Question

During which stage of sewage treatment microbes are used
A. Secondary treatment
B. Primary treatment
C. Tertiary treatment
D. All of these

Answer 1

Hint:
Before we proceed with the problem, we must know the definitions of Sewage treatment.
Sewage is produced by residential and industrial establishments. It includes liquid waste from toilets, baths, showers, kitchens, sinks, and other household appliances that are disposed of through sewers. The secondary treatment produces far superior effluent to a septic tank. Sewage treatment is divided into three stages: primary, secondary, and tertiary.

Complete step by step answer:
There is still much to learn about Sewage treatment. Primary treatment refers to the stage in which sewage is physically treated. The sediment removed during the primary treatment is referred to as primary sludge. Primary effluent is transported from primary settling to aeration tanks.
Tertiary treatment is a wastewater treatment process that removes nitrates and phosphates from treated water using precipitation techniques.
Secondary treatment is the stage at which biological sewage treatment takes place. The sediments formed during secondary treatment are known as activated sludge. Flocs form in aeration tanks during secondary treatment.
In the onsite wastewater sector, there are two types of secondary treatment systems: aerobic treatment units and biofiltration systems. These systems are offered commercially as pre-manufactured units designed to treat domestic wastewater generated by houses and, in certain circumstances, non-residential facilities.
Microbes are used in secondary treatment to form flocs, which are then settled and passed through an anaerobic sludge digester, where the microbes are killed.

Option ‘A’ is correct

Note:
Secondary treatment entails removing biodegradable organic matter (BOD) and suspended solids (TSS) using aeration and filtration. Secondary treatment systems must have a treatment capacity equal to or greater than the daily wastewater flow from a residence or non-residential facility. Secondary treatment systems are used to overcome difficult site conditions such as clay soils with low permeability, sandy soils with high permeability, and shallow depths to groundwater and bedrock. Secondary treatment may also include disinfection with chlorine or UV radiation to eradicate dangerous germs.