Water Treatment "Part 39": Precipitation.

Precipitates can be divided into two categories:

• 1- The separated particles, which have a constant leaking velocity, are included in the first category.
• 2- The second category consists of particles that have clumped together either naturally or as a consequence of a synthetic agglomeration procedure. These particles settle out on their own in a weakly concentrated medium, but as they fall, they encounter other particles, clump together, and collide with them, changing their speed. This increases particle size, which in turn accelerates the settling process. This kind of process is called diffuse precipitation, but the number of masses generated causes collective precipitation in mediums with large concentrations of suspended materials, consequently, it seems to split from the liquid phase and may be identified by a surface that divides the two phases.

Diagram showing the differences between a compound, a precipitate, a supernate, and a suspension.

Granular particle precipitation:

In a stationary liquid, a particle receives a downward force (Fm) equal to its own weight, and a force (Ft) that opposes movement is pointed upward. The particle has zero initial speed, but after a duration of (t), it accelerates until it's speed gets to a constant value, the early stage, which is marked by acceleration, is ignored since the time (t) is relatively minor in comparison to the whole precipitation period. The two opposing forces (Fm and Ft) are identical when the particle's speed reaches the constant terminal velocity.

Precipitation associated with agglomeration:

In this situation, the collision between the particles causes an increase in particle size during precipitation, which causes the velocity of falling to increase with time. In this instance, the velocity path is bent. For such precipitation, there are no mathematical correlations, nonetheless, the speed is calculated following laboratory experiments and the creation of curves showing the proportion of precipitation with time and the height of the precipitation basin.

References:

• [Introduction to Water Chemistry (Pollution- Treatment- Analysis). Dr. Nasser Al-Hayek. Publication of the Higher Institute for Applied Sciences and Technology (HIAST). Syrian Arab Republic, 2017.]
• Taparhudee, Wara (2002). "Applications of Paddle Wheel Aerators and Diffused-Air System in Closed Cycle Shrimp Farm System" (PDF). Witthayasan Kasetsart (Sakha Witthayasat). 36: 408–419. Retrieved 26 April 2020.
• Unsafe water kills more people than war, Ban says on World Day". UN News. 22 March 2010. Retrieved 10 May 2018
• Raymond Desjardins- Livre: Le traitement des eaux- 2éme edition- Ecole Polytechnique de Montréal- 1997- ISBN 2-553-00643-8
• Drinking Water Treatment- EDX- Delft University of Technology.
• Book- Drinking Water: Principles and Practices- by Hans J C Van Dijk (Author), Jasper Q J C Verberk (Author), Peter J De Moel