Operator terms
Operator terms, explained plainly
The terms a Texas Class D candidate meets on the exam and the job, each explained in plain language. Read one, then practice it. No jargon for its own sake, and no promise about your result.
- What is BOD in wastewater?BOD (biochemical oxygen demand) is the oxygen microbes use to break down organic matter in water: a core measure of how strong or polluted wastewater is.
- What is TSS (total suspended solids)?TSS (total suspended solids) is the weight of solid particles suspended in water, in mg/L. Removing it is a main goal of wastewater clarifiers.
- What is return activated sludge (RAS)?Return activated sludge (RAS) is settled, microbe-rich sludge pumped from the clarifier back to the aeration tank to keep activated sludge treatment healthy.
- What is MLSS?MLSS (mixed liquor suspended solids) is the concentration of solids, mostly microbes, in an activated sludge aeration tank. It measures active biomass.
- What is a clarifier?A clarifier is a tank where water slows so solids settle to the bottom and clearer water flows off the top, used in water and wastewater treatment.
- What is effluent?Effluent is the treated water that flows out of a wastewater plant. It must meet the plant's permit limits before discharge. Influent is what comes in.
- What is coagulation in water treatment?Coagulation is adding a chemical like alum that neutralizes the charge on tiny particles so they can clump together: the first step in clearing cloudy water.
- What is flocculation?Flocculation is the gentle mixing after coagulation that lets particles collide and stick into larger clumps (floc) that settle or filter out more easily.
- What is sedimentation in water treatment?Sedimentation is letting water sit still so heavier particles and floc settle out by gravity before filtration, removing most of the suspended load.
- What is pH in water?pH measures how acidic or basic water is, from 0 to 14, where 7 is neutral. It affects coagulation, disinfection, and corrosion, so operators watch it closely.
- What is alkalinity in water?Alkalinity is water's capacity to neutralize acid, mostly from bicarbonate. It buffers pH so it stays stable when treatment chemicals are added.
- What is a cross-connection?A cross-connection is any point where drinking water can mix with a non-potable source, risking backflow contamination. Backflow prevention stops it.
- What is chlorine residual?Chlorine residual is the chlorine still active in water after demand is met. A measurable residual proves disinfectant reaches the customer.
- What is contact time (CT) in disinfection?Contact time is how long disinfectant stays in water before use; CT is time times concentration. Enough CT is what actually inactivates pathogens.
- What are coliform bacteria?Coliform bacteria are an indicator group used to screen water safety. Their presence signals that harmful organisms could be getting into the water.
- What is a maximum contaminant level (MCL)?A maximum contaminant level (MCL) is the enforceable legal limit for a contaminant in drinking water. Systems must stay below it and act if they exceed it.
- What is filtration in water treatment?Filtration passes water through sand or media to strain out the fine particles and floc that settling missed, a key barrier before disinfection.
- What is disinfection in water treatment?Disinfection kills or inactivates disease-causing organisms so water is safe, usually by chlorination with enough contact time and a lasting residual.
- What is aeration in wastewater treatment?Aeration adds air and oxygen to wastewater so the microbes in activated sludge can breathe and break down waste, controlled to keep treatment healthy.
- What is grit removal?Grit removal takes out heavy sand and gravel early in wastewater treatment to protect pumps and equipment and keep it from settling downstream.
- What is detention time?Detention time is how long water stays in a tank, found by dividing volume by flow. Enough time is what lets a tank settle solids or disinfect.
- What is potable water?Potable water is water that is safe to drink, meeting drinking-water health standards after treatment and disinfection.
- What is influent in wastewater treatment?Influent is the untreated wastewater flowing into a treatment plant, before treatment. Effluent is the treated water that leaves it.
- What is a lift station?A lift station pumps wastewater from a lower to a higher elevation so it can keep flowing to the plant where gravity alone cannot carry it.
- What is chlorine demand?Chlorine demand is the chlorine the water uses up reacting with organisms and material, before any residual remains. Dose = demand + residual.
- What is backwash in water treatment?Backwash reverses the flow through a filter to flush out trapped particles, routine maintenance that keeps a filter removing turbidity.
- What is a water well?A water well is a hole drilled into an aquifer to pump groundwater to the surface, the source for a groundwater public water system.
- What is water hardness?Water hardness is the dissolved calcium and magnesium in water. Hard water leaves scale and uses more soap; it affects treatment and pipes.
- What is water fluoridation?Fluoridation is adding a controlled amount of fluoride to drinking water to help prevent tooth decay, dosed and monitored by the operator.
- What is sludge in wastewater treatment?Sludge is the settled solids removed during wastewater treatment, later thickened, digested, and handled as biosolids.
- What is a digester in wastewater treatment?A digester is a tank where microbes break down wastewater sludge, reducing its volume and stabilizing it for handling and disposal.
- What is dechlorination?Dechlorination removes chlorine from treated wastewater before discharge, because chlorine is toxic to fish and aquatic life in the receiving water.
- What is a bar screen?A bar screen is parallel bars at the head of a wastewater plant that catch rags and large debris before they reach pumps and treatment.
- What is a weir in water treatment?A weir is a wall water flows over at a set level, used in clarifiers and channels to spread flow evenly and to measure or control it.
- What is the headworks of a wastewater plant?The headworks is the front of a wastewater plant, where screening and grit removal protect the pumps and tanks before treatment.
- What is a package plant?A package plant is a small, prefabricated, self-contained wastewater treatment plant for subdivisions, parks, and small communities.
- What are disinfection byproducts (DBPs)?Disinfection byproducts (DBPs) form when chlorine reacts with organic matter in water; some are regulated for health at high levels.
