THE ROLE OF ANKISTRODESMUS-FALCATUS AND SCENEDESMUS-QUADRICAUDA IN SEWAGE PURIFICATION

Investigations have been made in laboratory continuous culture using sterile sewage as the medium for the start-up growth of Ankistrodesmus falcatus and Scenedesmus quadricauda. They were grown individually and in combination. Both algal forms after passing a lag phase showed logarithmic growth until day 6 and remained more or less steady thereafter. The former showed a higher cell number (2.4 x 10(6) cells/ml) chlorophyll content and dry weight than the latter (1.6 x 10(6) cells/ml) when grown separately. However, in mixed growth both exhibited almost equal peak cell populations on day 6, reaching a steady phase thereafter. In another study, when sewage pond effluent was used as inoculum containing a variety of algal forms only A. falcatus persisted in the medium at the termination of the experiment. Concurrent with the algal growth, in all cases a significant enhancement in pH (7.0 to 10.2) and DO (0.0 to 23.6 mg/litre) was observed, while a reduction in BOD, PO4 and NH3-N was marked. The study showed that both algal species, individually and in combination, were much better than a pond community with respect to BOD and nutrient removal.