activated sludge: Biomass produced by the growth of microorganisms in aerated reactors as a part of the secondary treatment process.
aeration: exposing to circulating air; adds oxygen to the wastewater and allows other gases trapped in the wastewater to escape (the first step in secondary treatment via activated sludge process.)
anaerobic: oxygen is not available in significant amounts.
biochemical oxygen demand(BOD): a laboratory measurement of oxidation in wastewater that is one of the main indicators of the quantity of pollutants present; a parameter used to measure the amount of oxygen that will be consumed by microorganisms during the biological reaction of oxygen with organic material.
biomass: mixed population of microorganisms contained in a bio-reactor as measured by the total suspended solids content.
biosolids: sludge that is suitable for beneficial use. Biosolids must meet certain government-specified criteria depending on it's use (e.g., fertilizer or soil amendment).
conventional treatment: treatment processes with established performance and capacities
decomposition: the process of breaking down (degrading) into constituent parts or elements
domestic wastewater: wastewater that comes primarily from individuals, and does not generally include industrial or agricultural wastewater
effluent: treated wastewater, flowing from a lagoon, unit operation basin, or treatment process
grit chamber: a chamber or tank used in primary treatment where wastewater slows down and heavy, large solids (grit) settle out and are removed
influent: untreated wastewater flowing into a treatment plant or partially treated wastewater flowing into a downstream unit operation
lagoons: (oxidation ponds or stabilization ponds): a wastewater treatment method that uses ponds to treat wastewater. Algae grow within the lagoons and utilize sunlight to produce oxygen, which is in turn used by microorganisms in the lagoon to break down organic material in the wastewater. Some wastewater solids settle in the lagoon, resulting in an effluent that is relatively well treated, although it does contain algae.
municipal: of, or related to a municipality (city, town, etc.). Municipal wastewater is primarily domestic wastewater.
non-conventional treatment: alternative or new treatment processes whose performance and capacity is not well established.
oxidation: biochemical decomposition of organic subtances in the presence of molecular oxygen, which produces and reduces BOD.
primary treatment: the first stage of wastewater treatment that removes settleable or floating solids only; generally removes 40% of the suspended solids and 30% of the BOD in the wastewater.
secondary treatment: a type of wastewater treatment used to convert dissolved and suspended pollutants into a form that can be removed, producing a relatively highly treated effluent. Secondary treatment normally utilizes biological treatment processes (activated sludge, trickling filters, etc.) followed by settling tanks and will remove approximately 85% of the BOD and TSS in wastewater. Secondary treatment for municipal wastewater is the minimum level of treatment required by the Federal Clean Water Act.
sedimentation: the process used in both primary and secondary wastewater treatment, that takes place when gravity pulls particles to the bottom of a tank ( also called settling).
settling basin (sedimentation tank or clarifier): a vessel in which solids settle out of water by gravity during wastewater or drinking water treatment processes.
sludge: any solid, semi-solid, or liquid waste that settles to the bottom of sedimentation tanks (in wastewater treatment plants or drinking water treatment plants) or septic tanks.
tertiary treatment: any level of treatment beyond secondary treatment, which include filtration, nutrient removal (removal of nitrogen and phosphorus) and removal of toxic chemicals or metals; also called "advanced treatment" when nutrient removal is included.
total suspended solids (TSS): a laboratory measurement of the quantity of suspended solids that are filtered from wastewater that is one of the main indicators of the presence of organic matter and biomass present in a treatment process.
trickling filter/biofilm process: a biological treatment process that uses coarse media (usually rock or plastic elements), contained in a tank, that serves as a surface on which a biofilm(attached microbiological growth) occurs on the media. Wastewater trickles over the media and microorganisms remove the pollutants (BOD and TSS). Trickling filters are followed by settling tanks to remove microorganisms that wash off and pass through the media.
turbidity: the cloudy or muddy appearance of a naturally clear liquid caused by the suspension of particulate matter that interferes with the transmission of light waves.
unit operation: each separate part of a treatment process.
wastewater: water that has been used for domestic or industrial purposes and contains substances that may interfere with water uses.