Printable Formula Sheet
Basics
- Pounds per day
- lb/d = flow (MGD) x conc (mg/L) x 8.34
- Volume, rectangular
- gal = L x W x D (ft) x 7.48
- Volume, circular
- gal = 0.785 x D² x depth (ft) x 7.48
- Detention time
- DT (hr) = volume (gal) x 24 / flow (gpd)
- Percent removal
- % = (in - out) / in x 100
Activated sludge
- SRT (MCRT)
- SRT (d) = lb MLSS in aeration / (lb/d WAS solids + lb/d effluent solids)
- F/M
- F/M = lb/d BOD to aeration / lb MLVSS under aeration
- SVI
- SVI (mL/g) = 30 min settled volume (mL/L) x 1,000 / MLSS (mg/L)
- RAS from settleometer
- RAS (MGD) = Q x SSV30 / (1,000 - SSV30), SSV30 in mL/L
- RAS from mass balance
- RAS (MGD) = Q x MLSS / (RAS SS - MLSS)
- WAS for target SRT
- WAS lb/d = inventory lb / target SRT - effluent solids lb/d
- WAS flow
- WAS (MGD) = WAS lb/d / (WAS SS mg/L x 8.34)
- Organic loading
- lb BOD/d/1,000 ft³ = lb/d BOD / (basin ft³ / 1,000)
Clarifiers
- Surface overflow rate
- SOR (gpd/ft²) = Q (gpd) / surface area (ft²)
- Solids loading rate
- SLR (lb/d/ft²) = (Q + RAS) (MGD) x MLSS x 8.34 / area (ft²)
- Weir overflow rate
- WOR (gpd/ft) = Q (gpd) / weir length (ft)
- Blanket holding time
- hr = blanket volume (gal) / RAS flow (gph)
Oxygen and alkalinity
- Oxygen demand
- AOR lb/d = 1.1 x lb BOD removed + 4.57 x lb N nitrified - 2.86 x lb N denitrified
- Air required
- scfm = SOR (lb O2/d) / (SOTE x 0.0173 lb O2/ft³ air x 1,440)
- OUR
- OUR (mg/L/hr) = DO drop (mg/L) / time (min) x 60
- SOUR
- SOUR (mg O2/g VSS/hr) = OUR / MLVSS (g/L), corrected x 1.05^(20 - T)
- Alkalinity balance
- Alk needed = 7.14 x NH3-N nitrified - 3.57 x NO3-N denitrified + 50 residual
Chemicals and pumps
- Chemical feed
- lb/d = dose (mg/L) x Q (MGD) x 8.34
- Liquid feed rate
- gpd = lb/d / (lb/gal of solution x % strength)
- Chlorine demand
- demand = dose - residual
- Water horsepower
- WHP = gpm x TDH (ft) x SG / 3,960
- Brake and motor hp
- BHP = WHP / pump eff, MHP = BHP / motor eff
- Pressure to head
- ft = psi x 2.31
Solids
- Volatile solids reduction
- VSR = (VSin - VSout) / (VSin - VSin x VSout), as fractions (Van Kleeck)
- Solids capture
- capture % = (feed lb - centrate lb) / feed lb x 100
- Digester VA/ALK
- ratio = volatile acids (mg/L) / alkalinity (mg/L), below 0.1 is healthy
- Polymer dose
- lb/dry ton = lb/d polymer / dry tons/d solids
8.34 lb/gal for water. US units. Metric versions are in each calculator. From ActivatedSludge.com, Wastewater Solutions, Inc., 503-701-2766.