Chapter 5 – water treatment

Chapter 5 - Water Treatment

5.1 Overview of Water Treatment

• Water treatment is necessary in both semi-closed and closed systems.

• Factors determining treatment type and degree:

  • Requirements for culture organisms.

  • Initial quality of water.

  • Cost considerations (capital and operating).

5.2 Methods of Water Treatment

• Filtration: Removal of particulates or dissolved materials.

• Disinfection: Techniques include using ozone (O3), ultraviolet (UV) light, or chlorination to eliminate unwanted organisms.

• Aeration: Enhances dissolved oxygen (DO) levels in the water.

• Degassing: Removal of excess nitrogen (N2).

• Temperature Control: Essential for optimal organism growth.

5.3 Filtration Methods

5.3.1 Mechanical Filters

• Screens: Simple filter screens placed at pump inlets.

5.3.2 Rotary Filters

• Water flows through rotating screens with both filtering and backwash capabilities.

5.3.3 Bag Filters

• Primarily used at raceway inlets and tanks; easy to clean and are available in various weaves to filter specific particle sizes.

5.3.4 Cartridge Filters

• Less common; useful in laboratory and hatchery systems.

5.3.5 Particle Filters

• Contain a housing with a filtering bed (sand/gravel). Smaller bed material removes finer particles but slows flow.

• Backwashing process:

  • Reverses water flow to dislodge accumulated particles and clear the filter.

5.4 Chemical Filters

5.4.1 Foam Fractionation

• Removes organic waste through a process of bubble formation.

5.4.2 Carbon Filtration

• Activated carbon filters remove polar and non-polar solutes.

  • High surface area due to microporosity, and must be arranged downstream of biological filters to avoid clogging.

5.4.3 Ion Exchange

• Utilizes resins to exchange ions from the water, commonly for softening hard water.

5.5 Disinfection Techniques

5.5.1 Ultraviolet (UV) Radiation

• Disrupts microbial DNA and RNA through exposure to specific wavelengths.

• Efficiency considerations: Suspended particles can hinder effectiveness.

5.5.2 Ozone (O3) Treatment

• A strong oxidizing agent that reacts with microbes.

• Produced via high voltage or UV exposure.

  • Requires decomposition to O2 before entering aquaculture systems to prevent toxicity.

5.5.3 Chlorination

• Common in wastewater treatment; involves electrolysis of salt and subsequent reactions forming hypochlorous acid for disinfection.

• De-chlorination methods:

  • Activated carbon, UV radiation, and sodium thiosulfate.

5.6 Aeration Techniques

• Necessary to raise dissolved oxygen (DO) levels, particularly in high-density culture environments.

• Factors affecting oxygen transfer:

  • Differential pressure gradients.

  • Water movement in the system.

5.7 Temperature Control in Water Treatment

• Critical for fish health and plant growth in aquaponics.

• Methods to regulate temperature include insulation, placement in shaded areas, and the use of heaters or chillers to maintain stability in varying climates.