Biological denitrification in marine aquaculture systems: A multiple electron donor microcosm study

There is a lack of information on denitrification of saline wastewaters, such as those from marine recirculating aquaculture systems (RAS), ion exchange brines and wastewater in areas where sea water is used for toilet flushing. In this study, side-by-side microcosms were used to compare methanol, fish waste (FW), wood chips, elemental sulfur (S⁰) and a combination of wood chips and sulfur for saline wastewater denitrification. The highest denitrification rate was obtained with methanol (23.4 g N/(m³·d)), followed by FW (4.5 g N/(m³·d)), S⁰ (3.5 g N/(m³·d)), eucalyptus mulch (2.6 g N/(m³·d)), and eucalyptus mulch with sulfur (2.2 g N/(m³·d)). Significant differences were observed in denitrification rate for different wood species (pine > oak ≫ eucalyptus) due to differences in readily biodegradable organic carbon released. A pine wood-sulfur heterotrophic-autotrophic denitrification (P-WSHAD) process provided a high denitrification rate (7.2-11.9 g N/(m³·d)), with lower alkalinity consumption and sulfate generation than sulfur alone.