Control of biofouling in hydropower cooling systems using HOD ultraviolet light

Reservoirs along the lower Colorado River are infested with Dreissena rostriformis bugensis (Andrusov, 1897) (quagga mussel) and Cordylophora caspia (Pallas, 1771) (colonial hydroid). These invasive species, along with native freshwater sponges and bacteria, pose significant biofouling issues for hydropower facilities in the area. Biofouling in the generator cooler systems at Parker Dam, on Lake Havasu, AZ has resulted in increased annual maintenance costs of approximately $ 80,000/year. Medium pressure, hydro-optic ultraviolet (HOD UV) light systems with a 100 mJ/cm(2) target dose were installed on four main turbine cooling water lines and a raw water supply for the onsite water treatment facility at Parker Dam to mitigate biofouling. This study was designed to monitor the impact of HOD UV on biofouling over a two-year period. Comparison of biofouling dry weight from settlement plates exposed to HOD UV-treated and untreated water indicate a significant reduction in total biofouling after HOD UV exposure. Mussel settlement and bacterial sludge formation were consistently reduced in test chambers (bioboxes) despite lower than expected average HOD UV dose and contamination with untreated water. Hydroid larvae were not found in any plankton samples collected from the forebay at Parker Dam during the study, indicating asexual reproduction was the main source of downstream colony formation. Hydroid settlement reduction data after HOD UV treatment were inconclusive. The Parker Dam facility manager confirmed that biofouling-related maintenance of the coolers was reduced by 75 percent after the first year of HOD UV operation and eliminated in the second and third years after implementation.