ND Water/Wastewater Operator flashcards

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

CT value

The product of disinfectant residual concentration in mg/L and contact time in minutes. Required CT rises as water temperature falls and, for free chlorine, as pH rises.

Breakpoint chlorination

The chlorine dose at which demand is satisfied and free residual begins to persist. It typically occurs near a 7–9:1 chlorine-to-ammonia-nitrogen mass ratio.

Jar test purpose

A bench test that simulates coagulation, flocculation, and settling at several chemical doses to identify the dose and pH giving the best settled water quality.

Turbidity rule limits

Combined filter effluent must be 0.3 NTU or less in at least 95 percent of monthly samples and never above 1 NTU; individual filters must never exceed 1 NTU.

Langelier Saturation Index

Calculated as pH minus pHs. A negative index indicates corrosive water, a positive index indicates scale-forming water, and near zero indicates balanced water.

Chlorine demand

The difference between the chlorine dose applied and the residual remaining after the contact period. It reflects consumption by ammonia, organics, and other reducing substances.

Pressure and head

One psi equals about 2.31 feet of water head. A 100-foot elevation difference therefore produces roughly 43.3 psi of static pressure.

Distribution residual minimum

A detectable disinfectant residual must be maintained throughout the distribution system; many states target about 0.2 mg/L free or 0.5 mg/L total chlorine as a minimum.

Air gap backflow protection

A physical separation between the potable water outlet and the flood-level rim of a receiving vessel. It provides the highest level of backflow protection.

RPZ assembly use

A reduced-pressure-zone assembly protects against both backsiphonage and backpressure. It requires annual testing and is used on high-hazard cross-connections.

Water hammer cause

A pressure surge caused by rapid changes in flow velocity, such as fast valve closure or pump trip. Slow valve operation reduces the surge magnitude.

Flow equation Q=AV

Flow equals cross-sectional area times velocity. Doubling pipe diameter quadruples area, so flow at the same velocity increases fourfold.

Sludge age (SRT)

The mass of solids in the aeration basin divided by the mass of solids leaving the system each day through wasting and effluent.

Food-to-microorganism ratio

The daily BOD or COD load entering the aeration basin divided by the mass of mixed liquor solids in the basin. Low ratios indicate long sludge age.

Sludge volume index

Settled sludge volume in mL/L after 30 minutes, multiplied by 1000, divided by MLSS in mg/L. Values near 80 to 150 indicate good settling.

Nitrification oxygen demand

Oxidizing ammonia to nitrate consumes about 4.6 mg of oxygen per mg of ammonia nitrogen and destroys alkalinity, roughly 7.1 mg/L as CaCO3 per mg/L nitrogen.

Filamentous bulking

A condition where filamentous bacteria dominate the mixed liquor, producing a high sludge volume index, poor settling in the clarifier, and solids carryover in the effluent.

Minimum sewer velocity

Gravity sewers are typically designed for at least 2 feet per second at design flow to keep solids moving and prevent deposition, with about 10 feet per second as a maximum.

Manning's equation

V equals 1.486 divided by n, times hydraulic radius to the two-thirds power, times slope to the one-half power. The constant applies to US customary units.

Infiltration versus inflow

Infiltration is groundwater entering through pipe defects and joints. Inflow is stormwater entering through direct connections such as roof drains and storm inlets.

Hydrogen sulfide corrosion

H2S forms in septic sewage, oxidizes to sulfuric acid on moist concrete above the waterline, and destroys pipe and manhole walls. Ventilation and liners reduce damage.

Confined space oxygen range

Acceptable entry oxygen is 19.5 to 23.5 percent. Below 19.5 percent is oxygen-deficient; above 23.5 percent creates an explosion hazard.

Chlorine gas exposure limit

The OSHA permissible exposure limit for chlorine is 1 ppm as a ceiling, and the NIOSH immediately dangerous to life or health value is 10 ppm.

Hydrogen sulfide IDLH

The immediately dangerous to life or health concentration for hydrogen sulfide is 100 ppm; the OSHA ceiling is 20 ppm. H2S is heavier than air.

Methane LEL

The lower explosive limit of methane in air is 5 percent by volume. Entry into a space above 10 percent of the LEL requires ventilation and controls.

Lockout tagout rule

All energy sources must be isolated and verified at zero energy, and each worker applies a personal lock. Only the person who applied a lock may remove it.

Total Coliform Rule

No more than 5 percent of samples may be total-coliform-positive per month for systems collecting at least 40 samples; an E. coli positive triggers public notice.

Stage 2 DBP limits

Running annual averages may not exceed 80 micrograms per liter for total trihalomethanes or 60 micrograms per liter for five haloacetic acids at each monitoring location.

Lead and Copper Rule

The action level is 0.015 mg/L for lead and 1.3 mg/L for copper, based on the 90th percentile of first-draw samples from high-risk sites.

Arsenic MCL

The maximum contaminant level for arsenic is 0.010 mg/L, or 10 micrograms per liter. Systems exceeding it must install treatment or change sources.

NPDES permit role

A Clean Water Act permit that sets effluent limits, monitoring, and reporting requirements for point-source discharges to surface waters. Discharging without one is prohibited.

Chemical feed formula

Pounds per day of chemical equals flow in million gallons per day, times dose in mg/L, times 8.34. This converts concentration and volume into mass per day.

Pump brake horsepower

Brake horsepower equals flow in gpm times head in feet times specific gravity, divided by 3960 times pump efficiency. It estimates power delivered to the pump shaft.

Pump cavitation cause

Cavitation occurs when available net positive suction head falls below required net positive suction head, producing vapor bubbles, noise, vibration, and reduced flow.