Wastewater Treatment Operator Class III flashcards

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

BOD5 test conditions

A sample is incubated five days at 20 degrees Celsius in the dark; the dissolved oxygen lost measures carbonaceous demand from biodegradable organic matter, usually about 68 percent of ultimate BOD.

Nitrification two-step process

Ammonia-oxidizing bacteria such as Nitrosomonas convert ammonium to nitrite, then nitrite-oxidizing bacteria such as Nitrobacter convert nitrite to nitrate, consuming about 4.57 mg oxygen per mg nitrogen.

Filamentous bulking

Excess filamentous bacteria such as Microthrix produce a low-density sludge with sludge volume index above 150 mL/g, causing slow settling and solids carryover in secondary clarifier effluent.

Food-to-microorganism ratio

F/M equals the mass of BOD or COD entering the aeration tank per day divided by the active biomass (MLVSS) in the tank; conventional activated sludge runs about 0.2 to 0.5 per day.

Primary clarifier overflow rate

Surface settling rate equals influent flow divided by clarifier surface area; typical primary design values are 30 to 50 cubic meters per square meter per day, or 800 to 1200 gallons per day per square foot.

Grit chamber velocity

Horizontal velocity is held near 0.3 meters per second (1 foot per second) so dense grit of about 2.65 specific gravity settles while lighter organic solids remain suspended and flow onward.

Primary clarification removal

A well-operated primary clarifier removes roughly 50 to 65 percent of influent suspended solids and 25 to 40 percent of BOD5, producing primary sludge of about 4 to 6 percent solids.

Primary clarifier detention time

Typical hydraulic detention at design flow is 1.5 to 2.5 hours; longer detention risks septic conditions and sulfide odors, while shorter detention reduces solids and BOD removal.

Sludge volume index

SVI equals the 30-minute settled sludge volume in milliliters per liter times 1000, divided by MLSS in mg/L; about 80 to 150 indicates good settling and above 200 indicates bulking.

Mean cell residence time

MCRT equals the solids mass held in the aeration tank and clarifier divided by the solids leaving each day in waste sludge and effluent; it controls nitrification and sludge production.

Trickling filter organic loading

Organic loading is kilograms of BOD applied per cubic meter of media per day; rock media typically runs 0.08 to 0.4 and high-rate plastic media 0.4 to 1.6, with recirculation diluting strong influent.

Return activated sludge rate

RAS flow is usually 50 to 150 percent of influent flow; it returns settled biomass to the aeration tank and is adjusted to keep the secondary clarifier sludge blanket shallow.

Hypochlorous acid versus hypochlorite

Below about pH 7.5 free chlorine is mostly hypochlorous acid, roughly 80 times more effective as a disinfectant than the hypochlorite ion that dominates at higher pH.

CT disinfection concept

CT equals disinfectant residual concentration in mg/L multiplied by contact time in minutes; the required CT varies with pH, temperature, and the target organism's resistance.

UV disinfection at 254 nm

Low-pressure mercury lamps emit near 254 nanometers, damaging microbial nucleic acids; effectiveness depends on UV transmittance, lamp cleanliness, and delivered dose in millijoules per square centimeter, and no residual remains.

Chlorine demand

Chlorine demand is the difference between chlorine applied and the residual measured after the contact period; reducing agents and ammonia in the water consume chlorine before disinfection is achieved.

Mesophilic anaerobic digestion

Mesophilic digesters operate near 35 to 38 degrees Celsius with a solids retention time of about 15 to 20 days, achieving 40 to 50 percent volatile solids destruction.

Volatile acids alkalinity ratio

A ratio of volatile acids to alkalinity below about 0.1, both as mg/L, indicates stable digestion; a rising ratio together with falling pH warns of digester upset.

Class A biosolids limits

Class A biosolids must contain fewer than 1000 fecal coliform per gram of total solids and fewer than 3 Salmonella MPN per 4 grams, and must meet a vector attraction reduction option.

Digester biogas yield

Anaerobic digestion produces roughly 0.8 to 1.2 cubic meters of gas per kilogram of volatile solids destroyed, containing about 60 to 65 percent methane and 30 to 35 percent carbon dioxide.

Manning equation

Velocity equals 1.486 divided by roughness n, times hydraulic radius to the two-thirds power, times slope to the one-half power; n is about 0.013 for concrete and PVC sanitary sewers.

Self-cleansing sewer velocity

Sanitary sewers should carry at least 0.6 meters per second (2 feet per second) at design flow to keep solids moving; velocities above about 3 meters per second can erode pipe.

Centrifugal pump affinity laws

At constant impeller diameter, flow varies with rotational speed, head with speed squared, and power with speed cubed; these laws predict performance when pump speed is changed.

Water horsepower

Water horsepower equals flow in gallons per minute times total dynamic head in feet times specific gravity, divided by 3960; brake horsepower equals water horsepower divided by pump efficiency.

BOD seed correction

Seeded BOD subtracts the oxygen consumed in the seed blank, multiplied by the fraction of seed in the diluted sample, from the sample's own oxygen depletion before calculating BOD.

Total suspended solids procedure

Filter a measured volume through a 1.5-micron glass fiber filter, dry at 103 to 105 degrees Celsius, cool in a desiccator, and weigh; residue divided by volume gives mg/L.

Settleable solids test

One liter of sample settles in an Imhoff cone for 60 minutes; the settled volume in milliliters per liter is reported and indicates whether grit removal or clarifier operation needs adjustment.

Volatile suspended solids ignition

Dried solids ignited at 550 degrees Celsius for about 15 to 20 minutes lose organic matter as weight; this loss is volatile suspended solids, typically 70 to 80 percent of mixed liquor suspended solids.

Confined space oxygen range

Entry requires an oxygen concentration between 19.5 and 23.5 percent by volume; concentrations outside that range require permit-required confined space procedures and supplied-air respiratory protection.

Hydrogen sulfide IDLH

Hydrogen sulfide has an immediately dangerous to life or health concentration of 100 ppm; it is heavier than air, accumulates in wet wells and manholes, and deadens the sense of smell.

Methane explosive range

Methane forms an explosive mixture in air between about 5 and 15 percent by volume; gas meters alarm at 10 percent of the lower explosive limit, which is 0.5 percent methane.

Sanitary sewer overflow reporting

An overflow must be reported to the state regulatory agency within the time required by permit or rule, with public notice, spill volume, cause, and corrective actions documented.