arrow08Water Treatment Process

City of Hays, KS > Departments > Water Resources > Treatment Process >

ToiletWhere it all begins-Flush it and forget it??? I think not! You would be surprised how much treatment is involved for wastewater.

There are six stages of treatment which occur as water passes through the plant. 


1. The first stage is preliminary treatment which consists of screening and grit removal. 

  • Dumpster Waste - Preliminary screenings are removed from the waste stream prior to treatment to cut down on wear on pumps. This waste is hauled to the Ellis County Transfer Station.
  • Bar Screen - This mechanical screen removes the majority of paper products in the wastewater prior to treatment. This accounts for 75% of the transfer station waste. Grit removal (sand/glass) accounts for
    the other 25%.
  • Grit Removal - After the incoming flow has been screened, it is pumped to the grit chamber which is aerated with two small blowers. In this tank, the heavy solids or grit are allowed to settle out things like sand, egg shells, coffee grounds, etc. and is collected and disposed of at the Ellis County Landfill.

2. The second stage is primary treatment where settable solids are removed by mechanical and biological means. The primary treatment starts taking place in the Primary Clarifiers which are two basins that mechanically remove the settable solids from the water. 

  • Primary Clarifiers - In this process, heavy solids settle to the bottom and grease floats to the top. Solids are pumped to the digester and grease is skimmed off the top. Grease is another product that is disposed of at the Ellis County Transfer Station.

3. The water is pumped from the Primary Clarifiers to the two aeration basins. These basins provide air, mixing and time for the reduction of Biochemical Oxygen Demand or BOD and the Suspended Solids to a form of Settable Solids. What does that mean? Basically breaking down all the organic material using live microorganisms that consume the organics. It's like farming these little microorganisms, we have to keep them happy so they can do their job. The difference between them and ordinary livestock is you have to look through a microscope to see them. There are two Trickling Filters but they are no longer being used in the process.

  • Activated Sludge Basin - This process begins with an anoxic zone which helps reduce the amount of nitrates in the water. The aeration process of the basin introduces air back in which gives the basin a mixing capability along with giving the microorganisms an oxygen supply which enables them to break down the solids.

4. Water from the Activated Sludge Basin gravity flows to the Final Clarifiers. This fourth stage provides basically the same function as the Primary Clarifiers in that they slow down the waste to allow the solids to settle. The settled solids are scraped into a hopper and returned to the ASB to go through the treatment process again.

  • Final Clarifiers - In this process the suspended solids that have been transformed into settable solids in the Activated Sludge Basin will be settled out in this clarifier.
5. The treated water then flows to the sand filters which is the fifth stage of treatment (also called tertiary treatment). The sand filters catch any residue that may pass through the other processes. Before the water is sent to the filters, it is chlorinated then sent to the Chlorine Contact Basin. After the Chlorine Contact Basin, the water is rechlorinated prior to pumping to the reuse areas and any water not going to the reuse areas is dechlorinated before it flows into Chetolah Creek which eventually flows into Big Creek.  
  • Sand Filters - Water from the final clarifiers gravity flows to chlorination and then into the sand filters where any solids that may have passed through the Final Clarifiers will be captured and pumped back to the headworks for processing again.
  • Chlorine Contact Basin - Water is pumped through this serpentine to allow a chlorine contact time with the water to insure the majority of microorganisms have been destroyed.
  • Reclaimed Water Basin - These basins are storage facilities for irrigation water that is used to irrigate various facilities within the city. The water in these basins is rechlorinated to maintain a water quality safe for irrigation purposes.

6. In the solids stream, (the sixth stage), the treatment process involves the remaining raw bio-solids which will be transformed into a product that can be disposed of without causing a nuisance. This is done by Anaerobic Biosolids Treatment. The solids are pumped from the various clarifiers into a digester that mixes and heats the bio-solids to promote the growth of a group of anaerobic bacteria. The bacteria "digests" the bio-solids into a safe, non-offensive substance that can be dispersed over local farmland as a soil conditioner.

  • Liquid Biosolids Truck - 90 to 95% of biosolids are disposed of using this truck to disseminate on local farmground.



  • Belt Press & Biosolids Drying Beds - 5 to 10% of biosolids are disposed of using this process which makes the solids seven times thicker. These solids are then stored in the drying beds for further dewatering. This process is used only when weather conditions prevent the use of the liquid disposal process.
  • Dry Biosolids Truck - 5 to 10% of biosolids are disposed of using this truck to disseminate on local farmground after being processed through the belt press and further drying in the drying beds.


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Last Modified 01/09/17 


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