Wastewater Treatment Processes: An In-Depth Look at Primary, Secondary, and Tertiary Treatment Methods

Untreated wastewater is an environmental hazard that can lead to unsanitary conditions and ecological damage. Wastewater treatment facilities run used water through a series of treatments to return it safely to the water supply. These physical, biological, and chemical processes help communities thrive.

What is wastewater?

Every home and business depends on a clean supply of water. However, after they send that water down the drain, it contains impurities that make it unsafe for reuse. Wastewater flowing into a treatment plant may have been flushed, used in industrial processes, or collected through stormwater runoff drains.

The Goal of Wastewater Treatment

The goal of a wastewater treatment system becomes clear by following the effluent path. Water released from a treatment plant often flows into natural resources like streams, rivers, and lakes. The process goal is to minimize its impact on the environment. Effluent should not have nitrates and phosphates that create algae blooms. It must also be clear of harmful bacteria and other biological hazards.

Reaching these treatment goals is even more critical as dry regions employ recycling strategies to conserve water. In these areas, effluent from the treatment plant will go directly into the clean water distribution system. Impurities could mean boil-water advisories and an insecure water supply.

Primary Wastewater Treatments

Primary wastewater treatments are physical processes that remove large matter from the water stream. These steps capture impurities that could harm the wastewater treatment equipment and disrupt the water flow.


Before the official primary water treatments, the plant wants to remove large impurities floating in the water. If the wastewater plant collects storm runoff, it is common for food wrappers, plastic bags, and other non-biodegradable items to be in the water flow. Large pre-filters remove materials that would block the more refined filters used during the primary wastewater treatment process.

Settling Tanks

The next primary wastewater treatment uses gravity to remove impurities. Water flows into tanks where suspended solids can settle over time. The treatment plant may also add chemical coagulants that encourage small solids to gather into heavier particles and sink to the bottom of the tank. The water may also run through filters as it moves from tank to tank.

Secondary Wastewater Treatments

After removing most solids during primary water treatments, the ensuing processes remove biological impurities. The series of secondary wastewater treatments use good bacteria to remove organic material.


In a biofiltration system, water flows through bacteria-filled filters that break down impurities. The plant may use crushed stone, sand, or ceramics as trickle filter media. A slow filtering process is necessary because complex organic impurities take time to break down.


In the aeration stage, water mixes with air to remove dissolved gases. This process also oxidizes dissolved metals, pulling them from the water supply.

Aeration tanks encourage the growth of good bacteria that continue to break down organic impurities. Flocks, resulting from bacterial digestion, settle out of the water, forming a sludge at the bottom of the secondary settling tank. A portion of this activated sludge returns to the aeration tank. The facility removes the rest for disposal.

Tertiary Wastewater Treatments

The final steps of wastewater treatment are chemical. Tertiary treatments perform nitrate removal, pH balancing, and disinfection functions.

Activated Carbon

Passing water through activated carbon removes many organic chemicals from the stream. This black substance has a large surface area filled with microscopic crevices. The slight charge of the carbon atoms attracts other molecules, adsorbing them into the structure. Treating water with activated carbon improves its taste and smell.


Even after the secondary treatment processes, viruses and other microorganisms can still be present in the water. Chlorine has been a common disinfectant for many years. However, treating water with UV light has grown in popularity because it eliminates the need for added chemicals.


Removing phosphorus from wastewater makes it safer to return to the environment. High phosphorus levels correlate with high algae levels and lower water quality. Adding alum (aluminum sulfate) to the supply is a safe way to improve effluent quality.


If a treatment plant uses chlorine as a disinfectant, chemical dichlorination may be the final tertiary water treatment. Adding sulfite salts can capture residual chlorine, bringing the effluent to a safe level.

SCADA Technology and Wastewater Management

System control and data acquisition (SCADA) technology fits well into every step of the water treatment process. Sensors in the system provide real-time information about basic metrics like flow volume and water pressure. Other reporting tools can assess specific measurements such as chlorine or nitrate levels. This information will ensure consistent water quality, alerting technicians at the first sign of a problem.

At High Tide Technologies, we specialize in SCADA solutions for municipal water collection, treatment, and distribution systems. Our team can improve the safety and efficiency of wastewater treatment plants using cloud-based technology. Contact us today to learn more.