On-line monitoring of biotechnological processes by gas chromatographic-mass spectrometric analysis of fermentation suspensions

An on-line monitoring system has been developed for the control of a biorreactor for the anaerobic pretreatment of an industrial waste water. The monitoring system is based on a process mass spectrometer with a temperature controlled membrane inlet. The membrane introduction mass spectrometer (MIMS) is coupled with a resistively heated metal gas chromatography capillary column, which serves as a transfer line between the bioreactor and the MIMS. Sampling and injection is performed by means of a pneumatically driven membrane probe, which enables monitoring of soluted and gaseous substances in the fermentation broth. The system can also be coupled to other processes.     

Continuous monitoring for cyanide in waste water with a galvanic hydrogen cyanide sensor using a purge system

A continuous monitoring system for cyanide with a galvanic hydrogen cyanide sensor and an aeration pump for purging was developed. Hydrogen cyanide evolved from cyanide solution using a purging pump was measured with the hydrogen cyanide sensor. The system showed good performance in terms of stability and selectivity. A linear calibration curve was obtained in the concentrating range from 0 to 15 mg dm³ of cyanide ion with a slope of −0.24 μA mg⁻¹ dm⁻³. The lower detection limit was 0.1 mg dm⁻³. The 90% response time of the sensor system was within 3.5 min for a 0.5 mg dm⁻³ cyanide solution, when the flow rate of the purging air was 1 dm³ min⁻¹. The system maintained the initial performance for 6 months in the field test. The developed galvanic sensor system was not subject to interference from sulfide and residual chlorine, compared with a potentiometric sensor system developed previously. The analytical results obtained by the present system were in good agreement with those obtained by the pyridine pyrazolone method. The correlation factor and regression line between both methods were 0.979 and Y=2.30×10⁻⁴+1.12X, respectively. This system was successfully applied for a continuous monitoring of cyanide ion in waste water.     

On-line monitoring of continuous beer fermentation process using automatic membrane inlet mass spectrometric system

A fully automatic membrane inlet mass spectrometric (MIMS) on-line instrumentation for the analysis of aroma compounds in continuous beer fermentation processes was constructed and tested. The instrumentation includes automatic filtration of the sample stream, flushing of all tubing between samples and pH control. The calibration standards can be measured periodically. The instrumentation has also an extra sample line that can be used for off-line sample collection or it can be connected to another on-line method. Detection limits for ethanol, acetic acid and eight organic beer aroma compounds were from μg l⁻¹ to low mg l⁻¹ levels and the standard deviations were less than 3.4%. The method has a good repeatability and linearity in the measurement range. Response times are shorter than or equal to 3 min for all compounds except for ethyl caproate, which has a response time of 8 min. In beer aroma compound analysis a good agreement between MIMS and static headspace gas chromatographic (HSGC) measurements was found. The effects of different matrix compounds commonly present in the fermentation media on the MIMS response to acetaldehyde, ethyl acetate and ethanol were studied. Addition of yeast did not have any effect on the MIMS response of ethanol or ethyl acetate. Sugars, glucose and xylose, increased the MIMS response of all studied analytes only slightly, whereas salts, ammonium chloride, ammonium nitrate and sodium chloride, increased the MIMS response of all three studied compounds prominently. The system was used for on-line monitoring of continuous beer fermentation with immobilised yeast. The results show that with MIMS it is possible to monitor the changes in the continuous process as well as delays in the two-phase process.     

On-line analysis of polymer melt processes

Molten polymer process streams are difficult to analyze either in- or on-line because of sampling problems due to the high temperature and viscosity of the molten state. Real-time monitoring of chemical compositions in these processes can significantly improve safety and product quality and minimize process costs and waste. The information content of the mid-infrared spectrum combined with the recent development of rugged process Fourier transform (FT) IR spectrometers is stimulating the application of process FT-IR to industrial polymer melt processes. Sampling considerations for polymer melts are reviewed. Also, the use of FT-IR spectrometry for on-line measurements of the polymer composition for polymer blends and copolymers in the melt, and the question of how this information could be used to monitor and control the quality of the product given by the process are discussed.     

