Glossary of Terms


  • Aerobic digestion – The decomposition of the organic matter in sewage sludge by micro-organisms into carbon dioxide and water, in the presence of oxygen.
  • Agronomic Rate – The rate at which biosolids can be applied which meets the nutrient requirements of a crop while preventing contamination of the soil, ground and surface waters.
  • Anaerobic digestion – The decomposition of the organic matter in sewage sludge by micro-organisms into methane, carbon dioxide and water, in the absence of oxygen.
  • ANZBP – Australian New Zealand Biosolids Partnership.


  • Beneficial Use – The use of biosolids for any purpose which provides benefit without harming or threatening public health and safety or the environment.
  • Biosolids – Sewage sludge that has been treated to reduce or eliminate health risks and improve beneficial characteristics. Biosolids are nutrient rich and may be suited to a range of beneficial uses in agriculture and other applications.
  • Blending – Mixing of several products to form one product.
  • Buffer zone – An area of vegetated land between an area of biosolids application and a drainage line, creek, river or sensitive area.


  • CFU – Colony Forming Unit (of faecal coliform bacteria) – A measure of viable bacterial or fungal numbers.
  • Classification – The process of assigning biosolids products into classes based on their quality. These classes vary from state to state. See individual state guidelines (Guidelines and regulations) for state specific classes. See also grading
  • Composting – A process in which solid organic materials are broken down by micro-organisms in the presence of oxygen. Biosolids are mixed with sawdust, wood chips or other organic material. High temperatures generated during this process kill harmful micro-organisms. A rich, soil-like product is the end result.


  • Dewatering, dewatered biosolids – A process which reduces the water content of liquid biosolids and produces a solid, spadeable product, typically in the range 15-35% solids content.
  • Digestion – See anaerobic or aerobic digestion.
  • Disposal – Method of final clearance of biosolids that does not provide any beneficial use, for example disposal of biosolids to landfill.


  • E. coli (or Escherichia coli) – Escherichia coli is a bacterium that is commonly found in the lower intestine of warm-blooded animals. Most E. coli strains are harmless. E. coli are not always confined to the intestine, and their ability to survive for brief periods outside the body makes them an ideal indicator organism to test environmental samples for faecal contamination.
  • EIP – Environmental Improvement Plan. A document prepared in accordance with the requirements of an environmental regulator which sets out how biosolids are to be beneficially used in a sustainable manner.
  • EMP – Environment Management Plan – A manual which sets out procedures to ensure that the environment is protected.
  • Endocrine disruptor – Endocrine disruptors are substances that act like hormones in the endocrine system and disrupt the physiologic function of people or animals.
  • Endocrine system – The endocrine system is a group of glands that work together and secrete many types of different hormones that regulate the body.


  • Faecal coliform – Faecal coliforms include a range of micro-organisms which originate in faeces. Presence of faecal coliforms indicates the potential presence of faeces.


  • Grading (contaminant grade, stabilisation grade) – See classification.
  • Groundwater – Water found below the Earth’s surface.


  • Incorporation – Mixing biosolids with the soil, for example by injection, ploughing, roto-tilling or tandem disc harrowing.
  • Inorganic fertiliser – Fertilisers are products which contain primary nitrogen, phosphorus and potassium to help plants grow. Inorganic fertilisers are mined or synthesised chemical fertilisers.


  • Land application – Application of biosolids to land.
  • Leaching – The process by which soluble matter is dissolved in water and carried downward and radially through the soil.
  • Liquid biosolids – Biosolids which is in a liquid form, generally containing less than 8% solids and most commonly with 2-5% solids.


  • Macro-nutrients – Essential elements used by plants in relatively large amounts for plant growth are called macronutrients. The major macronutrients are nitrogen (N), phosphorus (P), and potassium (K). Calcium (Ca), magnesium (Mg), and sulfur (S) are also macronutrients.
  • Micro-nutrients – Micronutrients are those elements essential for plant growth which are needed in only very small (micro) quantities. The micronutrients are boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn).
  • Micro-organisms – Micro-organisms are very small, one-celled organisms which are found everywhere in the world and include algae, bacteria, fungi, viruses, etc.
  • Lime amended or lime stabilised biosolids – Biosolids that have had sufficient lime added to destroy or inhibit pathogens and micro-organisms involved in the decomposition of the biosolids.


