The Role of Microorganisms in Secondary Treatment

In secondary treatment, biological processes take place in order to further treat the wastewater coming from primary treatment. There are three types of treatment methods in secondary treatment: aerobic, anaerobic, and anoxic - each has different bacteria colonies (microorganisms) which help in cleaning the water. 

Aerobic treatment uses microorganisms requiring oxygen to activate their metabolization processes. This type of treatment utilizes aeration, which is a system that provides air to the water. With this air, the microorganisms are able to consume waste within the wastewater. 

The image above shows a MicroFAST® system by Biomicrobics.

One common type of aerobic treatment in wastewater is activated sludge. This process uses aeration in accordance with flocculation to form flocs - the accumulation of fine particles in a clump, forming larger, heavier materials. These flocs sink to the bottom as they become more dense and form a layer of sludge which is dealt with through other processes. Solids and water are further separated when the sludge sinks. 

Diffusers in aeration tanks are used to activate the bacteria by pushing air through a membrane with tiny perforations. When the air is released through these holes as bubbles, it transfers oxygen throughout the water and activates aerobic digestion. 

Anaerobic treatment is a process used in wastewater treatment that occurs in the absence of oxygen. In this process, microorganisms break down organic matter into biogas (methane and carbon dioxide) and a small amount of residual sludge. Anaerobic treatment is highly efficient in degrading organic pollutants and is widely used in wastewater treatment plants. The process helps in reducing the volume of sludge produced, generates biogas as a byproduct, and is particularly useful in treating high-strength industrial wastewaters. It is an eco-friendly and cost-effective method for treating organic-rich wastewater.

Anoxic treatment is used in processes where nitrogen amounts are high. Nitrates are used to break down organic matter instead of oxygen. After the nitrate does its job, it has to be turned to nitrogen. Denitrification must then take place as nitrogen is a harmful compound that may cause eutrophication in receiving water bodies. This is done through the use of microorganisms that feed on nitrate, which turn nitrates to nitrogen gas. By removing nitrogen compounds from wastewater, anoxic treatment helps in reducing pollution and maintaining the ecological balance of water bodies receiving treated wastewater as well as keeping any damage to a minimum.