Characteristics of wastewater

Wastewater is characterized based on its physical, chemical, and biological composition.

Depending on the pollutant level and local regulations, physical, chemical, and/or biological treatment will be used. Most of the time, the three treatments are combined to achieve the best water quality.

The characteristics of wastewater vary considerably from one industry to another. Therefore, the specific characteristics will determine the treatment techniques to be used to satisfy the compliance discharge requirements.

Due to the large number of pollutants, characteristics are generally not considered for each substance. Materials with similar pollution effects are grouped into pollutant or characteristic classes.

Wastewater physical parameters

  • Color: Fresh wastewater is normally brown and yellowish, but over time, it turns black.
  • Suspended solids: these are insoluble solids suspended in a liquid and visible to the naked eye
  • Temperature: For wastewater, it is correlated with the outside temperature while being warmer because almost no one takes a cold shower
  • Turbidity: Due to suspended solids, wastewater will have higher turbidity.
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Chemical characteristics of wastewater

Wastewater contains different chemicals in various forms, as listed below.

    • Chemical Oxygen Demand (COD): It is a measure of the amount of organic matter in wastewater based on the oxygen required to oxidize it.
    • Nitrogen: It is measured in its different forms: nitrite, nitrate, ammonia, and organic nitrogen (which is the amount of nitrogen present in organic compounds)
    • Phosphorus: It is generally measured in its mineral and organic form, total phosphorus
    • Chlorine (Cl-)
    • Sulfates (SO4-2)
    • Heavy metals

Biological parameters of wastewater

  • Biochemical Oxygen Demand (BOD) – BOD is the amount of oxygen required to stabilize organic matter by means of microorganisms.
  • Oil and Grease – Oil and grease are generated from food waste and petroleum products.
  • Microbial life in wastewater: Wastewater contains the following microbes:
    • Bacteria
    • Protozoa
    • Mushrooms
    • Virus
    • Seaweed
    • Rotifers
    • Nematodes

FAQ

What are the Main Characteristics of Wastewater to be Analyzed?

Wastewater is characterized according to three main types of parameters:

  • Physical: color, temperature, total suspended solids (TSS), turbidity;
  • Chemical: COD (Chemical Oxygen Demand), nitrogen (NO₃⁻, NH₄⁺…), phosphorus, chlorides, sulfates, heavy metals;
  • Biological: BOD (Biochemical Oxygen Demand), presence of microorganisms such as bacteria, viruses, fungi, algae, etc.

These parameters make it possible to determine the pollution level and to adapt wastewater treatment.

  • COD (Chemical Oxygen Demand) measures the total amount of organic matter (biodegradable and non-biodegradable) oxidizable in water, by chemical reaction.
  • BOD (Biochemical Oxygen Demand) measures only the biodegradable fraction of organic matter, used by microorganisms over 5 days.

COD is often higher than BOD, and both are complementary for evaluating the pollutant load.

Wastewater may contain:

  • bacteria (some pathogenic),
  • protozoa,
  • viruses,
  • fungi,
  • algae,
  • rotifers and nematodes.

These organisms reflect the biological load of the water and can be treated by biological or disinfection processes (UV, chlorine, ozone).

Each industry generates wastewater with a different composition depending on its processes:

  • agri-food: rich in fats and organic matter,
  • textile: presence of dyes and heavy metals,
  • chemical/pharmaceutical: specific substances, solvents, acids, etc.

These differences require a tailored treatment, hence the importance of grouping pollutants into broad categories (organic, nitrogenous, phosphorous, etc.).

Temperature directly influences the activity of microorganisms used in biological treatments. Water that is too cold (< 10 °C) slows down biodegradation, while water that is too hot (> 35 °C) can kill certain bacterial strains. It is therefore a key parameter to monitor to ensure effective purification, especially in biological wastewater treatment plants (activated sludge, MBBR…).

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