Analysis and Design Flashcards
(30 cards)
What is the general mass balance equation for a control volume?
Input - Output + Generation - Consumption = Accumulation
In steady-state conditions, what does the accumulation term in the mass balance equation equal?
Zero
What does a negative accumulation indicate in a mass balance analysis?
That mass is being removed or decreasing within the system.
How do you calculate mass flow rate?
Mass flow rate = Density × Volumetric flow rate
What is the key assumption in a steady-state mass balance?
The mass within the system does not change over time.
What is the difference between a conservative and non-conservative substance in mass balance?
A conservative substance does not undergo chemical change; a non-conservative substance can be generated or consumed.
What is an example of a conservative substance in water treatment?
Chloride ion (Clâ»)
How do you handle multiple inputs in a mass balance calculation?
Sum all inputs, sum all outputs, and apply the mass balance equation.
What is hydraulic loading rate (HLR)?
HLR = Flow rate / Surface area of the treatment unit
Why is hydraulic loading rate important in wastewater treatment design?
It affects the retention time and performance of the treatment process.
How does increasing HLR affect sedimentation tanks?
It can reduce the removal efficiency by decreasing settling time.
What units are typically used for hydraulic loading rate?
gpd/ft² (gallons per day per square foot)
How do you calculate the surface area needed for a sedimentation tank given a specific HLR?
Surface area = Flow rate / HLR
What parameter is influenced by both HLR and solids loading rate?
Settling efficiency in clarifiers
What is the typical HLR range for a primary clarifier?
600 to 1,200 gpd/ft²
What is solids loading rate (SLR)?
SLR = Mass of solids / Surface area of the tank
Why is solids loading rate important in clarifier design?
It impacts the clarifier’s ability to settle and remove solids efficiently.
How is the mass of solids entering a clarifier calculated?
Mass = Flow rate × TSS concentration
What units are used for SLR?
lb/day/ft² or kg/day/m²
What is a typical range for solids loading in secondary clarifiers?
15 to 35 lb/day/ft²
How do sludge characteristics influence solids loading rate?
Thicker sludge or poorly settling sludge can reduce clarifier efficiency at the same SLR.
What happens if the solids loading rate is too high?
It can lead to solids carryover and poor effluent quality.
What is the most common device used to measure open channel flow?
A weir or flume
What is the formula for flow through a rectangular weir?
Q = (2/3) × C × L × H^(3/2)
