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Ammonia content is an important factor, which has to be considered when optimizing the processes in a biogas plant. A measurement system for a continuous monitoring of ammonia has been constructed, which can be placed in the gas room above the digester. The monitoring is based on the measurement of the electrical impedance. In this system, a condensate is generated on the surface of an interdigital electrode so that the whole stray field is covered by the condensate. For determining the ammonia content, impedance spectroscopy of these drops is performed. The ammonia of the biogas causes a decrease in the impedance in comparison to a pure aqueous condensate. A first evaluation of this measurement system using artificial slurries has been performed. [ABSTRACT FROM AUTHOR]

An ability to real-time and continuously monitor ammonium/ammonia profiles of coastal waters over a prolonged period in a simple and maintenance-free fashion would enable economic conducting large-scale assessments, providing the needed scientific insights to better control and mitigate the impact of eutrophication on coastal ecosystems. However, this is a challenging task due to the lack of capable sensors. Here, we demonstrate the use of a membrane-based conductometric ammonia sensing probe (CASP) for real-time monitoring of ammonia levels in coastal waters. A boric acid/glycerol receiving phase is investigated and innovatively utilized to overcome the high salinity of coastal water-induced analytical errors. A calibration-free approach is used to eliminate the need for ongoing calibration, while the issues concerning practical applications, such as salinity variation, ammonia intake capability, and biofouling, are systematically investigated. The field deployment at an estuary confluence water site over a half-moon cycle period confirms that CASP is capable of continuously monitoring the ammonia profile of coastal waters in real-time with high resolution and accuracy to unveil the dynamic ammonia concentration changes over a prolonged period.

Data from bi-weekly passive samplers from 18 of the longest operating National Atmospheric Deposition Program’s (NADP) Ammonia Monitoring Network (AMoN) sites (most operating from 2008 to 2015) show that concentrations of NH 3 have been increasing (p-value < 0.0001) over large regions of the USA. This trend is occurring at a seasonal and annual level of aggregation. Using random coefficient models (RCM), the mean slope for the 18 sites combined shows an increase of NH 3 concentration of +7% per year, with a 95% confidence interval (C.I.) from +5% to +9% per year. Travel blank corrected data using the same approach show increasing NH 3 concentrations of +9% (95% C.I. +5% to +13%) per year. During a comparable period (2008–2014) NADP precipitation chemistry sites in the same regions show significant increasing (p-value = 0.0001) precipitation NH 4 + concentrations trends for all sites combined of +5% (95% C.I. +3% to +7%) per year. Emissions inventory data for the study period show nearly constant rates of NH 3 emissions, but large reductions in NOx and SO 2 emissions. Seasonal air quality data from the Clean Air Status and Trends Network (CASTNET) sites in these regions show significant declines in atmospheric particulate SO 4 2− and NH 4 + , and particulate NO 3 − plus HNO 3 (total NO 3 − ) during the same period. Less formation of acidic SO 4 and NO 3 , due to reduced SO 2 and NOx emissions, provide less substrate to interact with NH 3 and form particulate ammonium species. Thus, concentrations of NH 3 can increase in the atmosphere even if emissions remain constant. A likely result may be more localized deposition of NH 3 , as opposed to the more long-range transport and deposition of ammonium nitrate (NH 4 NO 3 ) and sulfate (NH 4 ) 2 SO 4 ). Additionally, the spatial distribution of wet and dry acidic deposition will be impacted. [ABSTRACT FROM AUTHOR]

