Civil and Environmental Engineering
Date of this Version
Published in Water, Air & Soil Pollution 231 (2020), #26.
The treatment efficiency of Chlorella sorokiniana and Scenedesmus species, immobilized in sodium alginate, was evaluated for removing nitrate from groundwater. The experiments were performed initially in batch mode and the best-performing conditions were replicated in sequencing batch reactor mode. S. sp. showed a higher nitrate uptake in short term than C. sorokiniana. Immobilized S. sp. and C. sorokiniana cells showed 90% nitrate removal in 9 and 12 days, respectively. The optimal ratio of algal beads/water was found to be 12.5% (v:v). Comparatively, suspended S. sp. cells were able to remove only up to 35% of nitrate in 8 days. Alginate immobilized S. sp. beads were capable of uptaking nitrate for 100 consecutive days in sequencing batch reactor mode. When tested in actual groundwater, 90% of nitrate was eliminated in 2 days without need for any additional carbon source. Immobilized algal beads can be a low-cost alternative technique to remove nitrate from groundwater as they are water-insoluble, non-toxic, easy to harvest, and offer high removal efficiency.
Highlights: Utilization of immobilized algae is a practical method for nitrate treatment. • Cultivation of heterotrophic algae reduces retention time needed for treatment. • Actual groundwater is more suitable for nitrate removal than simulated lab water. • In natural water, additional carbon source is not required for successful removal. • Same algae beads could be reused for treatment for repeated cycles up to 100 days.
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