Partech (Electronics) Ltd.

Dissolved Oxygen Monitoring - Monitoring Dissolved Oxygen in the Activated Sludge Process

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Being able to act on accurate measurement of Dissolved Oxygen in activated sludge plants will enable you to maintain levels of bacterial activity, avoid breaches in discharge consents and operate as cost effectively as possible. Too little dissolved oxygen can lead to bacterial inactivity and ineffective treatment, whilst too much, wastes energy and can cause unnecessary wear and tear to the aeration system.

Partech's sensors make accurate dissolved oxygen measurement easy. They are highly reliable and accurate as well as straightforward to use and easy to install. They also benefit from the self cleaning action of the FlexTech probe holder and the fouling tolerance of the probes themselves - all of which mean longer service intervals and a consistently more efficient plant.

The use of sensors to measure Dissolved Oxygen was started over 50 years ago by Dr Clark initially in the medical industry and then in water analysis. The Clark cell and it's close cousin the Makereth cell are electrochemical (galvanic)cells where an electrical circuit consisting of an anode and cathode with an electrolyte sitting behind a gas permeable membrane. As the oxygen diffuses through the membrane a chemical reaction takes place that generates an electrical signal that is proportional to the amount of Oxygen present in the sample. Oxyguard have developed their probe so that this electrochemical reaction does not consume the electrolyte or anode, thus providing a measuring cell that has an operational life of 10 years or more.

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The galvanic probe offered by Partech utilises a unique combination of electrolyte, membrane and anode materials, together these factors give a real world working life in excess of five years. The Iron/Silver electrode combination ensures that no gas can build up in the cell and the electrolyte is not consumed, there is no warm up time and no zero adjustment required. The only maintenance is occasional removal of fouling and calibration. Routine calibration is required for any instrumentation, without it there is no validation of the measurement. The probe is easily repaired on site without specialist training, the membrane is quick and easy to replace. The membrane for the cell is only replaced if it is damaged, there is no internal drift, and the internal sensor design means that the electrolyte and anode are not consumed. Recently a technology from the 1970's has been revived, optical DO measurement has been offered as an alternative for all issues relating to monitoring in wastewater environments. Basically, the meter determines oxygen by measuring light. High-energy blue light is directed onto the sensor surface, which is coated with a luminescent material. Electrons of the luminescent material are excited to a higher energy level before then falling back to their basic energy level, emitting red light as they do so. This light is detected by a photo diode. Partech are now able to offer this technology in the WaterWatch² range.

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Partech are in the position of offering both galvanic and optical measurng techniques, the best technique will be selected to meet the requirements of the application . Use of the FlexTech mounting system helps alleviate the problems of fouling, and ensures that the sensor is located correctly for representative measurement. The unique combination of electrolyte, anode and cathode material, and physical probe design gives real world life of in excess of five years with many lasting much, much longer.

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