Glossary

Plain definitions of the process terms used in Beedy tools.

ASM1: Activated Sludge Model No. 1 (IWA), the standard set of equations for how bacteria remove carbon and nitrogen. The Suite's demonstration plant and the Engineer's Plant tab run on it.
BOD₅: Biochemical oxygen demand over five days: how much oxygen bacteria use to eat the organic matter in a sample. A measure of organic pollution.
CAS: Conventional activated sludge: a bioreactor followed by a clarifier where the sludge settles by gravity.
CEB: Chemically enhanced backwash: a short chemical clean of the membranes done in place, on a schedule.
COD: Chemical oxygen demand: the oxygen needed to oxidise everything oxidisable in a sample chemically. Always higher than BOD.
DO: Dissolved oxygen in the bioreactor, in mg/L. Too low and bacteria stop nitrifying; too high and you waste blower energy.
F/M: Food-to-microorganism ratio: how much BOD reaches the bioreactor per day for each kilogram of biomass.
First mover: In Troubleshooting, the signal that left its normal pattern first during an incident. A lead to check, not a verdict.
HRT: Hydraulic retention time: how long water stays in a tank on average (volume divided by flow).
MBR: Membrane bioreactor: a bioreactor whose water is drawn through membranes instead of settling in a clarifier. Smaller footprint, very clean effluent.
MLSS: Mixed liquor suspended solids: the concentration of sludge (biomass and solids) in the bioreactor, in mg/L or g/L.
MOC: Management of change: the process safety workflow that reviews and approves a change before it is made.
NH₄-N: Ammonium, as nitrogen. The main thing nitrification removes; often a permit limit.
PSM: Process safety management: the program that prevents major accidents with hazardous processes.
RAS: Return activated sludge: sludge pumped back from the clarifier or membrane tank to the bioreactor.
σ (sigma): Standard deviation. In Troubleshooting, how far a signal is from its normal pattern; 3σ starts a departure, 5σ is needed to name a likely cause.
SRT: Solids retention time, or sludge age: the average number of days sludge stays in the system. Controlled by how much sludge is wasted.
TMP: Transmembrane pressure: the pressure difference that pulls water through a membrane. Rising TMP means the membrane is fouling.
TP: Total phosphorus. Often removed by dosing alum (aluminium sulfate).
TSS: Total suspended solids: particles in the water, in mg/L.
WAS: Waste activated sludge: sludge removed from the process to hold the sludge age.