Flow-way water depth affects algal productivity and nutrient uptake in a filamentous algae nutrient scrubber

Filamentous algae treatment systems can provide cost-effective treatment of a range of wastewater types. In the current study, filamentous algae nutrient scrubbers (FANS), treating anaerobically digested food-waste centrate, were used to investigate the role of flow-way water depth (5, 10 and 15 mm) on productivity and nutrient removal. The study found that the proportion of light reaching the surface of the filamentous algae mat ( E mat ) increased with decreasing water depth, with 5-mm depth significantly higher than 10 mm ( p < 0.05) and 15 mm ( p < 0.01). On all sampling occasions, both the total solids and ash-free dry mass biomass productivities, as well as the chlorophyll a biomass, were all significantly higher ( p < 0.01) on the FANS operated at 5 mm depth compared with 15 mm. Both the percentage carbon (C) and percentage phosphorus (P) were significantly higher in the biomass from 15 mm compared with 5 and 10 mm deep. Percentage nitrogen (N) content did not differ significantly between treatments but biological nitrogen removal rates (particulate N removed m −2 day −1 ) were significantly higher on the 5-mm-deep FANS compared with the 10 mm deep ( p < 0.05) and the 15 mm deep ( p < 0.01). The C:N ratio of algal biomass varied but not with depth whereas the C:P ratio significantly decreased ( p < 0.01) with increasing water depth. These results indicate the important roles that light and water depth play on the performance of FANS.