Development of a new generation of reed-bed filters in France: first results

Since 1992, Reed-Bed Filters (RBF) wastewater treatment plants have been built to meet the needs of 15 rural authorities and, on an experimental basis, 2 farms to treat milking parlour washwater using this method. This paper presents results obtained at a plant designed for 200 p.e. after 15 months of operation, organic and hydraulic loads being 67% and 115% of the nominal loads respectively. With an overall area of the order of 2.2 m² per person equivalent, the plant produces an effluent which easily complies with the following water quality criteria : 90 mg l⁻¹ COD, 30 mg l⁻¹ TSS and almost 10 mg l⁻¹ TKN. Phosphorus removal is normally very low. A farm-located experimental plant, receiving milking parlour washwater (COD between 700 and 1400 mg l⁻¹), is providing promising results which will certainly be improved by extending the current RBF areas. RBFs are capable of directly treating raw sewage by applying procedures involving batch feeding and alternating several units operating in parallel; in this way aerobic conditions are maintained and physical surface clogging is controlled with the aid of rooted macrophytes. RBFs used for complementary treatment seem to accept continuously high hydraulic loads.