NM Water/Wastewater 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
- CT is disinfectant residual concentration in mg/L multiplied by contact time in minutes; required CT rises with pH and falls as water temperature rises.
- Jar test purpose
- A jar test simulates coagulation, flocculation, and settling at several chemical doses so the operator can choose the most effective coagulant dose and pH.
- Filter loading rate
- Filter loading rate equals flow in gallons per minute divided by filter surface area in square feet; rapid sand filters typically run 2 to 4 gpm per square foot.
- Filtered water turbidity limit
- Combined filter effluent must stay at or below 0.3 NTU in at least 95 percent of monthly samples and must never exceed 1 NTU.
- Detention time formula
- Detention time in hours equals basin volume in gallons divided by flow in gallons per minute, then divided again by 60 minutes per hour.
- Chlorine dose calculation
- Pounds per day of chlorine equals the milligrams per liter dose times flow in million gallons per day times 8.34 pounds per gallon of water.
- Fluoride drinking water standards
- The primary drinking water standard for fluoride is 4.0 mg/L, while 2.0 mg/L is the secondary standard that protects against dental fluorosis.
- Langelier saturation index
- The Langelier index compares measured pH to the pH at which water is calcium carbonate saturated; negative values indicate corrosive water, positive values indicate scale-forming water.
- Pressure and head
- One foot of water column produces 0.433 psi, and one psi equals 2.31 feet of head, so a 100-foot elevation difference is about 43.3 psi.
- Flow in a pipe
- Flow in gallons per minute equals 2.448 times the pipe inside diameter in inches squared times the velocity in feet per second.
- Minimum chlorine residual
- A detectable free chlorine residual of at least 0.2 mg/L must be maintained throughout the distribution system; the maximum residual disinfectant level is 4.0 mg/L.
- Air gap backflow protection
- An air gap is a physical separation of at least twice the supply pipe diameter above the flood rim, giving the highest protection against cross-connection backflow.
- New main disinfection
- New water mains are chlorinated with a 50 mg/L chlorine solution held 24 hours, then flushed and sampled for coliform bacteria before being placed in service.
- Water hammer cause
- Water hammer is a pressure surge caused by rapid velocity change when a valve closes quickly or a pump stops suddenly; surge tanks and slow-closing valves reduce it.
- Distribution storage purpose
- Distribution storage provides equalizing capacity for peak demands, fire flow reserves, and emergency supply; equalizing volume is commonly 15 to 25 percent of maximum day demand.
- Cavitation in pumps
- Cavitation is vapor bubble formation and collapse at a pump impeller caused by low net positive suction head; it produces noise, vibration, and impeller damage.
- F/M ratio
- Food-to-microorganism ratio equals pounds of BOD5 applied per day divided by pounds of MLVSS in the aeration tank; typical values are 0.05 to 0.4 per day.
- Sludge volume index
- SVI equals settled sludge volume in mL/L after 30 minutes times 1000 divided by MLSS in mg/L; values of 80 to 150 indicate good settling.
- Mean cell residence time
- MCRT equals pounds of solids in the aeration tank divided by pounds of solids leaving the system daily in waste sludge and effluent.
- Nitrification oxygen and alkalinity
- Oxidizing one pound of ammonia nitrogen to nitrate consumes about 7.14 pounds of alkalinity as calcium carbonate and about 4.6 pounds of oxygen.
- Return activated sludge
- Return activated sludge is settled biomass pumped from the clarifier back to the aeration tank to maintain the desired mixed liquor suspended solids concentration.
- BOD5 test meaning
- Biochemical oxygen demand measures oxygen consumed by microorganisms decomposing organic matter in five days at 20 degrees Celsius, indicating wastewater strength.
- Facultative lagoon
- A facultative lagoon has an aerobic upper layer and an anaerobic bottom layer; algae supply oxygen by photosynthesis while bacteria stabilize organic matter throughout the depth.
- Chlorine contact basin
- The disinfection contact basin must provide enough detention time, commonly 20 to 30 minutes at peak flow, for the chlorine dose to inactivate pathogens.
- Minimum sewer velocity
- Gravity sanitary sewers are designed for a minimum self-cleaning velocity of 2 feet per second to prevent deposition of grit and solids.
- Manning equation
- Manning's equation is V equals 1.486 divided by n, times hydraulic radius to the two-thirds power, times slope to the one-half power in English units.
- Infiltration and inflow
- Infiltration is groundwater entering sewers through defects, while inflow is storm water entering through direct connections such as roof drains and catch basins.
- Confined space entry oxygen
- Confined space entry requires oxygen between 19.5 and 23.5 percent, hydrogen sulfide below 10 ppm, and combustible gas below 10 percent of the lower explosive limit.
- Drop manhole purpose
- A drop manhole is used where a sewer entering a manhole is more than about 24 inches above the outgoing invert, preventing turbulence and hydrogen sulfide release.
- Smoke testing sewers
- Smoke testing forces nontoxic smoke into a sewer to reveal illegal storm connections, broken pipes, and manhole defects that admit inflow and infiltration.
- Lift station wet well
- A lift station wet well stores wastewater so pumps cycle between start and stop levels; usable volume is set from pump capacity and allowable starts per hour.
- Grease trap function
- A grease trap slows flow so fats, oils, and grease float and are retained while wastewater passes on to the sewer, reducing blockages and treatment upsets.