Wastewater Terms

Secondary Treatment

The wastewater that exits the primary clarifier has lost a significant amount of the particulate matter it contained, but it still has a high demand for oxygen due to an abundance of dissolved organic matter (measured as BOD).

Suspended-growth reactors

The organisms and wastewater are mixed together.

Attached-growth reactors

The organisms are attached to a support structure (medium), and the wastewater is passed over the organisms.

Homogeneous reactions

The reactants are distributed uniformly throughout the fluid so that the potential for reaction at any point within the fluid is the same. It can either be irreversible or reversible.

Heterogeneous reactions

Occur between one or more constituents that can be identified with specific sites, such as those on an ion-exchange resin and those that require the presence of a solid-phase catalyst.

Batch Reactor

Flow is neither entering nor leaving the reactor. The liquid contents are mixed thoroughly.

Plug-flow or Tubular flow

Fluid particles pass through the tank and are discharged in the same sequence in which they enter. The particles retain their identity and remain in the tank for a time equal to the theoretical detention time. This type of flow is approximated in long tanks with a high length-to-width ratio in which longitudinal dispersion is minimal or absent.

Continuous-flow stirred tank reactor (CFSTR)

The reactants entering the reactor (which are dispersed immediately) and the products flowing out from the reactor are considered as continuous.

Arbitrary Flow Reactor

Is any degree of partial mixing between plug-flow and complete-mix.

Packed Bed Reactor

Are filled with inert packing media for the growth of biomass. Wastewater flows continuously in and out of the reactor. This reactor is used for attached growth treatment systems.

Fluidized Bed Reactor

Is filled with the packing material that expands and gets fluidized when wastewater moves upward in the reactor. It is a combination of attached growth and suspended growth.

FBR - Captor

Biomass is grown inside polyester foam pads and pads can be periodically removed and biomass can be squeezed. Oxygenation is achieved using simple sparger.

FBR - Oxitron

Sand particles are used as a support medium, sand is allowed to overflow and is cleaned and then recycled. Oxitron uses a high purity oxygen dissolved into an influent stream.

Activated Sludge Process

It is a biological wastewater treatment process which speeds up waste decomposition. Activated sludge is added to wastewater, and the mixture is aerated and agitated. It is the most common biological treatment system.

Activated Sludge

Sludge particles produced in wastewater by the growth of organisms in aeration tanks. The term 'activated' comes from the fact that the particles teem with bacteria, fungi, and protozoa.

Synthesis

A process wherein microorganisms derive energy from carbonaceous organic matter in aerated wastewater for the production of new cells.

Respiration

Releasing energy through the conversion of this organic matter into compounds that contain lower energy, such as carbon dioxide and water.

Nitrification

Microorganisms obtain energy by converting ammonia nitrogen to nitrate nitrogen.

Aeration Tanks/s

Where the biological reactions occur.

Aeration Source

May be provided by pure oxygen, compressed air or mechanical aeration that provides oxygen and mixing.

Secondary Clarifier

Activated-sludge solids separate from the surrounding wastewater by the process of flocculation and gravity sedimentation.

RAS (Returned Activated Sludge) System

RAS must be collected from the secondary clarifiers and pumped back to the aeration tank(s) before dissolved oxygen is depleted.

WAS (Waste Activated Sludge) System

Activated sludge containing an overabundance of microorganisms must be removed, or wasted w/ the use of a pump.

Mixed Liquor

The mixture of activated sludge and the wastewater in the aeration tank.

Mixed Liquor Suspended Solids (MLSS)

The concentration of suspended solids in activated-sludge mixed liquor expressed in mg/L.

Mixed Liquor Volatile Suspended Solids (MLVSS)

The fraction of the suspended solids in activated sludge mixed liquor that can be driven off by combustion at 550oC which indicates the concentration of microorganism available for biological oxidation, expressed in mg/L. 60 - 80% of MLSS is MLVSS.

Mean Cell Residence Time (MCRT)

Also called solids retention time (SRT), is the average amount of time that microorganisms are kept in the system. Also called the sludge age.

Jet Aeration

Oxygen transfer efficiency is accomplished by mixing pressurized air and water within a jet nozzle and then discharging the air-liquid into the tank.

Mechanical Surface Aerators

Oxygen is entrained from the atmosphere.

Mechanical Submerged Aerators

Oxygen is entrained both from atmosphere and from air or pure oxygen introduced at the bottom of the tank.

Diffusers

Designed to produce fine, medium, or coarse (relatively large) bubbles.

Aerobic

A condition where oxygen is present.

Biological Oxygen Demand (BOD)

Measure of oxygen organic material in the water requires.

Bulking

Sludge that forms clouds in the secondary clarifiers when the sludge does not settle properly, usually caused by filamentous bacteria.

Carbonaceous BOD Removal

Biological conversion of the carbonaceous organic matter in wastewater to cell tissue and various gaseous end products. In this conversion, it is assumed that the nitrogen present in various compounds are converted to ammonia.

F:M

Food to Microbe Ratio.

Floc

Clumps of bacteria.

Flocculation

Agitating wastewater to induce the small, suspended particles to bunch together into heavier particles (floc) and settle out.

Loading

A quantity of material added to the process at one time.

Package Plant

Pre-manufactured treatment facility small communities or individual properties use to treat wastewater.

Substrate

The term used to denote the organic matter or nutrients that are converted during biological treatment or that may be limiting in biological treatments.

Supernatant

The liquid that is removed from settled sludge. It commonly refers to the liquid between the sludge on the bottom and the scum on the surface.

Wasting

Removing excess microorganisms from the system.

Obligate aerobes

Are microorganisms that must have oxygen as the terminal electron acceptor. When wastewater contains oxygen and can support obligate aerobes, it is called aerobic.

