PA 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

CT is disinfectant residual in mg/L multiplied by contact time in minutes. Required CT varies with disinfectant, pH, temperature, and the log inactivation credit needed.

Jar test

A bench test that doses coagulant into raw water samples while varying dose and pH, then measures settled and filtered turbidity to find the best operating conditions.

Filter L/d ratio

Media bed depth divided by effective grain size, in the same units. Rapid sand filters usually need L/d of at least 1000 for stable media and good filtrate.

Filter effluent turbidity limit

Conventional and direct filtration plants must keep combined filter effluent at or below 0.3 NTU in 95 percent of monthly samples, never above 1 NTU.

Surface overflow rate

Clarifier flow divided by its surface area, usually expressed in gpm/ft². Conventional sedimentation basins are typically designed between 0.3 and 1.0 gpm/ft².

Fluoride standards

The fluoride MCL is 4.0 mg/L and the secondary standard is 2.0 mg/L. About 0.7 mg/L is the recommended optimal concentration for dental protection.

TTHM MCL

Total trihalomethanes may not exceed 0.080 mg/L (80 micrograms per liter), evaluated as a locational running annual average at each compliance monitoring site.

Alum alkalinity demand

Alum consumes roughly 0.45 to 0.5 mg/L of alkalinity as CaCO3 per mg/L of alum fed, lowering pH and possibly requiring lime or caustic addition.

Minimum distribution pressure

Distribution systems must maintain at least 20 psi at all points at all times; typical operating pressures are 50 to 80 psi to serve customers and fire flows.

Unidirectional flushing

Flushing one direction through isolated main segments at 2.5 ft/s or more scours sediment and biofilm loose so it can be discharged rather than redeposited.

RPZ assembly

A reduced pressure zone backflow preventer uses two check valves with a relief valve between them, protecting against both backpressure and backsiphonage at high-hazard connections.

AWWA C651 disinfection

New mains are chlorinated at 25 to 50 mg/L for at least 24 hours, flushed until residual falls to 2.0 mg/L or less, then sampled for coliform bacteria.

Water age

The average time water spends in pipes and storage. High age depletes disinfectant residual, increases disinfection byproducts, and can trigger nitrification in chloraminated systems.

Hazen-Williams head loss

An empirical pipe friction equation: h equals 10.44 times length times flow to the 1.852 power, divided by C to the 1.852 times diameter to the 4.87.

Thrust block

Concrete placed against undisturbed soil behind tees, bends, and caps to resist the unbalanced pressure thrust that would otherwise separate pipe joints.

Coliform repeat sampling

A routine total coliform positive requires repeat samples within 24 hours at the original site plus upstream and downstream locations, with more repeats for each positive repeat.

Food to microorganism ratio

F/M equals pounds of BOD5 applied per day divided by pounds of MLVSS in the aeration basin; conventional activated sludge operates near 0.2 to 0.5.

Sludge volume index

SVI equals the 30-minute settled sludge volume in mL/L times 1000, divided by MLSS in mg/L; 80 to 150 mL/g indicates good settling.

Mean cell residence time

MCRT, or solids retention time, is the mass of solids in the aeration system divided by the mass wasted and lost daily; conventional plants run 5 to 15 days.

Nitrification alkalinity demand

Oxidizing ammonia to nitrate consumes about 7.14 mg/L of alkalinity as CaCO3 and 4.57 mg/L of oxygen per mg/L of ammonia nitrogen, lowering pH.

Primary clarifier design

Primary clarifiers typically use 600 to 1,200 gpd/ft² overflow rates and 1.5 to 2.5 hours detention, removing about 50 to 65 percent TSS and 25 to 40 percent BOD.

Solids loading rate

Solids applied to a clarifier per day divided by its surface area. Secondary clarifiers in activated sludge plants are typically designed for 20 to 30 lb/day/ft².

Mesophilic anaerobic digestion

Digesters held near 95 degrees F with 30 to 60 days solids retention destroy 40 to 50 percent of volatile solids and produce gas about 60 to 65 percent methane.

Aeration basin dissolved oxygen

Activated sludge aeration is normally held at 1.5 to 2.5 mg/L dissolved oxygen; nitrifying systems need about 2 mg/L or more to support nitrifiers.

Minimum self-cleaning velocity

Gravity sanitary sewers are designed to reach at least 2 ft/s at average daily flow so solids stay suspended, while staying below about 10 ft/s to limit scour.

Manning equation

Flow equals 1.486 divided by n, times area, times hydraulic radius to the two-thirds power, times slope to the one-half power; n is about 0.013 for PVC.

Infiltration versus inflow

Infiltration is groundwater seeping through defective pipes, joints, and manholes. Inflow is storm water entering directly through roof drains, area drains, and unsealed covers.

Low-pressure air test

A gravity sewer acceptance test where plugged sections are pressurized with air; the time allowed for a set pressure drop depends on pipe size, length, and specifications.

Mandrel deflection test

A rigid mandrel sized to 95 percent of the pipe inside diameter is pulled through flexible sewer pipe to prove deflection does not exceed 5 percent.

Force main velocity

Pumped force mains are usually designed for 2 to 5 ft/s; slower flow lets solids settle, while faster flow increases friction loss and surge pressures.

Excavation five-foot rule

OSHA requires a protective system such as sloping, benching, shoring, or a trench shield for excavations 5 feet deep or more, or any depth with identified hazards.

Smoke testing

Forcing non-toxic smoke into a sewer section shows where it escapes to the surface, revealing illegal storm connections, broken pipe, and defective manholes.