Water Treatment Plant
Water treatment is a fundamental process for ensuring access to safe water. Water supply issues lead to the use of aquifers that, in terms of both quantity and quality, contain salt concentrations unsuitable for human consumption. The solutions a company can adopt depend on the characteristics of the water and the water treatment technology used.
The foundation for finding an appropriate solution to a company’s water-related issues is a thorough analysis of the incoming or feed water, followed by a tailored design process that leads to the determination of the most suitable treatment method and the correct sizing.
Depending on the source, water may or may not meet the standards for potability, hygiene, and quality. The water treatment plant is designed to remove natural or man-made elements that have contaminated the water or are present in excess: pollutants, minerals, bacteria, and viruses.
Furthermore, depending on the available space, it is also possible to size and design the outdoor skid according to the required specifications.
Depending on the degree of contamination, pollution, or alteration of water quality, water requires different types of treatment. A water treatment plant can vary in complexity and may consist of different stages.
- Physical Treatments
- Chemical Treatments
- Aging
- Disinfection
The Legislative Decree 152/2006 classifies water into three categories that require different treatments:
- water requiring physical treatment and disinfection
- water requiring physical and chemical treatment and disinfection
- water that requires more intensive treatment, including polishing
Example of a Water Treatment Plant
Raw, untreated water enters the water treatment plant.
The first phase involves the introduction of substances capable of “intercepting” non-settling solids, which then aggregate into flocs through the flocculation process.
Introduction of Flocculants and Process Optimization
At this stage, flocculants—specifically aluminum sulfate or ferric chloride—are added to the treatment process, causing the particles to aggregate; these aggregates are then separated from the water through filtration.
Neutralizing surface charges facilitates the formation of the first small solid aggregates, which subsequently tend to grow larger through the adsorption of particles until the first flocs form in suspension. To improve the process, powerful agitators are used; however, agitation is not advisable during flocculation because it tends to break up the flocs that have formed.
Process Stages and Final Decanting
Flocculants, which can be anionic or cationic depending on the charge of the surface particles to be destabilized, are generally used within a specific pH range. One application that takes advantage of the flocculation phenomenon is clariflocculation systems used for water treatment. In this process, the suspended particles in the solution form larger aggregates that are heavy enough to settle and thus be separated from the wastewater as sediment.
In the first stage, the equipment used for coagulation must provide rapid and vigorous agitation to dissolve and disperse the coagulant. The second stage, flocculation, requires moderate and slow agitation so that the destabilized colloidal particles form flocs large enough to settle.
This process is carried out either in a tank equipped with agitation or within a series of settling tanks, using sludge recirculation. This type of system, which requires small amounts of water and involves relatively low costs, is used for preliminary treatment to make the water safe for drinking so that it can be chlorinated, stored, and sent to the distribution system via a pressurization unit.