Water Treatment "Part 4": Surface water.

Surface water is readily available in vast amounts, but after being extracted from rivers and lakes, it must undergo considerable treatment. Typically, pathogenic microorganisms, suspended particles, turbidity-causing agents, as well as organic and inorganic microscopic contaminants including heavy metals and pesticides, are removed from this water.

Surface water treatment to produce drinking water:

Establishing storage facilities is important prior to beginning the processing procedure. The treatment technique is typically done where the water bay is to avoid bacterial development and sedimentation in the conveying pipelines.

For instance, in the Netherlands, the Rhine and Meuse rivers provide the majority of the surface water used to produce drinking water. The ability to take water from the river is occasionally not possible due to the significant variations in quantity and quality. So, a storage facility must be available to cover periods when the supply process is interrupted in order to maintain the capability of supplying drinking water.

The process of coagulation-flocculation is necessary to remove the suspended particles that settle in the water due to the long retention time in the reservoirs.
Coagulation is a procedure that involves reducing the negative charges on the mucilage particles, which makes them unstable, by introducing iron or aluminium salt to the water. The next phase is flocculation, in which neutral particles collide to create bigger blocks, which are later eliminated following sedimentation at the bottom.

A jar test is being conducted for selecting the best dose of coagulant for water treatment

Heavy metals, organic materials, and viruses are also found in the blocks that are removed. Some small blocks, however, stay in the water and are later removed using rapid sand filtering. In order to eliminate organic microscopic contaminants from water, the rapid sand filtration procedure is followed by the activated carbon filtration process. Until it is saturated, active carbon can absorb small organic contaminants.

Microorganisms that can cause disease are also present in surface water. The impact of these germs must be eliminated through sterilization. For this purpose, chlorine is used, but because of its harmful side effects, it is no longer used in some countries, including the Netherlands. Ozone and UV light are two further means of sterilizing.

References:

• 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.