Microalgae are known for their immense potential in the production of biofuels and other valuable bioproducts. However, one of the major challenges encountered in microalgae cultivation is the efficient harvesting and dewatering of algal biomass. Among various techniques employed for this purpose, flotation has emerged as a promising method due to its low energy requirement and high efficiency.
Flotation is a separation process that exploits the differences in the buoyancy properties of various materials. In the context of microalgae harvesting, flotation involves the separation of algal cells from water based on their differential floating abilities. The process is aided by the introduction of gas bubbles into the cultivation medium, which attach to the algal cells and carry them to the surface, forming a float that can be easily skimmed off.
There are two main types of flotation used in algae harvesting: dissolved air flotation (DAF) and froth flotation. In DAF, air is dissolved in water under pressure and then released at atmospheric pressure. The sudden reduction in pressure causes the air to form tiny bubbles, which attach to the algal cells and lift them to the surface. Froth flotation, on the other hand, involves the injection of air directly into the cultivation medium to generate bubbles.
One of the main advantages of using flotation for algae harvesting is its high efficiency. Studies have shown that flotation can recover up to 90% of algal biomass, which is considerably higher than other methods such as sedimentation and filtration. Furthermore, flotation does not require any chemical additives, making it an environmentally friendly option.
However, like any other technique, flotation also has its limitations. One of these is that it may not be suitable for all types of algae. Certain species of algae have a natural tendency to float, making them ideal candidates for flotation harvesting. Others, however, tend to sink or remain suspended in water, making them difficult to harvest using this method.
After harvesting, the next step is dewatering, which involves removing excess water from the harvested biomass to concentrate it for further processing. This step is crucial as it significantly reduces the volume of biomass and thus lowers transportation and processing costs.
Several dewatering techniques are used in conjunction with flotation harvesting, including centrifugation and filtration. These methods work by applying mechanical force or pressure to separate water from algal cells. However, they often require significant energy input and may damage the algal cells in the process.
In recent years, researchers have been exploring more sustainable alternatives for dewatering such as solar drying and use of super absorbent polymers (SAPs). Solar drying utilizes solar radiation to evaporate water from algal biomass while SAPs are materials that can absorb and retain large amounts of water.
In conclusion, flotation presents a promising technique for efficient harvesting of microalgae biomass. Combined with sustainable dewatering methods, it offers a potential solution to one of the biggest challenges in algae processing. However, more research is needed to optimize these techniques and make them more applicable for different types of algae.
