BNR (Biological Nutrient Removal) Plants are still relatively scarce in the UK. In many other European countries, BNR Plants are far more common – as is an awareness of some of the problems associated with running them.
One of the biggest challenges facing BNR operators is the formation of surface scum on the anaerobic and/or anoxic tanks. If not removed continuously, this scum can build up and cause process issues which should not be underestimated. These include reduced retention time, high suspended solids in the final effluent, and poor overall plant performance.
Corgin were recently called in to propose a remedy for scum that was building up rapidly on a newly-constructed anaerobic tank.
“Over the course of a few weeks the scum would build up to a depth of 3 feet”
With no way of escape from the square tank, a vacuum tanker with 2 operators was having to be called fortnightly or monthly to suck out this sticky, odorous mess.
Based on successful European installations over 15 years and others in the UK wastewater utilities sector, Corgin recommended the Foam Skimmer. This unique equipment design removes surface scum and foam, collapsing and thickening it to between 3% and 6% dry solids before pumping it away for disposal. This low energy, high solids method of removal is a sustainable way of dealing with problem scum build-up like this.
Within days of commissioning the Foam Skimmer, the anaerobic tank was sporting a near scum-free surface. For the first time since the BNR Plant was commissioned, operators could see the water surface. Once again, the Foam Skimmer makes a clean sweep.