2024 Volume 80 Issue 25 Article ID: 24-25005
To mitigate global warming, seaweeds or marine algae are expected to capture carbon dioxide directly from the atmosphere. With the aim to transplant it to the coastal areas in the future, we tried to culture a brown algae Sargassum horneri, which is frequently found in the coastal area in Japan at a low cost using composted sewage sludge as a locally available nutrient source. As a fundamental study, we mixed 1 L seawater and 10 g composted sewage sludge and collected its supernatant as composted sewage sludge (CSS) extract. Then, the brown algae was grown at 20 °C in the seawater mixed with CSS extract at 0%, 1%, 10%, and 20% for seven weeks, replacing the mixture of seawater and CSS extract every week. As the result, the algal growth was observed only in the seawater with 1% CSS extract, achieving the maximum values of full length and fresh weight which were 1.2 and 2.1 times larger than those in the seawater without CSS extract, respectively. On the other hand, the extract application at 10% and 20% to the seawater significantly inhibited the algal growth, probably due to the oversupplies of ammonium and phosphorus from CSS. The algae grown in the seawater with 1% CSS extract had photosynthetic pigments at the comparable concentrations to those grown in the seawater without CSS extract, while they had less contents of heavy metals. These results revealed the potential of CSS to supply nutrients for seaweed growth but the size of brown algae grown in this study was not enough for its transplantation to the coastal areas, motivating further studies to use CSS more effectively.
