Suspended Media Biological Treatment Flashcards
What is the activated sludge process?
An aerobic process with suspended microorganisms suspended in a tank where they convert dissolved and suspend solids into cellular mass
Basic components of activated sludge process
Wastewater Activated sludge Aeration tank Aeration system Secondary settling tank with RAS/WAS
What is MLSS?
The amount of suspended solids in the mixed liquor of an aeration tank
What is MLVSS?
The amount of organic or volatile suspended solids in the mixed liquor of an aeration tank
What are the EPA secondary treatment standards?
BOD and TSS removal no less than 85% and 30 day average not to exceed 30 mg/L
What is the fundamental principle of operating an activated sludge process?
Maintaining the proper food to microorganism ratio by wasting excess microorganisms
What is sludge age?
The average amount of time that solids or bacteria remain in an aeration tank. Also called mean cell residence time or solid retention time
What are examples of process control tests for the activated sludge process?
Microscopic exam and TSS tests
What are examples of calculations used in process control of activated sludge?
Sludge volume index
F/M ratio
MCRT
What is the settleometer test?
Place a sample of MLSS in a 1-liter settleometer and measure the settled sludge volume every 5 minutes for 30 minutes. Then every 10 minutes until 60 minutes. Good SSV is <500
What does SVI measure?
Compactibility/settlability of sludge
- how much volume 1g of ML occupies after 30 minutes
What can SVI help to identify?
The presence of filaments if >150
What is mechanical aeration?
Agitates the surface creating turbulence that entraps oxygen as the mixed liquor travels through the air
What is diffused aeration?
Large volume of low pressure air is delivered near the bottom of the tank which allows mixing and oxygen diffusion as it rises
What is pure O2 aeration?
Pure O2 is delivered to mixed liquor with a sealed cover on the aeration tank
Describe the operating parameters of conventional activated sludge process
Plug flow aeration tank Air evenly distributed DO increases towards the effluent end Detention time 4-12 hours MLSS 1500-3000mg/L MCRT 5-15 days F/M 0.2-0.4 lbs BOD/day/lb MLVSS
Provide examples of modifications to the conventional activated sludge process
High rate aeration Contact stabilization High-purity oxygen Step-feed Complete mix Extended aeration Oxidation ditch Batch decant Sequencing batch reactor Counter current aeration system
What is a lagoon?
AKA stabilization pond
Earthen basin excavated and lined with clay or plastic
Sludge collects on the bottom of lagoon cells
What is the lagoon process?
Aerobic bacteria stabilize dissolved and suspended organic matter while producing CO2 and N and P
Algae use the CO2, N, and P for photosynthesis
Dissolved oxygen provided by mechanical or diffused aeration, photosynthesis, or wind/wave action
Types of lagoons
Aerobic
Anaerobic
Facultative
Aerated
What is pinpoint floc?
Small, dense, pinpoint shaped flocs
Indicates older sludge that flocculates poorly
What is straggler floc?
Floppy, transparent, very light, buoyant floc
Typical of young sludge
