1.) When you flush your toilet, place something in your kitchen drain, wash your hands or take a shower, you contribute to the waste stream that will eventually reach the treatment plant. The waste travels from your home or business through a pipe to a main line that then follows to our treatment plant for processing. Once it leaves your home or business it takes approximately several hours to days to reach the plant. In an average day the plant receives 2.85 MGD of raw wastewater.

2.) When raw wastewater enters the plant it passes through a preliminary treatment process in the headwork's building. Two mechanical bar screens (diagram below) collects larger solids in the flow stream, such a paper towels, feminine hygiene products and anything else that can be flushed or put down a drain. These items are mechanically de-watered before being conveyed to a dumpster for disposal.

3.) Following the bar screens, the flow passes through two vortex grit separators which removes heavy solids such as egg shells, sand and rice. The separators are concrete cylinders with a horizontal paddle turning slowly inside, creating enough current to keep the suspended particles from settling out while allowing the heavier solids to settle out and collect in the bottom of the collector. These solids are then pumped to the biosolids lagoon (diagram below) for treatment.

4.) From the headwork's building the screened and de-gritted wastewater is pumped to one of two aeration basins (diagram below). The basins each hold 2.3 million gallons of water and this is where the secondary treatment occurs. Large blowers (diagram below) are used to add air to the water as it passes through the basins, hence the term “aeration basin”. Oxygen is added to promote the growth of microorganisms that break down the organic material in the water and improve the settling characteristics of the remaining solids. The organisms include bacteria, fungi and protozoa.

5.) From the aeration basins the “mixed liquor” flows by gravity to final clarifiers (diagram below), where the settleable solids (RAS) and floatable material (scum) are separated from the water. From the clarifiers the RAS is pumped back to the aeration basins where the microorganisms are reintroduced to the food in the influent flow.

6.) In the lab (diagram below) the plant staff monitors the quantity of microorganisms in the process, and excessive organisms (waste activated sludge, or WAS) are pumped (“wasted”) to the biosolids pond. The floatable solids are skimmed off the top of the water surface and pumped to the biosolids pond.

7.) The clear effluent flows over the weirs in the clarifiers and on to the Operations Building (diagram below), where it is disinfected with ultraviolet light (diagram below). Two new banks of Trojan UV light tubes are in the effluent channel where the effluent passes through the lights (diagram below) and any remaining organisms are genetically altered so that they cannot reproduce and die off in a few hours, before reaching the St. Vrain Creek.

 

If you have any other questions about the St. Vrain Sanitation District Treatment Plant, please call (303) 776-4639