Effluent pH controlled

The pH of trade effluents often varies widely between different processes in the same plant. Add to this a quantity of organic solvents and some suspended solids and it becomes a difficult job for your average pH electrode. ‘Getting it wrong' is a costly business with Environment Agency fines running into tens of thousands of pounds. At this point Vauxhall Motors (the UK arm of General Motors) decided to seek specialist advice.

Ordinary electrodes suffer from several problems in long term ‘dirty' environments. Erratic readings are observed due to silver chloride solubility inequilibrium in the reference electrode. Silver ions in the reference electrode react with the sample causing blockage of the diaphragm. The biggest problem of all is a gradual drift in pH readings rendering calibration inaccurate and incurring more maintenance costs.

‘I've tried most electrodes over the years but I keep returning to Thermo Electron for their reliability', said John Morton, Effluent Treatment Plant Manager at Vauxhall Motors, Ellesmere Port, ‘most recently they supplied a new K-series electrode which has proved even better than before. The lifetime is as good if not better but what is most reassuring is the stable readings.'

The K-series electrodes have been developed by Thermo Electron, the UK's leading specialist electrode manufacturer, in conjunction with major international company. They all feature a unique polymer in the reference cell which exhibits phenomenal stability even in harsh conditions. Also, many effluents contain sulphides which react with the silver in a conventional electrode leading to ‘black death' - silver sulphide blocking the diaphragm. No silver ions are present in solution in K-series electrodes and so blockage from chemical reactions is not a problem.

‘For Vauxhall Motors application the K-series electrodes are the best I've used,' commented John Morton, ‘they have solved problems where some conventional pH electrodes were disappointing and solid state reference types did not perform at all'.

There is a whole range of K-series electrodes designed to meet the different demands of industry and laboratory. The polymer, which incorporates patented chemistry, differs from others on the market in that it des not hydrolyse. The effect of hydrolysis is a change in pH within the reference electrode which renders pH readings in accurate. The polymer is fully substituted and cross linked which results in exceptional stability with respect to long term drift. Hence calibration intervals can be extended with confidence, reducing maintenance and optimising efficiency with no loss of accuracy.

For more information contact:
Thermo Electron
Station Road
Auchtermuchty, Fife, KY14 7DP UK