PA Water/Wastewater Operator key terms

Adding a chemical such as alum or ferric chloride to raw water and mixing it fast so tiny suspended particles and color clump together. Those clumps can then be removed by settling and filtration.

Slow, gentle stirring that lets chemically treated particles bump into each other and grow into larger, heavier clumps called floc. These clumps settle faster and are easier for filters to catch.

A quiet basin where water moves slowly enough that floc and other solids sink to the bottom and collect as sludge. The clearer water flowing off the top goes on to the filters.

Passing settled water through a bed of sand, anthracite, or other granular media so remaining fine particles and some pathogens are trapped. Filters are a key physical barrier before disinfection.

Reversing flow upward through a filter bed to wash out the solids it has captured. Operators start a backwash when head loss or filtered-water turbidity reaches a set trigger point.

A measure of how cloudy water looks because of suspended particles, reported in nephelometric turbidity units (NTU). Cloudy water can hide pathogens from disinfectants and is closely regulated.

A treatment step that inactivates or kills harmful organisms, usually with chlorine, chloramine, ozone, or ultraviolet light. It works best after particles have been removed by settling and filtration.

The disinfectant concentration in mg/L multiplied by the effective contact time in minutes. Required CT depends on water temperature, pH, and the target organism, and shows whether disinfection is adequate.

The chlorine still left in the water after it has reacted with impurities. A measurable residual keeps water protected as it travels through pipes and is required in the distribution system.

A bench-scale test that mixes a raw water sample with several coagulant doses and stirs it through fast and slow stages. It shows which dose produces the best floc and settling.

Chemicals such as trihalomethanes that form when chlorine reacts with natural organic matter in water. Their levels are limited by regulation, so plants must balance disinfection against byproduct formation.

A buried pipe in the distribution network that carries finished water along streets and blocks. Mains come in sizes and materials such as ductile iron, PVC, and cast iron, and must stay pressurized.

A valve with a sliding gate used to start, stop, or isolate flow in a main. It is normally kept fully open or fully closed so the gate is not damaged by throttling.

A valved connection on a water main that lets fire crews draw large flows and lets utility staff flush mains and test pressure. Hydrants need periodic inspection, lubrication, and draining.

A pressure surge caused by a sudden stop or change in water velocity, such as rapid valve closure. The shock can crack pipes and damage fittings, so valves are closed slowly.

Any actual or potential link between the drinking water system and a source of contamination, such as a hose sitting in a bucket of chemicals. Cross-connections are the main reason backflow can occur.

A tested device, such as a reduced-pressure zone assembly or an air gap, that stops contaminated water from reversing into the drinking water supply. It must be tested on a schedule set by the state.

Pumps placed along the distribution system to raise pressure for higher ground or distant areas. They usually draw from a storage tank so suction pressure stays positive.

A tall tank that holds finished water and uses gravity to keep steady pressure in the distribution system. Its level rises and falls with demand and provides supply during fires and outages.

Opening hydrants in a planned sequence so water runs fast in one direction through a section of main. The higher velocity scours out sediment and stale water without stirring up other areas.

A process where wastewater is mixed with air and a dense community of microorganisms that consume organic matter. The mixture is settled afterward, and some settled organisms are returned to keep the process going.

The concentration of solids, mostly bacteria, suspended in the aeration tank. Operators measure MLSS to control how much biomass is kept in the activated sludge process.

Sludge settled in the secondary clarifier that is pumped back to the aeration tank to maintain the needed population of microorganisms. The portion not returned is wasted as excess sludge.

A settling tank after aeration where activated sludge floc sinks and separates from the treated water. The clear overflow goes on to disinfection while settled sludge is returned or wasted.

Also called sludge age, the average time solids stay in the treatment system, found by dividing the solids inventory by the solids leaving each day. It strongly affects settling and nitrification.

The pounds of BOD entering the aeration tank each day divided by the pounds of microorganisms there. A low ratio usually means more complete treatment and better nitrification.

Biochemical oxygen demand, a test of how much oxygen microorganisms use while breaking down organic matter in a sample over five days. It is the standard measure of organic strength in wastewater.

The weight of solids captured on a filter from a measured sample, reported in mg/L. In wastewater it shows how well settling and other solids-removal steps are working.

A number from a settled-sludge test that shows whether activated sludge settles well. A high SVI points to bulking sludge that may wash out over the clarifier weir.

The two-step biological conversion of ammonia to nitrite and then to nitrate by specific bacteria. It consumes oxygen and alkalinity and is often required for plants discharging to sensitive waters.

Holding sludge in a heated tank without oxygen so bacteria break down organic solids, shrinking the volume and producing methane gas. It also reduces pathogens before the sludge is dewatered or reused.

A pipe that carries wastewater downhill by slope alone, using no pumps. It must be laid at a grade that keeps flow fast enough to move solids but not so fast that it scours the pipe.

A facility with pumps and a wet well that raises wastewater so it can flow onward, often through a force main. Lift stations serve areas too flat or too deep for gravity sewers.

Infiltration is groundwater seeping into sewers through cracks and joints; inflow is storm water entering through direct connections such as downspouts or manhole covers. Both add clean water the plant must treat.

A release of untreated wastewater from the collection system before it reaches the plant, often caused by blockages, pump failures, or heavy rain. Overflows must be reported and corrected quickly.

The shaped channel at the bottom of a manhole that carries flow smoothly from one pipe to the next. A poorly built invert creates turbulence and lets solids build up.

Cooking grease and similar materials that cool and harden inside sewers, narrowing the pipe and causing blockages. Local programs require grease traps at restaurants to keep FOG out of the system.

A toxic gas with a rotten-egg odor that forms when sewage turns septic inside a pipe. In the damp air above the flow it becomes sulfuric acid that eats concrete, and it is a serious worker hazard.

Going into a manhole, wet well, or tank that has limited openings and may hold dangerous air. Entry requires a permit, air testing, ventilation, a standby attendant, and rescue equipment.