Patent ID: 8920642

Claim:
A biological wastewater treatment system comprising: (a) a watertight basin having an open top and configured for being placed on a substrate; (b) a filter located in the basin, the filter comprising: (b1) a first layer at the bottom of the basin, the first layer comprising a plurality of first coarse pieces of a first material having a predetermined surface, configured for enabling growth of bacteria; (b2) a second layer mounted above the first layer and comprising a plurality of second coarse pieces of a second material, the second pieces being smaller than the first pieces; (b3) a third layer mounted above the second layer and comprising a first granular material; (b4) a fourth layer mounted above the third layer and comprising a plurality of third coarse pieces of third material, the third pieces being smaller than the first pieces; and (b5) a fifth layer mounted above the fourth layer and comprising a second granular material; (c) a final layer mounted above the fifth layer, extending upward above the basin and extending laterally outward from the basin and downward toward the substrate, such that a section of the final layer contacts the substrate, the final layer comprising a third granular material which is finer than the first granular material and second granular material; (d) an exit pipe having exit perforations located in the first layer, the exit pipe being configured for receiving water from an input pipe and for enabling discharge of water into the first layer via the perforations; (e) a first perforated pipe having first perforations located in the second layer, and configured for receiving water from the second layer via the first perforations; (f) a second perforated pipe having second perforations located in the fourth layer and configured for enabling discharge of water from the fourth layer via the second perforations; and (g) a connection pipe in fluid communication with the first perforated pipe and second perforated pipe, and enabling passage of water from the first connection pipe to the second connection pipe, for bypassing the third layer.