Logistical systems vary based on technology, but these processes generally include harvesting algae from the cultivation system and then dewatering and concentrating the harvested biomass so that it's suitable for preprocessing into a product that can then be refined and upgraded into a biofuel.
Optimizing the algal harvesting operations is critical to maximizing yields of algal biomass as well as ensuring sustainability. Recycling the remaining water back into the cultivation system reduces total water consumption. Algal biomass can be harvested from cultivation systems continuously or in daily or weekly batches and harvesting can be timed to take advantage of the algae's natural growth cycle.
Microalgae and cyanobacteria cultivated in water grow at dilute concentrations so new dewatering technologies—capable of cost-effectively isolating algal solids from high-volume, low concentration effluents—are needed. Although, dewatering technology exists in wastewater treatment and mining issues today, microalgae and cyanobacteria do not require the same dewatering intensity.
Dewatered algal biomass may still be too dilute for effective preprocessing, and technologies are needed to boost these slurry concentrations. Concentration requirements are dictated by the preprocessing method that will be used. Centrifugation of membranes are typically used for concentrating the solids, but like dewatering, innovative adaptations and new technologies are needed to cut energy requirements and costs.
Algal preprocessing refers to production of energy-dense intermediate products from harvested algal biomass. Preprocessing steps and requirements vary based on technology design and type of biofuel that will be produced. Steps could include extracting lipids from algal cells or subjecting whole algal cells to high heat and pressure in a process, which is known as hydrothermal liquefaction.
The end results of the preprocessing steps should be products suitable for refining into biofuels, such as diesel, jet fuel, gasoline, or ethanol. The Renewable Carbon Resources program works closely with the Conversion Technologies program on intermediate production research and development.
To see an example of the potential algal biofuel intermediate production technologies, view a video on Pacific Northwest National Laboratory's hydrothermal liquefaction process.
The algal components that will not be converted to biofuels can comprise 40%–75% of the biomass moving through the logistical system. Processing this remaining biomass can provide nutrients and power back to the production and logistical system, or it can be converted to valuable co-products, such as animal feeds or commodity chemicals.