Aquaculture Engineering

Filtration - Classification - Gravitational separation

Unit 12 - Management of ponds

Filtration

Classification according to form of materials

Gravitational separation
Gravitational separation utilizes the force of gravity to extract particles from a fluid. Density differences between the particles and fluid cause the particles to travel down ward in a quiescent fluid column. There are three types of gravitational separation system.

• Sedimentation
• Centrifuge
• Hydro clone

Sedimentation
Sedimentation is the process of allowing particulate materials having density greater than that of the suspending liquid to settle out under gravitational forces in a quiescent or slowly moving liquid. Plain sedimentation is sedimentation under natural forces only. Aggregation of finely divided particles by addition of chemicals and/or other materials to increase settling velocity is referred to as coagulation. Chemical precipitation may be defined as the addition of chemicals to waste water, resulting in a chemical reaction that produces an insoluble compound. This insoluble material then settles out by sedimentation.

Centrifuge
Centrifuges are used to increase the gravitational force experienced by particles during settling the principal advantage being the increased settling rates.

Chemical filters
Chemical filters are primarily adsorption units. Adsorption may be defined as a process of accumulation or concentration of substances at a surface or interface. The interface may be between two liquids, between a liquid and gas, between a liquid and solid and so on. In waste water treatment adsorption usually occurs at a liquid –solid interface, such as in activated carbon-water or ion exchange resin–water interface or at a liquid–gas interface, such as an air- water interface in foam fractionation.