Obligate anaerobes

Are microorganisms that cannot survive in the presence of oxygen. They cannot use oxygen as a terminal electron acceptor. Wastewater that is devoid of oxygen is called anaerobic.

Facultative anaerobes

Can use oxygen as the terminal electron acceptor and, under certain conditions, they can also grow in the absence of oxygen.

Anoxic microorganisms

A group of facultative anaerobes called denitrifiers utilizes nitrite (NO2) and nitrates (NO3) as the terminal electron acceptor.

Anoxic denitrification

The process wherein Nitrite nitrogen is converted to nitrogen gas in the absence of oxygen.

Nitrosomonas

Bacteria convert Ammonia (NH3) Nitrogen to Nitrite (NO2) Nitrogen.

Nitrobacter

Bacteria convert Nitrite (NO2) Nitrogen to Nitrate (NO3) Nitrogen.

Phototrophs

Are able to use light as an energy source. They can be either autotrophic or heterotrophic.

Chemotrophs

Chemical reactions (redox) as an energy source.

Chemoautotrophs

Obtain energy from the oxidation of reduced inorganic compounds such as NH3, NO2, Fe, and SO2.

Chemoheterotrophs

Obtain energy from the oxidation of organic compounds.

Metabolism

Refers to all the chemical reactions occurring within a cell. The reactions are referred to as metabolic reactions.

Metabolite

Any molecule that is a nutrient, an intermediary product, or an end product in a metabolic reaction.

Catabolism

Involve the breaking of bonds; whenever chemical bonds are broken, energy is released.

Anabolism

Involve the creation of bonds; it takes energy to create chemical bonds.

Biochemical Pathways

A series of linked biochemical reactions that occur in a stepwise manner, leading from a starting material to an end product.

Respiratory Metabolism (Aerobic Respiration)

Organisms that generate energy by enzyme-mediated electron transport to an external electron acceptor.

Respiratory Metabolism

Organisms that generate energy by enzyme-mediated electron transport to an external electron acceptor.

Aerobic Respiration

When oxygen is used for the electron acceptor in respiratory metabolism.

Fermentative Metabolism

An internal electron acceptor is used and it is a less efficient energy yielding process compared to respiration.

Anaerobic Reactions

Reactions involving internal/other electron acceptors.

Enzymes

Organic catalysts produced by the living cell, which can either cause chemical reactions to occur or accelerate them.

Hydraulic Load

The amount of water entering the aeration tank.

Return Sludge Requirement

To maintain a sufficient concentration of activated sludge in the aeration tank for the required degree of treatment.

Sludge Blanket

The accumulation of settled sludge in the clarifier, ideally in the lower quarter of the clarifier.

Rotifers and Nematodes

Microorganisms most frequently found in systems with long aeration periods.

Amoeboids

Predominate in 'young' sludges, such as at plant start-up or after an upset.

Flagellates

Free-swimmers that predominate in light mixed liquors during high food to microorganism conditions.

Free-swimming Ciliates

Predominate as the F:M ratio decreases.

Stalked Ciliates

Predominate when there is an abundance of bacteria, typically indicating best effluent and sludge quality.

Filamentous Bacteria

Can cause sludge not to settle properly, leading to bulking.

Conventional Plug-flow Activated Sludge

Air application is uniform throughout the tank length.

Tapered Aeration

Diffusers are spaced close together to achieve a high oxygenation rate.

Step Aeration

Settled wastewater is introduced at several points in the aeration tank to equalize F/M ratio.

Modified Aeration

Identical with conventional or tapered aeration, but uses shorter aeration times (1.5 to 4 hours).

Contact Stabilization

The mixed liquor is settled in a secondary settling tank and RAS is aerated separately (3-6 hours) in a reaeration basin.

Extended Aeration

Identical with conventional plug-flow process except it operates in the endogenous respiration phase.

High Rate Aeration

Process modification in which high MLSS concentrations are combined with high volumetric loadings.

Oxidation Ditch

An extended aeration process consisting of a ring- or oval-shaped channel equipped with mechanical aeration devices.

Krauss Process

Aerating the supernatant from the sludge digesters for approx. 24 hours converting NH3 to NO3.

Carousel Process

Vertically mounted mechanical aerators are used to impart oxygen and prevent settling of solids.

High Purity Oxygen

Pure oxygen used as a substitute for air in the activated sludge process.

Sequential Batch Reactor (SBR)

A 'fill and draw' activated sludge process for wastewater treatment.

Attached Growth Process

Utilize a solid medium on which bacterial solids are accumulated in order to maintain a high population.

Trickling Filters

Consist of a bed of highly permeable media to which are attached and through which wastewater is percolated or trickled.

Rotating Biological Contactors (RBC)

The surface of the disk is covered with a biological slime similar to that on the media of a trickling filter. This means that about 40% of the total surface area of the disks is always submerged.

Packed Bed Reactor (PBR)

The catalyst pellets are held in place and do not move with respect to a fixed reference frame.

Advanced Waste Treatment

Treatment technology used to produce an extremely high quality discharge.

Average Monthly Discharge

Limitation the highest allowable discharge over a calendar month.

Average Weekly Discharge Limitation

The highest allowable discharge over a calendar week.

Buffer

A substance or solution which resists changes in pH.

Chemical Oxygen Demand (COD)

The amount of chemically oxidizable materials present in the wastewater.

Clarifier

A device designed to permit solids to settle or rise and be separated from the flow. Also known as a settling tank or sedimentation basin.

Coliform

A type of bacteria used to indicate possible human or animal contamination of water.

Combined Sewer

A collection system that carries both wastewater and stormwater flows.

Comminution

A process that shreds solids into smaller, less harmful particles.

Composite Sample

A combination of individual samples taken in proportion to flow.