Land Based Aquaculture

Land based aquaculture relates to any operation producing or maintaining aquatic livestock within facilities operating on land.

Land based aquaculture relates to any operation producing or maintaining aquatic livestock within facilities operating on land. This encompasses; large scale private commercial operations, University research and development systems, seafood holding systems and aquatic transport systems. Aqua EcoSystems has developed and installed them all.

The main focus of AES's work is focussed upon Recirculating Aquaculture Systems commonly referred by the abbreviation "R.A.S.". These systems are highly engineered to give the best in conditions to the fish. They are generally configured using a number of tanks to hold and grow the fish, linked to filtration units to process the water from the tanks and return the same water back to the fish under optimum conditions to promote the best growing conditions.

Systems classified as "RAS" are often done so by the extent to which they "reuse" their water. If a system does not reuse water its water it would be classified as a "flow through" system rather than a recirculation system. Then depending upon the percentage of water reuse, categorised as "Partial RAS", "Standard RAS" and "Zero exchange RAS".

To determine the type of system required, AES must review the requirements of the species, the environmental conditions and availability of good quality water within the location and the parameters to which the operation must work within (market price of the chosen species, environmental legislation, etc.).
RAS in general, follow similar principles and methods to ameliorate the wastes produced by growing fish and to supplement and replace water characteristics used by the fish.

Principles

Fish production produces waste materials in the form of solids, dissolved chemicals and gases that are all accounted for and reduced/ removed. Fish production also utilises water parameters which must be replaced and a levels of bacteria and pathogens can proliferate to adverse levels which have to be managed.

The most pertinent factors accounted for are;

1. Solids (Wasted feed and faeces).

2. ● Ammonia, NH3 (Excreted from gills & derived from feed & faeces).

● Nitrite, NO2- (Nitrosomonas bacteria break down NH3 into nitrite).

● Nitrate, NO3- (Nitrobacter bacteria break down NO2- into nitrate).

3. Bacteria, viruses and parasites.

4. Carbon Dioxide, CO2 (respiration from fish and bacteria).

The main aspects of water quality used during culturing are;

5. Alkalinity (used by bacteria during the nitrification process).

6. Oxygen, O2 (used by the fish for and bacteria for metabolism).

Processes

The factors described under "Principles" are controlled by a number of standard processes carried out within and after the filtration units.

There are 3 main filtration processes to ameliorate the wastes produced and to control bacterial and pathogenic populations. After ancillary processes address physical water parameters;

1. Mechanical filtration - removes solid wastes produced.

2. Biological filtration - removes the waste derivatives; NH3, NO2-, NO3-

3. Chemical filtration - controls proliferation of bacteria and pathogens.

Ancillary processes are used to control other water parameters

4. CO2 is removed through a process of "de-gassing"

5. Alkalinity is controlled by pH adjustments through addition of a alkalis such as Sodium Hydroxide (NaOH)

6. O2 is added to the water through aeration or direct oxygen injection.

Systems

All processes are enabled through the implementation of systems in sequence.

a) Heavy solid wastes are removed from the water as early as possible so as to reduce load on latter filtration processes and reduce the "chemical oxygen demand" (COD) of the water. This is achieved through appropriate hydraulic design of the fish tanks and mechanical filtration using drum filters with a fine micron mesh to remove heavy solids.b) Smaller "suspended solids" are also important to remove to maintain overall water quality and to deliver high quality fish. This is achieved through fine mechanical filtration and/or foam fractionation, a process using "Van der Waals" forces of bubbles to attract fine particles from the water then collected and ejected from the systems.
Water filtered of heavy solids, is allowed to pass into a bio-filter that contains bio-media to promote the growth of aerobic bacteria required to break down; Ammonia (NH₃) and Nitrite (NO₂-) into their less toxic form, Nitrate (NO₃-). Nitrate can also become toxic and inhibit growth above certain concentrations and so is either diluted or removed through anaerobic bio-filtration.
Chemical filtration is carried out by oxidative agents that will not bio-accumulate within the system. The 2 processes routinely employed are injection of Ozone (O₃) and/or Ultra violet (U.V.) treatment. These treatments are performed after mechanical filtration. Ozone is often used in conjunction with foam fractionation as it promotes the bubble forming process required for fine mechanical filtration of solids.
Carbon dioxide (CO₂) is removed through a process of "de-gassing" which essentially exposes the water to ambient air containing a comparatively lower concentration of CO₂ and so allowing it to dissipate from the water. This can be done through heavy aeration within the bio-filter (a process required to supply aerobic bacteria with oxygen) and/or trickling water over a large surface area to expose it to the air.
Alkalinity used during the bio-filtration process and is controlled via supplement of a alkalis such as Sodium hydroxide (NaOH) to maintain the optimal pH. This is injected into the water sump after the bio-filter.
Oxygen (O₂) is replenished through aeration and de-gassing processes to "normal" levels but within "intensive" systems higher levels of oxygen are required.. This is achieved through conditioning the water with pure O_²,
before it returns to the fish tank.

The "principles, processes and systems" have been described in simple terms but in reality there are many more parameters than described and chemical and physical interaction dynamics to control them which AES incorporate during planning, design and engineering.