Wastewater Treatment Operator Class I flashcards

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

Permit-required confined space

A space large enough to enter, with limited entry or exit, not designed for continuous occupancy, and containing a recognized serious hazard such as hazardous atmosphere, engulfment, or entrapment.

Safe entry atmosphere limits

Before entry, oxygen must be 19.5 to 23.5 percent, flammable gas below 10 percent of the lower explosive limit, hydrogen sulfide below 10 ppm, and carbon monoxide below 35 ppm.

Hydrogen sulfide hazard

A colorless gas heavier than air with a rotten-egg odor at low levels; it quickly deadens the sense of smell and is immediately dangerous to life at 100 ppm, so odor is no warning.

Lockout/tagout

The procedure of isolating all energy sources to a machine with locks and tags, releasing stored energy, and verifying zero energy before maintenance so equipment cannot start while workers are exposed.

NPDES permit

A National Pollutant Discharge Elimination System permit issued under the Clean Water Act that sets effluent limits, monitoring requirements, and reporting obligations for a point-source discharge to surface waters.

Discharge Monitoring Report

The monthly report submitted to the regulatory agency that records measured effluent values, violations, and required calculated results such as monthly averages and geometric means from the permit.

40 CFR Part 503

The federal rule governing use and disposal of sewage sludge, setting pollutant limits, Class A and Class B pathogen reduction, vector attraction reduction, and management practice requirements.

Infiltration versus inflow

Infiltration is groundwater seeping into sewers through defects, while inflow is storm water or drainage entering directly through manhole covers, roof leaders, or illegal connections; both add clear water.

Self-cleansing velocity

The minimum average sewer velocity, about 2 feet per second at design flow, needed to keep solids moving and prevent deposition of grit and organic material in a gravity collection line.

Wet well working volume

The storage volume between pump-on and pump-off levels in a lift station; it is sized to limit pump starts per hour and to hold incoming flow during power or pump failure.

Grit quantity per million gallons

Coarse heavy material accumulates at roughly 2 to 12 cubic feet per million gallons treated, depending on sewer conditions; grit is removed to protect pumps and prevent clarifier accumulation.

Parshall flume

A fixed-throat flow measuring device where flow passes freely and depth is measured at one point in the upstream converging section; discharge is computed from head with a standard rating.

Screenings quantity

Material captured on bar screens averages about 0.5 to 2 cubic feet per million gallons of flow, and is usually dewatered, bagged, and landfilled.

Surface overflow rate

Clarifier flow divided by surface area, expressed in gallons per day per square foot; it sets the settling velocity a particle must exceed to be removed.

Weir loading rate

Effluent flow divided by total weir length in gallons per day per foot; excessive weir loading creates high exit velocities that carry solids over the weir with the effluent.

Primary clarifier detention time

Detention time equals basin volume divided by flow and is commonly designed at 1.5 to 2.5 hours, allowing settleable solids to reach the sludge collector before leaving.

Food-to-microorganism ratio

F/M equals pounds of BOD entering the aeration tank per day divided by pounds of mixed liquor volatile suspended solids under aeration; conventional systems run about 0.2 to 0.4.

Sludge volume index

SVI is the volume in milliliters occupied by one gram of mixed liquor after 30 minutes of settling; 80 to 150 indicates good settling and above 200 suggests filamentous bulking.

Mean cell residence time

MCRT, or sludge age, is the pounds of solids in the aeration system divided by the pounds of solids leaving each day in waste sludge and in the effluent.

Facultative stabilization pond

A pond with an aerobic upper zone, an anaerobic bottom layer, and algae that produce oxygen; typical detention is 30 to 180 days and depth is 4 to 8 feet.

CT value

The product of disinfectant residual concentration in mg/L and contact time in minutes; the required CT depends on temperature, pH, and the target organism reduction.

Breakpoint chlorination

The chlorine dose at which all ammonia has been oxidized and free chlorine residual begins to rise sharply; past it, additional dose appears almost entirely as free residual.

UV disinfection dose

Ultraviolet disinfection is dosed in millijoules per square centimeter; about 30 mJ/cm2 is typical for coliform reduction and requires low turbidity and clean lamp sleeves.

Digester VFA-to-alkalinity ratio

Volatile acids divided by alkalinity in an anaerobic digester; below 0.1 is stable, 0.1 to 0.3 needs watching, and above about 0.35 indicates souring and imminent failure.

Digester gas composition

Anaerobic digestion produces gas of roughly 60 to 65 percent methane and 30 to 35 percent carbon dioxide, with about 15 to 18 cubic feet per pound of volatile solids fed.

Dewatered cake solids

Belt presses and similar dewatering equipment typically produce cake of 15 to 25 percent solids from digested sludge, with polymer conditioning used to improve capture and release water.

Pounds formula

Pounds of a substance equals concentration in mg/L times volume in million gallons times 8.34; the result is pounds per day when the volume used is a daily flow.

Total suspended solids test

A measured sample is filtered through a glass fiber filter, dried at 103 to 105 degrees Celsius, and weighed; weight gain divided by sample volume gives mg/L.

Geometric mean

The nth root of the product of n values, used for bacterial results because a few very high counts would otherwise distort an arithmetic average in permit compliance reporting.

Cavitation

Vapor cavities forming and collapsing on a pump impeller when suction pressure falls too low, causing noise, vibration, and pitting; corrected by reducing suction lift or clearing blockage.

Net positive suction head

The absolute pressure energy at the pump suction above the liquid vapor pressure; insufficient NPSH available compared with NPSH required causes cavitation and loss of pumping capacity.

Vibration analysis

A predictive maintenance technique that measures machine vibration to detect bearing wear, imbalance, misalignment, and looseness before a failure shuts down a treatment process.