Hydrogen sulphide dual H2S

Sulphides exist naturally in well water and waste water collection systems and build up due to anaerobic conditions. High concentrations of sulphides in waste water can cause odour problems in treatment facilities, as well as corrosive damage to concrete structures in collection systems. Sulphides also result in taste and odour problems in drinking water.


Hydrogen sulphide dual H2S
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Sulphides exist naturally in well water and waste water collection systems and build up due to anaerobic conditions. High concentrations of sulphides in waste water can cause odour problems in treatment facilities, as well as corrosive damage to concrete structures in collection systems. Sulphides also result in taste and odour problems in drinking water.

Traditionally used Techniques in Sulphide Monitoring

Gas phase H2S in wet wells is often measured to give an indication of whether a dissolved sulphide problem exists. Oxidants are then added if required. Another approach involves monitoring H2S in order to prevent sulphide formation occurring at all. The measured concentration of dissolved sulphide is then used to decide the dosing rate of oxidants such as hydrogen peroxide and ferric nitrate to eliminate sulphide before it causes problems. ntil now, the dosing control has been based on indirect measurements.

A traditional method of measuring dissolved sulphide concentration in water uses analysers employing selective ion electrodes (SIE). This method provides adequate results but is expensive and requires regular maintenance, including frequent zeroing and calibration adjustments to maintain accuracy.

Other systems use ORP to indicate dissolved sulphides. A semi-direct method is to measure ORP/Redox in water and use this to predict H2S levels. As the measurement is non-specific, the values can be affected by many other sample components. As Redox is not sensitive enough to measure low H2S levels, probes have to be immersed in the sample and as a result can foul easily.

Odour control in waste water treatment plants often requires the use of scrubbers, which are used to remove pollutants from exhaust streams. Monitoring of H2S in both inlet and discharge air has presented problems for standard gas sensors. Due to humid conditions and condensing levels of water vapour, the water droplets can be a barrier to the diffusion of H2S into the sensor, resulting in inaccurate measurements.

New Technologies

Analytical Technology has overcome issues associated with sulphide measurement and odour control. TheDissolved Sulphur Monitorprovides an enhanced process for sulphide measurement in solution, resulting in a system that can operate continuously with minimal maintenance and adjustment. Instead of using an SIE sensor, the measurement is achieved using a polarographic H2S gas sensor. As the sensor is separated from the sample, fouling does not occur, eliminating one of the major problems of H2S measurement.

In addition, our Q45S Wet H2S Gas Detector, used in scrubber systems, provides a lower priced alternative to expensive tape based H2S monitors. This gas detector is used to monitor the efficiency of odour control systems and alert the operator of any drop in efficiency. New sensor technology allows continuous monitoring of H2S where condensing humidity conditions are normal. Measurements may be made either at the inlet to scrubber systems where concentrations can run as high as 200 PPM or at the outlet where concentrations are ideally down below 0.5 PPM.
As these systems often monitor gas streams with condensing levels of water vapour, provision has been made to eliminate water droplets from the sensor as this could present a barrier to the diffusion of H2S into the sensor. An optional air-purge system controlled by the transmitter periodically delivers a blast of air across the critical sensor surfaces to remove water droplets. This system ensures a clear gas diffusion path to the sensor and reliable measurements on a continuous basis.

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