Fig. 3. Effect of recycling post-harvested spent water on the harvesting efficiency, biomass productivity and urea recovery for the growth of Chlorella sp. FC2 cells in six consecutive batches of cultivation (one control (C) followed by five recycled batches (1–5)). The batch with fresh medium and fresh FC2 cells as the inoculum was considered the control batch. RWFC represents the batches with the recycling of spent water after harvesting and fresh FC2 cells as the inoculum for the successive batch. RWHC represents the batches with the recycling of spent water after harvesting and harvested FC2 cells as the inoculum for the successive batch. Harvesting experiments were performed with the microalgal biomass grown in mini-reactors with a working volume of 350 ml. Harvesting experiments were performed with FeSO₄ (Panel A) and FeCl₃ (Panel B) with an F/X ratio of 2.5 and 3, respectively. The letters on the bar graphs represent the significant differences between the harvesting efficiency, biomass productivity, and urea recovery obtained from the harvesting of microalgal biomass using FeSO₄ and FeCl₃ analyzed using the one-way analysis of variance based on Tukey's method. Harvesting efficiency, biomass productivity and urea recovery that do not share a common letter are significantly different.