WASTEWATER CONTAMINANTS & NITRIFICATION

Components of Wastewater

The components of wastewater may be divided into four categories:

Water Contaminants01
Biochemical
Oxygen Demand,
Total Suspended
Solids, and Fats,
Oils and Grease
(BOD₅, TSS, FOG)
02
Pathogens
Fecal Coliform,
Viruses
03
Nutrients
Nitrogen
Phosphorus
04
Other
Chemicals
Pharmaceuticals
Chemicals and
Hazardous Waste

Biochemical Oxygen Demand, Total Suspended Solids, & Fats , Oils, and Grease

What is Biochemical Oxygen Demand (BOD5)?

Biochemical oxygen demand (BOD5) is the most widely used parameter applied to wastewater. BOD5 is a measure of the dissolved oxygen required by microorganisms to oxidize or decompose the organic matter in wastewater. A typical BOD5 value for septic tank effluent is 150 milligrams per liter.

What causes a high BOD5?

High organic loading from over-occupancy in residential systems.

Food preparation methods and use of garbage disposals in homes/restaurants.
Toilet water is a major contributor to BOD₅ and natural microorganisms.
Effluent BOD₅ may increase due to broken baffles, poor tank maintenance, or low biological activity.
Harsh household chemicals (bleach, detergents, cleaners) can kill beneficial microbes, reducing BOD₅ treatment efficiency.

What are the Consequences of high BOD5?

Promotes excessive biomass growth
Can clog soil treatment areas and reduce system lifespan
Limits septic tank efficient if baffles fail or sludge/scum is not removed

What is Total Suspended Solids (TSS)?

Total Suspended Solids or TSS is the most common measure of the amount of solids in wastewater effluent.
It is measured by filtering a well-mixed sample through a standard glass fiber filter and dying the residue retained on the filter at 217 to 221 degrees F (103 to 105 degrees C).
The increase in the weight of the filter represents the amount of total suspended solids.

What is the impact of TSS on systems?

High TSS can place a great demand on the downstream devices and could lead to clogged components and orifices in distribution manifolds. Although low TSS is not a problem for the system, it could indicate that something else is wrong with the system.

Fats, Oils, and Grease (FOG)

FOG (fats, oils, and grease) is a constituent of sewage typically originating from food stuffs (animal fats or vegetable oils) or consisting of compounds of alcohol or glycerol with fatty acids (soaps and lotions), typically measured in mg/L.

Pathogens

Pathogens can be present in wastewater from any part of the house. Human contact with water can introduce pathogens into the environment.

Their presence makes wastewater treatment a key public health concern.

Include viruses, protozoa, parasites, and bacteria (e.g., Salmonella, Vibrio cholera, Entamoeba histolytica, Cryptosporidium). Viruses are microscopic and rely on host cells for survival and reproduction.

Nutrients

Phosphorus in Wastewater and Its Environmental Impact

In temperate regions, phosphorus (P) is the main nutrient responsible for the eutrophication of freshwater bodies due to its limited natural availability. Wastewater introduces phosphorus primarily through feces and household detergents. In septic tank effluent, total phosphorus (TP) typically ranges from 7–10 mg/L. While septic tanks remove only about 10% of phosphorus through settling, further treatment occurs in soil, depending on specific conditions.

What are the forms of Nitrogen?

In wastewater and water systems, nitrogen exists in multiple forms including ammonia (NH₃), ammonium (NH₄⁺), nitrite (NO₂⁻), nitrate (NO₃⁻), and organic nitrogen. These forms are interrelated components of the nitrogen cycle, capable of transforming into each other through biochemical processes.

Effects of Nitrogen to Environment and Health

High nitrogen levels in drinking water can pose health risks, particularly methemoglobinemia (blue baby syndrome) in infants due to excess nitrate.
Ammonia in surface water is also harmful to aquatic life. Because of these risks, advanced pretreatment may be needed to reduce nitrogen discharge.
Environmental nitrogen is often reported in terms of nitrogen content (e.g., NO₃⁻-N) rather than the full compound. For instance, 10 mg/L of NO₃⁻-N is equivalent to 45 mg/L of NO₃⁻ ion.
Accurate measurement and treatment are essential to protect public health and ecosystems.

What is Nitrification?

Nitrification is a biological oxidation process where ammonium (NH₄⁺) is converted to nitrate (NO₃⁻) through a two-step process carried out by autotrophic bacteria.

Nitrification and Its Environmental Impact

The nitrate (NO₃⁻) produced through nitrification can serve as a valuable nutrient for plant growth. However, if not absorbed by plants or further processed, it can leach into groundwater, potentially leading to contamination.
In the broader nitrogen cycle, nitrate can also be converted to nitrogen gas (N₂) through denitrification, completing the transformation back into a harmless atmospheric form. Thus, nitrification is a critical step in nutrient cycling and wastewater treatment, but it must be managed properly to protect water quality.

Other Chemicals

Pharmaceuticals and Household Chemicals in Wastewater

Pharmaceuticals and Personal Care Products (PPCPs) like drugs, cosmetics, and sunscreen agents are increasingly found in wastewater due to widespread use.

Even in trace amounts, PPCPs and other organic contaminants (from pesticides, consumer goods, industrial agents) may pose ecological and health risks.

Nonhazardous chemicals (e.g., shampoos, soaps, detergents, water softener salt) typically do not harm treatment systemsat normal levels.

Excessive use of household chemicals can disrupt wastewater treatment efficiency.
Problematic substances include:

Continuous toilet cleaners – can overload systems due to high flow contribution.
Formaldehyde – commonly used in chemical toilets and harmful to treatment processes.