General Terms


Single-celled microorganisms that lack chlorophyll. Some bacteria are capable of causing human, animal or plant diseases; others are essential for the decomposition of organic matter in soils, in secondary wastewater treatment, and in digestive processes in animals.


Essential element

An element that is required by all organisms in order to survive and reproduceA


Heavy metal

Metallic elements whose densities are equal to or greater than 5.0 g/cm3 including, but not limited to chromium, lead, zinc, copper, cadmium, mercury, nickel, silver, and iron. Some heavy metals are required in trace concentrations for all animal and plant life. These include manganese, iron, copper, zinc, and molybdenum. Others like cadmium, mercury, and lead can be toxic to living organisms. Still others have no known effects on living organisms.



An essential element needed in large amounts by a plant or animal in order to survive and reproduce. Plant macronutrients include nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, carbon, hydrogen and oxygen.


Microconstituent/trace organic compounds

Any orgnanic compound (usually from pharmaceuticals, personal care products, and other chemicals), detected in biosolids in extremely small amounts, usually several parts per million (mg/kg, or approximately 1 drop of water in a 10 gallon fish tank) or less.



An essential element needed in very small amounts by a plant or animal in order to survive and reproduce. Plant micronutrients include iron, boron, manganese, zinc, copper, chloride, cobalt, and molybdenum. Soils that have had a lot of agricultural use or synthetic fertilizer use often lack micronutrients.



A microscopic organism, especially a bacterium, virus, or fungus.



An essential element needed in certain amounts by plants or animals in order to survive and reproduce.



Any microorganism that has the potential to cause disease, including pathogenic bacteria, viruses, helminths, and protozoans. These may include certain fungi.



Results when contaminants in human, animal, vegetable, mineral, chemical or thermal waste or discharges reach water, making it less desirable for domestic, recreation, industry, or wildlife uses.


Priority pollutants

A group of chemicals specifically listed in the Code of Federal Regulations (40 CFR 423, Appendix A; 40 CFR 122 Appendix D) given priority for regulatory control by the Environmental
Protection Agency.


Trace metal

Any metallic element found in biosolids in extremely small amounts. Trace metals are micronutrients for plants, although not all micronutrients are metals.



The smallest of the microorganisms, often capable of causing disease, these are obligate parasites composed of a nucleic acid (RNA or DNA) core and a protein coat. They cannot grow or reproduce outside a host organism.


Volatile organic compounds (VOC’s)

VOC’s are emitted as gases from certain solids or liquids found in a wide array of products, including fuels, solvents, and degreasers; paints, paint strippers, and wood preservatives; household products, cleansers and disinfectants.


Treatment process

Aerobic digestion

The decomposition of organic matter (plant and animal material) by microorganisms with the presence of oxygen.


Anaerobic digestion

The decomposition of organic matter (plant and animal material) by microorganisms, without the presence of oxygen. Anaerobic digestion of wastewater solids takes place in tanks where the solids are decomposed by anaerobic bacteria and converted to biogas and a semi-solid biosolids product. Anaerobic digestion also typically reduces viruses and pathogens by 90 percent or more.



Is the natural biological decomposition of organic material in the presence of air to form a stabilized, humus-like material.



Any of several processes used to remove water from biosolids in order to reduce its volume and weight prior to recycling. These processes may include evaporation, passage through a belt filter press that squeeze water out of biosolids, or centrifuging which drives water out by spinning, much as water is driven out of clothes during the “spin” cycle of a clothes washing machine.



Digestion of solids takes place in heated tanks where microorganisms break down material.



The use of chemicals to kill any disease causing organisms in the polished wastewater. UV light can also be used.



Involves combustion of the organic matter in sewage sludge, producing a residual inert ash that generally must be landfilled.



Is a shallow pond in which algae, aerobic and anaerobic bacterial purify wastewater.


Mesophilic digestion

Biological degradation process where the temperature in the digester is maintained within the range of 85-100oF (30-38oC).



Is a disinfection process where ozone is generated and added to wastewater effluent to kill pathogenic organisms.



