Algal Harvesting
Quick Links:
The next step in the processing is to separate the microalgae from the water and recover their biomass for further downstream processing. These processes currently pose one of the greatest challenges facing algae biofuel commercialisation and are widely debated. Large amounts of energy are required in this step of the process, which contribute to higher costs and detract from the environmentally sustainable advantages of the fuels.
Photo courtesy of http://mmm.multiedition.fi/
Rapidly accelerating algal mixtures in a centrifuge as well as filtration methods have proven to be extremely effective means of separating substances based on their density and size. Currently however, the processes are considered to be too cost and energy intensive to be used as the sole method of harvesting but may play a role in seperating valuable by-products from the mixture.
The addition of chemicals, which can enhance aggregation of algal cells, has been proposed as a less energy intensive alternative. This process is known as flocculation. Once aggregated, sediments can form upon a barrier, in an adjacent pond in an open raceway system, or float on the surface of water where they can be easily collected. The water from the aggregates can then be seperated using further dewatering techniques.
Toxicity associated with the contamination from the chemical flocculants as well as the costs of large quantities of expensive chemicals needed for large scale harvesting have prevented this method from being a cheap and sustainable option. To be financially feasible, breakthrough discoveries yielding cheaper and safer flocculants must be adopted.
Bioflocculation
A novel harvesting method known as bioflocculation has been proposed as far more cost effective method of separation. Bioflocculation uses one, flocculating, algae species, to concentrate the algae of interest. In a recent study, this method showed to increase the seperation and collection of algal biomass from a mixture. This method is as easy and effective as chemical flocculation but does not require the input of expensive chemicals, providing a sustainable and cost effective method of algal harvesting.
Engineering Developments
Other attempts to enhance current harvesting methods have focused on improving production systems through developing the technology of photobioreactors and open ponds.
To learn more about recent developments in this area, please follow the link below.