HI Water/WW Operator key terms

The rapid mixing of a chemical such as alum into raw water so that small particles lose their repelling charge and begin to clump together. It is the first step of conventional clarification.

Gentle, prolonged stirring after coagulation that encourages destabilized particles to collide and grow into larger, settleable clumps called floc. Speed is slow enough to avoid shearing the floc apart.

A quiet settling basin where water moves slowly enough for floc and heavy solids to sink to the bottom as sludge. Also called clarification or settling, it follows flocculation in conventional treatment.

Passing water through a bed of sand, anthracite, or other media to trap particles too small or too light to settle out. Filters also host biological and chemical removal, and must be backwashed periodically.

Reversing flow upward through a filter bed at a rate that lifts and scrubs the media, flushing trapped solids to waste. Operators trigger it on headloss, turbidity breakthrough, or a set run time.

The cloudiness of water caused by suspended particles that scatter light. Measured in nephelometric turbidity units, it is a key indicator of filtration performance and a regulated limit.

The unit reported by a turbidimeter, which measures light scattered at a defined angle by particles in a sample. NTU is the standard reporting unit for finished-water clarity limits.

Killing or inactivating disease-causing organisms in water, usually with chlorine, chloramine, ozone, or ultraviolet light. Effectiveness depends on dose, contact time, temperature, and pH.

The product of disinfectant concentration (mg/L) and contact time (minutes) used to demonstrate that a required level of pathogen inactivation has been achieved. CT requirements rise as water gets colder.

The concentration of chlorine still present in treated water after demand has been satisfied. Free residual protects the distribution system; total residual includes combined chloramines.

A bench-scale simulation using several stirred beakers dosed with different coagulant amounts to find the best chemical dose and pH. Operators use it to respond to changing raw-water quality.

A group of bacteria used as indicator organisms for fecal contamination and treatment failure. Their presence in finished water signals a problem even when no pathogen is found.

The drop in pressure or water level caused by friction as water moves through pipes, valves, or filter media. Rising filter headloss indicates clogging and a need to backwash.

A public health advisory telling customers to boil tap water before drinking, cooking, or brushing teeth because contamination or a treatment failure is suspected. It stays in effect until testing confirms safety.

A large pipe that carries treated water through streets to serve many customers and fire hydrants. Mains are typically looped to maintain flow and pressure throughout the system.

The smaller pipe running from the distribution main to a customer's meter or building. Leaks and material problems on service lines are a common source of lost water and complaints.

A pressure surge caused by a sudden change in flow velocity, such as a fast-closing valve or pump trip. It can break pipes and damage fittings, so operators close valves slowly.

Any actual or potential link between potable water and a source of contamination, such as a submerged hose or a boiler feed line. Control relies on air gaps and backflow prevention devices.

A mechanical assembly such as a reduced-pressure zone or double check valve that stops contaminated water from reversing into the potable supply. Devices usually require annual testing by a certified tester.

An instrument that displays the static or flowing pressure at a point in the system, usually in psi or kPa. Operators use it to spot low-pressure areas and surges.

A device that measures the volume of water delivered to a customer for billing and for tracking unaccounted-for water. Common types include positive displacement and magnetic flow meters.

The difference between water produced and water billed, including leaks, theft, meter error, and flushing. High values prompt leak surveys and meter testing in a distribution system.

Deliberately opening fire hydrants to move high flows through mains and scour out sediment, stale water, and biofilm. It also verifies hydrant operation and helps maintain chlorine residual.

A wastewater treatment process in which a mixed community of bacteria and other organisms is kept suspended in aerated tanks to consume organic matter. The mixture is later separated in clarifiers.

Supplying oxygen to wastewater so aerobic microorganisms can break down organic matter. It is the largest energy user at most treatment plants and is delivered by blowers, diffusers, or mechanical mixers.

The concentration of suspended organisms and solids in the aerated tank, abbreviated MLSS. Operators track it to set the sludge age and to control the food-to-microorganism ratio.

The pounds of incoming organic food divided by the pounds of microorganisms in the aeration tank, abbreviated F/M. It guides how much sludge to waste and predicts effluent quality.

The average time a microorganism stays in the treatment system, also called mean cell residence time or solids retention time. Longer ages favor nitrification and produce less excess sludge.

A settling tank that separates treated water from the biological solids grown in the aeration tank. It produces a clear effluent and a concentrated return sludge stream.

Biological solids settled in the secondary clarifier and pumped back to the aeration tank to keep the microorganism population at the desired level. Its rate is a key daily control adjustment.

Excess biological solids deliberately removed from the process to control sludge age and prevent solids from accumulating. It is thickened and stabilized before disposal or reuse.

The two-step biological conversion of ammonia to nitrite and then nitrate by specialized bacteria. It consumes oxygen and alkalinity and is sensitive to cold temperatures and low dissolved oxygen.

The concentration of oxygen dissolved in water, reported in mg/L. In aeration tanks it must stay high enough for the biology; in receiving streams it must stay high enough for fish.

The amount of oxygen microorganisms consume while breaking down organic matter in a sample, usually over five days at 20 degrees Celsius. It is the standard measure of organic strength.

The raw wastewater entering a treatment plant or a particular process unit. Its flow and strength vary through the day and drive downstream loading calculations.

Extraneous water entering sewers from the ground through cracks and joints, or from surface sources such as roof drains and manhole covers. It inflates flows during storms and can cause overflows.

A release of untreated wastewater from a collection system before it reaches the treatment plant, often caused by blockages, root intrusion, or storm-driven excess flow. It must be reported to regulators.

An access opening in a sewer line that lets crews inspect, clean, and test the pipe. Covers and frames must be sealed where inflow enters, and confined-space entry rules apply.

Tree and shrub roots growing into sewer joints and cracks, where they catch grease and debris and eventually block the pipe. It is a leading cause of backups and overflows.

The permit-controlled procedure for entering a manhole, wet well, or vault with limited exit and possible hazardous atmosphere. It requires atmospheric testing, ventilation, attendants, and rescue provisions.

A toxic, flammable gas with a rotten-egg odor produced by bacteria in septic wastewater and sludge. It causes corrosion in sewers and can deaden the sense of smell at dangerous levels.