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City of Paso Robles
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Wastewater Division Treatment Plant
3200 Sulphur Springs Road
Paso Robles, CA 93446
(805) 237-3865
(805) 237-3886 FAX
Mon-Fri 7am to 3:30pm


The following links describe each process:

 Physical Treatment  |  Primary Treatment  | Trickling Filters

Secondary Clarifiers  |  Bio Solids  |  Disinfection

Polishing Ponds  |  Laboratory

The Plant treats approximately 1094 million gallons of wastewater per year. The Plant also produces approximately 2200 tons of biosolids per year.

Physical Treatment


Image numbers are in parenthesis.

The first process that the waste stream meets is the headworks (1). This process consists of the physical removal of large material in the waste stream. Bar screens (1A) and bar rakes collect and remove all large material which could damage the downstream pumps.

1. 1A.

The second part of this process is the aerated grit chambers (3). Air is pumped into the stream creating a boiling effect, which drives the grit to the bottom of the tank where it is removed by air lift pumps (4). The grit is deposited into a large dumpster, along with the material from the bar screens and rakes using an auger (4A). The dumpsters are then taken to the local landfill for disposal.

3. 4.



Primary Treatment

The waste stream is pumped to the primary clarifiers (5) to slow the flow where skimmers (6) remove any material that is still floating or that sinks to the bottom of the tank. This material called primary sludge is pumped (6A) to the digesters. What is left in the waste stream is called suspended solids.


6. 6A.


Trickling Filters

The waste stream is pumped (7) to the first form of biological treatment called primary trickling filters (8) or roughing filters (9).

7. 8.

The flow is pumped through rotating arms and distributed over plastic media (10 - image to the right). The media has a micro organism growth called zoogleal mass covering the surface. As the waste stream flows over the media the micro-organisms feed on the suspended solids.

The stream then flows to a secondary pump pit (11) where it is pumped onto secondary trickling filters (12). These older filters have rocks as the media with the same type of growth or zoogleal mass (12A) to further remove or polish the waste stream. Some ammonia removal is also accomplished over the filters by nitrifying bacteria. The removal of Ammonia is important as it is toxic to some forms of aquatic life.

11. 12.

More about The Treatment Plant Process:
Secondary Clarifiers  |  Bio Solids  |  Disinfection
Polishing Ponds  |  Laboratory

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