At a water treatment plant, filtration is a key step where water passes through specialized filter beds to remove remaining small particles.
The Filtration Process Explained
Filtration is typically the next stage after processes like coagulation and sedimentation, aiming to catch the tiny impurities that didn't settle out.
Here's how it generally works:
- Entry: The water enters on top of the filter media. This media usually consists of layers of materials like sand, gravel, and sometimes anthracite coal.
- Downward Flow: [Water] passes down through the filter beds by gravity. Gravity pulls the water downwards through the layers of filter media.
- Straining and Trapping: The different materials work like a giant strainer and trap remaining particulates. As water flows through the spaces between the media grains, suspended solids, including silt, clay, and some microorganisms, get caught and held back.
- Cleaning: When the filters have trapped a significant amount of material and start to become less effective or slower, they need cleaning. When the filters start to get packed full of particles, the operators clean them using a procedure called backwashing.
Understanding Backwashing
Backwashing is a process where the flow of water is reversed, sometimes with the aid of air. Clean water is pumped upwards through the filter bed. This lifts and expands the filter media, releasing the trapped particles. This dirty water, now containing the removed contaminants, is then directed to a separate waste stream for further treatment or disposal. Backwashing restores the filter's capacity and efficiency.
Why is Filtration Important?
Filtration is crucial for ensuring drinking water is clear, clean, and safe. It removes particles that can cause turbidity (cloudiness) and helps to remove or reduce the levels of certain pathogens. It's an essential barrier in the multi-step process of transforming raw source water into potable tap water.
Filtration is just one part of a comprehensive treatment process that often includes aeration, coagulation, sedimentation, disinfection (like chlorination or UV treatment), and sometimes pH adjustment or fluoridation.
