On-line pH Monitoring Research Articles

PH Monitoring Online

As the largest coal exporting country in the world, Indonesia needs efforts to prevent various negative things for coal mining activities to maintain the balance of the surrounding nature. One of the many affected by mining activities is water. The wastewater quality must be checked regularly before it flows into water bodies. This research aims to describe the company's program created by the Safety Health & Environment (SHE) department and Center of Excellence (CEO) Department to monitor wastewater generated from mining activities for 24 hours. This research uses a descriptive method with a qualitative approach. This descriptive research explains the program for monitoring pH in mining wastewater. The results showed that this online pH monitoring was made to measure the pH of water from mining waste and was carried out to reduce the potential for disruption of biodiversity in the environment around wastewater disposal. The creation of this program also has an impact on cost efficiency because it can be used online and can be controlled remotely.

Alizarin-graphene nanocomposite for calibration-free and online pH monitoring of microbial fuel cell

Microbial fuel cells (MFCs) are sensitive to acidity variations in both bioelectricity generation and biochemical digestion aspects, therefore online pH monitoring is of necessity to guarantee optimal function of MFCs. Present pH meters hardly fulfill this special need. In this work, we designed a novel voltammetric pH sensor based on electrochemically reduced graphene oxide (rGO) modified screen printed electrode. By surface doping of alizarin, good linearity of pH sensing over the range of 4.0–9.0 can be realized. Fast readout can be acquired within 15 s for each test. pH monitoring for artificial wastewater with inoculum of granular activated sludge in a MFC was successfully illustrated. Specially, it was verified that the performance was improved with alizarin doping due to the enhanced rGO surface proton diffusion. This approach provides an online, calibration-free and long stable pH monitoring method for the future MFC development.

Online pH monitoring based on a wireless electrodeless quartz crystal microbalance with dissipation

Online real-time detection is crucial for biochemical and healthcare monitoring. Methods that could conduct the measurements in low-volume analytes are essentially required. A wireless electrodeless quartz crystal microbalance with dissipation (WE-QCM-D) based sensor was proposed to realize real-time pH monitoring in low-volume solutions. The WE-QCM-D pH sensor was fabricated by coating with a pH-sensitive poly (hydroxyethyl methacrylate-co-methacrylic acid) (poly (HEMA-co-MAA)) film and observed the dynamic pH variation in the range from 4 to 9. The sensitivity of the WE-QCM-D pH sensor nearby the pKa was 1.47 V/pH and the maximum response time was around 80 s. The pH sensor performed well in synthetic urines with a measurement deviation less than 1% compared with that measured by a pH meter and reversible responses has been achieved when 140μl buffer solutions at pH 4.18, 5.6 and 7.62 were loaded on the quartz disc that was located in a glass vial. The results indicated that the WE-QCM-D pH sensor could be potentially used for online low volume detections.

Optical pH Detection with U-Shaped Fiber-Optic Probes and Absorption Transducers

In medicine knowledge of pH values can provide us with information not only about the patients’ status but also about physiological processes in the patient’s body. Measurements of pH in small-sample volumes and online pH monitoring in vivo can be employed to obtain such information. For such measurements we have developed and investigated U-shaped fiber-optic probes with immobilized pH indicators in this paper. U-shaped probes with a diameter of about 2 mm were prepared. Three different pH indicators, methyl red, methyl orange, and bromothymol blue, were immobilized in two types of matrices, namely, porous silica (PS) and ethylcellulose (EC), and applied on the U-shaped probes. Changes in spectra of transmitted power were measured and calibration curves were determined from these spectra. It has been found that a working pH range of prepared probes was from 3.1 to 7.6. The maximum sensitivity was about 0.1 1/pH unit. Effects of structural relaxations of detection layers and indicator leaching observed in experiments are discussed.

Nitrification and denitrification characteristics in a sequencing batch reactor treating tannery wastewater

Long-term evaluation of a SBR fed with tannery wastewater (SBRtww) was carried out to study the periods of satisfactory and unsatisfactory performance in the nitrification and denitrification properties. Another SBR fed with synthetic nitrogen medium simulating tannery wastewater (SBRsww) was used to assess separately the end points of nitritation and nitratation by online monitoring of pH and DO. Flex point in the DO and pH profiles of the SBRsww cycle corresponding to the end point of nitritation was well observed, whereas the end point of nitratation was vaguely detected. The end point of nitritation suggested that the aeration phase can be reduced considerably and denitrification via nitrite can be facilitated to minimize oxygen requirements and reduce operational costs. During the long-term operation of SBRtww, stable and unstable phases of nitrification were observed. A maximum nitrification rate of 14.1 mg/L h was obtained during the stable phase of the reactor. Inhibiting substances in tannery wastewater was found to be the possible reason for the instability in nitrification. Denitrification property, however, was not much affected as that of nitrification. The maximum denitrification rate observed was 10.7 mg/L h. Nitrogen removal in an aerobic SBR through simultaneous nitrification-–denitrification could be a good option for tannery wastewater. SBR is a viable option for tannery wastewater compared to the conventional aerobic systems provided pollution control measures are conducted at the source level through the use of eco-friendly chemicals and cleaner processing methods to avoid nitrification inhibiting compounds in the effluent.

