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Conventional Wastewater Treatment
Transcript of Conventional Wastewater Treatment
Raw Sewage, or influent, is strained by
bar screens to remove larger objects
that could damage the pumps or mixing
equipment. The bar screens are cleaned
by a machine or manually.
After the Bar screens the influent is sent into channels where its velocity is carefully controlled so that the sand, gravel, and other larger and or heavier particles (grit) fall to the bottom. The grit is then removed from the channel.
All of the large objects and grit
removed in preliminary treatment
are sent to the landfill, all of the liquid is sent to Primary treatment.
Many plants have a sedimentation stage where the sewage is allowed to pass slowly through large tanks, commonly called primary clarifiers or primary sedimentation tanks. The tanks are large enough that sludge can settle and floating material such as grease and oils can rise to the surface and be skimmed off.
Attached Growth Process
Suspended Growth Process
In attached growth (or fixed film) processes, bacteria, algae, fungi and other microorganisms grow and multiply on the surface of stone or plastic media, forming a microbial growth or slime layer (biomass) on the media. Wastewater passes over the media along with air to provide oxygen, and the bacteria consume most of the organic matter in the wastewater as food.
Suspended growth is very similar to
attached growth, however, instead of the microorganisms being attached to a surface they are suspended in the wastewater. Air is pumped into the tank and the water is vigorously mixed.
Tertiary treatment is the final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment. The treatment removes remaining inorganic compounds and substances such as nitrogen and phosphorus. Bacteria, viruses and parasites, which are harmful to public health, are also removed at this stage.
These processes are vital for wastewater reuse.
+ Relatively inexpensive
+ Long history of effectiveness
- Corrosive and toxic
- Can form carcinogens in effluent
+No chemicals/ no effect down
+Renders microbes incapable of
-Constant lamp maintenance
-Need for highly treated influent
+Oxidizes organic material
+Thought to be safer than
+On site generation
+Relatively inexpensive (depending
on how far away the landfill is)
+Possibility for co-generation
-Can create methane (CO2) and other
+Composting and land spreading is
good for agriculture
+More expensive than landfill, but
still relativly inexpensive
-Sludge requires a higher level of
treatment than other options
-Run off can cause algae blooms
+Destroys volatile solids
-Lots of CO2
At the conclusion of this process, clean, non-potable water is returned to lakes, rivers and streams or can be used for agriculture.