Operator Toolbox
36 free calculators for wastewater operators, each with the formula and a worked example from the White River training plant. No sign-up.
- Activated sludge process control
- Clarifiers and solids
- Hydraulics and pumps
- Chemicals and disinfection
- Lab
- Solids and digestion
- Instruments and controls
- Conversions
Activated sludge process control
F/M RatioF/M compares the daily BOD load with the biomass under aeration.SRT and MCRTSolids retention time is the average number of days solids stay in the system.Sludge Age (Gould)Gould sludge age compares the solids under aeration with the suspended solids entering the aeration basin each day.MLSS InventoryThe solids inventory is the starting point for SRT, F/M and wasting calculations.RAS FlowThree ways to estimate the RAS flow you need.WAS RateCalculate how much sludge to waste each day to hold a target SRT.Aeration Basin LoadingVolumetric loading compares the BOD load with basin volume.BOD LoadingCalculate the daily BOD load and the approximate population equivalent.Ammonia LoadingCalculate plant ammonia load, including a return stream like centrate, and the oxygen needed to nitrify it.Oxygen Requirement and AirEstimate the oxygen the process needs, then convert it to blower air flow.Alkalinity for NitrificationEstimate residual alkalinity after nitrification and the chemical needed to reach a target.
Clarifiers and solids
State Point Clarifier and RAS Control ToolCheck whether your secondary clarifiers can thicken the solids you send them, and find a RAS range that keeps the blanket under control.Clarifier Surface Overflow RateSOR is flow divided by clarifier surface area.Solids Loading RateSLR is the mass of solids applied to a clarifier per unit area.Weir Overflow RateWeir overflow rate is flow per foot of weir length.SVISVI is the volume in mL occupied by 1 gram of mixed liquor after 30 minutes of settling.
Hydraulics and pumps
Pump CalculationsThree common pump calculations: flow from a wet well test, total dynamic head, and horsepower.Pump Affinity Laws and VFD SpeedWhen a VFD slows a centrifugal pump, flow drops with speed, head with speed squared and power with speed cubed.Detention TimeDetention time is tank volume divided by flow.Flume and Weir FlowOpen channel flow meters measure head and convert it to flow with a fixed equation for the primary device.Tank Level, Volume and Hydrostatic PressureChemical, sludge and wet well levels are often measured as pressure and then shown as a level or volume.
Chemicals and disinfection
Lab
Oxygen Uptake Rate (OUR)OUR measures how fast the biomass uses oxygen.SOURSOUR is OUR per gram of volatile solids.pH Electrode Slope and BufferA pH electrode makes about 59 mV per pH unit at 25 °C, less when cold and more when warm.DO Saturation and Sensor CheckA DO analyzer is calibrated against the oxygen that water can hold at saturation, which falls with temperature and elevation.
Solids and digestion
Instruments and controls
4-20 mA Signal ConverterMost plant transmitters send a 4 to 20 mA signal where 4 mA is the bottom of the range (LRV) and 20 mA is the top (URV).Instrument Accuracy and Calibration CheckAn accuracy spec means very different things depending on whether it is a percent of span, of reading, or of the sensor upper limit.Mag Meter VelocityA mag meter measures velocity and multiplies by the pipe area.Three-Phase Motor PowerClamp-on amps and a voltage reading tell you a lot about a motor.
Conversions
More free tools
These calculators also appear on ActivatedSludge.com, our consulting site. Results are estimates for operator use. Check units and inputs, and confirm decisions with plant data and procedures.
Want to go deeper?
Our online classes teach the process behind these numbers, from Activated Sludge Basics to Advanced Activated Sludge.