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Technical Focus: Phosphate Removal – Dosing Trim Control using Turbidity

Posted by Angus Fosten on December 17, 2014
TurbiTechw² LA

Phosphorus consents are the bane of many plant’s working lives, and metal discharge limits means the use of aluminium sulphate, sodium aluminate and similar ferric metals must be used carefully for safe, effective phosphorus and phosphate removal.

In 50 years we’ve yet to meet a site that likes to operate blind, but still many operations within the wastewater industry rely on diurnal profiles (measurements attained within a 24-hour period) or flow-proportional control algorithms to dose metal salts. Such dependence on recorded phosphorus levels effectively introduces an unwanted element of the unknown into this procedure.

As phosphates are a catalyst for plant and algal growth, the negative optic effect this has on wastewater can easily be picked up by a turbidity sensor, therefore acting as an autonomous measurement that can effectively play a role as a trim for dosing control.

This is especially useful when dealing with field runoff (an idiosyncrasy present most notably in the agricultural industry), where the potential for a major increase of phosphate inlet levels means metal salt dosing would need to be trimmed rapidly to accommodate these increased measurements.

A live turbidity reading (from such units as the Turbitechw2 LR and Turbitechw2 LS turbidity sensors) cannot only help you avoid the threat of exceeding discharge consents; it also acts as a source of secondary data to diurnal or flow proportional control algorithms, also doubling up as a troubleshooting tool in the case of equipment malfunction.

Quite simply, we feel that by using turbidity as a dosing trim tool in regards to phosphate removal is worth every penny – how about you?

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