ABC Wastewater Treatment Class IV key terms

A number calculated from the volume occupied by settled activated sludge after 30 minutes divided by the mixed liquor suspended solids concentration, used to judge how well sludge settles and compacts.

The mass of organic food entering the aeration tank each day divided by the mass of microorganisms kept in the system; it guides how much sludge to waste and how much air to supply.

The average time, in days, that solids remain in the activated sludge system, calculated by dividing total solids inventory by the solids leaving each day; it controls sludge age and nitrification.

A condition in which thread-like bacteria grow excessively in activated sludge, producing a light, fluffy floc that settles slowly and can leave the clarifier with a high sludge blanket and poor effluent.

Very small, dense sludge particles that settle fast but stay suspended in the clarifier because they are too tiny to be captured, often appearing when the plant is young or lightly loaded.

The oxygen consumed per gram of volatile suspended solids per hour by a mixed liquor sample, measured in the lab; rising values suggest high organic loading while low values suggest toxicity or starvation.

A series of dissolved oxygen readings taken along the length of an aeration basin or at different depths; the pattern shows where oxygen demand is highest and whether mixing and airflow are adequate.

A biological treatment process in which wastewater is mixed with air and a community of bacteria and other organisms that consume organic matter, then separated in a clarifier and partly returned to the basin.

Sludge collected in the secondary clarifier and pumped back to the aeration tank to keep enough microorganisms in the process; operators adjust the rate to control sludge blanket depth and solids inventory.

A fill-and-draw activated sludge process in which one tank performs filling, aeration, settling, and decanting in timed steps rather than using separate basins and clarifiers.

An activated sludge system that uses submerged or external membranes instead of a clarifier to separate solids from water, producing high-quality effluent in a small footprint but requiring careful membrane cleaning and maintenance.

A fixed-film biological unit in which wastewater trickles over a bed of rock or plastic media coated with microorganisms that remove organic matter; it needs recirculation and good ventilation to work well.

A settling tank that follows biological treatment and separates the microorganism-rich sludge from the treated water, producing a clear overflow and a concentrated underflow returned or wasted.

A process that inactivates bacteria, viruses, and other pathogens by exposing treated water to ultraviolet light; effectiveness depends on water clarity, lamp intensity, and proper contact time.

Adding metal salts such as alum or ferric chloride so dissolved phosphorus forms particles that can be settled or filtered out, helping meet strict effluent limits and reduce algae growth downstream.

A heated, airless process in which bacteria break down sludge solids, reducing their volume and producing methane-rich biogas; it stabilizes biosolids and reduces pathogens and odors.

The percentage decrease in volatile solids achieved by digestion, calculated from feed and digested sludge samples; regulators use it to judge whether the process is meeting stabilization requirements.

A tank that concentrates sludge by letting solids settle to the bottom while supernatant flows over the top, reducing the volume that must be pumped to digesters or dewatering equipment.

Adding a synthetic long-chain chemical to sludge so small particles bind into larger, stronger flocs that release water more easily in dewatering devices, improving cake solids and solids capture.

A dewatering machine that squeezes conditioned sludge between moving belts and rollers to produce a transportable cake, with performance judged by cake solids and solids capture.

Recycling treated sewage sludge as a soil amendment on permitted farmland under pathogen and vector attraction reduction rules, with loading limits for metals and nitrogen.

Groundwater entering sewers through cracks and joints plus stormwater entering through illegal connections, roof drains, and manhole covers; high I&I overloads pump stations and treatment units during wet weather.

A chamber that receives incoming wastewater and stores it briefly so pumps can operate at a steady rate; its size and pumping cycle settings affect odor, solids settling, and pump wear.

A graph showing the flow and head a pump can produce; plotting it with the system curve shows the actual operating point and reveals whether a pump is running out of its efficiency range.

A specially shaped open channel with a narrowed throat that creates a measurable depth change; a staff gauge or sensor reading converted through a formula gives flow rate.

A discharge of untreated sewage and stormwater from a system that carries both in one pipe when heavy rain exceeds capacity; permitted CSOs need treatment, monitoring, and public notification.

The amount of dissolved oxygen consumed by microorganisms while breaking down organic matter in a sample held at 20 degrees Celsius for five days; it estimates the strength of the waste.

The mass of solid particles captured on a glass fiber filter after a measured volume of sample is filtered and dried at a specified temperature, reported in milligrams per liter.

A sample made by combining several portions collected at set times or flow intervals, giving a representative picture of wastewater quality over a shift or day rather than a single moment.

A statistical estimate of coliform bacteria density obtained by inoculating several tubes or wells with different sample volumes and observing which show growth and gas.

A written record tracking who collected, handled, and stored a sample from the field to the lab, preserving its legal defensibility for permits and enforcement actions.

A federal permit, usually administered by the state, that sets the allowable levels and monitoring requirements for pollutants discharged from a treatment plant to a receiving water.

A required periodic report summarizing sampling results, flow, and compliance status for each permit limit, signed by a responsible official and submitted by the deadline.

Entering a tank, vault, or pit with limited access and poor ventilation under a written permit, with atmospheric testing, attendants, rescue plans, and continuous communication required before and during the job.

A procedure that isolates hazardous energy sources with locks, tags, and verification so equipment cannot start or release energy while workers service or clear it.

A standardized document that lists a chemical's hazards, safe handling practices, first aid, and spill response, kept where workers can reach it during an emergency.

Scheduled inspections, lubrication, and part replacements performed on equipment before failure, based on manufacturer intervals or condition data, to reduce breakdowns and extend asset life.

Software that stores asset records, work orders, parts inventories, and maintenance histories, letting managers plan jobs and track costs and equipment reliability over time.

A structured method for finding the underlying reason an equipment failure, safety incident, or permit exceedance happened, so corrective actions address the real problem instead of a symptom.

A written, step-by-step instruction for performing a routine task consistently and safely, used for training and reference during operations, maintenance, and emergencies.