NC Phase W key terms

The rapid mixing of a chemical such as alum into raw water so that small particles destabilize and begin to clump together. It happens before flocculation and settling.

Gentle, slow stirring after coagulation that encourages destabilized particles to collide and grow into larger, settleable clumps called floc. Mixing energy is kept low so the floc does not break apart.

A bench-scale procedure that stirs several beakers of raw water with different chemical doses to find the best coagulant amount and pH. Operators use results to set full-scale treatment dosages.

A measure of how cloudy water is because suspended particles scatter light. Reported in nephelometric turbidity units, it is a key indicator of filtration performance and microbial risk.

A quiet tank where water moves slowly enough for floc and other solids to settle to the bottom as sludge. Settled water then flows on to filters for final particle removal.

Reversing or scouring flow through a filter to wash captured particles out of the media and send them to waste. Backwash is triggered by head loss or turbidity limits.

The drop in pressure or water level as water pushes through filters or pipes. Rising filter head loss signals clogging and is one cue that a filter needs backwashing.

The product of disinfectant residual concentration and contact time, used to judge how effectively pathogens are inactivated. Required CT values depend on disinfectant, temperature, pH, and target organism.

The concentration of chlorine still present in treated water after demand is satisfied. A detectable residual protects water in the distribution system from contamination.

The treatment step that inactivates or kills pathogens in water before it leaves the plant. It is distinct from maintaining a residual for protection during distribution.

The concentrated solids removed from settling basins and filter backwash water. Treatment plants dewater, thicken, or lagoon sludge before disposal or beneficial reuse.

The network of pipes, pumps, tanks, valves, and meters that carries finished drinking water from the treatment plant to customers. It includes storage and pressure controls.

A large buried pipe that carries drinking water along streets and feeds smaller service lines. Material, diameter, and condition affect flow capacity and break frequency.

A defined area of the distribution system kept within a set pressure range by pumps, valves, or storage tanks. Zones are separated to control pressure and reduce leakage.

A reservoir or elevated tank that holds treated water to meet peak demand, provide fire flow, and keep steady pressure in the distribution system.

Adding a small dose of chlorine at points in the distribution system to maintain disinfectant residual far from the plant. It helps control regrowth and contamination risk.

Any actual or potential link between drinking water piping and a source of contamination, such as a hose submerged in a drain. Backflow through it can pollute the system.

Devices or practices such as air gaps and reduced-pressure assemblies that stop contaminated water from reversing into drinking water piping. They protect the distribution system from cross connections.

A failure that opens a water main or service line, causing lost water, low pressure, and risk of contamination. Repairs require shutdown, isolation, and disinfection.

The difference between water produced and water billed to customers, including leaks, meter error, and unauthorized use. High values often point to distribution losses.

A pipe system that carries only domestic and industrial wastewater, not storm runoff, to a treatment plant. Keeping stormwater out protects capacity and treatment performance.

A single pipe that carries both wastewater and stormwater. During heavy rain it can overflow untreated to receiving waters unless controls are in place.

A discharge of untreated mixed sewage and stormwater from a combined system during wet weather. Regulators require controls to reduce these releases and their pollution.

Groundwater entering sewers through defects is infiltration; stormwater entering through illegal connections or drains is inflow. Both add clean water that burdens collection and treatment.

A vertical access opening in a sewer that lets crews inspect, clean, and repair the line. Covers and frames must be secure to keep surface water and debris out.

A pump facility that raises wastewater so it can keep flowing downhill toward treatment. Wet wells, pumps, and controls must be maintained to prevent overflows.

A wastewater pipe laid on a slope so flow moves by gravity alone. Proper grade and capacity prevent solids from settling and blockages from forming.

The first wastewater step, using screens and grit removal to take out large debris and heavy solids that would damage or clog downstream equipment.

A settling tank where wastewater slows down so heavier solids sink as sludge and grease floats as scum. It removes a large share of suspended solids before biological treatment.

A biological process where aerated wastewater mixes with microbe-rich sludge that consumes organic matter. Operators control air, return sludge, and wasting to keep the community healthy.

Sludge collected from the secondary clarifier and pumped back to the aeration tank to keep enough microbes there. The return rate strongly affects treatment performance.

Deliberately removing excess sludge from the activated sludge system to control the amount of solids and the age of the microbial population. Wasting rate is a core operating lever.

The settling tank after biological treatment where microbes and solids separate from the treated water. Clear overflow moves on to disinfection while settled sludge is returned or wasted.

A test measuring the oxygen that microbes use while breaking down organic matter in a wastewater sample over a set period. It indicates how much pollution remains.

The mass of solid particles suspended in a wastewater sample, found by filtering and drying. It is a common permit limit and a measure of clarifier performance.

The biological conversion of ammonia to nitrite and then nitrate by specialized bacteria. It consumes oxygen and can be lost if aeration or solids retention is inadequate.

The biological conversion of nitrate to nitrogen gas under low-oxygen conditions. It removes nitrogen from wastewater but can cause rising sludge if it happens in a clarifier.

The treated water that leaves a wastewater plant and is discharged to a receiving water or reused. It must meet permit limits for pollutants and other parameters.