NC Water/Wastewater Operator key terms

Adding a chemical such as alum or ferric chloride to raw water so that tiny suspended particles and color-causing matter lose their repelling charges, clump together, and can be removed by later settling and filtration.

Gentle, slow stirring of chemically treated water that causes small particle clumps to collide and grow into larger, heavier masses called floc, which settle out more easily in the basin that follows.

A quiet basin where water moves slowly enough that heavier particles and floc sink to the bottom as sludge while clearer water flows on to the filters; also called clarification.

A reverse flow of water, often assisted by air, pushed upward through a filter bed to lift and rinse out trapped particles and restore the filter's ability to produce clear water.

A measure of how cloudy water appears because of suspended particles, reported in nephelometric turbidity units and used as an indicator of how well filtration and disinfection are working.

The product of disinfectant residual concentration (C) and the contact time (T) achieved at a given temperature and pH, used to judge whether enough pathogen inactivation, such as for Giardia, has occurred.

The amount of chlorine still present in treated water after it has reacted with impurities, showing that a protective disinfectant level remains as water travels through the distribution system.

A bench-scale procedure in which several beakers of raw water receive different chemical doses and are stirred at set speeds, letting the operator choose the most effective coagulant dose and pH.

The highest concentration of a regulated contaminant allowed in drinking water delivered to the public, established under the federal Safe Drinking Water Act and enforced by the state.

Any actual or potential link between a drinking water pipe and a pipe, tank, or source holding nonpotable water or other material that could allow contamination to be drawn or pushed into the public supply.

Reverse flow of water or other liquids into the drinking water system, caused either by a loss of pressure in the main or by higher pressure on the customer's side of the meter.

A physical separation with open space between the end of a supply pipe and the rim of the receiving vessel, giving the most reliable protection against backflow because no mechanical part can fail.

A pressure surge, often heard as a bang, created when moving water is stopped or redirected suddenly by a valve or pump; the shock wave can crack pipes, joints, and fittings.

A portion of a distribution system held within a set pressure range by pumps, valves, or storage, so that higher ground is served adequately without over-pressurizing lower elevations.

The elevation to which water would rise in an open standpipe connected to a pipe at a given point, used to show the pressure available throughout the distribution network.

Deliberately running water at high velocity through mains and out of blowoffs or hydrants to remove sediment, stale water, and loose biofilm, and to restore chlorine residual in slow-flowing areas.

A section of main with no outlet, so water there barely moves; sediment collects and disinfectant residual fades, making routine flushing necessary to keep quality acceptable.

Wastewater flowing into a treatment plant or into a particular treatment unit; its flow rate and strength in BOD and suspended solids set the loading the process must handle.

Treated wastewater leaving a treatment process or plant, which must meet the limits in its discharge permit before being released to a stream, land, or reuse system.

A settling tank near the head of the plant where heavy solids sink and grease and scum rise, removing a large share of suspended solids and organic load before biological treatment.

A biological process in which wastewater is mixed and aerated with a dense population of microorganisms that consume dissolved organic matter; the solids are later settled and partly reused.

The concentration of suspended solids, mostly living and dead bacteria, in the aerated tank of an activated sludge system; it is measured to control how much biology is kept at work.

A calculated test value describing how well activated sludge settles in a graduated cylinder; a high index points to bulking sludge that settles slowly and may escape over the secondary clarifier weirs.

Solids that settle in the secondary clarifier and are pumped back to the aeration tank to keep enough microorganisms in the system to treat the incoming wastewater.

The settling tank after biological treatment where activated sludge floc separates from the liquid, producing a clear overflow that goes to disinfection or discharge and a underflow returned or wasted.

A measure of the oxygen microorganisms use while breaking down organic matter in a sample over a set period, used to express organic strength and to judge treatment performance.

The two-step biological conversion of ammonia to nitrite and then to nitrate by specific bacteria, a process that consumes oxygen and alkalinity in the aeration tank.

Holding sludge in a sealed, often heated tank without oxygen so bacteria break down organic solids, reducing volume and producing methane-rich gas plus a more stable residual solid.

The treated and stabilized solids produced by wastewater treatment that may be land-applied or disposed of, provided they meet the required pathogen and metal limits.

An opening in a sewer with a removable cover that allows workers to inspect, clean, and repair the line, often located where pipe size, slope, or direction changes.

A facility with a wet well and pumps that raises wastewater to a higher elevation so it can continue flowing by gravity or be pushed through a pressurized force main.

A pipe carrying wastewater under pressure from a pump station to a point where gravity flow can resume; it needs no downhill slope but requires air release and valve provisions.

Groundwater that seeps into a sewer through cracks, poor joints, or defective manholes, adding clear water that the collection system and treatment plant must still handle.

Stormwater or other surface water that enters a sewer directly through routes such as roof drains, foundation drains, yard drains, or unsealed manhole covers during rain events.

A release of untreated sewage from the collection system before it reaches the plant, usually caused by blockages, heavy infiltration and inflow, or pump failure, and reportable to regulators.

The lowest inside surface of a pipe at a given point; invert elevations establish gravity sewer slope and determine how incoming and outgoing pipes line up inside a manhole.

A device or management practice that keeps fats, oils, and grease from food service and other sources out of sewers, where they cool, congeal, and cause costly blockages.