Determination of cyanide using flow-injection multisensor system

A flow-injection multisensor system (FIMS) comprising potentiometric sensors of different types for determination of free cyanide activity in basic solutions for extraction of noble metals was developed. The solvent polymeric membrane sensors based on metalloporphyrin and crystalline sensors were combined in the sensor system. The system allowed determination of cyanide activity in the range 10⁻⁴–1 mol l⁻¹ with an error less than 5% in individual cyanide solutions and acceptable precision (about 20%) in process liquids. The system was able to analyse up to 20 samples per h. The FIMS was also applied to detecting of silver ions in the presence of cyanide. Chalcogenide glass sensor was used as the detector that ensured the precision of 20%.     

On-line gas chromatographic monitoring of catalyst processes in a microfabricated chemical reactor

A microfabricated catalyst reactor, prepared from glass and polydimethylsiloxane, has been directly interfaced to a gas chromatograph permitting real time reaction monitoring allowing rapid catalyst characterisation.     

On-line determination of cyanide in the presence of sulfide by flow injection with pervaporation

A pervaporation-flow injection (PFI) method is described for the analysis of cyanide in the presence of sulfide. The interfering sulfide ion in the injected sample is precipitated on-line using an acidified lead nitrate reagent solution before the donor stream enters the pervaporation cell. Using amperometric detection at a silver electrode set at −50 mV (vs Ag/AgCl), linear calibration was obtained in the range 0.02–100.0 mg l⁻¹ with a detection limit of 1.0 μg l⁻¹. Sample throughput was of the order of 12–15 h⁻¹. When the method was applied to the analysis of synthetic samples, there was no significant interference from sulfide at concentrations up to 50 mg l⁻¹. Thiocyanate did not interfere at levels up to 1000 mg l⁻¹. When applied to industrial samples containing sulfide and thiocyanate ions where the cyanide ions are predominantly complexed with various metal ions the PFI method was found to give results close to those obtained by standard distillation methods for weak acid dissociable (WAD) cyanide.     

Non-invasive monitoring of fouling in hollow fiber membrane via UTDR

Fouling is the most critical problem associated with membrane separations in liquid media. But it is difficult to control the inevitable membrane fouling because of its invisibility, especially on the inside surface of hollow fiber membranes. This study describes the extension of ultrasonic time-domain reflectometry (UTDR) for the real-time measurement of particle deposition in a single hollow fiber membrane. A transducer with a frequency of 10 MHz and polyethersulfone hollow fiber membranes with 0.8 mm inside diameter (ID) and 1.2 mm outside diameter (OD) were used in this study. The fouling experiments were carried out with 1.8 g/L kaolin suspension at flow rates 16.7 and 10.0 cm/s. The results show that UTDR technique is able to distinguish and recognize the acoustic response signals generated from the interfaces water/upper outside surface of the hollow fiber, lumen upside surface/water, water/lumen underside surface and lower outside surface/water in the single hollow fiber membrane module in pure water phase. The systemic changes of acoustic responses from the inside surfaces of the hollow fiber in the time- and amplitude-domain with operation time during the fouling experiments were detected by UTDR. It is associated with the deposition and formation of the kaolin layer on the inside surfaces. Further, the acoustic measurement indicates that the deposited fouling layer is denser on the lumen underside surface of the hollow fiber than that on the lumen upside surface as a result of weight. Moreover, it is found that the fouling layer grows faster on the inside surface of the hollow fiber at a flow rate of 10.0 cm/s than that at 16.7 cm/s due to the lower shear stress. The fouling layer formed is thicker at a flow rate of 10.0 cm/s than that at 16.7 cm/s. The flux decline data and SEM analysis corroborate the ultrasonic measurement. Overall, this study confirms that UTDR measurement will provide not only a new protocol for the observation of hollow fiber membrane fouling and cleaning, but also a quantitative approach to the optimization of the membrane bioreactor system.     

