Waste Water Treatment Plant Lab.

Assignment : 

Introduction: A water treatment plant is necessary to recycle water in order to conserver water. 

Objective : A tour of the water treatment plant is to familiarize you with the components (figure 1) of the plant and to explain the purpose of each part

Results: Write a description of the the components of the treatment plant and explain how each component works. 



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Figure 1  A schematic diagram of a water treatment plant.

Wastewater Treatment Plant at Las Cruces

  General description of wastewater treatment plant

          The wastewater treatment plant is designed to purify city waste water so that it can be returned to the Rio Grande River to be reused. 

Primary treatment 

1.  It does this by receiving all city wastewater in a big vat where three large screw pumps lift the wastewater up about 15 or 20 feet.

2.It then goes through a series of screening machines which comb and filter all the trash out of the waste water such as wrappers, etc. These are grate or bar screen made of parallel bars.


3.  The wastewater then is transported to aeration tanks where the oxygen content is increased in the wastewater to facilitate better digestion by microbes.



4.   From there the waste water flows to the primary clarifiers which are large round tanks with concave bottoms where the solid matter or sludge settles out of the wastewater.   There is a large arm that rotates around the tank very slowly which skims the floaties off of the top of the waste water. 


5. The sludge from the primary clarifers is then pumped into two anaerobic digestion tanks which are covered with a rising roof.  The methane that these anaerobic digestion tanks produce creates a pressure which lifts the roof on these tanks.  


The methane from these digestion tanks is used to power a huge generator half of the time.  The other half of the time this generator is powered by natural gas.  The digested sludge is removed periodically and dumped into drying beds these drying beds are simply large, open, circular areas contained by short little cement walls. 


  The beds are dug about a foot and a half or two below grade and are roughly 30 or 40 feet in diameter.  Each layer of sludge is exposed to the air and as a result dries out over several days.  After subsequent layers of sludge have been added to the pits and dried out for about a week, the semi-dried sludge is removed and taken to a big flat open area where it is continuously turned over with a little tractor so that it will finish drying.  Then it is piled up where it can be used by farmers, landscapers, citizens, etc. as fertilizer.  When more sludge is produced than can be processed at the plant it is transported by truck to a site on the west mesa where it is injected into the ground. 

Secondary treatment 

6. After being clarified the wastewater goes through a huge tank of trickle filters.   These filters are basically large blocks of honeycombed metal strips which are all stacked up in this tank and the wastewater permeates down through hundreds of these filters.  In doing so, much of the remaining solid material attaches to the metal fins in these filters and is thereby mechanically separated from the water. 

A secondary treatment is activated sludge treatment in addition to the trickle filters. The water goes through the trickle filter to the activated sludge which is sludge and air continually mixed. 



Tertiary treatment 

7. From there the wastewater goes into a secondary clarifier much like the first only there is no need for an arm to skim floaties off the top, nor is there near as much sludge.  In the primary clarifier there remained approximately three feet of sludge on the bottom, but in this one only about an inch or two of sludge settle to the bottom, this sludge is then transported to the digestion tanks as well.  

8. The waste water then goes into a pump house where it is pumped into another large vat where it is injected with chlorine to disinfect it.  It circulates around this tank for a while to give the chlorine time to do its job and then before exiting the tank, there is another chemical injected into the water to deactivate the chlorine.  The treated water then leaves the tank and is transported to the Rio Grande.