Growth ofEnteromorpha linza in sewage effluent and sewage effluent-seawater mixtures

Enteromorpha linza (L.) J. Ag. was grown in full strength sewage effluent, various combinations of sewage effluent and seawater, and in natural seawater. It was found that full strength sewage effluent with a salinity of 14 supported best growth of the alga. After a 12 day cultivation period, growth ofE. linza in full strength sewage effluent and 75% sewage effluent- seawater mixture showed 3.5-fold and 2-fold increase in fresh weight over that grown in natural seawater; respectively. Uptake of PO _inf4 ^sup3– -P, NH₃-N and NO _inf3 ^sup– -N by cells ofE. linza was extremely efficient in all tested media. Data obtained from the experiments indicated that inorganic nitrogen rather than phosphorus was the limiting nutrient factor for growth ofE. linza in full strength sewage effluent and in other sewage effluent- seawater mixtures. NH₃-N at concentrations above 4.5 ppm was found to inhibit uptake of NO _inf3 ^sup– -N in the same culture medium by the algal cells. The fact that sewage grownE. linza contained comparatively much higher protein content (30.2% dry weight) than that grown in natural seawater (12.5% dry weight) leads to the conclusion that sewage grownE. linza could serve as an economically feasible feed for livestock in Hong Kong where the sewage is characterized by having a salinity of approximately 14. It is proposed that this multicellular green alga is a suitable algal species to serve the dual function of wastewater purification through the production of algal protein from sewage effluent having high salinities.