Aim:
This study evaluates the effectiveness of calcium hydroxide (Ca(OH)₂) for phosphate removal in a Zero Water Concept Phosphate Removal System used in a commercial land-based salmon Recirculating Aquaculture Systems (RAS).
Materials and Methods:
A phosphate removal sub-system was integrated into the RAS, featuring tanks for pH regulation (Ca(OH)₂), iron(III) chloride dosing, mixing, and sedimentation. Phosphate removal was tested by alternately using Ca(OH)₂ and iron(III) chloride. Water samples were collected daily and analyzed for phosphate and iron concentrations using Hach Lange methods.
Results:
Calcium hydroxide removed over 80% of phosphate at a pH of 9-11, integrating well with existing pH regulation and providing economic benefits by supplying alkalinity for the nitrification process. Iron(III) chloride was less effective due to high system alkalinity and iron efflux.
Discussion and Conclusions:
Calcium hydroxide is highly effective for phosphate removal in RAS, offering practicality and cost-efficiency. The predominance of calcium phosphates in sludge enhances reuse potential in agriculture or industry. Regular sludge removal is crucial for maintaining system efficiency, i.e., pH-balance. Calcium hydroxide is recommended for phosphate removal due to its efficiency, safety, and economic advantages. Effective sludge management is essential to ensure optimal operation and support sustainable reuse.