Media size optimisation in BAFs treating citrus waste

The main aim of the present research was to check the applicability and optimise the design parameters of biological aerated filters (BAFs) for the treatment of effluents from the food and agricultural industries, and specifically in this study, from citrus plants. Expanded clay was used as a support material. Two different material sizes were tested, 2–5 mm and 3–7 mm. Cocurrent flow was used and the process aeration level was 10·47 Nm³/h per m². Backwashing was carried out on a daily basis. The results showed that in order to obtain an effluent with a maximum concentration of 1100 mg chemical oxygen demand (COD)/l, the system performance was optimal for a material size of 3–7 mm. In this case, the maximum admissible volumetric load was 72 kg COD/m³ per day. However, in order to obtain an effluent with a maximum concentration of 600 mgCOD/l, the optimal system performance was with a material size of 2–5 mm, and a maximum admissible volumetric load of 30 kg COD/m³ per day.