Like most wastewater treatment plants, the Clear Creek WWTP has multiple processes in place to separate, treat, and filter wastewater and the contaminants it contains. The Clear Creek WWTP must currently treat and dispose of nearly 8 mgd (roughly equivalent to 267,700 bathtubs) during dry weather, and treat or store for later treatment up to 45 mgd during wet weather. The following is a brief description of the various components of the treatment process.

Headworks
At the headworks, where all the wastewater enters the plant, bar screens (large metal racks) remove trash, sticks, plastic materials, rags, etc. This material must be removed early in the process or risk damage to equipment used in the treatment process.

Primary Treatment
Primary clarifiers provide an efficient process for the removal of solids that are heavy and sink to the bottom as well as materials that float to the top and can easily be skimmed off. The material that sinks to the bottom is known as primary sludge; the floating material is called scum. Both types of materials are typically pumped to the solids treatment process.

Secondary Treatment
The workhorses of the treatment processes are the aeration basins, which create a natural environment where microorganisms feed upon the remaining organic materials and nutrients in the wastewater. Mixers and aerators provide a suitable environment for the microorganisms and keep the water flowing. In the secondary clarifiers, microorganisms settle to the bottom allowing clear effluent to flow to the filters. The settled microorganisms and recycled back to the aeration basins.

Filters and Disinfection
To make sure the wastewater meets stringent regulatory requirements, the wastewater is filtered through sand and crushed coal to remove small particles. These particles are periodically flushed from the filters and sent to the solids treatment process. In the disinfection stage, chlorine is added to the water to kill bacteria and viruses. Finally, sulfur dioxide is added to neutralize the remaining chlorine before the treated water is discharged to the Sacramento River.

Solids Processing
The sludge collected and produced in the treatment process is converted to stabilized "biosolids" through various means. Digesters are large tanks that use microorganisms to "digest" or "biodegrade" the solids and convert them to byproducts such as methane gas, which can be burned to produce heat. Once digested, dewatering equipment is used to "wing" excess water from the biosolids. This reduces volume and saves transport costs for disposal. Where space is available, and climate allows (such as at the Clear Creek WWTP), an inexpensive method of dewatering sludge involves the use of large drying beds where biosolids can be spread out to dry before being transported for disposal.

Source: Clear Creek Wastewater Treatment Plant Facilities Plan, May 2005