Rock Filter Research Articles

Settling Rates of Algae from Wastewater Lagoons

The settling rates of algae are considered to be a controlling factor in the operation of rock filters that are used for the removal of algae from lagoon effluents. The settling rates of Scenendesmus acuminatus , Chlorella vulgaris and Microcystis aeruginosa were measured for various temperatures, for dark aerobic and anoxic incubation, and for various mixture ratios of the three species. Of all variables tested temperature seems to have the largest influence on settling rates. Settling rates in m per day decreased from 0.262 at 21°C to 0.094 at 5°C for S. acuminatus and from 0.128 at 21°C to 0.016 at 5°C for M. aeruginosa . Incubation under either aerobic or anaerobic conditions for up to 15 days does not significantly alter the algal settling rates. The settling rate of a mixed algal culture can be estimated from the known fraction and settling rate of each algal species present.