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When is tertiary wastewater treatment needed?
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Tertiary wastewater treatment, also known as advanced treatment, is implemented under specific circumstances where higher levels of purification are required than those achieved by secondary treatment. It is generally utilized in the following situations:1
- Vulnerable Receiving Waters: When the intended body of water receiving the effluent is highly susceptible to the negative impacts of pollution, tertiary processes are employed to provide additional protection.2
- Stringent Removal Requirements: It is necessary when regulatory standards demand the removal of more than 85 percent of total suspended solids and biochemical oxygen demand (BOD).1
- Nutrient Control: Tertiary treatment is used when it is essential to reduce levels of plant nutrients, specifically phosphates and nitrates, to prevent eutrophication in lakes and other water bodies.31
Because these processes can be very expensive—often doubling the cost of secondary treatment—they are reserved for special circumstances where the high quality of the final effluent, which can reach near drinking-water standards, is deemed necessary for environmental or public health protection.1