On-line fermentation gas analysis: Error analysis and application of mass spectrometry

On-line fermentation gas analysis is of general interest because it permits the determination of metabolic rates in almost any biological process using living organisms. The consumption and production of gases (O₂, CO₂, CH₄, etc.) and volatile compounds may be determined without causing any risk of infection. Elemental balancing permits the determination of other metabolic rates if the stoichiometry is known. This was studied with the production of poly-β-hydroxybutyrate (PHB) by Alcaligenes latus. Estimations were based on the measurement of gas partial pressure and flow-rates, pH and alkali consumption rate. Experiments with a small quadrupole mass spectrometer showed unacceptable error propagation. Therefore, dynamic error propagation for all rates was studied using simulation. It was found that, for example, a 1% relative offset-calibration error for oxygen can result in an error in PHB estimation of > 50%. It is suggested that this culture is used in combination with elemental balancing for thorough tests of the accuracy of on-line gas analysis equipment. An on-line process gas analyser based on a quadrupole mass spectrometer (Balzers PGM 407) gave the following precision values (abs. vol.?%) during cultivation of Bacillus subtilis: nitrogen (m/z 14), 0.024; oxygen (m/z 32), 0.020; argon (m/z 40), 0.0011; and carbon dioxide (m/z 44), 0.0034. These values, combined with automatic recalibration, would be sufficient for reasonable estimation of PHB, biomass and substrates.     

On-line analysis of volatile fatty acids in anaerobic treatment processes

In this paper, an on-line spectrofluorimetric system is proposed for a simple, rapid and accurate measurement of volatile fatty acids (VFA) in anaerobic treatment processes. The determination method is based on the derivatization of VFA with N-(1-naphthyl)ethylenediamine (EDAN) followed by a spectrofluorimetric detection of the corresponding amide. The analytical procedure is automated with a flow analysis technique, coupling multisyringe (MSFIA) and multi-pumping (MPFS) methods. Operative conditions have been investigated with a special attention paid to the activation and amidation steps and to the liquid-liquid extraction of the derivatized final product. Fluorescence intensities (λ_em = 335 nm, λ_ex = 395 nm) were found to be proportional to the concentration of VFA, expressed as acetic equivalent, in the range 19-1000 mg L⁻¹, with a detection limit (3σ) of 5.1 mg L⁻¹. Our results showed a good selectivity for VFA as compared to other organic and inorganic compounds usually found in sewage sludges. Validation of the on-line system developed has been assessed by application of the procedure to aqueous samples originating from sewage sludge treatment plants. The results were in good agreement with ion chromatography measurements.     

Sequential injection analysis system for on-line monitoring of l-cysteine concentration in biological processes

A sequential injection analysis (SIA) system was developed to monitor the concentration of l-cysteine in biological processes on-line. It is based on the redox reaction of l-cysteine with iron(III) in the presence of 1,10-phenanthroline (phen) and the detection of the red-iron(II)-phen complex with a spectrophotometry. The system was fully automated using software written in the LabVIEW™ development environment. A number of system variables such as the flow rate of the carrier buffer solution, the volume ratio of the sample to the reagents, and the reaction coil length, etc., were evaluated to increase the sensitivity and performance of the SIA system. Under partially optimized operating conditions the performance of the SIA system was linear up to a concentration of l-cysteine of 1 mM (R² = 0.998) with a detection limit of 0.005 mM and a sample frequency of 15 hr⁻¹. The SIA system was employed to monitor the concentration of l-cysteine on-line in a continuously stirred reactor and a fermentation process of Saccharomyces cerevisiae. The on-line monitored data were in good agreement with the off-line data measured by a HPLC with a fluorescence detector (n = 15, R² = 09899).     

