In this study microalgal biomass produced in an experimental HRAP
treating urban wastewater was used to test the harvesting efficiency of
two natural flocculants. The natural flocculants Ecotan and Tanfloc
attained microalgal biomass recoveries over 90% with low concentrations
(10 and 50 mg/L for Ecotan and Tanfloc, respectively). With this
dose sedimentation of flocculated biomass was achieved within
10 min for Ecotan and 20 min for Tanfloc in a 40 cm column, compared
to 80 min for microalgal biomass sedimentation without flocculants.
This means that larger volumes of microalgae suspension could be
recovered in less time and/or smaller settlers. None of the studied flocculants
showed negative impacts in terms of pH and anaerobic biodegradability
as shown in BMP tests with flocculated biomass (162–
166 m LCH4/g VS).