Question

By what percentage does the decomposition of organic matter by aerobic bacteria in aeration tanks typically lower the BOD during secondary treatment?

Options

• 35–45%

• 95–100%

• 70–80%

• 10–20%

Answer 1

During secondary (biological) treatment, vigorous aerobic bacterial activity within flocs rapidly oxidises organic matter, reducing the Biochemical Oxygen Demand (BOD) of the effluent by roughly 70–80%.