MT 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. Used to demonstrate pathogen inactivation credit; required CT increases at lower temperature and higher pH for free chlorine.

Jar test

Bench-scale test that mixes coagulant at varying doses and pH to find the optimum for turbidity removal. Results guide full-scale coagulant dose, rapid mix, and flocculation conditions.

Combined filter effluent limit

Conventional filtration systems must keep combined filter effluent turbidity at or below 0.3 NTU in at least 95 percent of monthly measurements, and never above 1 NTU.

Alkalinity consumption by alum

Each mg/L of alum dosed consumes about 0.45 mg/L of alkalinity as CaCO3 and lowers pH. Lime or caustic soda is added to restore pH and prevent coagulation failure.

Enhanced coagulation

Optimized coagulation to remove total organic carbon, a disinfection byproduct precursor. Required TOC removal percentages increase with source water TOC and decrease with higher alkalinity.

Backwash bed expansion

Filter backwash rate must fluidize the media, typically expanding the bed 50 to 60 percent. Insufficient expansion leaves mudballs; excessive rates wash media to waste.

Hazen-Williams head loss

Empirical pipe friction formula: hf = 10.44 L Q^1.852 / (C^1.852 d^4.87) in US units. Higher C means smoother pipe and less head loss for the same flow.

Minimum distribution pressure

Systems must maintain at least 20 psi at all points under normal conditions and never drop below 20 psi during main breaks or fire flow. Normal service is often 40 to 80 psi.

Boil water notice

Issued when pressure drops below 20 psi or contamination is suspected. Lifted only after repair, flushing, and two consecutive negative bacteriological samples taken 24 hours apart.

Air gap backflow protection

A physical separation between the potable water outlet and the flood-level rim of a receiving vessel. It is the most reliable backflow prevention method and needs no testing.

Storage tank turnover

Time for stored volume to be replaced by system flow. Long turnover increases water age, disinfectant decay, and disinfection byproduct formation; target roughly three to five days or less.

Lead and copper action level

Ninetyth-percentile action levels are 0.015 mg/L for lead and 1.3 mg/L for copper. Exceedance triggers corrosion control treatment, source water monitoring, and public education.

BOD5 test

Five-day biochemical oxygen demand measured at 20 degrees Celsius with nitrification suppressed. Typical untreated domestic wastewater has 200 to 250 mg/L BOD5 and similar suspended solids.

F/M ratio

Food-to-microorganism ratio: pounds of BOD applied per day divided by pounds of MLVSS in the aeration tank. Conventional activated sludge operates near 0.2 to 0.4 per day.

Solids retention time

Mass of solids in the aeration system divided by the mass leaving daily. Nitrifying bacteria require roughly 8 to 15 days or more depending on temperature; short SRT washes them out.

Sludge volume index

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; above 200 suggests filamentous bulking.

Nitrification stoichiometry

Oxidizing ammonia to nitrate consumes about 7.14 mg/L alkalinity as CaCO3 and 4.57 mg/L oxygen per mg/L of ammonia nitrogen. Denitrification recovers about 2.86 mg/L oxygen per mg/L nitrate.

Secondary clarifier overflow rate

Surface overflow rate equals flow divided by clarifier surface area. Activated sludge clarifiers typically run 400 to 800 gallons per day per square foot at average flow.

Anaerobic digestion conditions

Mesophilic digestion runs at 35 to 38 degrees Celsius and thermophilic at 52 to 57 degrees Celsius. Volatile solids reduction of at least 38 percent meets Class B biosolids under Part 503.

Manning's equation

V = (1.486/n) R^(2/3) S^(1/2) in US units, where n is roughness, R is hydraulic radius, and S is slope. Used to size gravity sewers and check velocity.

Sewer velocity limits

Gravity sanitary sewers are designed for a minimum self-cleansing velocity of 2 feet per second and a maximum near 10 feet per second to limit scour and erosion of pipe.

Infiltration versus inflow

Infiltration is groundwater entering through defective pipes, joints, or manholes. Inflow is direct stormwater from downspouts, sumps, or yard drains connected to the sewer.

Lift station cycle time

Time between pump starts, set by usable wet well volume divided by inflow. Minimum cycle time limits starts, often to 10 or 15 per hour, protecting motors and controls.

Confined space atmospheric limits

Acceptable entry conditions: oxygen 19.5 to 23.5 percent, combustible gas below 10 percent of the lower explosive limit, and hydrogen sulfide and carbon monoxide below exposure limits.

Surface Water Treatment Rule

Requires 99.9 percent (3-log) Giardia and 99.99 percent (4-log) virus removal or inactivation for surface water systems, plus filtration and combined filter effluent turbidity limits.

Total Coliform Rule response

Any total coliform positive requires repeat samples at the site and upstream and downstream. E. coli positives or repeat positives trigger public notice within 24 hours.

Consumer Confidence Report

Annual water quality report delivered to customers by July 1 covering the prior calendar year. It lists contaminant results, MCLs, violations, and source water information.

Public notice tiers

Tier 1 requires notice within 24 hours for immediate health risk, Tier 2 within 30 days, and Tier 3 in the annual report. The tier depends on the violation and its health significance.

Hydrogen sulfide hazard

A heavier-than-air gas with a rotten-egg odor that deadens the sense of smell at higher concentrations. The IDLH is 100 ppm, so entry testing and supplied air are required.

Methane explosive range

Methane is lighter than air and explosive between 5 and 15 percent in air. It forms in anaerobic sewers and digesters, so confined spaces require gas testing before entry.

Lockout tagout

Procedure to isolate all energy sources, verify zero energy, and apply locks and tags before maintenance. Only the worker who applied a lock may remove it.

Non-revenue water

Difference between water produced and water billed, including leaks, flushing, firefighting, and meter error. It is a key performance indicator for distribution system efficiency.