A comprehensive investigation was carried out using a bench-scale plant (70l) with the aim of evaluatingthe potential of two hybrid processes that use plastic moving carriers for nitrification and denitrification, given the restriction that low and stable values of ammonium and nitrate had to be met. In one process, the nitrification aerobic reactor operated with the biomass in biofilm exclusively and achieved a nitrification rate of 0,8 gN/m2·d. In the other process, nitrification operated as a hybrid process and a similar nitrification rate in the biofilm was found. Batch tests revealed that suspended solids in the hybrid reactor provided an additional 20% nitrification rate. This resulted in a potential volumetric nitrification rate of 380 gN/m3·d at 20°C, which is 2.5 times the expected rate in activated sludge plants under the same conditions. A high anoxic fraction (55%) was used in both processes with hybrid denitrification, since it minimized inhibition of nitrification in the biofilm due to the biodegradable COD applied load. Batch tests undertaken with high suspended solids (4 g/l) revealed that 60% of the denitrification took place in the biomass in suspension, and 40% in biofilm, providing a high level and robust performance. The dosage of methanol was crucial in regulating effluent nitrate. It is concluded that both processes offer great potential regarding the design of more compact new plants and the upgrading of existing facilities.

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