For recirculating aquaculture systems to be environmentally sustainable nutrient wise, removal of N at the RAS or at the end-of pipe treatment is required. In-line denitrification configuration has advantages such as allowing more intensive use of water, reducing heating/cooling as well as a reduced usage of makeup water. In-line denitrification systems are not frequently used due to their complexity on the addition of carbon sources (methanol, ethanol) that can hamper the RAS water quality. Solid-phase denitrification could be a safer alternative technology, as carbon sources are not dosed in the reactor, but rather bacteria harvest the carbon on demand from the solid phase material (ForzeasTM ).
The application of solid-phase in-line denitrification in a marine RAS rearing rainbow trout was evaluated at different hydraulic retention times (5.6, 3.2 and 1 hour) for 117 days, using ForzeasTM biodegradable plastic as material in a serial configuration reactor. The solid-phase in-line denitrification reactor showed the highest N removal capacity (411 gN/m3 ForzeasTM ) at HRT 1 hour with a removal efficiency of 40% NOx entering the reactor. The usage rate of the reactor at evaluated conditions during the 117 days trial was 2.7 kg ForzeasTM /kg N considering an entering oxygen concentration of 7 mg/L in the RAS system .
The configuration of the reactor allows low energy consumption (0.4-0.6 w/kg N), no addition of suspended solids to the RAS and a minimal operational dedication. Presenting an easy, efficient and sustainable technology for in-line denitrification.