- What is water hammer?Water hammer is a pressure surge from stopping or starting flow suddenly, like a slammed valve, that can damage pipes if not controlled.
- What is a maximum contaminant level goal (MCLG)?An MCLG is the non-enforceable health-goal level of a contaminant with no known risk; the enforceable limit is the MCL, set close to it.
- What is a water distribution system?A water distribution system is the pumps, tanks, mains, and valves that carry treated water to customers at safe pressure without letting contamination back in.
- What is a wastewater collection system?A wastewater collection system is the sewers, manholes, and lift stations that carry used water from customers to the treatment plant, mostly by gravity.
- What is free chlorine?Free chlorine is the unreacted, available chlorine residual left after demand is met: the strongest, fastest-acting disinfecting form operators measure.
- What is combined chlorine?Combined chlorine is chlorine bonded with ammonia as chloramine: a slower but longer-lasting disinfectant used to hold a residual across the distribution system.
- What is groundwater?Groundwater is water stored underground in soil and rock, drawn up through wells: usually clearer than surface water but able to carry dissolved minerals.
- What is surface water?Surface water is open water from lakes, rivers, and reservoirs: more exposed to turbidity and organisms than groundwater, so it needs fuller treatment.
- What is primary treatment in wastewater?Primary treatment is the first wastewater stage: settling that lets heavy solids sink and grease float so both can be removed before biological treatment.
- What is secondary treatment in wastewater?Secondary treatment is the biological wastewater stage where microbes break down dissolved organic matter, lowering BOD before disinfection and discharge.
- What is a water storage tank?A water storage tank holds treated water to meet demand, hold steady pressure, and keep a reserve for fire flow; elevated tanks add pressure by height.
- What is backflow prevention?Backflow prevention stops contaminated water from flowing back into the clean supply, using air gaps, vacuum breakers, and assemblies at cross-connections.
- What is a wet well?A wet well is the tank at a lift station that holds incoming wastewater until level controls start the pumps that move it on through the collection system.
- What is infiltration and inflow (I&I)?Infiltration and inflow (I&I) is groundwater and storm water leaking into sewers through cracks and bad connections, overloading the system and the plant.
- What is total chlorine?Total chlorine is free chlorine plus combined chlorine: the whole chlorine residual present, both the fast-acting and the slower, longer-lasting forms.
- What is chlorination?Chlorination is adding chlorine to disinfect water: the most common disinfection method, leaving a residual that keeps protecting water downstream.
- What is a trickling filter?A trickling filter is a secondary process: wastewater trickles over media coated with microbes that consume organic matter, lowering BOD before it moves on.
- What is a pressure reducing valve (PRV)?A pressure reducing valve (PRV) lowers and holds downstream water pressure at a set level, protecting low-elevation areas from unsafe high pressure.
- What is a gravity sewer?A gravity sewer is a sloped sewer pipe that carries wastewater downhill by gravity alone, no pump needed: most of a collection system works this way.
- What is a clearwell?A clearwell is a basin that stores filtered, disinfected water at the plant, giving disinfectant contact time and holding finished water ready to distribute.
- What is a force main?A force main is a pressurized sewer pipe carrying wastewater pumped from a lift station: it flows full and under pressure, unlike a gravity sewer.
- What is water main flushing?Flushing is running water fast through a main, usually through a hydrant, to wash out sediment and stale water and restore quality in the distribution system.
- What is a sewer manhole?A manhole is an access point into a sewer line for inspection and cleaning, placed where pipes join or change direction; a good seal keeps storm water out.
- What is a check valve?A check valve lets water flow one way and closes if flow reverses: used to stop backflow, such as on a pump discharge so water cannot run back.
- What is a gate valve?A gate valve is an on-off valve that isolates a section of water main by raising or lowering a gate across the pipe: used fully open or fully closed.
- What is a fire hydrant?A fire hydrant is a valved connection to a water main for firefighting; operators also use it to flush mains and test flow in the distribution system.
- What is a blow-off valve?A blow-off is a valved drain at a low or dead-end point of a water main, used to flush out settled sediment and pull fresh water into the line.
- What is an air relief valve?An air relief valve automatically vents trapped air from the high points of a water main, where air would otherwise block flow or cause pressure surges.
- What is a water meter?A water meter measures the volume of water through a service line for billing, demand tracking, and spotting leaks when it registers flow with no use.
- What is a sanitary survey?A sanitary survey is an on-site review of a water system's sources, treatment, storage, and operations to find conditions that could affect drinking water safety.
- What is a curb stop?A curb stop is a small valve on a customer's service line near the property line, used to shut water off to one service without affecting neighbors.
- What is a water service line?A service line is the small pipe carrying water from the main to one customer's meter and building: the last connection between a property and the supply.
- What is an altitude valve?An altitude valve controls a storage tank's level, closing the inflow at a set height so the tank fills without overflowing and reopening as it drops.
- What is a standpipe (water storage)?A standpipe is a tall ground-based cylindrical water tank; its upper water adds pressure, acting like a cross between a ground and an elevated tank.
- What is a hydropneumatic tank?A hydropneumatic tank holds water and a cushion of compressed air that keeps the water pressurized, steadying pressure and reducing pump cycling on small systems.
- What is a booster pump?A booster pump adds pressure to water already in the distribution system, lifting it to higher ground or holding pressure in zones that would otherwise drop.
- What is a thrust block?A thrust block is concrete poured behind a bend, tee, or dead end of a pressurized main to resist the thrust force that would otherwise push joints apart.
- What is a vacuum breaker?A vacuum breaker admits air when pressure drops, breaking the suction that could siphon contaminated water back into the supply; common on hose bibbs.