Water does not simply disappear after use; rather, it gets increasingly contaminated; so, waste water and water supply cannot be considered separately. In order to enhance the water's quality for future use in certain industries or agriculture or for reintroduction into the natural water cycle, the water is collected in the sewage system after usage and transferred to a wastewater treatment facility.
Secondary settlement tank of a sewage treatment plant
A diverse combination of dissolved and insoluble compounds are present in wastewater, some of these substances possess the ability of biodegradation, while others are poisonous to both plants and animals and some of them could even prevent bacterial proliferation, and it can be divided as follows:
- Mineral or organic dissolved substances.
- Colloidal and emulsion substances (Soluble fatty and oily substances, hydrocarbons, surfactants.....).
- Suspended materials.
There are three classifications of wastewater contamination criteria:
1- General measures of water pollution:
The fundamental characteristics of wastewater, suspended matter, oxidizable chemicals, and biodegradable materials, which are quantified in terms of oxygen demand, are some examples of general pollution metrics that can be expressed in numbers.
2- Qualitative analyses:
Depending on the examination of one or more contaminants that need particular treatment to be eliminated (like cyanide), qualitative analyses are carried out on various types of wastewater that have specific features.
3- Bioanalysis:
According on the source of the wastewater, both basic biological analyses and specialised analyses are performed. Additional testing must be done for the hospital waste water since it has a high concentration of pathogenic microbes.
Excavation of public sewers:
- The public sewers in the city of London were the oldest in all of Europe, and they included different pathways for rainwater and household sewage. During his exile in London, Napoleon III was inspired by the notion of building public sewers, and upon his return, he issued an order to build them for the city of Paris.
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