Flow injection analysis-flame atomic absorption spectrometry system for indirect determination of cyanide using cadmium carbonate as a new solid-phase reactor

A new and simple flow injection system procedure has been developed for the indirect determination of cyanide. The method is based on insertion of aqueous cyanide solutions into an on-line cadmium carbonate packed column (25% m/m suspended on silica gel beads) and a sodium hydroxide with pH 10 is used as the carrier stream. The eluent containing the analyte as cadmiumcyanide complexes, produced from reaction between cadmium carbonate and cyanide, measured by flame atomic absorption spectrometry. The absorbance is proportional to the concentration of cyanide in the sample. The linear range of the system is up to 15 mg L⁻¹ with a detection limit 0.2 mg L⁻¹ and sampling rate 72 h⁻¹. The method is suitable for determination of cyanide in industrial waste waters with a relative standard deviation better than 1.22%.     

Ion chromatographic determination of sulfide and cyanide in real matrices by using pulsed amperometric detection on a silver electrode

The determination of free sulfide and cyanide by pulsed amperometric detection (PAD) at a silver-working electrode was improved through a deep de-oxygenation (at least 10 min) of both standard and real solutions containing the two analytes and adopting a two-potential waveform able to eliminate Ag working electrode fouling. The waveform stepped around the oxidation of Ag in the presence of 0.1-0.4 M hydroxyl ion, from -0.1 to 0.1 V versus saturated calomel electrode (SCE). The eluent composition (0.4 M NaOH plus 7.5 mM oxalate solution) allowed a very good column efficiency and selectivity. The presence of a polysulfide species was hypothesized in sulfide solutions that had not been de-oxygenated and aged. The polysulfide eluted just before sulfide and was confirmed by a chemical test with SO3(2-) producing the elimination of the polysulfide peak. Detection limits, according to the Hubaux-Vos method, were 1.0 and 2.0 microg/l for S2- and CN , respectively. We demonstrated good performance of the optimized method by repeatedly injecting standard solutions and by analyzing different real matrices. The method exhibited very good accuracy and repeatability (10 microg/l and a 500 microl injection loop, had a repeatability better than 3% for sulfide and 100 microg/l had a repeatability better than 1% for cyanide). The two-potential waveform ensured long-term stability of the electrode surface that required no manual polishing procedure for at least 1 month (20 analysis per day).     

On-line and in situ monitoring of oxygen concentration and gas temperature in a reheating furnace utilizing tunable diode-laser spectroscopy

Increased demands on energy savings and quality control in metallurgical processes have created incentives for new methods to monitor and control the process. In this paper we will present a field trial that shows the potential of tunable diode-laser spectroscopy (TDLS) for simultaneous contact free measuring and monitoring of the oxygen concentration as well as the gas temperature in a reheating furnace during production. The field trials were carried out at an oil-fueled reheating furnace during 7 weeks of production. The tunable diode-laser spectrometer was measuring in situ across the preheating zone and the soaking zone in the furnace. During the campaign the oxygen concentration and the gas temperature in the furnace environment were simultaneously monitored and instantaneous variations in these parameters could easily be recorded and subsequently correlated to actual changes in the process. Furthermore, the much shorter response-time of the TDLS technique compared with conventional measurement methods such as thermocouples and extractive gas analyzers was also demonstrated during the trials. The results show the potential for the TDLS technique to be used for energy savings as well as product quality improvements by controlling the burners in the reheating furnace. The results show that it would be possible to control and optimize the oxygen concentration with TDLS in the control loop of the reheating furnace.     

Membrane separation of nitrogen from natural gas: A case study from membrane synthesis to commercial deployment

Fourteen percent of U.S. natural gas contains excess nitrogen, and cannot be sent to the national pipeline without treatment. Nitrogen is difficult to economically separate from methane, by any technology. Currently, the only process used on a large scale is cryogenic liquefaction and fractionation, but this technology requires economies of scale to be practical. Many owners of small gas fields cannot produce their gas for lack of suitable nitrogen separation technology. This paper describes the development of selective membranes to treat natural gas containing high concentrations of nitrogen. Membranes selectively permeate either nitrogen or methane, the principal constituent of natural gas. Our work has shown that methane-selective membranes are generally preferable and membranes with high permeances and methane/nitrogen selectivities of approximately 3–3.5 were developed. This selectivity is modest, so commercial systems often require multi-stage or multi-step process designs. Despite the design complexity and compression requirements, multi-step/multi-stage membrane systems are the lowest cost nitrogen removal technology in many applications. To date, 12 membrane-based systems for nitrogen removal for natural gas processing have been installed.     

