selective cultivation of easily harvestable algae using crossflow-microscreening

The implementation of algal systems as a viable wastewater treatment option has been seriously limited by the availability of cost effective techniques for removing algae from the effluent stream. In this study, the problem of biomass separation was overcome by the selective cultivation of algae species which could be removed effectively by simple screening. The selection of desired species was achieved by a combination of short hydraulic space time and various size micro-screens operating as algae selectors on the effluent stream. A high rate algae growth system, in which the mean cell residence time and hydraulic space time could be manipulated independently, was developed. With humus tank effluent as feedstock, a hydraulic space time of 10 hours and a 200 µm opening size crossflow-microscreen, the filamentous green algae, Stigeoclonium, became the dominant species. This selected culture could be readily maintained at any predetermined concentration in the system with less than 20 mg/ℓ suspended solids in the effluent. The biomass produced was exceptionally easy to harvest.