WWTP Processes

Treatment at the Plant

There are six major types of treatment processes at the plant: preliminary, primary, secondary, tertiary, disinfection and solids treatment. These processes are integrated to treat wastewater so that our community can thrive without creating negative impacts to the St. Vrain River.

Preliminary Treatment

Preliminary treatment removes trash and grit from wastewater. As wastewater passes through a screen, trash is removed, washed, compacted and placed in a dumpster for disposal in a landfill. Grit is removed by settling. Settled grit is pumped from the bottom of a basin to a washer to remove organics before being discharged to a dumpster. The wastewater then flows to primary treatment.

Primary Treatment

Primary treatment removes small particles from wastewater by a process called primary clarification. In this phase, wastewater enters large round clarifier tanks which provide time for settleable solids to drop to the bottom. The solids at the bottom of the tanks are sent to a thickening process that reduces volume before being pumped to solids handling for additional stabilization and disposal. The remaining wastewater is pumped to the secondary process.

Secondary Treatment

Secondary treatment is a biological process called Activated Sludge. The wastewater is mixed with microorganisms that consume most of the remaining organic material. The process takes place in large basins that are aerated so that the organisms have both a food source and oxygen for survival. After leaving the aeration basins, the mixed-liquor flows to secondary clarifiers where the solids are removed through settling. The clear water on top of the clarifiers moves on for the final steps of treatment. Most of the solids that collect on the bottom of the clarifiers are sent back to the aeration basin to continue the process of activated sludge treatment. Some of the solids are sent to thickening and then solids handling.

Secondary Treatment

Tertiary Treatment

Tertiary treatment at the plant is a nitrifying process performed in trickling filters. A portion of the effluent from the secondary clarifiers flows (trickles) over a media which contains organisms that remove ammonia. Ammonia is toxic to aquatic life and must be mostly removed before treated wastewater is discharged to the river.

Disinfection

Disinfection in-activates the few remaining microorganisms that may potentially cause disease. The facility uses Ultra-Violet (UV) light processes for disinfection. UV disinfection alters the DNA of microorganisms so that they are unable to reproduce causing them to die off.

Solids Handling

Solids are generated from the various wastewater treatment processes, and they must be collected and broken down by digestion before they are removed from the facility. Anaerobic digesters are used for this process which ultimately yields a stable and nutrient rich sludge that can be land applied in either a liquid or dewatered form for beneficial reuse.

Filaments

One potential interference to the activated sludge process is the formation of filamentous organisms. Filaments can cause bridging of flocs and poor settling, and are managed by closely monitoring and adjusting processes.

Lab Examination

A well equipped operations lab is used to examine wastewater samples collected throughout the treatment process. Highly trained operators perform numerous tests and correct problems such as filaments growth before they impact treatment.

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Wastewater Treatment Plant |Public Works & Natural Resources|City of Longmont

This page was updated September 28, 2012

City of Longmont Public Works & Natural Resources

Wastewater Treatment Plant