A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1980

High-rate oxidation pond has high efficiency of BOD removal and algal production of high protein content. Auto-flocculation is used successfully and is the most economical process for algal harvesting. The objective of this study is to recover maximum algal yield by auto flocculation at various growth conditions and to study the effects of these conditions on algal auto-flocculation. AIT sewage was used for feeding the pond, and mixing were carried out by manual brooming twice a day, once a day and without mixing. Sampling of algae-laden water was done through upper and lower tap located at 5 cm and 30 cm under water surface. The algae-laden water is siphoned into the settling pond through these taps, after it is mixed twice a day, once a day and without mixing. The settling pond water is adjusted to pH 8, pH 9, pH 10 and pH 11. Auto-flocculation is used for algal harvesting. Economic considerations of drying techniques costs are presented. Algal production and protein content are calculated. It was found that highest algal concentration was at 30 cm depth at 1 pm to 2 pm and by mixing the pond water once a day at 9 am. Detention time for algal auto-flocculation was 7 hours and pH more than 10 was not suitable for algal auto-flocculation.