NE Water/Wastewater Operator flashcards

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

Jar test

Bench-scale test that mixes coagulant at several doses and pH values to find the dose producing the best turbidity removal and settleability.

CT

Product of disinfectant residual concentration in mg/L and contact time in minutes; required CT increases as pH rises and temperature falls.

Chlorine demand

Difference between the chlorine dose applied and the residual remaining after a specified contact time; it reflects oxidant consumed by water constituents.

Surface overflow rate

Clarifier flow divided by its surface area, expressed as gpm/ft² or m³/m²·d; it equals the settling velocity of the slowest particle captured.

Langelier Saturation Index

An index calculated from pH, temperature, calcium hardness, alkalinity, and total dissolved solids; negative values indicate corrosive water and positive values scaling water.

Filter backwash

Reverse flow through a filter that expands the media 20–30% and flushes captured solids to waste; the rate is typically 15–20 gpm/ft².

Turbidity limits

Conventional and direct filtration combined filter effluent must be ≤0.3 NTU in at least 95% of monthly samples and never exceed 1 NTU.

Lime-soda softening

Process that adds lime to raise pH and precipitate calcium carbonate, and more lime plus soda ash to remove magnesium as magnesium hydroxide.

Minimum distribution pressure

Distribution systems must maintain at least 20 psi at all points under normal and emergency conditions; typical operating pressures are 40–80 psi.

Maximum chlorine residual

The maximum residual disinfectant level for free chlorine is 4.0 mg/L, measured as a running annual average at each monitoring location.

Air gap

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

RPZ backflow preventer

Reduced pressure zone assembly with two check valves and a relief valve; used for high-hazard cross connections where backpressure or backsiphonage is possible.

New main disinfection

AWWA C651 requires a new water main to be chlorinated at 50 mg/L for 24 hours, flushed, and left with at least 25 mg/L residual.

Hazen-Williams C factor

Empirical roughness coefficient in the Hazen-Williams head-loss formula; lower values mean rougher pipe and greater friction loss, as with tuberculated old mains.

Water hammer

Pressure surge caused by a rapid change in flow velocity, such as fast valve closure or pump trip; it can rupture pipes and damage fittings.

Distribution flushing velocity

Flushing should achieve at least 2.5–3 ft/s in the main to scour and carry away sediment and stale water.

Food-to-microorganism ratio

F/M equals BOD mass applied per day divided by MLVSS mass in the aeration tank; conventional activated sludge operates near 0.2–0.5 day⁻¹.

Mean cell residence time

MCRT or sludge age equals solids mass in the aeration system divided by solids leaving per day in waste sludge and effluent.

Sludge volume index

SVI is the settled sludge volume in mL after 30 minutes per gram of MLSS; 80–150 mL/g indicates good settling and above 200 indicates bulking.

Mixed liquor suspended solids

MLSS is the concentration of suspended solids in the aeration tank, typically 2,000–4,000 mg/L in conventional activated sludge.

Secondary clarifier solids loading

Solids loading rate equals solids applied per day divided by clarifier area; typical design values are 15–30 lb/day/ft².

Nitrification alkalinity demand

Oxidizing ammonia to nitrate consumes about 7.14 mg of alkalinity as CaCO3 per mg of ammonia nitrogen and requires dissolved oxygen above 2 mg/L.

Mesophilic anaerobic digestion

Digestion at about 35°C (95°F) with a solids retention time commonly 15–30 days; it reduces volatile solids and produces methane.

Facultative stabilization pond

Pond with an aerobic surface zone and anaerobic bottom; algae supply oxygen to bacteria, and bacteria release nutrients and carbon dioxide to algae.

Manning equation

Open-channel flow formula Q = (1.486/n) A R^(2/3) S^(1/2); n is roughness, A is cross-sectional area, R is hydraulic radius, and S is slope.

Self-cleaning sewer velocity

A minimum velocity of about 2 ft/s at design flow keeps solids moving and prevents deposition in sanitary sewers.

Infiltration

Groundwater that enters a sewer through defective pipes, joints, or manholes; it raises dry-weather flow and treatment costs.

Inflow

Direct storm water or surface water that enters a sewer through improper connections such as roof drains, yard drains, or manhole covers.

Trench protective system

OSHA requires shoring, shielding, sloping, or benching for excavations 5 feet or deeper where there is no stable rock.

Confined space oxygen level

Acceptable entry oxygen is 19.5–23.5%; the atmosphere must be tested before entry and a permit is required for permit spaces.

Minimum 8-inch sewer slope

Typical minimum grade is 0.4% (0.004 ft/ft) for 8-inch pipe and 0.22% for 12-inch pipe to maintain self-cleansing velocity.

Lift station check valve

Valve on each pump discharge that closes when the pump stops to prevent backflow and keep the wet well from being refilled.