ABC Biological Industrial Waste Treatment Operator key terms

A laboratory measure of the oxygen consumed by microorganisms while breaking down organic matter in a water sample over a set incubation period, usually five days. It estimates how much biodegradable pollution the wastewater carries.

A test that measures the oxygen equivalent of organic and some inorganic material oxidized by a strong chemical oxidant. It is faster than BOD and includes matter that microorganisms cannot easily degrade.

The concentration of solid particles suspended in water that can be captured on a filter and dried to constant weight. TSS drives solids loading on treatment units and is a common effluent permit limit.

The portion of suspended solids that burns off when a dried sample is ignited at high temperature, approximating the organic or biological fraction. Operators use it to estimate active biomass in mixed liquor.

The ratio of organic food entering an aeration basin, expressed as BOD or COD mass per day, to the mass of microorganisms present in the basin. It guides how much sludge to waste and how to control aeration.

The average length of time microorganisms remain in the treatment system, calculated from the mass of solids in the aeration basin divided by the mass leaving daily in waste and effluent. Also called solids retention time.

The average time wastewater spends inside a treatment unit, found by dividing the unit's volume by the flow rate through it. HRT affects how completely biological reactions can proceed.

The concentration of solids, mostly microorganisms and inert material, suspended in the aerated biological reactor. Operators monitor it to set wasting rates and keep the process in balance.

The organic, mostly living fraction of the solids in the aeration basin, determined by igniting a filtered sample. It is often used as a closer estimate of active biomass than total MLSS.

A calculated number describing how well activated sludge settles, based on the settled volume of a mixed liquor sample after thirty minutes relative to its suspended solids concentration. High values suggest poor settling.

A simple bench procedure in which a mixed liquor sample sits in a graduated cylinder for a set time and the settled sludge volume is read. It gives a quick picture of sludge settling behavior.

A condition where long, thread-like bacteria dominate the sludge, producing a loose floc that settles slowly and can escape in the effluent. It often follows low oxygen, low nutrient levels, or high organic loading.

Very small, weak floc particles that do not settle or compact well and tend to carry over into the effluent. It can result from young sludge age, low organic loading, or sudden changes in conditions.

Settled biological solids collected in the secondary clarifier and pumped back to the aeration basin to maintain the desired microorganism population. The return rate is adjusted to control sludge blanket depth.

Excess biological solids deliberately removed from the treatment system to control sludge age and keep the biomass at a healthy level. Wasting rate is a primary lever for process control.

The layer of settled solids that accumulates on the bottom of a clarifier. Its depth is measured regularly so solids are not carried over the weirs or left too long to go septic.

The settling tank following biological treatment where microorganisms are separated from the treated water. It produces a clear overflow and a concentrated underflow that is returned or wasted.

The tank where wastewater and microorganisms are mixed and oxygen is supplied so aerobic bacteria can consume organic matter. Its volume, mixing, and oxygen levels strongly influence treatment performance.

The concentration of oxygen gas dissolved in the water, usually reported in milligrams per liter. Aerobic treatment requires enough DO to keep microorganisms active without wasting energy on excess aeration.

A portion of a biological system kept free of dissolved oxygen but containing chemically bound oxygen such as nitrate. It supports organisms that convert nitrate to nitrogen gas, removing nitrogen from the water.

The biological conversion of ammonia to nitrite and then to nitrate by specialized bacteria, which consumes oxygen and alkalinity. It is sensitive to temperature, pH, and toxic shocks.

The biological reduction of nitrate to nitrogen gas, carried out by bacteria in low-oxygen conditions with a suitable carbon source. It removes total nitrogen and can release gas that affects clarifier settling.

A biological treatment process in which a mixed community of microorganisms is kept suspended in aerated wastewater and then separated in a clarifier, with solids returned to the reactor. It is the most common secondary treatment method.

A fixed-film biological reactor in which wastewater flows over a bed of media coated with a microbial slime layer. Air moves through the bed to supply oxygen while the biofilm treats the water.

A fixed-film system of closely spaced disks that rotate partly submerged in wastewater, alternately contacting the water and the air. A biofilm grows on the disks and treats the organic matter.

A thin layer of microorganisms and their secretions attached to a solid surface such as media or pipe walls. In fixed-film treatment the biofilm does the biological work, and its thickness affects performance.

A pond treatment system with an aerobic upper layer, an anaerobic bottom layer, and an intermediate zone where both types of organisms operate. Sunlight, wind mixing, and algae help supply oxygen.

The mass of organic material applied to a treatment unit per unit of volume or surface area per day. It helps predict whether a biological system can keep up with the incoming waste strength.

A sudden, large increase in flow, organic strength, or toxic material entering a treatment plant. It can overwhelm biological treatment, cause permit violations, or kill the microbial population.

A holding tank that stores and blends industrial wastewater so flow and strength reach the treatment plant at a steadier rate. It protects biological processes from swings and spikes.

Physical, chemical, or biological steps applied at an industrial facility to reduce or remove pollutants before wastewater is discharged to a treatment plant or sewer. It protects the collection system and treatment organisms.

The harmful effect a substance has on living organisms, including the microorganisms that perform biological treatment. Toxic shocks can reduce treatment efficiency and may require reseeding or recovery time.

A material that slows or stops biological activity without necessarily killing the organisms outright. Heavy metals, solvents, and extreme pH are common examples in industrial wastewaters.

Adding acid or base to bring wastewater into a range where biological treatment and chemical processes work properly. It also protects pipes and equipment from corrosion or scaling.

The water's capacity to neutralize acid, mainly from bicarbonate and carbonate. It is consumed during nitrification and helps keep pH stable in biological treatment.

Removing water from sludge to reduce its volume before hauling or disposal, often using presses, centrifuges, or drying beds. It lowers transport and disposal costs and affects cake quality.

Concentrating sludge by gravity or mechanical means to increase its solids content before further treatment. It reduces the volume that downstream dewatering and digestion equipment must handle.

A biological process in which microorganisms break down sludge in the absence of oxygen, producing biogas and reducing volatile solids. It stabilizes biosolids and reduces odors and pathogen levels.

Treated sewage sludge that meets regulatory quality standards for beneficial use, such as land application. Its handling is governed by pathogen and pollutant limits.

The amount of chlorine remaining in treated water after the initial demand is satisfied, which provides ongoing disinfection. Operators measure it to confirm dose adequacy and protect aquatic life before discharge.

Removing or neutralizing leftover chlorine from treated effluent before discharge, often with sulfur-based chemicals. It protects fish and other aquatic organisms from chlorine toxicity.

A group of bacteria used as indicators of fecal contamination and overall disinfection effectiveness. Their presence in effluent suggests treatment or disinfection problems.

A sample made by combining several portions collected over time or across a flow, often proportional to flow. It better represents average conditions than a single grab sample.

A single portion of water collected at one place and time. It is useful for monitoring changing conditions or parameters that cannot be held, but it captures only a snapshot.

A written record tracking who collected, handled, and stored a sample from collection through analysis. It preserves the legal defensibility of monitoring results.

An enclosed area with limited entry and exit that is not designed for continuous occupancy and may contain hazardous atmospheres. Entry requires testing, permits, and attendants under safety rules.

A toxic, flammable gas with a rotten-egg odor produced by anaerobic decomposition of organic matter. It can deaden the sense of smell at higher concentrations and is a serious hazard in wet wells and digesters.

A safety procedure that isolates energy sources and applies locks and warning tags before maintenance or repair. It prevents unexpected startup or release of stored energy that could injure workers.