2024A-GS11-2 Experimental study on highly efficient nitrification of methane fermentation residues by pure oxygen aeration

Abstract

Osaka Bay in Japan suffers from nutrient imbalances, resulting in problematic seaweed growth and decreased fish catches due to nutrient depletion at its mouth, while explosive outbreaks of organisms due to eutrophication at its inner part. A method is proposed to address these problems to use marine biomass from inner part of the bay to generate methane and then use the fermentation residues as fertilizer at its mouth for nutrient-poor area. However, nitrification is required before spreading to the ocean, due to high ammonia levels in the residues. Nitrification typically uses air aeration, but this paper proposes using pure oxygen aeration instead, which reduces energy consumption. Experiments were performed using residues kept at 30 degree Celsius in a 2 L jar fermenter and pH levels, ammonia, nitrite, and nitrate concentrations were measured, maintaining dissolved oxygen above 7.0 mg/L. The results of this research showed pure oxygen aeration for nitrification was 1/80th of air aeration, indicating a significant reduction in energy consumption with pure oxygen aeration.