Use of processes to remove or reduce pollutants from non-domestic wastewater before discharging it to the wastewater conveyance system. Also referred to as source control.


Primary treatment

The first phase of wastewater treatment in which solids are removed through gravitational settling.


Secondary treatment

The second phase of wastewater treatment that uses aeration (adds oxygen through mixing) and microorganisms to further remove dissolved and suspended organic matter remaining in wastewater after primary treatment.


Tertiary treatment

A third phase of wastewater treatment in which most of the remaining pollutants are removed from effluent (water) following secondary treatment. The processes used can include sand filtration and membrane filtration.


Thermophilic digestion

Biological degradation process where the temperature in the digester is maintained within the range of 120-140oF (50-60oC).


Ultraviolet Disinfection (UV)

The use of ultraviolet light to kills bacteria and other microorganisms in water and wastewater. Typically a final treatment step.




Milligram per kilogram; equivalent to a part per million.



Million Gallons per Day – 694.4 gallons per minute.



A measure of acidity or alkalinity of water, or any given substance. The scale is 1 to 14 with 7 being neutral. Over 7 is alkaline or caustic, under 7 is acid or base.



Part per million, equivalent to a milligram per kilogram dry weight. One part per million (ppm) is approximately equal to one drop of water in a 10 gallon fish tank.
For reference:

  • ppb: part per billion is approximately equal to one drop of water in average sized swimming pool.
  • ppt: part per trillion is approximately equal to one drop of water in an Olympic sized swimming pool.



The treated solids taken out of the used water that goes down toilets and drains to the wastewater treatment plant. Finished biosolids have been cleaned and stabilized to destroy pathogens and meet rigorous standards allowing for safe reuse of this material as a soil conditioner and fertilizer replacement. Biosolids are a rich, soil-like product made mostly of water, sand, organic matter (plant and animal material), and microorganisms.


Biosolids beneficial use

Using biosolids on land as a soil conditioner or fertilizer replacement to build the soil and improve plant growth in way that protects human health and the environment.


Class A biosolids

The Environmental Protection Agency (EPA) designation for biosolids that are pathogen free and available for the public for general use in landscaping or gardening.


Class B biosolids

The EPA designation for high quality biosolids that have been treated to remove 95-99% of pathogens, a level deemed safe for land application (the remaining pathogens die quickly from sunlight, heat, and competing microorganisms) Class B biosolids have site management, harvest, and access rules and are only available to permitted sites.



The final water flowing out of a wastewater treatment plant.


Exceptional quality (EQ) biosolids

Biosolids that are pathogen free, are below federal standards for metals (40 CFR Part 503.13 Table 3), and meet certain treatment requirements that make the biosolids less likely to attract disease spreading organisms such as mosquitos and flies.



A produced used to add nutrients to the soil for increased plant growth.



Fats, soaps, oils, waxes and etc. in wastewater.



Wastewater flowing into a treatment plant.


Land Application

The controlled application of wastewater or biosolids onto the ground for use as a fertilizer replacement or soil conditioner.


Organic Matter

The carbon-based material contained in plants or animals and plant and animal wastes.


Raw Sewage

Untreated sanitary wastewater from human and domestic use such as toilets and drains.


Reclaimed/Recycled Water

Water that has been treated to such a high standard it can be reused for many non-potable (non-drinking water) uses, such as irrigation, street cleaning, or industrial use. Water can be treated to different levels (called Classes, A-D) and the Class determines which uses are allowed and what regulations apply.


Sewage sludge

Refers to the solids separated during the treatment process of municipal wastewater. Includes domestic septage (such as from septic tanks). Sewage sludge becomes biosolids when the treatment process is complete and the product can be used as a soil conditioner and fertilizer replacement.


Soil amendment/soil conditioner

A product used to add nutrients and organic matter to the soil to build the soil and improve it.



Water that has been previously used in homes, businesses or industry and is cleaned and treated before it can be reused as biosolids (solid portion) or recycled water (water portion) or returned to surface waters.