The microorganisms draw nutrients, organic matter, and oxygen from the wastewater and air that passes through the sand bed.
(The microorganisms; draw; nutrients, organic matter, and oxygen from the wastewater and air) (the wastewater and air; passes; through the sand bed)
The microorganisms the wastewater and air
draw passes
nutrients, organic matter, and oxygen from the wastewater and air
through the sand bed