On-line monitoring of a frontal chromatographic separation using inductively coupled plasma atomic emission spectroscopy

A test array is described employing a destructive analytical technique for the long-term monitoring of an industrial-scale separation process. As an example, we chose frontal chromatography as the separation and ICP/AES as the analytical method. The feed solution of the process was conveyed by a process pump via the separation unit to a sample station, where a small portion was diverted and transported by a roller pump into the spectrometer. We equipped our array with different loops for operating the process, calibrating the instrument and verifying the calibration. We obtained identical results for the different loops by absorbing the pulsation of the process pump and arranging for identical suction lines of the spectrometer pump. Based on the results, we redesigned the sample station for a technical application using only commercially available parts.     

Coumarinyl aldehyde as a Michael acceptor type of colorimetric and fluorescent probe for cyanide in water

A simple aldehyde-functionalized coumarin (1) was utilized as a doubly activated Michael acceptor type of chemodosimeter for cyanide in water. The probe has shown a selective and sensitive response to the cyanide anion over other various anions through the Michael addition reaction of the cyanide to 1. When cyanide anions were added, the prominent color changes as well as fluorescence changes of 1 were observed so that millimolar concentrations of cyanides were detectable by the naked eye.     

On-line combination of liquid chromatography and capillary gas chromatography. Preconcentration and analysis of organic compounds in aqueous samples

This paper describes the design of a new, versatile, and low-cost on-line LC-GC interface that allows the fast and reliable introduction of large sample volumes onto a capillary GC column. The sample introduction procedure consists successively of: evaporation of the entire sample (LC fraction), selective removal of the solvent and simultaneously cold-trapping of the solutes, splitless transfer of the solutes to the GC column, on-column focusing, GC separation and detection. Quantitative and qualitative aspects of various experimental parameters are evaluated and optimum conditions are reported. The applicability of the method is demonstrated on a synthetic aqueous sample of chlorinated pesticides.     

Rapid colorimetric sensing of cyanide anion in aqueous media with a spiropyran derivative containing a dinitrophenolate moiety

A spiropyran derivative containing a dinitrophenolate moiety (2: 1′,3′,3′-trimethyl-6,8-dinitro-spiro-[2H-1-benzopyran-2,2′-indoline]) behaves as a receptor for selective detection of cyanide anion (CN⁻) in aqueous media. Compound 2, when dissolved in aqueous media, spontaneously produces the spirocycle-opened merocyanine (MC) form even in dark condition. The absorption band of the MC form decreases selectively upon addition of CN⁻, via a nucleophilic addition of CN⁻ to the spirocarbon of the MC form. The nucleophilic addition occurs very rapidly (within 1 min) and enables rapid and selective quantification of very low levels of CN⁻ (>0.8 μM) by an absorption analysis.     

Prediction of axial concentration profiles in an extractive membrane bioreactor and experimental verification

A steady-state mathematical model has been developed to predict axial-concentration profiles of a pollutant in an extractive-membrane bioreactor (EMB). Typically, the previous models describe the pollutant concentration profiles in the membrane-attached biofilms in a direction perpendicular to the membrane. In contrast, the model presented in this work describes not only the radial profiles, but also the axial profiles along the membrane length. Biofilms of Xanthobacter autotrophicus GJ10 were grown on the surface of silicone rubber tubes. A diffusion-reaction model was employed to describe the diffusion and reaction in the biofilm in the radial direction. Membrane tubes were modelled as a series of mixed tanks to allow the prediction of axial concentrations. The model predictions were verified by experimental data from a range of operating conditions. These included different dissolved oxygen concentrations in biomedium and different wastewater flowrates. Finally, the rate-limiting step in the reactor was determined to be the mass-transfer resistance of the pollutant in the biofilm.