© 2020 Elsevier B.V. The specific growth rate of a brown alga, Sargassum macrocarpum, was evaluated by supplying bio-filtered wastewater (BFW) and synthetic nutrient medium (SNM) adjusted to the same nutrient concentration as BFW. The nutrient uptake characteristics were examined under various temperature conditions. The growth rates in the 0.5% and 5.0% (v/v) BFW treatments (0.015–0.025 wet weight day−1) were approximately the same as those in the 0.5% and 5.0% (v/v) SNM treatments (0.016–0.023 wet weight day−1), and were significantly higher (p < 0.05) than those in the non-enriched treatment (control) (0.006 day−1). The total phosphorus contents in 5.0% (v/v) BFW and SNM were significantly higher than those of the initial values (p < 0.01) because of excess phosphorus supplied above their demand. These results suggested that BFW can be utilized for seaweed growth and contribute to phosphorus accumulation in seaweed tissues. The maximum uptake rate (Vmax) for phosphate at a temperature ranging from 15 °C to 25 °C was constant (0.40–0.45 μmol g−1(dry weight) hrs−1), and increased at 30 °C (0.69 μmol g−1-(dry weight) hrs−1) probably because of their high phosphate demand induced by high respiration rate. The ratio of Vmax to Km for phosphate generally increased with increasing temperature (0.09 ± 0.02–0.27 ± 0.09), which was characterized as demand-driven uptake. These results indicated that fertilization effects based on the physiological response of seaweeds in response to temperature changes need to be considered when providing wastewater-derived nutrients.