Wastewater Treatment Plant Operator flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Surface overflow rate

Primary clarifier loading expressed as flow in gallons per day divided by clarifier surface area in square feet; typical design values are 600 to 1,200 gpd/ft².

Grit settling velocity

Grit with specific gravity near 2.65 is removed by holding a horizontal velocity near 1 ft/s so grit settles while lighter organic solids remain suspended.

Type III zone settling

Hindered settling in which particles form a blanket that drops as a mass at a constant rate; the interface depth tracks clarifier solids handling capacity.

Primary clarifier solids loading

Pounds of influent suspended solids per square foot of clarifier area per day, calculated as mg/L × MGD × 8.34 divided by area; typical design is 25 to 30 lb/ft²/day.

Food to microorganism ratio

Pounds of BOD5 applied per day divided by pounds of MLSS or MLVSS in the aeration tank; conventional activated sludge runs about 0.2 to 0.4.

Mean cell residence time

Pounds of solids in the aeration system divided by pounds of solids leaving per day in waste sludge and effluent; it sets sludge age and whether nitrification occurs.

Sludge volume index

Settled sludge volume in milliliters per liter after 30 minutes times 1,000 divided by MLSS in mg/L; values of 80 to 150 indicate good settling.

Nitrification oxygen demand

Oxidizing ammonia to nitrate consumes about 4.57 mg of oxygen per mg of ammonia nitrogen and 7.14 mg/L of alkalinity as CaCO3 per mg/L oxidized.

Trickling filter organic loading

Pounds of BOD5 applied per day per 1,000 cubic feet of filter media; low-rate filters run 5 to 25 and high-rate filters 25 to 100.

Membrane flux

Permeate flow per unit membrane area, usually expressed as gallons per square foot per day; falling flux at constant pressure indicates fouling or scaling.

Reverse osmosis salt rejection

The percentage of dissolved salts excluded from permeate, typically 95 to 99 percent; feed water should have low turbidity and a silt density index below 5.

Denitrifying filter

An anoxic granular media filter that converts nitrate to nitrogen gas using an added carbon source, applied for tertiary total nitrogen polishing.

CT value

Disinfectant residual concentration in mg/L multiplied by contact time in minutes; the required CT increases as water temperature falls and pH rises.

Breakpoint chlorination

The chlorine dose, near a chlorine-to-ammonia-nitrogen weight ratio of 7.6 to 1, beyond which a free chlorine residual begins to persist.

UV transmittance

The fraction of 254 nm light passing through the water, reported as percent; low transmittance from color or particles reduces the delivered UV dose.

Volatile solids destruction

The percentage of volatile solids fed to a digester that is converted to gas and destroyed; well-operated anaerobic digesters achieve 40 to 60 percent.

Digester volatile acids ratio

Volatile acids divided by alkalinity in mg/L; a ratio above about 0.3 signals impending digester upset along with falling pH and rising carbon dioxide.

Biosolids Class A

Biosolids treated below 1,000 fecal coliform per gram dry solids and meeting alternative pathogen and vector attraction reduction requirements of 40 CFR Part 503.

Infiltration versus inflow

Infiltration is groundwater seeping through defective pipes and joints; inflow is stormwater entering directly through improper connections, catch basins, or manhole covers.

Self-cleaning sewer velocity

A minimum velocity of about 2 feet per second at design flow keeps grit and solids moving and prevents deposition in sanitary sewers.

Pump affinity laws

For a centrifugal pump, capacity varies directly with speed, head with the square of speed, and power with the cube of speed.

BOD5 incubation requirements

Sample incubated 5 days at 20 degrees Celsius in the dark; depletion must be at least 2 mg/L with at least 1 mg/L residual oxygen or the test is invalid.

Pounds formula

Pounds per day of a substance equals concentration in mg/L times flow in million gallons per day times 8.34, converting lab results into mass loadings.

Composite versus grab sample

A grab sample captures conditions at one moment; a flow-proportioned composite collected over 24 hours represents average loading and is used for permit reporting.

TSS filter drying temperature

Suspended solids are retained on a glass-fiber filter, dried at 103 to 105 degrees Celsius, and weighed; volatile solids are the portion lost on ignition at 550 degrees.

Pump cavitation cause

Vapor bubbles form when available net positive suction head falls below required; symptoms include rattling noise, vibration, and reduced head and capacity.

Four to twenty milliamp signal

An analog instrument loop in which 4 mA represents zero percent and 20 mA represents 100 percent of span, providing a live zero to detect broken wiring.

Permit-required confined space

A space with limited entry containing a hazardous atmosphere, engulfment, or other serious hazard; entry requires a permit, atmospheric testing, an attendant, and rescue provisions.

Hydrogen sulfide exposure limits

Hydrogen sulfide is heavier than air with a 100 ppm IDLH; olfactory fatigue deadens the smell, so entry decisions must rely on calibrated meters, not odor.

Oxygen deficient atmosphere

Any atmosphere below 19.5 percent oxygen is oxygen deficient and requires supplied-air respiratory protection; permit entry is prohibited without it.

Discharge monitoring report

The periodic report of effluent monitoring results submitted under an NPDES permit; it must be signed by the authorized official and retained at least three years.

Part 503 biosolids rule

Federal rule governing biosolids quality, including ceiling and exceptional quality metal limits, pathogen reduction classes, vector attraction reduction, and reporting requirements.