouroethylene (PTFE) supports for the transport of Pb2+ chosen as a typical divalent metal ion, and using di-2 ethyl hexyl phosphoric acid (D2EHPA) as the carrier, it is unambiguously proved that diffusion of the metal complex across the membrane is the rate controlling step in metal ion transport in SLM-based processes. An overview of the experimental findings along with future outlook and suggestions for further work are presented in this paper.     

Inhibition by fatty acids during fermentation of pre-treated waste activated sludge

Fermentation of waste activated sludge produces volatile fatty acids (VFAs), which can be used as the carbon sources for numerous biological processes. However, product inhibition can limit extent of fermentation to VFAs. In this study, product inhibition during fermentation of waste activated sludge pre-treated by a thermal hydrolysis process (THP-WAS) was investigated. Product inhibition was confirmed as spiking reactors with high levels of a mix of VFAs prevented fermentation taking place. Various inhibition models were trialled and it was found that a threshold model (based on thermodynamics) provided the best fit between model and data. This is the first time that threshold type inhibition has been shown for a mixed substrate, mixed population system. Batch fermentations carried out with THP-WAS of different dilutions were used to evaluate the impact of different organic loadings. The threshold VFA concentration for the systems studied was determined to be 17±1gCOD(VFA)L(-1). Inhibition was shown to be due to the presence of a combination of VFAs containing 2-6 carbon atoms each. When evaluated individually, by spiking individual VFAs, all VFAs except for acetate had the same impact at this threshold; acetate being approximately 50% as inhibitory as the other organic acids (COD basis). Based on this, a weighted model could be proposed to better represent the data. Strategies to improve overall yield could be increased production of acetate, or dilution to below the inhibitory level.     

Dynamic Transition of a Methanogenic Population in Response to the Concentration of Volatile Fatty Acids in a Thermophilic Anaerobic Digester

In this study, the microbial community succession in a thermophilic methanogenic bioreactor under deteriorative and stable conditions that were induced by acidification and neutralization, respectively, was investigated using PCR-mediated single-strand conformation polymorphism (SSCP) based on the 16S rRNA gene, quantitative PCR, and fluorescence in situ hybridization (FISH). The SSCP analysis indicated that the archaeal community structure was closely correlated with the volatile fatty acid (VFA) concentration, while the bacterial population was impacted by pH. The archaeal community consisted mainly of two species of hydrogenotrophic methanogen (i.e., a Methanoculleus sp. and a Methanothermobacter sp.) and one species of aceticlastic methanogen (i.e., a Methanosarcina sp.). The quantitative PCR of the 16S rRNA gene from each methanogen revealed that the Methanoculleus sp. predominated among the methanogens during operation under stable conditions in the absence of VFAs. Accumulation of VFAs induced a dynamic transition of hydrogenotrophic methanogens, and in particular, a drastic change (i.e., an approximately 10,000-fold increase) in the amount of the 16S rRNA gene from the Methanothermobacter sp. The predominance of the one species of hydrogenotrophic methanogen was replaced by that of the other in response to the VFA concentration, suggesting that the dissolved hydrogen concentration played a decisive role in the predominance. The hydrogenotrophic methanogens existed close to bacteria in aggregates, and a transition of the associated bacteria was also observed by FISH analyses. The degradation of acetate accumulated during operation under deteriorative conditions was concomitant with the selective proliferation of the Methanosarcina sp., indicating effective acetate degradation by the aceticlastic methanogen. The simple methanogenic population in the thermophilic anaerobic digester significantly responded to the environmental conditions, especially to the concentration of VFAs.