3. What is Wastewater?
โข Wastewater is a term that is used to describe waste
material that includes industrial liquid waste and
sewage waste that is collected in towns and urban
areas and treated at urban wastewater treatment
plants.
4. Wastewater treatment
โข A process to convert wastewaterย -
which is water no longer needed or
suitable for its most recent use - into
an effluentย that can be either returned
to the water cycle with minimal
environmental issues or reused.
6. Where does wastewater come
from?
โข Residences
โ human and animal excreta and waters used for washing, bathing,
and cooking.
โข Commercial institution
โข Dairy and industrial establishment
โ slaughterhouse waste, dairy waste, tannery wastewater, etc.
7. Where does it all go!
Where does the
water from the
washer go?
When you flush the
toilet where does
the contents go?
By gravity flow, the waste is on its way
to your local wastewater treatment plant!
8.
9. Why treat wastewater?
โข Causes a demand for dissolved oxygen (lower
DO levels of streams)
โข Adds nutrients (nitrate and phosphate) to
cause excessive growth
โข Increases suspended solids or sediments in
streams (turbidity increase)
10. โข Reduce organic content i.e., BOD
โข Removal/reduction of nutrients i.e., N,P
โข Removal/inactivation of pathogenic
microbes
Objectives of WWT
11. Levels of Treatment
Primary
โ removal by physical separation of grit and large
objects (material to landfill for disposal)
โ Sedimentation and screening of large debris
Secondary
โ Biological and chemical treatment
โ aerobic microbiological process (sludge)
organic matter + O2 ๏ CO2 + NH3 + H2O
NH3 ๏ NO3
- aquatic nutrient
Mostly dead
microbes
12.
13. Treatment stages - Primary
treatment
โข typical materials that are removed
during primary treatment include
โ fats, oils, and greases
โ sand, gravels and rocks
โ larger settle-able solids including human
waste, and
โ floating materials
14. Methods used in primary
treatment
โข Bar screens
โข Grinding
โข Grit Chamber
โข Sedimentation Tank- primary Settling
tank
โข Chlorination of effluent
15.
16. Sedimentation Tank-
primary Settling tank
โ Remove grease, oil
โ Fecal solid settle, floating material rise to the
surface
โ Produce a homologous liquid for later biological
treatment
โ Fecal sludge are pumped to sludge treatment plant
19. Activated sludge process
โข Primary wastewater mixed with bacteria-rich
(activated) sludge and air or oxygen is pumped into
the mixture
โข Both aerobic and anaerobic bacteria may exist
โข Promotes bacterial growth and decomposition of
organic matter
โข BOD removal is approximately 85%
โข Microbial removal by activated sludge
โข 80-99% removal of bacteria
โข 90-99% removal of viruses
20. 5 physical components
โข Aeration tank
โข oxygen is introduced into the system
โข Aeration source
โข ensure that adequate oxygen is fed into the tank
โข provided pure oxygen or compressed air
โข Secondary clarifiers
โข activated-sludge solids separate from the surrounding
wastewater
โข Activated sludge outflow line
โข Pump activated sludge back to the aeration tank
โข Effluent outflow line
โข discharged effluent into bay or tertiary treatment plant
23. โข Trickling filters are beds made of coke (carbonized coal),
limestone chips or specially fabricated plastic media
โข Optimize their thickness by insect or worm grazing
โข The primary wastewater is sprayed over the filter and
microbes decompose organic material aerobically.
โข Low pathogen removal
- Bacteria, 20-90%
- Viruses, 50-90%
- Giardia cysts, 70-90%
Trickling filters
25. Stabilization or oxidation
ponds
โข Oxidation ponds are a few meters deep, and up to a
hectare in size.
โข They are low cost with retention times of 1 to 4 weeks.
โข Odor and mosquitoes can be a problem
โข Pathogen removal:
- Bacteria, 90-99%
- Virus, 90-99%
- Protozoa, 67-99%
โข Mechanisms include the long detention time, high pH (10-
10.5) generated by photosynthesis, predation, sunlight,
temperature
26. Continuedโฆ
Stabilization ponds are the preferred
wastewater treatment process in developing
countries due to low cost, low maintenance.
This is balanced by larger land requirement.
27. When the treatment is doneโฆ
โข Effluent back to stream after
โ a final carbon filtration and
โ chlorination/de-chlorination
โข Sludge โ very nutrient rich
โ applied directly to land as fertilizer
โ incinerated (good fuel after drying)
โ composted
28. Sludge Treatment Processes
Thickening (water removal)
Digestion (pathogen inactivation and odor control)
Conditioning (improved dewatering with
alum and high temp, 175-230o
C)
Dewatering (pathogen inactivation and odor control)
Incineration (volume and weight reduction)
Final disposal