Wastewater Computations

These vocabulary flashcards cover the fundamental terms and calculation parameters encountered in the wastewater-treatment lecture notes, including BOD, flow metrics, activated-sludge concepts, and loading rates.

BOD (Biochemical Oxygen Demand)

A measure of the amount of oxygen microorganisms need to stabilize decomposable organic matter in water, expressed in mg/L or lbs/day.

BOD Loading

The total mass of BOD applied to a treatment process per unit time, typically calculated as concentration × flow rate and expressed in lbs BOD/day.

Population Equivalent (PE)

An estimate of the number of people that would generate a given BOD load; often calculated using 0.17 lbs BOD/day per person.

Flow Rate (Q)

The volume of wastewater passing a point per unit time, commonly expressed in m³/day or MGD (million gallons per day).

Concentration

The amount of a substance (e.g., BOD, TSS) present in a unit volume of water, expressed in mg/L.

Activated Sludge

A suspension of microorganisms used to metabolize organic matter in aerobic biological treatment processes.

Waste Activated Sludge (WAS)

The excess biomass removed from an activated-sludge system to maintain a desired solids retention time.

Food-to-Microorganism Ratio (F/M Ratio)

The ratio of influent BOD (food) to the mass of microorganisms (MLSS) in the aeration tank, indicating loading rate on the biomass.

MLSS (Mixed Liquor Suspended Solids)

The concentration of suspended solids, including microorganisms, in the aeration basin, expressed in mg/L.

MCRT / SRT (Mean Cell Residence Time or Solids Retention Time)

The average time solids remain in the biological system, calculated as mass of solids in the reactor divided by solids removed per day.

TSS (Total Suspended Solids)

The total concentration of suspended solids in wastewater or effluent, measured in mg/L.

Average Flow (Q_ave)

The mean daily wastewater flow to a plant over an extended period, used for design and loading calculations.

Peak Flow (Q_peak)

The maximum instantaneous or short-duration flow expected, often expressed as a multiple of average flow.

HLR (Hydraulic Loading Rate)

The volume of wastewater applied per unit surface area of a treatment unit per day, commonly given in m³/m²·day or gpd/ft².

OLR (Organic Loading Rate)

The mass of BOD (or COD) applied per unit volume (or area) of a biological treatment unit per day, e.g., lbs BOD/1000 ft³·day.

Effluent

Treated wastewater that exits a treatment process and is discharged to the environment or for reuse.

Removal Efficiency

The percentage reduction of a contaminant (e.g., BOD, TSS) across a treatment unit, calculated as (influent − effluent) / influent × 100.

Surface Area (A)

The plan-view area of a basin or clarifier used in hydraulic calculations, often expressed in m² or ft².

Volume (V)

The three-dimensional capacity of a tank or basin, used in detention time and loading calculations, expressed in m³ or ft³.

Detention Time

The theoretical time a water parcel spends in a tank or basin, found by dividing volume by flow rate.