Aerobic Treatment: Is the use of air or oxygen to support biological conversion of organic material to carbon dioxide.  

Anaerobic Digestion: A process in which microorganisms break down biodegradable material in the absence of oxygen.  Anaerobic digestion produces: (1) methane-rich biogas that is suitable for renewable energy production, and (2) nutrient-rich effluent that can be used as fertilizer.

Biogas: Gas produced by anaerobic digestion of such waste materials as domestic, industrial, and agricultural sewage.  Biogas from domestic sludge digestion is typically comprised of approximately 2/3 methane and 1/3 carbon dioxide, with minor amounts of nitrogen gas, hydrogen sulphide, and siloxanes. Biogas can be collected and used as an energy source.

Biogas Cleaning: Removal of impurities from biogas, such as carbon dioxide, water, hydrogen sulphide, siloxanes, and particulates.

Biological oxygen demand or BOD: Oxygen consumed by wastewater sample at 20°C for 5 days.  BOD is a measure of the biodegradable organic strength of a wastewater sample.

Biomethane:  Biomethane is the methane from biogas less impurities removed by biogas cleanup. Biomethane is generally produced by collecting methane emitted from anaerobic digestion, landfill sites, or other forms of anaerobic degradation of organic matter.

Biosolids: A term used by industry to describe treated sludge which is a by-product from treating municipal wastewater in a wastewater treatment plant.

Combined heat and power or CHP: CHP uses a reciprocating engine or a power station to simultaneously generate both electricity and heat.

Class A Biosolids: A US EPA term that defines sludge that is stabilized, pathogen reduced, and low in metals content.

Class B Biosolids: A US EPA term that defines sludge with higher levels of pathogens and metals compared to Class A Biosolids.

Cell Disrupter:  Modified high pressure homogenizer used to break apart the cell membranes of microorganisms.

Cell Lysis:  The breaking apart of cell membranes of microorganisms to release cytoplasm.

Centistoke:  A measurement of viscosity.

Chemical Oxygen Demand or COD:  A measure of organic strength of a wastewater sample as determined by the consumption of chemical oxidizing agents.  

CMAD:  Conventional mesophilic (35 to 37°C) anaerobic digestion.

ETAD: Extended thermophilic (typically 50 to 55°C or 120 to 130°F) anaerobic digestion.

Footprint: Required equipment area at a wastewater treatment plant.

Fuel Cell: An electrochemical energy conversion device that produces electricity from various fuel types, such as hydrogen, methane, and alcohol.

GHG: Greenhouse gases are gases that contribute to global warming.  GHGs that are relevant to the wastewater treatment industry are carbon dioxide, methane, and nitrous oxide.

GHG Intensity: The amount of CO2 (or equivalent) generated by different fuel sources.  For example, electricity derived from natural gas has a GHG intensity of 0.431 kg CO2/kWh, and electricity derived from coal has a GHG intensity of 1.073 kg CO2/kWh.

Homogenizer: A high pressure pump and a special valve that is used in a number of industries to process liquids.  Paradigm has adapted this technology in developing the MicroSludge Cell Disrupter to break apart and liquefy microbes in waste activated sludge.

Hydraulic Retention Time or HRT: The number of days that sludge is held in the anaerobic digester.  HRT = Digester Volume /Flow Rate.  The lower the HRT, the greater the sludge throughput.

Hydrogen Sulphide: A chemical compound with formula H2S that is colourless, toxic, and has a distinctive odour of rotten eggs.  H2S is produced by bacterial break down of sulphur-containing organic matter in the absence of oxygen.

Land Application:  A disposal option for sludge from wastewater treatment plants.  Regulations dictate when, where, and how often sludge can be land applied.

Mesophilic Digester:  Mesophilic anaerobic digestion operates at temperatures between 20°C and about 40°, typically 37°C.

MicroSludge®: A patented process that uses a chemical (caustic) and high pressure to pre-treat WAS to improve both the rate and the extent of anaerobic digestion or aerobic stabilization.

Micro-turbines: Small combustion turbines that produce between 25 kW and 500 kW of power.  Typical micro-turbine biogas to electricity conversion efficiencies are 25 to 35%.  When used in a combined heat and power co-generation system, total thermal efficiencies of greater than 80% may be achieved.

N2O: Nitrous oxide is a major greenhouse gas that has 296 times greater impact on global warming than carbon dioxide.

Primary Treatment: Primary sewage treatment removes larger floating objects through screening and sedimentation. The incoming wastewater flows through one or more screens and then enters a grit chamber where it slows down enough to allow sand, gravel, and other inorganic matter to settle out. The sludge, or sedimentation of larger solids, is removed, dried, and disposed of. Primary treatment removes 50 to 65 percent of suspended solids and decreases biological oxygen demand (BOD) by 25 to 40 percent. Primary treatment alone is not considered adequate for protection of the environment or people's health.

Reciprocating engine:  An engine that uses pistons to convert pressure into a rotating motion.  At WWTPs, reciprocating engines burn cleaned biogas to produce electrical power and recoverable waste heat.

Secondary Treatment: A process to reduce the BOD of sewage or other wastewater by introducing air plus microorganisms to reduce its impact on receiving waters.

Siloxanes: Silica-based compounds are found in products such as cosmetics, deodorants, food additives, and some soaps that eventually end up in sewage.  When biogas from anaerobic digestion of sludge is combusted, siloxanes are produced, forming hard deposits on pistons and cylinder heads of combustion engines, causing fouling and damage to the engine.

Surplus Activated Sludge or SAS:  A term that is used in the UK for waste activated sludge (WAS).

Thermophilic digesters:  Anaerobic digestion that operates at temperatures above 50°C to produce biogas.

TWAS: Thickened waste activated sludge (see WAS below).

Waste Activated Sludge or WAS: Is the microbial cell waste by-product from secondary wastewater treatment.

WWTP: A wastewater treatment plant is a facility where physical, chemical, and biological processes are used to remove contaminants from wastewater to produce a treated liquid effluent that is suitable for discharge to the environment.

Viscosity: A measure of the resistance of a fluid which to stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity.

Volatile Organic Sulphur Compounds  or VOSCs: Are compounds produced from sulphur containing amino acids that are associated with the odours of sludge.