Continuous discharge of solids as a slurry is possible with the nozzle-type disc centrifuge. The shape of the bowl is modified so that the slurry space has a conical section that provides sufficient storage volume and affords a good flow profile for the ejected cake (Shelef et al., 1984). The bowl walls slope toward a peripheral zone containing evenly spaced nozzles. The number and size of the nozzles are optimized to avoid cake buildup and to obtain reasonable concentrated algal biomass.

The application of a nozzle-type disc centrifuge for algae harvesting was suggested by Golueke and Oswald (1965). The influence of nozzle diameter on flow rate, algae removal efficiency, and resultant slurry concentration was looked into. Through comparison with other algae harvesting methods, it was concluded that the nozzle-type centrifuge seemed promising, albeit it is less attractive because of power requirements and capitalization costs. In other studies, the centrifuge appeared to be more effective to harvest Scenedesmus than Coelastrum (Mohn and Soeder, 1978; Mohn, 1980). By returning the centrifuge underflow to the feed, the solids content of the algae suspension (0.1%) can be concentrated by a factor of 15-150%. The reliability of this device can be ensured as long as the clogging of the nozzles is avoided.