The lack of selectivity is one of the problems of chemical sensor technologies in real world applications. In an effort to develop chemical sensors of improved selectivity, we integrated electrochemistry and optical spectroscopy into one single transducer. An electrically conductive polyaniline (PANi) membrane has been coated on the end of an optical fiber to form a fiber optoelectrode. Two electrodes were glued on the side of the optical fiber for measuring the membrane's electrical resistance. At the same time, a light beam was delivered to the membrane coated on the end of the optical fiber using a 1 × 2 optical fiber coupler. The light reflected back from the PANi membrane was delivered with the second arm of the optical fiber coupler to an optical fiber compatible spectrometer. This makes it possible to simultaneously monitor optical spectroscopic and electrical resistance signals from a single fiber optoelectrode transducer. The responses of the fiber optoelectrode to trace ammonia and water vapor in air samples have been investigated. It was found that the electrical resistance of the fiber optoelectrode changes when exposed to ammonia or water vapor. However, the fiber optoelectrode showed optical spectrometric response to trace ammonia in air, but did not show optical spectrometric response to water vapor in air in the tested concentration range (relative humidity from to 83%). The nature of electrical and optical spectrometric responses of this fiber optoelectrode gives an opportunity to design a sensor for simultaneously monitoring both trace ammonia and water vapor in air. [ABSTRACT FROM PUBLISHER]

Abstract: A miniaturized method based on liquid-phase microextraction (LPME) in combination with microvolume UV–vis spectrophotometry for monitoring ammonia in waters is proposed. The methodology is based on the extraction of the ion pair formed between the blue indophenol obtained according to the Berthelot reaction and a quaternary ammonium salt into a microvolume of organic solvent. Experimental parameters affecting the LPME performance such as type and concentration of the quaternary ammonium ion salt required to form the ion pair, type and volume of extractant solvent, effect of disperser solvent, ionic strength and extraction time, were optimized. A detection limit of 5.0μgL−1 ammonia and an enrichment factor of 30 can be attained after a microextraction time of 4min. The repeatability, expressed as relative standard deviation, was 7.6% (n =7). The proposed method can be successfully applied to the determination of trace amounts of ammonia in several environmental water samples. [ABSTRACT FROM AUTHOR]

A new approach of using free-ammonia measurements as the basis of a control strategy to optimise a chloraminated water distribution system was tested in a laboratory evaluation. A test rig with a newly developed low level on-line free-ammonia analyser was constructed to investigate two different control configurations, the currently used feedback and the proposed feedforward. The results of this trial showed that only using the free-ammonia analyser for feedback control is not ideal due to its inability to detect chlorine overdosing situations. Better results regarding the maximum yield of disinfectant residuals when using the feedforward configuration were observed, and free-ammonia concentrations below 0.065 mg/L were consistently achieved. [ABSTRACT FROM AUTHOR]

An ammonia traces analyser based on photoacoustic spectroscopy is described. The system uses a CO2 laser and a properly designed resonant photoacoustic cell to achieve ammonia detection at sub-parts-per-billion (ppb) level. The instrument features unattended automatic on-line monitoring of ammonia with a detection limit of 0.1 ppb. Interferences from atmospheric CO2 and H2O are efficiently suppressed by a careful selection of the laser wavelength and a compensation of the water vapour signal made with a high-precision hygrometer. The cell design enables continuous measurement at high flow rates (up to 5 l/min), which guarantees a fast response time of the system for the monitoring of ammonia, a sticky polar molecule that adheres to most surfaces. Various examples of applications of the instrument in the semiconductor industry and for atmospheric pollution monitoring are presented. They demonstrate the excellent performances of the system and its suitability for these applications. [Copyright &y& Elsevier]

A gas sensor, comprised of a gas-responsive multiwall carbon nanotube (MWNT)-silicon dioxide (SiO2) composite layer deposited on a planar inductor-capacitor resonant circuit is presented here for the monitoring of carbon dioxide (CO2), oxygen (O 2), and ammonia (NH3). The absorption of different gases in the MWNT-SiO2 layer changes the permittivity and conductivity of the material and consequently alters the resonant frequency of the sensor. By tracking the frequency spectrum of the sensor with a loop antenna, humidity, temperature, as well as CO2 , O2 and NH3 concentrations can be determined, enabling applications such as remotely monitoring conditions inside opaque, sealed containers. Experimental results show the sensor response to CO2 and O2 is both linear and reversible. Both irreversible and reversible responses are observed in response to NH3, indicating both physisorption and chemisorption of NH3 by the carbon nanotubes. A sensor array, comprised of an uncoated, SiO2 coated, and MWNT-SiO2 coated sensor, enables CO2 measurement to be automatically calibrated for operation in a variable humidity and temperature environment [ABSTRACT FROM PUBLISHER]