The correct option is (a) Biological wave contractor
To elaborate: Biological wave contractor, known as bio wave based on deliberate generation of wave motion, hence, it is defined as a low energy consuming system for waste water treatment, high rate bio filters usually constructed as tower models treating food waste which has considerable potential to rough high strength industrial effluents prior to sewage discharge, Conventional bio filters are also called as Percolating filters in which the waste trickles and is oxidized and hence removed by biological degradation and Rotating biological contractors absorb oxygen from the air and pollutants from the wastewater when the spherical disc is in contact with the air and with the waste water respectively during its rotation which can be decomposed aerobic microorganisms.