Accumulation characteristics of soluble algal products (SAP) by a freshwater microalga Scenedesmus sp. LX1 during batch cultivation for biofuel production

► Accumulation of soluble algal products by a lipid-producing Scenedesmus was studied. ► The SAP content, yield and rate were analyzed under various nitrogen conditions. ► Higher nitrogen led to more SAP accumulation particularly in stationary phase. ► Relationship of SAP production rate to growth rate and cell density was determined. ► SAP accumulation was mainly due to the release of growth-associated products. Algae cultivation is the essential basis for microalgal biofuel production. Soluble algal products (SAP) are significant obstacle to large-scale, high-cell-density cultivation processes. SAP accumulation during batch cultivation of Scenedesmus sp. LX1 (a unique strain accumulating lipid substantially while growing fast under low-nutrient conditions) with different initial nitrogen concentrations (7.4–34.0 mg N L −1 ) was investigated. The SAP content varied in the range of 3.4–17.4 mg DOC L −1 at stationary phase, with average yield per cell of 0.5–2.5 pg DOC cell −1 . High SAP accumulation up to 15.2–17.4 mg DOC L −1 were observed with initial nitrogen above 20.2 mg N L −1 . The maximum SAP production rate per unit culture volume ( r SAP ) was 2.6 mg DOC (L d) −1 and that per cell ( ν SAP ) was 1.5 pg DOC (cell d) −1 . The r SAP increased with cell growth rate and decreased with cell density linearly. The SAP accumulation was majorly due to the release of growth-associated products.