Canary in a membrane plant: A sentinel against membrane scaling

A two-element membrane pressure vessel was installed as a “canary” unit on a full-scale reverse osmosis (RO) membrane process to monitor scale formation while changes in the plant's pretreatment processes were implemented. Sulfuric acid pretreatment ahead of an RO process was to be progressively reduced and discontinued per the findings of a pilot study. To safeguard the full-scale membrane process against unforeseen failure caused by scaling when sulfuric acid was eliminated from the RO feedwater, the canary unit was introduced. Concentrate from the second stage of the RO process train served as the feed stream to the canary unit, thereby allowing the canary to provide an earlier indication of scaling in lieu of scaling the full-scale RO process. The canary unit was intended to act as an early warning to operators who could intervene to protect the RO plant from unforeseen loss of membrane productivity resulting from scaling.