  • Nitrogen Limited Biosolids Application Rate (NLBAR) – The NLBAR is the rate at which biosolids can be applied to crops without exceeding the crop’s nitrogen requirements, thereby protecting groundwater from nutrient leaching. The NLBAR is calculated taking into account nitrogen that is immediately available (bioavailable) to crops; that which will become available over time as less soluble nitrogen mineralises; and that which is already available in the soil.
  • Nutrient management – Identifying how the major plant nutrients (nitrogen, phosphorous and potassium) are to be annually managed for expected crop production and for the protection of water quality.
  • Nutrient Management Plan (or Review of Environmental Factors- REF) – A site specific plan which describes how the major plant nutrients (nitrogen, phosphorous and potassium) are to be managed. The goal of farm nutrient management planning is to maximise crop yields, while minimising environmental impact.


  • Organic material – Organic material (or organic matter) is matter that has come from a once-living organism; is capable of decay, or is the product of decay; or is composed of organic compounds.
  • Organo-chlorine compounds – An organic compound containing at least one chlorine atom. Their wide structural variety and divergent chemical properties lead to a very broad range of useful applications. Many derivatives are controversial because of the negative effects of these compounds on the environment.


  • Pathogen – A micro-organism which can make people or animals ill.
  • Pathogen reduction – Decreasing the presence of disease-causing organisms in sewage sludge through processing and site management practices.
  • PCBs – Polychlorinated biphenyls. A persistent and toxic group of chemicals which have been banned from import in Australia since 1975.
  • Pelletisation – A process where biosolids is compacted into small pellets to simplify transport and handling. This process is rarely used because modern thermal drying processes produce a granule directly from the process.
  • Pellets – Small, round granules of dried biosolids which are produced by most thermal dryers. The pellets can be high in nitrogen and phosphorus and be used as fertiliser.
  • Percolation – The movement (normally downward) of water through and out of the soil. This downward movement accentuates the leaching process or aquifer recharge.
  • Phosphorous Limited Biosolids Application Rate (PLBAR) – The rate at which biosolids can be applied without exceeding the crop phosphorus requirements, thereby protecting groundwater from nutrient leaching. (Note that the method for calculating the PLBAR is currently under review as it may be overly conservative)
  • Plant Available Nitrogen (PAN) – The calculated quantity of nitrogen made available during the growing season after application of biosolids.
  • Plant Available Phosphorous (PAP) – The calculated quantity of phosphorus made available during the growing season after application of biosolids.
  • Porosity – The percentage of the soil volume not occupied by soil solids.
  • Public contact or public use sites – Land with a potential for use or contact by the public. It does not include agricultural land.


  • Recreation area – Any area used by the public for recreation, for example golf courses, parks, camping grounds, picnic grounds, athletic fields, fairgrounds and race tracks.
  • REF (Review of Environmental Factors) – A report which is prepared as a preliminary assessment of environmental impacts which determines the need or not for a more comprehensive environmental impact assessment.
  • Restricted use – Any use for biosolids which is not classified suitable for unrestricted use.
  • Routine storage – The storage of biosolids in a purpose build area prior to application to land.


  • Sewage sludge – A solid, semi-solid or liquid residue generated during the treatment of domestic sewage in a treatment works.
  • Sewage treatment plant (STP) or wastewater treatment plant (WWTP) – A processing facility that treats sewage and in the process produces biosolids and treated water or effluent (which can be treated further to use as recycled water) and minor residuals (screenings and grit).
  • Sludge lagoon – An impermeable earthen basin that receives sludge that has been removed from a wastewater treatment facility.
  • Soil conditioner – A substance used to improve the physical (e.g. soil structure) or chemical (e.g. pH) properties of soil.
  • Soil pH – An index of the acidity or alkalinity of the soil.
  • Soil profile – A cross section of the soil from the surface down to and including the parent material.
  • Soil saturation – The water content of a soil beyond which no more water is absorbed.
  • Soil structure – The arrangement of soil particles into larger particles or aggregates. This arrangement modifies the bulk density and porosity of the soil.
  • Stabilisation – The process used to reduce harmful bacteria and odours in biosolids.
  • Stabilisation Grade – See Classification.
  • Subsoil – The part of the soil profile beneath the surface soil that has been altered from its original geologic characteristics. In many instances, it is called a ‘B horizon’.
  • Surface runoff – The portion of water (rainfall, irrigation water or recycled water) that does not soak into the soil.


  • Unrestricted use – An unrestricted use classification indicates biosolids of the highest quality, which can be used anywhere including home and horticulture.


  • Vector attraction – The characteristics of biosolids that attracts rodents, flies, mosquitoes or other organisms capable of transporting disease.
  • Vector attraction reduction – Decreasing the characteristics of biosolids that attract rodents, flies, mosquitoes or other organisms capable of transporting disease
  • Vectors – Rodents, flies, mosquitoes or other organisms capable of transporting disease.
  • Volatile solids – Solids which can be broken down into their constituent elements (which are expressed as a portion of the total amount of solids present).