Recirculation of wastewater in a filtration bed

In a filtration system wherein wastewater from a septic tank is directed into substantially parallel perforated primary distribution pipes on an upper surface of an upper coarse sand layer over a second lower layer of pea gravel and a third lower layer of fine sand and a fourth lower layer of clean gravel, said layers together comprising a filtration bed through which bed the wastewater from the primary pipes descends to perforated collection pipes in the fourth layer of clean gravel, and wastewater emerging from the collection pipes is then directed through flow divider means from which some wastewater is discharged and remaining wastewater is recirculated back through said filtration bed, the improvement comprising

• a) substantially parallel perforated secondary distribution pipes through which said remaining wastewater is recirculated in the second lower layer of pea gravel substantially parallel to the primary pipes,
• b) the direction of flow of wastewater in the primary distribution pipes being opposite to the direction of flow in the secondary distribution pipes, and
• c) respective coextensive perforated plastic hood elements arched over the respective secondary pipes spacing them from the pea gravel above and to each side.