The water used in the facility is circulated in a closed loop system with fresh make-up water replacing losses due to evaporation, spillage or discharge. The AquaMaof Filtering System was designed with efficiency in mind.
Figure 1, below, illustrates water cycle in the facility. The water is continuously enriched with oxygen by the Oxygen Dissolving System (ODS) that is backed up by a pure oxygen emergency supply in case of failure.
The Settling Filter is the second step in the solid waste removal process and has media through which the water flows. The concept is for the discharged water to slowly percolate upward so that any heavier than water solid particles carried in the water will settle on the floor after only a short flow distance. This technology improves solid settling capability and reduces the total basin without media. The majority of the solid waste is collected at the bottom of the Settling Basin with some remaining on the inclined surfaces of the media.
A second function for the settling filter is to provide some denitrification of the nitrate (nitrogen) content of the water. This is an anaerobic process, and requires water level entering the tank to be as low as possible.
The Biofilter is an important non-mechanical part of the water treatment system. The Biofilter is a section for growing bacteria on a filter media designed to provide a large surface area in a small volume. The growing process of bacteria neutralizes toxic fish wastes into by-products that are not harmful to them such as changing ammonia to nitrate. Circulating water flow from the Settling Tanks is controlled automatically for flowing onto the Biofilter bed. The process of bacteria growing needs a food source (fish waste products-including ammonia), oxygen and alkaline water. The bacteria convert them into nitrate, carbon dioxide, and hydrogen ions as by-products. The bacterial conversion (nitrification) of ammonia is a two phase process with the first converting ammonia to nitrite to be followed by converting nitrite to nitrate as shown below:
* Phase 1: NH4+ + 1.5 O2 = 2H+ + H2O + NO2- Ammonia
+ oxygen = acid + water + nitrite
* Phase 2: NO2- + 0.5 O2 = NO3-
Nitrite + oxygen = Nitrate