A novel pH optical sensor using methyl orange based on triacetylcellulose membranes as support

A novel pH optical sensor based on triacetylcellulose membrane as solid support was developed by using immobilization of methyl orange indicator. The prepared optical sensor was fixed into a flow cell for on-line pH monitoring. Variables affecting sensor performance, such as pH of dye bonding to triacetylcellulose membrane and dye concentration have been fully evaluated and optimized. The calibration curve showed good behavior and precision (RSD<0.4%) in the pH range of 4.0–12.0. No significant variation was observed on sensor response with increasing the ionic strength in the range of 0.0–0.5M of sodium chloride. Determination of pH by using the proposed optical sensor is on-line, quick, inexpensive, selective and sensitive in the pH range of 4.0–12.0.

A novel closed system bubble column photobioreactor for detailed characterisation of micro- and macroalgal growth

Growth of the marine microalga Tetraselmis striata Butcher and the macroalga Chondrus crispus Stackhouse was investigated in batch cultures in a closed system bubble column photobioreactor. A laboratory cultivation system was constructed that allowed online monitoring of pH and dissolved oxygen tension and was used for characterization of photoautotrophic growth. Carbon dioxide addition regulated pH and was used to optimise irradiance. Oxygen was removed from the system by addition of hydrogen over a palladium catalyst to quantify oxygen production. In addition, the bubble column photobioreactor was suited for cultivation of algae due to fast gas-to-liquid mass transfer (kLa) and fast mixing provided by split and dual sparging. Specific growth rates (SGRs) were measured using both offline and online measurements. The latter was possible, because rectilinear correlation was observed between carbon dioxide addition and optical density, which shows that carbon dioxide addition may be used as an indirect measurement of microalgal biomass (x). The slope of the rectilinear fit of ln (dx/dt) as a function of the time (t) then revealed the SGR. These determinations revealed detailed information about changes in growth with up to three different SGRs in the different batch cultures of both micro- and macroalgae. The maximum SGRs found by online determination were 0.13 h−1 for T. striata and 0.12 day−1 for C. crispus. We have developed and described a system and presented some data handling tools that provide new information about growth kinetics of algae.

Microfluidic free-flow electrophoresis chips with an integrated fluorescent sensor layer for real time pH imaging in isoelectric focusing

Functional microfluidic free-flow electrophoresis chips with integrated fluorescent pH sensors are presented. Polyethylene glycol based structures were fabricated that allowed for integration of both functions on a single microchip. Microchips were applied in free-flow isoelectric focusing of model compounds and proteins with on-line monitoring of pH during microscale electrophoretic separation.

Laboratory investigations on continuous bio-methanization of energy crops as mono-substrate without supplementation

Abstract Continuous bio-methanization of an energy crop, namely the beet silage, was investigated in this laboratory-scale work as mono-substrate, using a mesophilic biogas digester controlled by a fuzzy logic control (FLC) technique and without using any supplementing or buffering agent, despite the low pH of the substrate around 3.80. The temperature, pH, redox potential (ORP), daily biogas production and composition of digester biogas were continuously measured online. During the operation, the hydraulic retention time (HRT) varied between 24.8 and 9 days, as the organic loading rate (OLR) ranged from 2.6 to 4.7 g L −1 d −1 . The average pH, specific gas production rate (spec. GPR) and volumetric gas production rate (vol. GPR) were determined to be 7.12, 0.31 L g VS −1 d −1 and 1.084 L L −1 d −1 , respectively. The average methane (CH 4 ) content of digester biogas was about 56%. The FLC technique, which was developed at HAW Hamburg for anaerobic conversion of acidic energy crops to methane, determined the daily feeding volume (∼ OLR/HRT) for the biogas digester, depending on the feedback from online pH and methane measurements, and on the calculation of the spec. GPR. The spec. GPR was calculated by the corrected daily biogas production. Through online monitoring of pH, biogas production rate and composition, and by use of the FLC technique, the acidic beet silage could continuously be converted to biogas, without using manure or any other kind of buffering or supplementing agent(s). The lab-scale anaerobic biogas digester performed stable and safe, without encountering any problems of instability, as indicated by an adequate amount of buffering capacity, a VFA content below 0.5 g L −1 and a neutral pH range throughout the study.

