Drinking water supply system
The path of water from a surface source to the consumer includes several consecutive stages ensuring its intake, purification, storage, and distribution.
Water flow diagram:
- Water intake.
- First-lift pumping station.
- Treatment facilities (settling tanks and coagulation building).
- Filters.
- Chlorination station (for chemical disinfection).
- Clean water reservoir.
- Second-lift pumping station.
- Water pipeline, water tower, and municipal network.
Basic water treatment methods
To ensure water meets hygienic standards, various water quality improvement methods are used. Modern technologies include oxidation-sorption, membrane, electrochemical, and physical methods.
Main water treatment processes:
- Clarification — removal of suspended particles.
- Decoloration — elimination of dissolved substances and colored colloids.
- Deodorization — elimination of foreign odors.
- Disinfection — destruction of infection agents.
- Conditioning — targeted alteration of the chemical composition (removal of harmful elements or addition of beneficial ones).
The basic method of purification (clarification, decolorization, and deodorization) is mechanical sedimentation followed by filtration through special materials.
Coagulation
Coagulation is a preliminary chemical treatment that increases the efficiency of sedimentation. Reagents (e.g., aluminum sulfate or ferric chloride) are added to the water and react with hardness salts. As a result, flakes form, adsorbing suspended matter. These flakes clump together and settle to the bottom.
Coagulation not only purifies water from suspended solids by increasing its transparency, but also reduces color, odor, and the number of microorganisms. To accelerate the process, flocculants (polyacrylamide) are sometimes added.
A promising area is the use of titanium-based coagulants. They have low toxicity, do not accumulate in the body, work at various temperatures and pH levels, and the resulting titanium hydroxides excellently sorb radionuclides and heavy metals.
Types of filters
After sedimentation, water is directed to reservoirs filled with layers of crushed stone, gravel, and quartz sand. Filtration traps particles larger than 1 µm.
Slow filters:
- Rate: 10 cm of water column per 1 hour.
- Purification: occurs due to the biological film on the sand surface (suspended matter, plankton, bacteria). The film traps fine particles and up to 99% of microbes.
- Maintenance: clog quickly, cleaned manually (2–3 cm of sand removed every 1.5–2 months). Require large areas.
- Pros: coagulation is not needed, the process is close to natural.
Rapid filters:
- Rate: 5–6 m of water column per 1 hour (50–60 times faster than slow filters).
- Purification: instead of a biofilm, a film of fine coagulant flakes that did not settle earlier works here. Traps about 95% of bacteria.
- Maintenance: clog quickly, but cleaned mechanically (backwashed with water 1–2 times a day). Take up less space and are more economically viable.
Briefly: answers to topical questions
What physical and chemical water disinfection methods exist?
Water disinfection methods are divided into chemical (reagent-based) and physical (reagent-free).
- Chemical methods — include chlorination (normal and increased doses, double chlorination, preammoniation, chlorine dioxide) and ozonation.
- Physical methods — include ultraviolet irradiation (using bactericidal mercury-quartz or argon-quartz lamps), ultrasound treatment, and others.
What is the mechanism of the bactericidal action of chlorine during water disinfection?
The bactericidal action of chlorine is based on hydrolysis with the formation of hypochlorous acid, which breaks down into active components depending on the medium's pH.
- In an acidic and neutral medium — the acid breaks down into atomic chlorine and oxygen. Atomic chlorine acts on the amino groups of proteins, blocking the formation of polypeptide chains. Oxygen acts as a strong oxidizing agent, causing protein coagulation.
- In an alkaline medium — the acid dissociates to form a hypochlorite ion, which also causes protein oxidation and coagulation.
The combined action of these oxidizing agents ensures the death of infectious agents.
Class and exam questions
What serves as the primary filtering element in a slow filter?
In a slow sand filter, the primary filtering barrier is the biological film that forms on the sand surface from trapped suspended solids and microorganisms.
Why is coagulation needed?
It is necessary for clumping small suspended particles. The resulting flakes sorb contaminants and precipitate, which significantly improves water clarification.
What water is subject to mandatory disinfection?
Water from all surface water sources, as well as from underground sources classified as classes II and III, must be disinfected.
What else to study on this topic
- Design of contact clarifiers (bottom water supply)
- Types of modern membrane water treatment methods
- Physical disinfection methods
- Chemical disinfection methods (chlorination station operation)
- Classification of underground water sources by class
Master the entire topic in the "Hygiene" course
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Other topics in "Chapter 2. Ecological and Hygienic Problems of the Hydrosphere and Water Supply"
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