Ozone Generators for Aquaculture

(To obtain more information on recirculating aquaculture systems, a complete set of tables, figures and references shown on this and related pages please refer to the book "Recirculating Aquaculture Systems, 2nd Edition", M. B. Timmons, et al, 2002, Cayuga Aqua Ventures, Ithaca, NY. You can obtain a copy of the publication from Cayuga Aqua Ventures by visiting their website at www.c-a-v.net.)

Ozone must be generated on-site. The most efficient method is by the electric corona discharge technique, which involves the passage of oxygen gas, oxygen concentrated from air or air, across a gap of narrowly spaced electrodes under high voltage, Fig. 12.1 (machines that produce ozone in this fashion are called ozone generators). According to Masschelein (1998), effective ozone generation depends upon the composition of the feed gas, e.g., feed gas impurities, particulates, moisture, and pressure of the feed gas, efficiency of dielectric cooling, characteristics of the electrical current, concentration of the ozone produced, and dielectric design. Protecting the dielectrics within the corona discharge cells requires a feed gas supply that is dry, free from particulate matter and coalescible oil mists, and contains less than 15 ppm hydrocarbons (Dimitriou 1990; Masschelein, 1998). Also, some ozone generators may require some nitrogen gas impurity (>0.5% nitrogen) within the oxygen feed gas in order to achieve maximum ozone production efficiency. To meet this level of nitrogen contamination, some liquid oxygen supplies may require adding a small quantity of nitrogen to the feed gas before it enters the ozone generator.

Purified oxygen is already used to maximize carrying capacity within many intensive aquaculture systems. Corona discharge generators using purified oxygen feed gas require about 10 kWh of electricity to produce 1.0 kg of ozone (Masschelein, 1998). However, ozone production within an air feed gas is 2–3 times less energy efficient than using purified oxygen feed gas (Masschelein, 1998). Also, generating ozone in oxygen feed gas can produce a 10–15% (by weight) concentration of ozone, which nearly doubles the concentration of ozone that can be generated using air as the feed gas. The relatively high concentrations of ozone can be generated to reduce the overall mass of oxygen required to supply ozone. Yet, it is less energetically efficient to produce ozone concentrations of 10–15% (by weight) than to produce ozone concentrations of 4–6% (Carlins and Clark, 1982). Taking all of this into account, ozone production can be optimized according to the demands of the aquaculture system and economic considerations of feed gas cost and energy usage.