Control of biofouling by Cordylophora caspia in freshwater using one-off, pulsed and intermittent dosing of chlorine: laboratory evaluation.

Cordylophora caspia is a hydrozoan which causes biofouling in power plants and is an increasing problem in UK drinking water treatment works. Thermal control is not usually feasible without a ready source of hot water so laboratory experiments were conducted to assess whether using pulsed doses of chlorine is an alternative solution. C. caspia polyps disintegrated after a single 20 min dose (the length of one backwash cycle in water treatment work filter beds) of 2.5 ppm chlorine. Without further treatment colonies regenerated within 3 days, but repeated dosing with chlorine for 20 min each day inhibited this regeneration. The resistance of surviving colonies to chlorine increased over time, although colony size and polyp regeneration continued to fall. These results suggest pulsed treatment with chlorinated backwashes at 2 ppm could be used to control C. caspia biofouling in rapid gravity filters and this may have relevance to other settings where thermal control is not feasible.