Ozoniser

However even with the quality of today’s aquarium filtration, there are a few dissolved and fine organics components that tend to accumulate in an aquarium which the ordinary filtration systems fail to remove. Generally the only way to reduce them is by frequent water changes.

Conventional means of solids removal, such as sponge/ perlon floss filters and sand filters address the removal of coarse settleable and filterable solids, but not the removal of fine colloidal solids. Similarly, nitrifying bacteria in bio-filters remove dissolved ammonia and nitrite, but not all dissolved organic wastes. As an aquarium matures, the accumulation of dissolved organic colloidal solids increases. This organic build-up decreases the performance of the nitrifying bacteria that convert nitrite to nitrate, thus causing harming nitrite build-up. The biochemical oxygen demand also rises, so the oxygen levels decrease over time. These shifts in water parameters stress the aquarium inhabitants and may even cause mortality. To reduce the necessity of large water changes, that can change the systems chemical parameters (PH, salinity, alkalinity etc.), there is a very efficient alternative method of breaking down these organic wastes using a strong oxidizing agent, this method is “Ozonation”.

Ozone (O3) has been used, for a long time as a disinfectant and as an oxidizer that removes turbidity, algae, odour, colour and taste in the municipal drinking water supply. Applying ozone to fresh water, marine and reef aquariums will achieve the following properties:

• Removal of Micronics solids (1-100 microns) by clumping them together to bigger dimension particles that can be removed by the protein skimmer or activated carbon.
• Removal of complicated dissolved organics that cannot be handled by ordinary bio-filter. The ozone oxidizes them and breaks them to simple organics that are now available for degradation by heterotrophic bacteria.
• Reduction of harmful ammonia (NH3-) and nitrite (NO2-) levels by oxidizing them to nitrate (NO3-).
• Precipitation of metals, such as aluminium.
• Algae control
• Destruction of harmful inorganic components, such as sulphides.
• Degradation of pesticides and detergents.
• Bacterial disinfections & viral inactivation: 0.4 mg/L at a 4-minute contact time easily kill bacteria and inactivate 99% of viruses.

Ozone is a very unstable molecule that is formed when an Oxygen molecule (O2) bonds to a third oxygen atom by passing the oxygen through an electrical charge or U.V. light at the proper wavelength. Because of the loosely bound third atom, ozone exhibits a far greater oxidative potential compared to oxygen. The ozone reacts with organic molecules at unsaturated carbon bonds, which quickly decompose in water to form carbonyl components and hydrogen peroxide. In solution ozone has been shown taking to pathways as it decomposes and oxidizes materials. The first pathway is by direct reaction with molecular ozone and the second is by indirect action of the oxidized compound with radicals formed by the decomposition of ozone.

The advantages of ozone are:

• Powerful oxidizing agent. Reduces BOD and COD levels.
• Very rapid reaction time.
• 5 times more effective as a disinfectant for bacteria and viruses, than Cl2.
• Requires short contact time.
• Produces a complete reaction because of its short half-life (20-30 min.)
• Leaves a beneficial oxygen residual

Production and utilization of ozone:
Most commercially available ozone generators use corona discharge to establish a strong electric field. Dried air or oxygen gas is fed through the electric field. Due to the electrical energy, a proportion of the oxygen molecules become excited, creating oxygen atoms that bind to other molecules to create ozone.

The feed gas must be dry and free from impurities. If a feed gas of air or low purity oxygen contains moisture, nitric acid is formed, which rapidly decomposes the produced ozone and is also highly corrosive.

The design of the ozone-to-water contact chamber is the most critical design element in using an ozone system. Since ozone in the carrier gas (air) is at relatively low concentration, mass transfer of the ozone from a gas into the water must be done at maximum efficiency. In marine and reef aquariums, we already have an efficient reactor vessel in which to utilize ozone, our protein skimmer. The protein skimmer materials must be highly resistant or inert to ozone. Use of improper materials can lead to erosion of the unit and cause leakage.

Ozone can be applied continuously, as a series of treatments, or as single batch treatment per day. The optimum rate for disinfection is highly variable and represents the sum of ozone demand from dissolved organics, colloidal solids, etc. The amount of ozone necessary is largely dependent on the background organic loading of the water to be treated. In pure water, residual concentration of 0.01-0.1 ppm for period of 15 seconds can be effective in reducing bacterial loads. In most of our aquarium systems 5-15 mg/hr/100 liters is sufficient amount to get proper disinfection. A more accurate rule is 1.5 mg for 1hr/day/ 1 gr of fish weight. If the purpose of the ozone is to treat the dissolved organic matter, the optimum rate should be according to daily feed rate. It is recommended 10 mg ozone per gram of fish food, to reduce accumulated organics.

The best method to monitor ozone input is by measuring the oxidation-reduction potential (ORP) with probes or by a Redox meter/controller. The term Redox potential refers to the electrons transfer from one substance to another that takes place in every chemical reaction. The substance that receives electrons is said to have been oxidized, while the one that loses electrons is said to have been reduced. In sea water, many of these so called ‘redox reactions’ occur simultaneously. Because of the constant exchange of electrons the amount of prevailing oxidative or reductive reaction can be measured as a voltage, by means of a platinum electrode and a volt meter. The higher the redox potential, the greater the oxidizing capacity of the water. In sea water the redox potential is between 350-400 mV. Redox potential values of between 300 and 350 mV are recommended as the desirable level, which indicate an oxygen rich environment with low dissolved organics. The redox potential can therefore be used as an indication of the quality of your Aquarium environment. Values below 200 mV indicate an accumulation of disolved organics and a low oxygen level.

As ozone is applied to aquarium water it will raise the oxygen level and break down organic wastes, i.e. sterilizing the water thus raising the redox potential. A too high redox potential is as undesirable as a low redox potential therefore it is advisable to keep the redox potential stable by applying ozone. When the redox potential is lower than the desired value, ozone should be applied and when the upper limit of the redox potential is reached the ozone should be turned off. This control can be achieved by combining a Redox controller to the ozone generator.

Red Sea manufactures a range of technically advanced ozonisers (The AquaZone) with 50, 100 and 200 mg/hr output. Red Sea also offers AquaZone PLUS which combines an Ozoniser and Redox controller. The following chart will help to determine the ozoniser suitable for each kind of system up to the maximum volume indicated.

Safety Precautions for using Ozone:

Ozonized air should be prevented from escaping into the room; it is advisable to install a carbon filter on your protein skimmer or ozone reactor where ozonized air escapes. Do not let the redox value of the aquarium water exceed 400 mV as harmful substances (commonly in the form of hypochloric and hypobromic acids) can be produced, which could damage sensitive organisms. The aquarium inhabitants should be protected from exposure to free ozone and /or oxidation products. The recommended method to remove any residual free ozone and any free oxidation products is by vigorous aeration followed by filtration through activated carbon. After this treatment the amount of residual ozone should be checked regularly – maximum 0.05mg per liter.