Biological Wastewater Treatment Flashcards
Why is biological waste water treatment important for health?
Minimises risk of waterborne disease
Why is biological waste water treatment important for ecology?
Minimises the risk to ecological balance
Why is biological waste water treatment important aesthetically?
The water’s appearance is maintained
Why is biological waste water treatment important economically?
Effective treatment protects from environmental pollution
Draw the urban water cycle
There are 3-4 main steps
Details in the answer
Extraction from natural water source
Drinking water treatment
Use in industry/ homes
Sewage treatment
Disturbed for us on crops, sewage biosolid is either recycled or disposed
Crop water goes back into nature
What are the main 5 waste water treatment steps?
Screening
Grit removal
Primary sedimentation
Secondary WWT
Secondary sedimentation
What does a screen do in WWT?
Removes solid debris which goes to landfill
What happens in grit removal?
Grit settles after flow is slowed down in a removal flume.
This grit has hard abrasive grains
What happens in primary sedimentation?
Solid fecal matter is removed and we get:
Primary sludge 5% DS (dry solids)
After primary sedimentation we get
Settled sewage
Settled sewage goes through
Secondary WWT
Secondary WWT gives us
Treated WW and new biomass
Secondary sedimentation gives us
Secondary sludge 2-3% DS
After secondary sedimentation we have
Treated affluent
Which gets returned to the water system
What are the two big biological filter processes
Aerobic microbial oxidation
&
Sludge processes
Why did sludge processes beat aerobic microbial oxidation?
30-50% less energy needed but a higher footprint
What does the circular attached growth biological system entail?
Percolating bio filter
5-10cm aggregate bed
1.5-2m deep overall
What is the process of attached growth (4)
Soluble organic and O2 diffuse into biofilm
Extra cellular enzymes hydrolyse organic matter
Direct ingestion by metazoa + Protozoa
Nitrification
What are the pros of attached growth?
Low maintenance
Withstands shock loads
Biomass retained, no washout risk
(Overall robust and easy to run)
What are the cons of attached growth
Microbial growth blocks filters
Open to air (flies + odour)
Requires pre treatment and primary sedimentation
What is suspended growth and what does it involve
Activated sludge process
Uses biomass as a freely suspended floc
What are the stages of suspended growth treatment?
Rapid stage
Oxidation stage
What does the process of suspended growth involve?
Mixed liquor of biomass and WW in tank
Cell retention 8-12d
Hydraulic retention 8h
High microbial population deliver max rate of decomposition
What happens in the rapid stage?
The floc absorbs rapid absorption of solubles:
Capture of particulate solid matter
Rapid reduction of BOD (what is this?)
