What happens during the secondary treatment of sewage? - Leaving Cert Chemistry - Question 1 - 2012

During the secondary treatment of sewage, the primary focus is on the biological treatment of wastewater, which primarily involves the breakdown of organic matter. This process typically encompasses oxidation and aeration techniques that encourage the growth of microorganisms.

1. Oxidation: Microorganisms consume organic pollutants as a food source, converting them into carbon dioxide and water, along with new microbial biomass. This microbial digestion significantly reduces the organic load in the effluent.

2. Aeration: The sewage is often aerated to maintain adequate oxygen levels, promoting aerobic bacteria that thrive in oxygen-rich environments. This step ensures efficient breakdown of wastes.

3. Digestion: The metabolic processes of these microorganisms lead to the decomposition of complex organic compounds into simpler substances.

4. Settling: After the biological treatment, the mixture is allowed to settle in a clarifier, where the microbial biomass (often referred to as sludge) can be separated from treated water, allowing for further processing or disposal.

Through these processes, secondary treatment effectively reduces the concentration of organic matter, making the wastewater more suitable for discharge or further treatment.