Most of the microalgae present in aquatic systems competed for the same available inorganic nutrients. The successful competitors would eventually dominate the rest because of their adaptive advantageous. Based on this premise, it was important to understand the effect of nutrients input rate on microalgal species-diversity and population. This was investigated in batch experiments of 14 days with pond water samples having natural ecosystem by varying nutrients dosing pattern under natural day light. Nutrients were supplied as single dose and multiple doses to the fresh water microalgal culture of fresh water. Prominent growth of many microalgal species was the key result of multiple dosing of nutrients compared to single or concentrated dosing of nutrients. Simulation towards oligotrophic condition was supporting the diverse population of microalgae. Whereas in the experiments with higher dosing of nutrients in one or two times had dominant growth of two or three microalgae and higher growth of heterotrophic bacteria. This condition resembled the eutrophic or hyper-eutrophic condition of water. This study thus showed the influence of the nutrients supply pattern on the growth and diversity of microalgae in freshwater and the nutrients added on eight, ten and twelve consecutive days from first day were considered as the effective nutrient addition pattern to promote maximum microalgal population present in a freshwater system.

The goal of this study was to develop a self-settling microalgal consortium in raceway pond reactor (RPR). Experiments were carried out with cultures that developed without additional seeding, but naturally promoted by process conditions in a raceway pond reactor. The changes in microalgal communities and total biomass under nitrogen and phosphorous limitations were studied in both batch and continuous systems. At the steady state batch had the population of 46% Euglena sp., 16% Closterium sp., 14% Chlorella sp., 14% Scenedesmus sp. and 10% Ankistrodesmus sp. with a maximum biomass of 900 mg/L. In order to get self-settling microalgal consortium, the operation was changed to continuous continuous mode with the aid of a specially designed settler for daily harvest and recycling of the biomass. Grazing fauna could be controlled by managing reduced liquid and solid retention time. At steady-state condition, an autofloculating and self-settling consortium was developed which had mainly Fragilaria sp., Scenedesmus sp., and filamentous Ulothrix sp. The maximum biomass concentration obtained was 140 mg/L. The presence of neutral lipid droplets in the consortium was identified by staining with Nile Red. Development of the lipid rich consortium could be a suitable method for producing biofuel.