Purification systems for small collectivities: attached growth cultures on fine media

Abstract

France counts a large number of communities with less than 2 000 inhabitants. The adjustment of wastewater treatment plants, easy to implement and to use, needed by these rural communities, enlarges the number of processes already widely used, such as waste stabilization ponds and activated sludge. The purpose of this article is to describe five wastewater treatment systems called "attached-growth cultures on fine media". A high and reliable quality level is obtained by supplying very small organic loads and an alternate feeding of the reactors leading to a self-regulation of the fixed biomass (these treatment plants don't have any secondary settlement tank). The effluent's quality reaches 125 mg.L-1 in COD and 25 mg.L-1 in BOD5. A high nitrification is obtained (NK-N < 10 mg.L-1). Nitrate contents are variable depending on feeding cycles. A reliable functioning is obtained thanks to a regular operation with a reasonable cost.