Development and application of an excitation ratiometric optical pH sensor for bioprocess monitoring

The development of a fluorescent excitation ratiometric pH sensor (AHQ-PEG) using a novel allylhydroxyquinolinium (AHQ) derivative copolymerized with polyethylene glycol dimethacrylate (PEG) is described. The AHQ-PEG sensor film is shown to be suitable for real-time, noninvasive, continuous, online pH monitoring of bioprocesses. Optical ratiometric measurements are generally more reliable, robust, inexpensive, and insensitive to experimental errors such as fluctuations in the source intensity and fluorophore photobleaching. The sensor AHQ-PEG in deionized water was shown to exhibit two excitation maxima at 375 and 425 nm with a single emission peak at 520 nm. Excitation spectra of AHQ-PEG show a decrease in emission at the 360 nm excitation and an increase at the 420 nm excitation with increasing pH. Accordingly, the ratio of emission at 420:360 nm excitation showed a maximum change between pH 5 and 8 with an apparent pK(a) of 6.40. The low pK(a) value is suitable for monitoring the fermentation of most industrially important microorganisms. Additionally, the AHQ-PEG sensor was shown to have minimal sensitivity to ionic strength and temperature. Because AHQ is covalently attached to PEG, the film shows no probe leaching and is sterilizable by steam and alcohol. It shows rapid (approximately 2 min) and reversible response to pH over many cycles without any photobleaching. Subsequently, the AHQ-PEG sensor film was tested for its suitability in monitoring the pH of S. cereviseae (yeast) fermentation. The observed pH using AHQ-PEG film is in agreement with a conventional glass pH electrode. However, unlike the glass electrode, the present sensor is easily adaptable to noninvasive monitoring of sterilized, closed bioprocess environments without the awkward wire connections that electrodes require. In addition, the AHQ-PEG sensor is easily miniaturized to fit in microwell plates and microbioreactors for high-throughput cell culture applications.

Development of high throughput optical sensor array for on-line pH monitoring in micro-scale cell culture environment

On-line pH detection of cell culture environment is necessary in a bioprocess or tissue engineering. Devices by means of electrochemical mechanisms for this purpose have been reported to be less suitable compared with optical-based sensing principles. More recently, some non-invasive optical sensing systems have been proposed for online pH monitoring of cell culture environment. However, these devices are not for multi-target pH monitoring purpose, and are large in scale and thus not appropriate for the pH monitoring at a micro scale such as in microbioreactor or microfluidic-based cell culture platform. To tackle these issues, an optical fiber sensor array for on-line pH monitoring was proposed using microfluidic technology. The working principle is based on the optical absorption of phenol red normally contained in culture medium. Different from other device of the similar working principle, the proposed device requires less liquid volume (less than 0.8 microl), is non-invasive, and particularly can be configured as an array for high throughput pH monitoring. The present device has been optimized for the shape of detection chamber in a microfluidic chip with the aid of computational fluid dynamics (CFD) simulation, to avoid flow dead zone and thus to reduce the response time of detection. Both simulation and experimental results revealed that the design of oval detection chamber (axis, 1.5 and 2.0 mm) can considerably reduce the response time. Preliminary test has proved that the optical pH detection device is able to detect pH with average detection sensitivity of 0.83 V/pH in the pH range of 6.8-7.8, which is normally experienced in mammalian cell culture.

A wide range pH optical sensor with mixture of Neutral Red and Thionin immobilized on an agarose film coated glass slide

Abstract A new pH optical sensor for a wide pH range was prepared by chemical immobilization of a mixture of two indicators of Neutral Red and Thionin on an agarose film coated glass slide (ACGS). For preparation of the sensor, the two dyes were immobilized on an epoxy activated agarose support and the effects of the coupling pH and the dyes ratio and concentrations were optimized. The sensor was mounted in a flow cell and successfully applied for on-line pH monitoring in a wide pH range of 0.5–12 with two linear calibration curve regions. The pH sensor could perform fast response (within 1–2 min) and long-term stability (continuous use for at least 3 months) with no evidence of dye leaching. The sample ionic strengths up to 0.5 mol L−1 did not significantly influence the responses. A reproducibly better than 0.20% (R.S.D.) was obtained for 6 replicated pH measurements.

