This is where the magic happens. We add billions of hungry, good-natured bacteria. These tiny dudes are like Pac-Man for pollutants. They gobble up the dissolved organic matter (think soap, food bits, and poo particles) that’s still left in the water. It’s a microscopic rave, and everyone’s eating.
There are two main ways to throw this party. One is the activated sludge process, where we bubble oxygen into the water (like a jacuzzi for sludge) so the bacteria can breathe and eat faster. The other is a trickling filter, where the water drips over a bed of rocks coated in a slimy layer of bacteria—they literally feast as the water trickles by.
After the bacteria have full bellies, the water goes into another clarifier to settle out the bacterial slime (which gets recycled to eat more yuck!). The result? The water is now 95% clean. It’s no longer gross—it’s just a little murky.
