Woodchip denitrification

Denitrification in woodchip beds has been successfully accomplished in freshwater recently also including effluents from recirculating aquaculture systems.

Woodchip reactors can support sulfur-based autotrophic denitrifiers requiring inorganic carbon and reduced sulfur compounds for growth in addition to the heterotrophic denitrifiers requiring organic carbon for growth. Woodchip bioreactors can thus support denitrification with no need for external carbon input, making it a potential cost-efficient nitrogen removal method, further enhanced by the excess CO2 produced in the recirculating aquaculture systems. 

Furthermore, saline sulfate-rich water may enhance the sulfate-reduction observed in woodchip reactors and consequently favor sulfur-based, autotrophic denitrification. 

Conditions favoring autotrophic denitrification are currently unknown, and the interactions between these nitrogen removal processes have not been studied. BONUS CLEANAQ aims to examine these interactions in woodchip reactors and to optimize the N-removal and cost-efficiency of the process through controlled lab-scale experiments as well as pilot-scale try-outs on commercial fish farming operations.

Integrated aquaculture and bioenergy production
An integrated aquaculture and bioenergy production are planned to reduce both nutrient load and CO2-emissions to the environment (Sybimar, Finland). 

Woodchip denitrification also provides an opportunity to combine aquaculture with energy production. The industrial project-partner Sybimar has already established a full-scale system where plant biomass binds nutrients produced in fish tanks which can later be utilized as food or for biogas production. 

A similar set-up might perhaps be applied in more saline environments, replacing the plants by woodchip based denitrification reactors. The inorganic carbon that is needed for autotrophic denitrification could be provided either directly from the fish tanks or from the biogas production; and the woodchip-remains might perhaps be utilized for energy (e.g. biogas) production. The applicability of such a set-up will be studied and further described in BONUS CLEANAQ.



27 OCTOBER 2021