Investigating The Effect of Mechanized Disinfectant Device Using Ultraviolet Radiation on the Outlet of Rainbow Trout Farm

Aquaculture includes the propagation and husbandry of aquatic plants, animals, and other organisms for various purposes, including commercial, recreational, and scientific use, which has gained significant attention in recent times. However, its uncontrolled development like any other production activity, can have adverse environmental effects, Thus, the removal of water pollutants is crucial. This study aimed to investigate the impact of a mechanized water disinfection device that uses ultraviolet (UV) radiation at different doses to reduce microorganisms in the effluent of rainbow trout farms.  Also, the efficiency of the device in deactivating pathogens was investigated in different flow rates and water turbidity levels.

The study was conducted in a rainbow trout farm with a 30-ton capacity, located in Kiyar County, approximately 30 kilometers from the center of Chaharmahal and Bakhtiari province. The UV device, at various doses (60, 120, 180, and 240 mW/cm2 = joule), was applied to the farm's effluent, considering different levels of turbidity and flow rates (ranging from 2.5 to 25 liters per second). Water samples were collected both before and after the installation of the UV disinfection device. Subsequently, the average counts of total coliforms, fecal coliforms, fungi, and yeast were calculated with three replications. Probit regression was utilized within the SPSS software environment, with a statistical significance level of 0.001, to examine changes in the removal percentage of microorganisms at different UV doses. Graphs were created using Microsoft Excel 2016 software.

The findings indicated that increased water flow rates and water turbidity reduced the efficiency of removing the targeted microorganisms. The findings indicated that increased water flow rates and water turbidity reduced the efficiency of removing the targeted microorganisms. Moreover, higher UV doses led to a higher removal percentage of total coliforms, fecal coliforms, fungi, and yeast. For instance, at a dose of 56 mJ/cm2, the total counts of total coliforms, fecal coliforms, fungi, and yeast decreased by 1.7, 3.2, 0.7, and 0.86 logs, respectively. However, complete removal of yeasts required significantly higher UV doses, depending on water flow rates and turbidity (up to a maximum of 240 mJ/cm2). Additionally, the results of the probit regression indicated that at doses of 40.50 mJ/cm2, 20.22 mJ/cm2, 30.31 mJ/cm2, and 14.36 mJ/cm2, approximately fifty percent of the yeast population (P<0.001), fungi (Z=13.5, P<0.001), fecal coliform (Z=22.77, P<0.001), and total coliform (Z=6.8, P<0.001) would be removed.

In summary, this research demonstrated that at a dose of 20 mJ/cm2, the gradual elimination of microorganisms begins, but at doses higher than 120 mJ/cm2, the intensity of elimination decreases. Therefore, adjusting the doses of ultraviolet radiation based on the water quality of fish farms can help maintain system health and subsequently increase productivity. The insights obtained from this study can be valuable for commercial water treatment systems and recirculating aquaculture systems. More studies are needed for the efficiency of removing viruses in water by UV rays. It is recommended to construct a sediment pond and employ various water filtration methods, including sand filters, before utilizing ultraviolet rays. This approach aims to decrease the presence of suspended particles in the water and enhance the efficiency of the disinfection system.