In 1983 and 1986, surveys were conducted all over France on wastewater stabilization by “natural” ponds (lagoons), including an almost exhaustive inventory of the 1400 plants then operating. The statistical interpretation of collected data made it possible to analyse the spread of this technique, which became truly popular only ten years ago, and to discern the usual design basis and regional features. With a mean plant area of 5500 m2, lagoons are usually restricted to the treatment of effluents from rural communities, with the exception of large plants in coastal touristic areas. Partially planted ponds are a competing alternative to conventional algal lagooning. Current conditions of pond management are reviewed, with results of effluent quality.
Domestic wastewater treatment by infiltration basins is a process that is becoming common in France. In the absence of accurate operating data, we felt it would be useful to conduct a case study at an existing plant. The Saint Symphorien de Lay plant, serving a population-equivalent of 500, was chosen because the basins are watertight and drained. The study revealed 85% TSS, COD and Total Phosphorus removal. Nitrogen yields varied over the flooding period, with a high production of nitrates at the beginning of the period. The rate of decontamination (1 to 2 Log unit) was lower than expected. The infiltration surface should increase from 1 to 1.5 m2/p.e. and spread over three basins. Research is now focusing on finding the biologically active depth of an infiltration basin.
SUMMARY compact facilities together with modular and environment-friendly appearance are arguments in favour of Biological Aerated Filters(B. A. F. ) in coastal areas where the amount of available land imposes strict limitations on technological choices. The operation of B. A. F. in combination with a physico-chemical process was studied using the data obtained from two wastewater treatment plants located in coastal areas (Barcares and Saint Palais/Mer, France). The main conclusions are the following.-Effluent quality in terms of COD, BOD5 S.S. proved satisfactory for organic load conditions higher than those applied when using conventional procedures.-Adaptation to organic load variations is not a basic problem for this type of coastal community,but hydraulic flow-rate control should be the main concern.-Restarting plant operation after a long shutdown only takes a few days.-Furthermore technical and economical optimisation required continuous monitoring, especially in the field of washing and aerating control. This type of management involves the use of reliable, high- performance control equipment.
France has a large number of small rural waste treatment plants. A fairly wide range of technologies suitable for small local authorities has been developed in recent years. The choice of process is now based on a detailed analysis of the limitations imposed by local conditions, with particular regard to those involving the quality objectives for the receiving environment. The main processes used are presented, together with the design basis generally applied. An overview is presented of the situation of France's small treatment plants, through an analysis of a sample of 976 plants with a capacity of less than 2000 inhabitant-equivalents in 11 mainly rural departments covering 13% of France surface area. The distribution of the processes used and the evolution of the choices adopted are analyzed with regard to the size of the plants. The activated sludge process, widely used in all size classes ten years ago, has been gradually replaced by extensive processes, essentially where the capacity is less than 800 inhabitant-equivalents. In some departments, local practices have a great influence over the choice of process.
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