Effects of different levels of ozone on ammonia, nitrite, nitrate, and dissolved organic carbon in sterilization of seawater

Abstract

Ozone is applied to the recirculation aquaculture system to reduce bacteria and parasites. Besides the sterilization effects, it is known that ozone has oxidizing effects on some water quality parameters. Therefore, oxidizing effects of ozone on ammonia (NH 4 -N), nitrite (NO 2 -N), nitrate (NO 3 -N), and dissolved organic carbon were tested in this study. During the test, ozone effects on pH, dissolved oxygen (DO) and bromination were also monitored. Ozone concentrations were originally set to 0.05, 0.1, 0.15, 0.2, and 0.25 ppm, but actual treatment concentrations were maintained at 0.04, 0.11, 0.15, 0.19, and 0.23 ppm. The 5 ppm of NH 4 -N was oxidized within 12 h in all concentrations of ozone treatments, with the average oxidizing rate of 0.65 ± 0.28 mg NH 4 -N/L per h. The 5 ppm of NO 2 -N was oxidized within 1.5 h in all concentrations of ozone treatments at a rate of 4.5 mg NO 2 -N/L per h. One of 5 ppm NO 3 -N was oxidized by all concentration of ozone treatment after 24 h. In addition, ozone also oxidized dissolved organic carbon and maintained the concentration at about 2.9 ± 0.77 ppm from the 15 ppm of initial concentration by 12 h. DO was increased from 5.9 to 9.4 ppm within 30 min in all ozone treatment and stabilized thereafter. Bromate concentrations increased sharply within the first 6 h of ozonation at the rate of 7.3 ± 2.4 mg/L per h in almost all ozone treatments; the rate decreased to 2.5 ± 0.15 mg/L per h thereafter. However, bromate concentration was not increased in the ammonia experiment until all ammonia was oxidized. Therefore, further studies are needed to determine the relationship between NH 4 -N concentration and bromate formation in seawater.

Controlling of geosmin and 2‐methylisoborneol induced off‐flavours in recirculating aquaculture system farmed fish—A review

“…In aquaculture, ozone can be used for treatment of incoming water, effluent water or control of circulating water (Powell & Scolding, ). Ozone can be used to inactivate and kill pathogens before entering the aquaculture systems (Summerfelt & Hochheimer, ) or to remove suspended solids, reduce nitrite and non‐biodegradable organic molecules and increase dissolved oxygen (Rahmadi & Kim, ; Summerfelt & Hochheimer, ). For incoming water, dosages can be relatively high (0.4–0.5 mg/L, oxidation‐reduction potential (ORP) 700 mV) with 5–10 min contact time (Cheremisinoff, ; Powell & Scolding, ).…”

“…The ozone‐produced disinfection by‐products, such as hypobromous acid and bromamines, are toxic or carcinogenic and able to reduce pH. These by‐products can be removed by activated carbon filtration or by UV radiation, among other methods (Gonçalves & Gagnon, ; Rahmadi & Kim, ). All in all, ozone should be used cautiously in RAS (Martins, Pistrin, Ende, Eding, & Verreth, ).…”

Direct application of ozone in aquaculture systems

“…The rate of ozone decay increases with time after deployment, whilst higher flow rates (differing hydraulic retention time) or low initial dosages and high water pH may reduce ozone concentration (previously reviewed by Lage Filho ; Gonçalves & Gagnon ; Rahmadi & Kim ). Sharrer and Summerfelt () also suggested that bacteria embedded within particulate matter, or that formed bacterial aggregates, provided shielding from oxidation.…”

“…This technique can also be used in quarantine systems and upon effluents, before neutralisation and discharge into the environment (Summerfelt & Hochheimer 1997). Benefits also include removal of suspended solids, reductions in nitrite and non-biodegradable organic molecules, and increased dissolved oxygen, thus improving the quality of incoming and effluent water (Summerfelt & Hochheimer 1997;Rahmadi & Kim 2014). More specifically, ozone can enhance conventional water treatment techniques, such as near complete chemical destruction and reduced immunoreactivity of oestrogens (or analogues) that remain in tertiary-treated sewage wastewater (Ning et al 2007;Altmann et al 2012;Umar et al 2013).…”

“…The production of disinfection by‐products (ozone‐produced oxidants) such as oxidised halide species (hypobromous acid, bromamines) is toxic or carcinogenic and can also potentially reduce pH. However, these compounds can be removed via treatment methods such as activated carbon filtration, UV radiation and other water treatment methods (reviewed by Gonçalves & Gagnon ; Rahmadi & Kim ). Ozone can also reduce the bioavailability of iodine, with incidences of fish presenting with goitres, requiring iodide supplementation of the diet or water (e.g.…”