The system is proposed to compliment and overcome the drawback of each HSF and VSF technology. The idea is to put the VSF and HSF in series due to the fact that VSF is more effective in terms of low space requirement and nitrification, despite of poor denitrification due to its unsaturated nature and HSF is more effective in terms of bacteria removal and denitrification due to its saturated nature.

For more details concerning this kind of system please look in Cooper, 1999.