The potential use of macroalgae for removal of nutrients from sewage water in East Africa

Preliminary studies were carried out to investigate the possibility of using local species of macroalgae for the purification of polluted water, primarily sewage water, from village households in East Africa. The work was done on Unguja Island, Zanzibar, Tanzania. Seaweed species diversity of intertidal flats on the east coast of Unguja was studied outside villages with beach hotels. Nutrient samples (N and P) were taken in the sea close to sewage outlets. Growth characteristics and nutrient uptake rates were investigated for 14 macroalgae and 3 were selected for further study in a model system for wastewater treatment. No effects on macroalgal species composition were found. High uptake rates for ammonium, nitrate and phosphate were found in the three selected species. Nutrient load and composition, mainly N:P ratio, were varied to optimize uptake efficiency. We conclude that local macroalgae are suitable for efficient nutrient removal and suggest that a system with simple tanks or ponds with macroalgae be used for small-scale purification of sewage water in the region.