Inorganic nitrogen removal in a combined tertiary treatment—marine aquaculture system—I. Removal efficiences

Abstract

The increasing awareness that nitrogen is often a key nutrient controlling algal growth in coastal marine waters has led to a concerted effort to find ways to remove ammonia and nitrate from wastewaters. A novel approach to this problem involves the combining of algal and seaweed nutrient stripping processes with a marine aquaculture. Not only is nitrogen removed from wastewater, but important commercial shellfish and seaweeds are produced. A prototype process consisting of growth systems for marine algae, oysters and seaweed, joined in series, was fed secondarily treated wastewater, diluted 1:4 with seawater, for 11 weeks during the Summer of 1972. During this time 95 per cent of the influent inorganic nitrogen was removed by algal assimilation. The oysters in turn removed 85 per cent of the algae, but regenerated as soluble ammonia 16–18 per cent of the nitrogen originally bound in the algal cells. All of the regenerated nitrogen was removed in the seaweed system so that the total inorganic nitrogen removal efficiency of the system was 95 per cent. Phosphorus removal on the other hand was not nearly as complete as only 45–60 per cent was removed. The process has the capability of being expanded to include additional trophic levels in an integrated and highly controlled food chain system to serve the dual function of tertiary wastewater treatment and waste recycling through the production of shellfish and seaweeds.