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, sinks, showers, and laundry. This used water, laden with human waste, food scraps, detergents, and various other pollutants, is called sewage or wastewater.

It's a complex mixture, primarily water, but containing significant amounts of organic matter, disease-causing microbes (pathogens), nutrients like nitrogen and phosphorus, and sometimes toxic substances.

Directly releasing this untreated sewage into rivers, lakes, or oceans would be catastrophic for the environment and human health. It would deplete oxygen in water bodies, kill aquatic life, spread diseases, and make water unusable.

This is where sewage treatment comes in. It's a systematic process designed to clean this wastewater before it's discharged back into the environment. The goal is to remove pollutants, especially organic matter and pathogens, to make the water safe. The entire process is broadly divided into several stages, but the most crucial part, where the bulk of the cleaning happens, involves tiny living organisms – microbes.

Initially, the sewage undergoes 'primary treatment,' which is a physical process. Think of it like a giant sieve. Large floating debris, grit, and solid particles are removed through screening and sedimentation. This stage doesn't involve microbes much, but it prepares the water for the next, more intensive cleaning phase.

The real magic happens in 'secondary treatment,' which is a biological process. Here, the water (now called primary effluent) is introduced into large aeration tanks. These tanks are continuously supplied with air, creating an oxygen-rich environment.

This oxygen is vital for the growth and activity of beneficial aerobic microbes – bacteria, fungi, and protozoa. These microbes form 'flocs,' which are masses of bacteria associated with fungal filaments.

These flocs consume the organic matter present in the sewage as their food source, breaking it down into simpler, less harmful substances like carbon dioxide and water. As they consume the organic matter, they significantly reduce the 'Biological Oxygen Demand' (BOD) of the water, which is a measure of its organic pollution.

The more organic matter, the higher the BOD, and the more oxygen microbes need to break it down. By reducing BOD, these microbes make the water much cleaner.

After the aerobic treatment, the microbial flocs settle down, forming 'activated sludge.' A part of this activated sludge is recycled back into the aeration tanks to inoculate fresh incoming primary effluent, ensuring a continuous supply of active microbes.

The remaining sludge is then transferred to large, closed tanks called 'anaerobic sludge digesters.' In these digesters, a different set of microbes – anaerobic bacteria – take over. These bacteria thrive in the absence of oxygen and further break down the organic matter in the sludge, producing a mixture of gases like methane, hydrogen sulfide, and carbon dioxide, collectively known as biogas.

This biogas can be used as an energy source, making the sewage treatment process more sustainable. The treated water, now called secondary effluent, is significantly cleaner and can be safely discharged or subjected to further advanced treatment if required.

Thus, microbes are the unsung heroes of sewage treatment, transforming hazardous waste into harmless components and even generating useful energy.