RAS offers the advantage that temperature and other variables can be controlled, in order to maximise growth and maintain fish health. Recirculating systems also require much less incoming water, some newer plants require only approx. 1 – 5%, compared to flow through farms, minimising the discharge to the environment and allowing operations to be established even where water supplies are quite small.

Generic Recirculation System Design

All modern RAS systems generally have the following components;

• Pump
• Bio-filter
• Solids collection systems (a rotating drum filter)
• A foam fractionation unit (also known as a protein skimmer or dissolved air floatation device)
• Carbon dioxide degasser
• Nitrate filter
• Sterilisation points (usually UV sterilisation)
• Tank drainage system that separates wastes from main outflows
• Temperature control (heat pump or evaporative cooling)
• Heat exchange of effluent waters
• Oxygen injection system
• A pH control and alkalinity dosing system

Often it is necessary for several of these components to be combined (i.e. biofilter, carbon dioxide degasser, nitrate filter and foam fractionation) for simplicity and capital savings.  The resulting system is however generally compromised.

There are many ways to build a RAS system and no “one way” can be said to be best across all species, budgets and situations. eWater provide the best system for a particular application  based on: 

• Proven commercial production performance
• Capital cost (feasible within the funds available)
• Operational cost
• Reliability
• Availability of backup and technical advice
• Durability (useful lifetime of equipment)
• Ease of associated support activities (maintenance, feeding, grading, harvesting)
• Suitability for species cultured
• Technology that fits technical ability
• Redundancy/backup/unitisation so plant can continue to operate if there is an issue with part of it
• Flexibility to make changes as required without compromising production
• Expertise and experience of the operator