ABC Wastewater Treatment Class II key terms

A written authorization listing hazards, atmospheric test results, isolation steps, attendants, and rescue provisions required before a worker enters a space with limited entry and exit that is not designed for continuous occupancy.

Testing the air inside a confined space or work area for oxygen content, combustible gases, and toxic gases such as hydrogen sulfide before entry and continuously while occupied.

Contact with the toxic, corrosive gas formed by anaerobic decomposition of sulfur-bearing wastes; it deadens the sense of smell at higher concentrations and can cause unconsciousness or death.

A procedure for de-energizing equipment, applying personal locks and tags, and verifying zero energy so machinery cannot start or release stored energy during maintenance or repair.

Clothing and gear such as gloves, eye protection, respirators, and boots worn to shield a worker from chemical, biological, and physical hazards at the plant.

A device with rotating cutting teeth that shreds rags and large solids in the incoming flow so downstream pumps and pipes are less likely to clog.

A row of parallel bars placed in the influent channel that traps large debris such as rags, sticks, and plastics while allowing wastewater to pass through.

The process of settling out heavy, abrasive material like sand, gravel, and eggshells in a grit chamber so it does not wear pumps or accumulate in downstream tanks.

A settling tank that removes settleable solids and floating material from raw wastewater by gravity, producing primary sludge and partially clarified overflow.

The average length of time water spends in a tank or process, calculated by dividing the tank volume by the flow rate; often expressed in hours.

A suspended-growth process in which a mixed population of microorganisms consumes organic matter in an aerated tank, and the biomass is separated from the treated water in a clarifier.

The concentration of biological solids suspended in the aeration tank, measured by filtering and drying a sample; it represents the working biomass of the activated sludge process.

Biomass settled in the secondary clarifier and pumped back to the aeration tank to maintain the desired concentration of organisms in the mixed liquor.

Excess biomass deliberately removed from the activated sludge system to control the solids inventory and prevent overloading the secondary clarifiers.

The average time biological solids remain in the treatment system, calculated by dividing the mass of solids in the aeration tank by the mass leaving each day; also called sludge age.

The pounds of organic food entering the aeration tank per day divided by the pounds of microorganisms present; a key control value for loading and sludge production.

A settling test value found by dividing the settled sludge volume after 30 minutes, in milliliters per liter, by the mixed liquor suspended solids concentration and multiplying by 1,000; high values suggest poor settling.

Sludge that settles poorly and compacts to a low density, often because of filamentous organisms, causing solids to carry over the secondary clarifier weirs.

An attached-growth process in which wastewater trickles over a bed of media coated with a biological film that consumes organic matter, followed by a clarifier to capture sloughed solids.

An attached-growth system of closely spaced disks that rotate partly submerged in wastewater, letting a biological film grow on the wetted surfaces and contact both wastewater and air.

The amount of chlorine consumed by organisms, ammonia, and other reducing substances in the water before any free chlorine residual can remain.

The concentration of chlorine remaining in treated water after the demand has been satisfied; it provides the measurable disinfection safeguard in the effluent.

The period during which disinfectant and wastewater remain in contact, commonly measured as the detention time in the chlorine contact basin; adequate time is needed for effective kill.

A group of organisms used as indicator bacteria in wastewater testing; their presence in effluent signals that disinfection is incomplete or that contamination has occurred.

A subset of coliform bacteria originating in the intestines of warm-blooded animals, used as a regulatory indicator of sewage pollution and disinfection effectiveness.

A solids-handling step that concentrates sludge by removing free water, reducing the volume that must be pumped, digested, or dewatered downstream.

A tank where sludge is allowed to settle and compact under its own weight, with clarified supernatant drawn off the top and concentrated sludge removed from the bottom.

A thickening or clarification process in which fine air bubbles attach to suspended solids and float them to the surface for removal by skimming.

Mechanical or physical removal of water from sludge to produce a drier cake that is easier and cheaper to haul, land-apply, or dispose of.

A dewatering machine that conditions sludge with polymer, drains free water on a moving belt, and squeezes the remaining solids between rollers to form cake.

A dewatering device that spins sludge at high speed so centrifugal force separates dense solids from water, yielding a cake and a centrate stream.

Adding a synthetic organic chemical to sludge so fine particles bind into larger flocs that release water more readily during thickening or dewatering.

A process in which microorganisms break down sludge in the absence of oxygen, reducing volatile solids and producing biogas, with stages including hydrolysis, acid formation, and methane formation.

The percentage decrease in volatile solids achieved by digestion, calculated from the volatile solids entering and leaving the digester; a measure of digestion performance.

The mixture of methane and carbon dioxide produced during anaerobic digestion, which can be burned for heat or power but must be handled with care because it is flammable and can displace oxygen.

A pump that uses a spinning impeller to impart velocity and pressure to liquid, moving it from a lower level or lower pressure to a higher one.

Formation and collapse of vapor bubbles in a pump when suction pressure drops too low, producing noise, vibration, and damage to the impeller and casing.

The margin of absolute pressure above the liquid's vapor pressure at the pump suction; insufficient margin allows cavitation to occur.

A graph showing how a pump's head and flow rate relate, used with the system curve to predict the operating point of the pump.

Scheduled inspection, lubrication, adjustment, and replacement of parts performed before failure occurs, intended to keep equipment reliable and reduce unplanned downtime.

Monitoring the vibration signature of rotating equipment to detect imbalance, misalignment, worn bearings, or other developing faults before they cause failure.

A sample made by combining portions collected at intervals or in proportion to flow, giving a representative picture of conditions over a period rather than at one instant.

A single portion of wastewater collected at one time and place, used when conditions change quickly or when only an instantaneous value is needed.

A written record documenting who collected, handled, and transported a sample, and when, so its integrity can be defended in regulatory or legal proceedings.

The amount of oxygen microorganisms consume while breaking down organic matter in a sample under controlled conditions, commonly over five days; it indicates the strength of the waste.

The mass of solids captured on a filter when a measured sample is filtered, dried, and weighed; a primary measure of effluent quality and treatment performance.

A regulatory permit that sets effluent limits, monitoring requirements, and reporting obligations for a facility that discharges treated wastewater to surface waters.

A periodic report submitted to the regulatory agency summarizing monitoring results, exceedances, and operating data as required by the facility's discharge permit.

The required notification to regulators when untreated or partially treated wastewater is diverted around a treatment unit, including the volume, duration, and cause.