CO Water Operator flashcards
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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 inactivation credit; the required CT rises as pH increases and as water temperature falls.
- Jar test
- Bench-scale test that stirs coagulant into raw water at several doses, then settles and filters the samples to identify the dose and pH giving the best finished turbidity.
- Combined filter effluent limit
- Under the surface water treatment rule the combined filter effluent must be 0.3 NTU or less in at least 95 percent of monthly samples and never above 1 NTU.
- Langelier Saturation Index
- A calculated number comparing measured pH with the calcium carbonate saturation pH; negative values mean the water is corrosive, positive values mean it tends to deposit scale.
- Alum alkalinity demand
- Each 1 mg/L of alum dose consumes about 0.5 mg/L of alkalinity as CaCO3, so low-alkalinity waters need lime or caustic added to hold coagulation pH.
- Filter backwash rate
- Rapid gravity filters are backwashed near 15 to 20 gpm per square foot with about 50 percent bed expansion, stopping when washwater turbidity falls to roughly 10 NTU.
- HOCl versus hypochlorite ion
- Free chlorine's pKa is about 7.5, so below that pH most of it is hypochlorous acid, the stronger disinfectant, while above pH 8 hypochlorite ion dominates and disinfection slows.
- Surface loading rate
- Overflow rate equal to clarifier flow divided by surface area in gpm per square foot; running above the design rate shortens detention and carries solids over the weir.
- Psi per foot of head
- One foot of water column exerts 0.433 psi, so a 100 foot elevation difference gives about 43 psi of static pressure, and one psi equals 2.31 feet of head.
- Minimum distribution pressure
- Distribution systems should maintain at least 20 psi at every point under normal demand and during fire flow, because lower pressure allows backflow and contamination entry.
- Hazen-Williams C factor
- A roughness coefficient where higher numbers mean smoother pipe; new cement lined main runs about 130 to 140 while old tuberculated iron falls near 80.
- Gallons per foot of pipe
- A one foot length of pipe holds 0.0408 times the diameter in inches squared gallons, so an 8 inch main contains about 2.6 gallons per foot.
- RPZ backflow assembly
- A reduced pressure zone backflow preventer uses two check valves and a relief valve that discharges when the differential drops, protecting against both backpressure and backsiphonage.
- Sewer and water separation
- Water mains are kept at least 10 feet horizontally from sanitary sewers and 18 inches above them, with encasement or pressure rated pipe required at closer crossings.
- Flushing velocity
- Unidirectional flushing should move water at 2.5 feet per second or more in the main to scour and carry away sediment, rust, and biofilm.
- Water hammer
- A pressure surge caused by rapid changes in flow velocity, controlled with slow closing valves, air and vacuum valves, surge tanks, and adequate thrust restraint.
- Food to microorganism ratio
- Food to microorganism ratio, pounds of BOD entering per day divided by pounds of mixed liquor volatile solids under aeration; conventional plants run about 0.2 to 0.5 per day.
- Mean cell residence time
- Mean cell residence time, the pounds of solids in the aeration basin divided by the pounds leaving daily in waste and effluent; it sets sludge age and nitrification.
- Sludge volume index
- Sludge volume index, the 30 minute settled sludge volume in mL/L times 1000 divided by MLSS in mg/L; values near 80 to 150 indicate good settling.
- Nitrification alkalinity and oxygen
- Oxidizing one milligram of ammonia nitrogen to nitrate consumes about 7.14 milligrams of alkalinity as CaCO3 and about 4.6 milligrams of oxygen.
- Digester gas composition
- Mesophilic anaerobic digesters held near 95 to 100 degrees Fahrenheit destroy about half the volatile solids and produce gas that is roughly 60 to 65 percent methane.
- Return activated sludge
- Return activated sludge moves settled biomass from the secondary clarifier back to the aeration basin to hold the desired MLSS, set as a percentage of influent flow.
- Clarifier solids loading rate
- Pounds of solids applied per day per square foot of clarifier surface; secondary clarifiers are typically designed near 0.8 to 1.2 and overloading raises the sludge blanket.
- Fecal coliform permit limit
- Disinfection must meet the permit's fecal coliform limit, commonly a monthly geometric mean of 200 colonies per 100 mL, adjusted by chlorine dose and contact time.
- Manning equation
- Flow equals 1.486 divided by roughness n, times cross sectional area, times hydraulic radius to the two thirds power, times slope to the one half power, in English units.
- Minimum sewer velocity
- Collection mains are designed to achieve at least 2 feet per second at average daily flow so grit and solids stay suspended rather than depositing in the pipe.
- Minimum slope eight inch sewer
- An 8 inch public sewer is typically laid at 0.4 percent slope or steeper, about 0.004 feet per foot, to sustain self cleaning velocity at low flow.
- Infiltration versus inflow
- Infiltration is groundwater seeping through defective pipe and joints; inflow is stormwater entering directly from roof drains, sumps, and manhole covers.
- Confined space entry limits
- Acceptable entry conditions are oxygen between 19.5 and 23.5 percent, flammable gas under 10 percent of the lower explosive limit, hydrogen sulfide under 10 ppm, and carbon monoxide under 35 ppm.
- Lift station cycle time
- Cycle time equals the wet well volume between pump start and stop divided by the pump rate minus inflow; wider swings lengthen cycles and protect the pump motor.
- Crown corrosion by sulfide
- Bacteria in anaerobic slime reduce sulfate to sulfide, which escapes and is converted to sulfuric acid above the waterline, corroding concrete pipe and manholes.
- Trench protective system
- OSHA requires a protective system in trenches 5 feet deep or deeper unless solid stable rock, and a ladder within 25 feet of every worker.