Concentrated effluent treatment by attached-growth cultures on gravel and pozzolana: experimental study

Effluents coming from small food processing industries are mainly characterised by a high concentration (about 10 g.l" of COD) and a rather low daily volume. An adaptation of the domestic wastewater treatment process by attached-growth cultures for this type of effluent is under study. Coarser granulometries than those currently used and the recycling of the effluent allow yields better than 95 % in COD. The alternation principle between feeding and rest periods allows to avoid filter clogging and to decrease bioñlm release phenomena. A better understanding of the biomass regression during the rest periods is necessary to obtain a long-lasting system and to decrease the suspended solids rejects