Effluent meter project falters

The project, which originally set out to define performance standards for a model effluent meter that would continuously monitor flow, suspended solids and chemical oxygen demand (COD), has faltered in the face of currently unassailable technical and economic problems that contrive to make such an “all-in-one” trade effluent monitor unviable.

The problem lies initially in attempting to create a general specification for all trade effluents. “But that has been a problem from day one,” Sira’s David Lewis, chairman of the meeting, commented. “Verification of individual elements, yes, but how can they all be taken as a whole? They are very different sorts of animals.”

Whilst verification of the flow and solids components of the proposed model was in fact addressed in terms of the project’s aim of satisfying the requirements of dischargers, effluent receivers and regulators – identified as practicality, achievability, flexibility, economy, relevance and auditability – on the issue of COD monitoring, the consensus was a resounding “none of the above”. Consultant Rob Bogue, who put forward the team’s findings on the issue of COD, said: “We have to realistically ask ourselves if we can do this meaningfully and at reasonable cost. And the more I think about on-line COD the less I like it.”

The insurmountable hurdles identified included: a prohibitive purchase price – around £40,000 per measurement point; high running costs – a further £30,000 per year; a high degree of complexity; and the fact that different instruments tend to provide different results. The meeting concluded that the only feasible means of measuring COD was by surrogate test, most likely for TOC. This, however, was rejected as requiring site-specific correlation.

Joan Cocksedge, technical programmes supervisor for the National Measurement System Policy Unit at the DTI, who had already admitted to the programme being “a bit ahead of the game”, said at the meeting: “The outcome from the project at this stage may be that we can’t produce anything at all.”