Abstract:Marine macroalgae is used as a biofilter for aquaculture wastewater treatment. Marine macroalgae is used as a biofilter for aquaculture wastewater treatment. Ulva prolifera was cultivated at four different water temperatures (22.5℃, 25.5℃, 28.5℃, and 31.5℃) with a different inorganic nitrogen source (NH4Cl, NaNO2, and NaNO3) for each temperature to evaluate the purification efficiency of marine macroalgae U. prolifera on wastewater; all measurements were carried out in triplicate. The results show that, in the temperature range 22.5℃~31.5℃, the TAN uptake rates were 14.65, 14.88, 14.48, and 13.53 μmol/(g·h) in 96 h; the nitrite and nitrate uptake rates were 11.28, 10.48, 9.11, and 8.38 μmol/(g·h) and 9.41, 8.62, 8.80, and 7.35 μmol/(g·h) in 144 h, respectively. Both the temperature (P<0.01) and the nitrogen source (P<0.05) had significant effects on the growth rate of U. prolifera. The growth rate decreased as the temperature increased; further, at the same temperature with an ammonium source, U. prolifera showed the largest growth rate, followed by that with nitrite and nitrate sources. For the ammonium and nitrite sources, the content of chlorophyll a (Chl-a) increased with an increase in temperature; however, for the nitrate source, the content of Chl-a decreased first and then increased. Both the temperature and the nitrogen source had a significant effect on the carotenoid content (P<0.01), which increased with an increase in temperature. In the temperature range of 28.5℃~31.5℃, the carotenoid content in the nitrate source were found to be significantly higher than that in the other sources (P<0.05). The temperature and nitrogen source, thus, has a significant influence on the growth rate, Chl-a, and carotenoid content of U. prolifera. Overall, the TAN uptake rate was the highest, followed by the nitrite and nitrate uptake rates. However, the inorganic nitrogen uptake rate decreased as the temperature increased.
