p. 155 - 168 MASS PRODUCTION OF UNICELLULAR ALGAE IN OUTDOOR CULTURES BY UTILIZING WASTE WATERS AS A TROPHIC SOURCE Pia-Elena Mihnea and Iulia Voinescu Romanian Marine Research Institute Constanta Abstract Results of the utilization of treated waste in culturing Chaetoceros simplex var. calcitrans Pauls, and Nitzschia closterium (Ehr.)W.Sm. in outdoor experiments are here presented. The N-NH4 and P-PO4 concentrations in waste water - sea water mixtures and the proper time for harvesting are concerned, as well as a cheap and very convenient device for culturing.