Sub-surface biological filter for surface waters drains through gravel layers

摘要

An inverse biological filter treats effluent water arising from surface waters, rain water, domestic and industrial effluent by means of several layers of gravel. The novelty is that: (a) the filter is an inverse biological filter (3) with at least three superimposed layers of gravel (5, 6, 7) held within a soil-sealed basin; (b) the uppermost (5) layer of gravel is composed of the finest grade material, and the coarsest grade of gravel (7) is on the base layer (15), intermediate gravel (6) grade being between the upper and lower layers; (c) the inverse biological filter is planted with suitable shrubs, trees, grasses; (d) the outer surface margin (8) is formed by a further quantity of gravel; (e) drainage pipes (4) are incorporated in the base layer (15). The base layer (15) and associated side inclines (10) are formed of shaped blocks (11) resting on a non-woven fibre mat (12) and foil (13).