HI Water/WW Operator flashcards

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

CT value

Product of disinfectant residual concentration in mg/L and contact time in minutes, used to verify disinfection. Required CT depends on temperature, pH, and disinfectant type.

Chlorine demand

The difference between chlorine dose applied and chlorine residual remaining after a set contact time. Demand comes from reducing agents, ammonia, organics, and metals in the water.

Breakpoint chlorination

The chlorine dose at which combined chlorine residual is destroyed and free chlorine residual begins to rise, occurring roughly at a 7.6 to 1 weight ratio of chlorine to ammonia nitrogen.

Jar test purpose

A bench test that varies coagulant dose and pH to find the lowest chemical dose producing acceptable settled turbidity, simulating rapid mix, flocculation, and sedimentation.

Surface overflow rate

Clarifier flow in gallons per minute divided by clarifier surface area in square feet, expressed in gpm/ft². It governs particle settling performance independent of basin depth.

Detention time formula

Detention time in hours equals basin volume in gallons divided by flow in gallons per day, then divided by 24. Use actual basin volume, not footprint.

Combined filter effluent limit

Under conventional treatment, combined filter effluent turbidity must be 0.3 NTU or less in at least 95 percent of monthly samples and never exceed 1 NTU.

Backwash rate and temperature

Filter backwash rate is set by water temperature because cold water is more viscous and expands the bed less. Winter backwash rates are lower than summer rates.

Pressure and head conversion

One psi equals 2.31 feet of water head, and one foot of head equals 0.433 psi. These convert between pressure gauge readings and elevation head.

Hazen-Williams head loss

Head loss in a pipe increases with flow raised to the 1.852 power and decreases as the C factor rises. Rougher, older pipe has a lower C and more loss.

Water hammer cause

A pressure surge caused by rapid velocity change in a pipe, such as fast valve closure or pump trip. Mitigation includes slow closure, surge tanks, and air valves.

Air gap backflow protection

The only non-mechanical backflow protection: a physical separation between the supply outlet and the flood-level rim of the receiving fixture, preventing both backpressure and backsiphonage.

RPZ assembly

A reduced pressure zone backflow preventer with two check valves and a relief valve that discharges if pressure reverses, protecting against both backpressure and backsiphonage.

Storage tank turnover

Tank volume in million gallons divided by average daily demand in million gallons per day gives turnover time in days. Long turnover ages water and depletes disinfectant residual.

Pipe haunch compaction

Backfill placed and compacted in lifts around the lower sides of a pipe to support it and prevent ovaling, joint deflection, and settlement before the rest of the trench is filled.

Minimum distribution residual

A detectable disinfectant residual must be maintained throughout the distribution system; a common target is at least 0.2 mg/L free chlorine at the farthest sampling point.

BOD5 definition

Five-day biochemical oxygen demand measured at 20 degrees Celsius, estimating biodegradable organic matter consumed by microorganisms. Carbonaceous BOD excludes nitrogenous oxygen demand.

F/M ratio

Food to microorganism ratio: pounds of BOD applied per day divided by pounds of MLSS under aeration. Low F/M means long sludge age, favoring nitrification.

MCRT formula

Mean cell residence time in days equals pounds of MLSS in aeration divided by pounds of solids leaving daily through wasting plus effluent suspended solids.

Sludge volume index

SVI in mL/g equals the 30-minute settled sludge volume in mL/L times 1000 divided by MLSS in mg/L. Values above about 150 indicate poor settling and bulking.

Nitrification oxygen demand

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

Secondary clarifier solids loading

Solids loading rate in pounds per day per square foot equals flow plus return flow times MLSS times 8.34, divided by clarifier surface area. Overflow rate uses influent flow only.

Anaerobic digester gas

Volatile solids destruction in a heated, mixed anaerobic digester produces gas that is roughly 60 to 65 percent methane, with carbon dioxide making up most of the remainder.

Fecal coliform limit

Typical secondary treatment limit: monthly geometric mean of 200 colony-forming units per 100 mL, with no sample exceeding 400 per 100 mL.

RAS and wasting control

Return activated sludge rate controls MLSS concentration in the aeration basin, while the wasting rate controls mean cell residence time. More wasting lowers MCRT and MLSS.

Manning's equation

Velocity equals 1.486 divided by roughness n, times hydraulic radius raised to two-thirds, times slope raised to one-half. Hydraulic radius is flow area divided by wetted perimeter.

Self-cleansing velocity

A minimum design velocity of about 2 feet per second at design flow, keeping solids suspended and moving. Slower flow lets grit and solids deposit and cause blockages.

Infiltration versus inflow

Infiltration is groundwater entering through pipe defects and joints. Inflow is direct stormwater entering through downspouts, sump pumps, and manhole covers.

Surcharge and SSO

Surcharge is flow exceeding pipe capacity that raises the hydraulic grade line above the crown. If it reaches manholes or backups, a sanitary sewer overflow results.

Confined space testing order

Before sewer entry, test for oxygen (19.5 to 23.5 percent), flammable gas as LEL, hydrogen sulfide, and carbon monoxide, then monitor continuously during the entry.

Smoke testing purpose

Blowing smoke into a sewer section locates inflow sources and illegal connections where smoke escapes from roofs, downspouts, yard drains, or cracked pipe.

Lift station wet well cycling

Pump cycling frequency depends on wet well volume between lead and lag pump levels and inflow rate. Too little storage causes short cycling that overheats and damages motors.