Microbes in Sewage Treatment — Definition

Definition

Imagine all the water that goes down our drains from homes, schools, and offices – this includes water from toilets, showers, sinks, and washing machines. This used water, full of human waste, food scraps, detergents, and other pollutants, is called sewage or wastewater.

It's a complex mixture, rich in organic matter and often containing harmful bacteria, viruses, and parasites. If this sewage were released directly into rivers, lakes, or oceans, it would cause severe pollution.

The organic matter would decompose, consuming all the dissolved oxygen in the water, leading to the death of aquatic life like fish and plants. Furthermore, the pathogens would spread diseases, posing a serious threat to human health.

This is where sewage treatment comes in. It's a vital process designed to clean this dirty water before it's returned to the environment. Think of it as a multi-step purification system. The unsung heroes of this purification are tiny living organisms – microbes, including bacteria, fungi, and protozoa. These microscopic organisms are naturally present in sewage and are harnessed in a controlled environment to do the heavy lifting.

The treatment typically involves two main biological stages: primary treatment and secondary treatment. In primary treatment, physical methods like filtration and sedimentation are used to remove large solid particles and some suspended solids. This is like a rough screening process. However, the water still contains a lot of dissolved and fine suspended organic matter. This is where the microbes become indispensable.

In the secondary treatment stage, the water is introduced to large aeration tanks where it's constantly agitated and air is pumped in. This creates an oxygen-rich environment, perfect for the growth of 'aerobic' microbes.

These microbes, forming 'flocs' (masses of bacteria associated with fungal filaments), consume the organic pollutants in the sewage, converting them into simpler substances like carbon dioxide and water, and also using them for their own growth.

As they consume the organic matter, the Biological Oxygen Demand (BOD) of the sewage significantly decreases, meaning there's less organic material for oxygen-consuming decomposition. After this aerobic digestion, the microbial flocs are allowed to settle, forming 'activated sludge'.

A small portion of this activated sludge is recycled back into the aeration tanks to inoculate the incoming wastewater, ensuring a continuous supply of active microbes. The remaining sludge is then transferred to anaerobic digesters, where 'anaerobic' microbes (those that thrive without oxygen) further break down the organic matter, producing biogas (a mixture of methane, carbon dioxide, and hydrogen sulfide) as a valuable byproduct.

The treated water, now significantly cleaner, can then be disinfected (e.g., with chlorine or UV light) before being safely discharged into natural water bodies.