MO Water/Wastewater 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 effective contact time in minutes; required CT increases at lower temperature and higher pH for free chlorine.

Chlorine demand

The difference between the chlorine dose applied and the free chlorine residual remaining after a defined contact time; it reflects oxidizable material in the water.

Turbidity limit

Under the Surface Water Treatment Rule, combined filter effluent must be 0.3 NTU or less in 95% of monthly samples and never exceed 1 NTU.

Jar test

Laboratory procedure that mixes raw water with varying coagulant doses and settling times to identify the optimum coagulant dose and pH for treatment.

Filter loading rate

Flow through a filter divided by its surface area, usually expressed in gpm/ft²; rapid sand filters typically operate between 2 and 5 gpm/ft².

Backwash bed expansion

The percentage increase in filter media depth during backwash; rapid sand filters are typically expanded 20 to 30 percent to release trapped solids.

Langelier Saturation Index

A calculated value comparing water pH to its calcium carbonate saturation pH; near zero is balanced, negative is corrosive, positive is scale-forming.

Giardia inactivation credit

Log removal credit granted for Giardia based on disinfectant type, residual, contact time, pH, and temperature; UV or ozone required for Cryptosporidium credit.

Minimum distribution residual

Missouri requires at least 0.2 mg/L free chlorine or 0.5 mg/L chloramine residual at points of entry and throughout the distribution system.

Twenty psi rule

Distribution pressure must remain at or above 20 psi at all points; a drop below this during a main break or pump failure triggers a boil order.

Water horsepower

Theoretical power to move water, calculated as (gpm × head in feet) ÷ 3960; brake horsepower equals water horsepower divided by pump efficiency.

Tank detention time

Storage volume divided by flow rate; for example, a 500,000-gallon tank at 1,000 gpm provides 500 minutes of detention.

Hydrant flow test

Field test measuring static pressure, residual pressure, and pitot pressure to estimate available fire flow; 20 psi residual is the standard reference point.

Total coliform positive

A routine positive total coliform sample requires repeat samples; an E. coli-positive or repeat-positive result requires public notice within 24 hours.

Air gap backflow prevention

A physical separation between the potable water outlet and the flood-level rim of a receiving vessel; the only true backflow prevention method.

Pipe velocity calculation

Flow divided by cross-sectional area; convert gpm to cfs by dividing by 448.8, then divide by area in square feet to get feet per second.

BOD5

Five-day biochemical oxygen demand measured at 20°C; typical domestic wastewater influent is about 200 to 250 mg/L BOD and similar TSS.

F/M ratio

Food-to-microorganism ratio: pounds of BOD applied per day divided by pounds of MLVSS in aeration; conventional activated sludge runs 0.2 to 0.5.

MCRT

Mean cell residence time, or sludge age: pounds of MLSS in aeration divided by pounds of solids leaving the system per day.

Solids loading rate

Pounds of solids applied per day per 1,000 square feet of clarifier surface; typical secondary clarifier design is 12 to 30 lbs/day/1,000 ft².

Sludge volume index

Volume in milliliters occupied by one gram of sludge after 30 minutes of settling; values above 150 indicate poor settling and possible bulking.

Return activated sludge rate

Flow of settled sludge returned from the clarifier to the aeration basin, typically 50 to 150 percent of influent flow to maintain MLSS.

Mesophilic digestion

Anaerobic digestion at about 95 to 98°F that reduces volatile solids and produces methane; temperature swings upset the process.

Wastewater fecal coliform limit

Missouri typically requires a monthly geometric mean of 200 fecal coliform per 100 mL in disinfected effluent; ammonia raises chlorine demand.

Minimum sewer slope

An 8-inch gravity sewer typically requires about 0.40 percent slope; smaller pipe needs steeper slopes and larger pipe can be flatter.

Manning's equation

Velocity = (1.486/n) × R^(2/3) × S^(1/2), where n is about 0.013 for new vitrified clay or PVC and R is hydraulic radius.

Self-cleansing velocity

A flow velocity of about 2 feet per second that keeps solids suspended and moving; lower velocities allow deposition and eventual blockage.

Infiltration versus inflow

Infiltration is groundwater entering through pipe defects and joints; inflow is direct stormwater entering through manholes, roof drains, or illegal connections.

Wet well detention time

Wet well volume divided by pump flow; should stay under about 30 minutes to prevent septic conditions, odor, and corrosion from sulfide.

Confined space entry testing

Before entry, test atmosphere for oxygen between 19.5 and 23.5 percent, LEL below 10 percent, and hydrogen sulfide below 10 ppm.

Smoke testing

Blowing non-toxic smoke into a sewer to reveal inflow sources, illegal connections, and broken pipe by observing where smoke escapes to the surface.

CCTV sewer inspection

Closed-circuit television camera passed through a sewer to record condition, cracks, roots, and offsets; results are graded on a 1 to 5 condition scale.