| dc.description.abstract | Removal of particulate matter in Recirculation Aquaculture System (RAS) is considered one of the most critical parameters in controlling water quality and has gotten considerable attention. The most commonly used mechanical methods for removal of particles are inefficient for particles smaller than 40 – 60 µm. Protein skimmer (PS) or foam fractionation has been considered as an efficient water treatment technology to remove fine particles. Hydrogen peroxide (HP) as an easy degradable oxidizing disinfectant can be used in aquaculture to affect water quality by eliminating bacteria and reducing bacteria activity. HP may also improve the removal efficiency of particles in the PS process by oxidizing them. Moreover, increased salinity can positively affect the efficiency of PS by increasing water surface tension. However, there are clear gaps in the knowledge of operation and efficiency of PS on water quality in freshwater, including the effects of HP and salinity in water quality and PS efficiency.
This study included two experiments to investigate the efficiency of PS with different HP concentrations and salinities, on microbial water quality and removal of fine particles in freshwater. Experiment 1 was a 2×3 factorial design, with the addition of HP at three concentrations (0, 10, 50 ppm) and with/without PS. Experiment 2 was a 3×2×2 factorial experiment, testing the combined effects of PS (with/without), HP (0 vs. 10 ppm), and salinity (0, 3 and 10 ppt).
The inclusion of a protein skimmer improved water quality by reducing fine particles (2-5 times) and turbidity (on average 30-32%) in freshwater RAS. The addition of salt improved the PS efficiency by, on average, a factor two at 10 ppt. Adding HP to water treatment with PS tends to have a positive effect on removing particles in PS. However, the efficiency was not statistically significant, and further research is needed to evaluate this combination effect. Moreover, HP had a significant antimicrobial effect and affected water quality by reducing bacterial activity. The combination of HP and PS enhanced the reduction in bacterial activity by 30 - 60%. Furthermore, HP in combination with salinity may improve particle removal by PS process, particularly at 10 ppt where 10.4% higher removal was seen, although these differences were not statistically significant. This thesis has provided novel and valuable knowledge on PS effects and its combination with HP and the addition of salt in freshwater RAS. | |