Evaluation of membrane filtration and UV irradiation to control bacterial loads in recirculation aquaculture systems

Ultraviolet (UV) irradiation is commonly used to control pathogen loads in recirculation aquaculture systems (RAS), although these micro-organisms can be shielded by particles in the water, and some species tolerate very high UV doses. The objective of this study was to evaluate membrane filtration (MF) as an alternative, or complimentary, treatment to UV irradiation for pathogen control in RAS, as well as examine the operation and cost of each treatment. In a pilot-scale RAS, both MF and UV were used to treat wastewater for 30 days and water samples were collected biweekly and analysed for culturable bacteria, suspended solids, UV transmittance and other parameters. Bacterial control efficiencies were similar between both MF and UV treatments, which removed 99% of total bacteria and 98% of heterotrophic bacteria, respectively. Surface fouling was negligible for the UV while MF required biweekly cleaning to maintain operation. However, MF had the additional benefit of removing 96% of suspended solids, which resulted in increased UV transmittance. Capital and operating costs of MF were similar to UV, but only when MF treated a fraction of the wastewater compared with UV. We conclude that MF represents a potential complimentary technology to enhance UV irradiation, especially to minimise pathogens in RAS that are shielded by particles or tolerate UV.