Concentration and removal of microaglae by flocculation

• Main Author: Wong, Shuhui.
• Other Authors: Wang Jing-Yuan
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/15913
• Institution: Nanyang Technological University

This report provides a detailed research and experiment on algae removal by flocculation for harvesting of algae and to resolve algae blooming problems in water bodies. Algae have many useful environmental applications such as wastewater treatment and biofuel production. They can also be a nuisance where they cause serious human health and environmental issues when blooming uncontrolled in water bodies. In today’s world, there is still no cost efficient method to separate or remove algae. Hence, this project would investigate the potential of flocculation with biodegradable polymer such as chitosan and optimise the process under various conditions and configurations. Jar tests were used to determine the parameters for flocculation and settling. The homogenous solution was fractionated into six beakers containing 500mL of algae suspension for each experiment. Four tests were carried out to determine the influence of algae and coagulant concentrations, pH and flocculation time on the flocculation efficiency. Turbidity, apparent colour and pH of the samples were recorded before and after the experiments. The optimum point was found to occur at 3mg/L of coagulant and 0.48g/L of algae with a ratio of 1:160, producing a maximum reduction of 82% and 85% in the turbidity and apparent colour respectively. The largest floc size produced was around 2.25 to 3 mm and required 8 minutes to settle with a velocity of 0.0154cm/s at the optimum condition. The flocculation efficiency can be further optimized by reducing the mixing time from 15 to 9 minutes. It was observed that a reduction in coagulant concentration and increase in the algae concentration decrease the efficiency while increasing both concentrations enhance the process. This was because the algae concentration was directly proportional to the coagulant concentration. From the results obtained, the flocculation efficiency could be further optimised by using a more acidic media for the preparation of chitosan It was also found out that a reduction in the mixing time for flocculation to take place could greatly enhance the efficiency. Therefore, less time and less energy would be required to carry out the flocculation process which in turn helped to save cost and provide a more economical method for removing or harvesting algae. In conclusion, the flocculation of algae using chitosan shown to be an effective way of removing algae from water bodies, achieving at least 80% reduction in the turbidity and apparent colour.