Keterangan :

In multi-step sewage plant, mechanical racks remove raw contaminants at first. Afterwards, smaller contaminants like sand and fluids are removed in the grit channel. The left organic contaminants are treated with micro organisms. These microbes convert the contaminants into inorganic biomass. For the best performance, the microbes need a constant supply of contaminants and air. As the last step, the sewage sludge is withdrawn and the water is released to the water cycle.