Preparation of a novel optical sensor for low pH values using agarose membranes as support

A simple and effective method for the preparation of a new generation of optical sensors based on optically transparent agarose membranes was developed. An optical pH sensor for low pH values was accordingly fabricated by immobilization of Congo Red on epoxy-activated agarose. In an optimized coupling pH of 10 and a dye concentration of 10−5molL−1, a sensitive sensor with long term stability was obtained.It was found that the acidity constant of Congo Red in the immobilized form is smaller than in solution. The sensor responds rapidly to the pH changes in a range of 0.5–5 with a response time of 3.0min and a reproducibility better than 0.30% (R.S.D). The sensor was mounted in a flow cell and successfully applied for on-line pH monitoring. No evidence of leaching of the dye or any signal drift was observed.

Molecular Analysis of Microbial Communities in Nitrification and Denitrification Reactors Treating High Ammonia Leachate

Molecular analysis of microbial populations in two bench-scale nitrification and denitrification reactors fed with high ammonia landfill leachate was conducted in this study by using DGGE, cloning, and FISH techniques in addition to classical efficiency control parameters. Nitrification tank was operated with a computer-controlled alkalinity dosing system to supply the alkalinity intermittently as consumed on the basis of on-line pH monitoring. By keeping the pH at 7.0 with this system, 99% nitrification efficiency and rates of about 0.14–0.18 mg-N/mgVSS day were obtained. Meanwhile, as ammonia oxidizing bacteria Nitrosomonas and Nitrosococcus mobilis-like cells and as nitrite oxidizing bacteria Nitrobacter-related cells were intensively indicated. Moreover, some aerobic denitrifiers as Thauera species were also identified. After the termination of pH adjustment in the preceding anaerobic reactors, nitrification tank was loaded with more biodegradable COD as a result of reduced COD removal in anaerobic reactors. Microbial diversity was immediately affected from this alteration and heterotrophic carbonaceous bacteria and aerobic denitrifiers have dominated. To provide the former high efficiencies, retention time has increased from 24 to 48 h and a second pump dosing HCl was included to the automatic control system. Subsequent to these precautions, numbers of ammonia (Nso190) and nitrite oxidizing bacteria (NIT3) were comparatively increased. In denitrification system, about 98% denitrification efficiencies were obtained at 2000 mg/L NO x -N concentrations if sodium acetate was supplied as carbon source. Meanwhile, with 20 gVSS/l biomass concentration, denitrification rates of about 1.34 mgNO x -N/mgVSS day were obtained. All sludge samples have represented similar DGGE patterns and Paraccoccus-related species were identified as dominant denitrifying bacteria.

Dual excitation ratiometric fluorescent pH sensor for noninvasive bioprocess monitoring: development and application.

The development and application of a fluorescent excitation-ratiometric, noninvasive pH sensor for continuous on-line fermentation monitoring is presented. The ratiometric approach is robust and insensitive to factors such as source intensity, photobleaching, or orientation of the patch, and since measurements can be made with external instrumentation and without direct contact with the patch, detection is completely noninvasive. The fluorescent dye 8-hydroxy-1,3,6-pyrene trisulfonic acid was immobilized onto Dowex strongly basic anion-exchange resin, which was subsequently entrapped into a proton-permeable hydrogel layer. The sensor layer was polymerized directly onto a white microfiltration membrane backing that provided an optical barrier to the fluorescence and scatter of the fermentation medium. The ratio of emission intensity at 515 nm excited at 468 nm to that excited at 408 nm correlated well with the pH of clear buffers, over the pH range of 6-9. The sensor responded rapidly (<9 min) and reversibly to changes in the solution pH with high precision. The sterilizable HPTS sensor was used for on-line pH monitoring of an E. coli fermentation. The output from the indwelling sensor patch was always in good agreement with the pH recorded off-line with an ISFET probe, with a maximum discrepancy of 0.05 pH units. The sensor is easily adaptable to closed-loop feedback control systems.

An on-line pH monitoring system for flow solution analysis with pH-ISFETs and flow-through cell

An on-line pH monitoring system consisting of a specially designed sampling probe, flow-through cell with double pH-ISFETs alternatively operated as a reference device and measurement sensor and a peristaltic pumping system is presented. The features of the system show good future for on-line monitoring of ion concentration of electrolyte.

