The removal of sodium (Na) from seawater using two photosynthetic bacteria was investigated using Rhodobacter sphaeroides SSI (SSI) and Rhodovulum sp. which is a marine photosynthetic bacterium. Both Rhodovulum sp. and acclimated SSI were shown to grow well in a 3% NaCl supplemented glutamate-malate medium. The maximum rate of Na removal was 39.3% by SSI and 64.9% by Rhodovulum sp. after two days cultivation under static light conditions. However, Na was re-released back into the medium after two to three days. When a nutrient-supplemented seawater medium (3.3% NaCl, 13.10 gNa/l) was used, the maximum Na removal rates were 30.3% (9.05 gNa/l) by SSI and 48.9% (6.69 gNa/l) by Rhodovulum sp., under static light conditions. Similar growth and Na removal rates were found under aerobic dark cultivation. In this case, no re-release of Na was observed with either bacterium. Two stages culturing was conducted first, with Rhodovulum sp. and then with SSI replacement. The Na concentration was reduced to 0.79 gNa/l (94.0% removal) after cultivation for eight days under aerobic darkconditions. The supernatant was applied successfully as a liquid fertilizer in the cultivation of Japanese radish.
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