Not every wastewater treatment plant looks like the sprawling aeration basins and blower buildings of a big-city activated sludge facility. Across Colorado's small mountain towns, ranching communities, and rural districts, a large share of wastewater treatment happens in systems that look nothing like that: a rock-filled tower with water trickling over it, a slow-turning wheel of plastic discs, or simply a big earthen pond doing its work quietly under the sun and wind. These are the fixed-film and alternative biological processes — and understanding how they work is essential for any Class D wastewater operator, because they are often the only treatment technology a small system can afford to build, staff, and operate.
Two Ways to Grow Bacteria: Suspended vs. Attached Growth
All biological wastewater treatment relies on the same basic principle: billions of microorganisms — mo