Intraoperative on-line monitoring of cerebral pH by microdialysis in neurosurgical procedures

The objective of this study was to improve the ability to detect cerebrovascular complications in patients undergoing complicated neurosurgical procedures using on-line monitoring of cerebral pH with in viva microdialysis. We employed on-line pH monitoring in patients with a variety of neurosurgical procedures including high-flow bypass surgery, aneurysm clipping, and temporal resection in epilepsy treatment. The pH was monitored with a microdialysis probe, usually inserted into the frontal cortex and pH of the dialysate was measured on-line with a pH electrode. We monitored 17 cases: 12 high-flow extracranialintracranial (fC-IC) bypass procedures, 3 surgeries to clip large basilar tip aneurysms under protection of hypothermic circulatory arrest, and 2 surgeries for intractable seizure disorders. In the patients undergoing high-flow bypass, the pH remained stable in 5 patients and all had an uneventful outcome. In 3 patients, the pH decreased during surgery. One patient had a severe hemiparesis on awaking from anesthesia. The fall in pH in another patient was corrected when the blood pressure was raised during surgery. The pH was also responsive to changes in intraoperative ventilation and probably also to brain edema with elevation of pH values. In the three patients undergoing basilar tip aneurysm clipping under hypothermic circulatory arrest, the pH fell to 6.41 in one patient. This patient awoke with a mild hemiparesis. In the other two patients, the pH was stable during the hypothermia and neither patient had complications. In the patients undergoing temporal lobectomy and hippocampectomy, the pH fell rapidly with the onset of ischemia. We conclude that it is possible to monitor the cerebral extracellular pH with on-line microdialysis. The information obtained may alert the surgeon to the possibility of impending cerebral ischemia or other complications. However, further experience is needed before the technique can be recommended for general use. [Neural Res 1998; 20: 142–148]

Reverse flotation of pyrite from a zinc-concentrate using nitrogen

A mobile flotation facility, based on two 5 L minicells equipped with on-line monitoring of pH, dissolved oxygen and pulp potential, was used to study flotation of pyrite from zinc concentrate (i.e. reverse flotation) at the Trout Lake circuit of Hudson Bay Mining and Smelting Co. Ltd., Flin Flon, Manitoba. A combination of 2 levels of pH (pH 7 and 5.5 adjusted with sulphur dioxide) and temperature (60°C and 80°C controlled by steam) in conditioning and 3 levels of gas composition (air, 95% N 2, 100% N 2) in flotation were tested. For all conditions compared to the use of air, 95% or 100% N 2 gave higher pyrite recovery. Taking 3% sphalerite loss to the float product as a base line, nitrogen increased pyrite recovery by about 10% (absolute) even under the least severe conditions (pH 7 and 60°C). In contrast, the flotation of chalcopyrite was retarded when using nitrogen. From monitoring of the pulp chemistry, oxygen appears to be necessary in conditioning to de-activate sphalerite but its absence in flotation favours selective pyrite recovery. The use of sulphur dioxide in conditioning may help oxygen achieve these conflicting roles: the sulphur dioxide/oxygen combination gives initially strong oxidizing conditions but finally results in consumption of the oxygen. The use of nitrogen in flotation effectively maintains the low pulp potential and dissolved oxygen levels achieved in conditioning permitting less severe conditioning to be used.

5354359 Hydrometallurgical process for the recovery of precious metal values from precious metal ores with thiosulfate lixiviant

A mobile flotation facility, based on two 5 L minicells equipped with on-line monitoring of pH, dissolved oxygen and pulp potential, was used to study flotation of pyrite from zinc concentrate (i.e. reverse flotation) at the Trout Lake circuit of Hudson Bay Mining and Smelting Co. Ltd., Flin Flon, Manitoba. A combination of 2 levels of pH (pH 7 and 5.5 adjusted with sulphur dioxide) and temperature (60°C and 80°C controlled by steam) in conditioning and 3 levels of gas composition (air, 95% N2, 100% N2) in flotation were tested. For all conditions compared to the use of air, 95% or 100% N2 gave higher pyrite recovery. Taking 3% sphalerite loss to the float product as a base line, nitrogen increased pyrite recovery by about 10% (absolute) even under the least severe conditions (pH 7 and 60°C). In contrast, the flotation of chalcopyrite was retarded when using nitrogen.From monitoring of the pulp chemistry, oxygen appears to be necessary in conditioning to de-activate sphalerite but its absence in flotation favours selective pyrite recovery. The use of sulphur dioxide in conditioning may help oxygen achieve these conflicting roles: the sulphur dioxide/oxygen combination gives initially strong oxidizing conditions but finally results in consumption of the oxygen. The use of nitrogen in flotation effectively maintains the low pulp potential and dissolved oxygen levels achieved in conditioning permitting less severe conditioning to be used.