Energy Products
Monitoring Algal Biofuel Cultivation
Microalgae are becoming an important new source of renewable biodiesel transport fuel. As an aquaculture crop, microalgae are typically at least an order of magnitude more productive than the fastest growing terrestrial feedstock crops, and they don't compete for scarce agricultural land or the production of food. Although some production facilities, such as the one shown above (photo from isiria.wordpress.com), are land-based plantations, many rely on algae harvested and transported from impaired waterways.
AAI's water quality products can provide a valuable means for assessing and monitoring the condition and productivity of microalgae crops. The products can, for example, be effectively used to remotely locate plumes of algae in impaired waterways, measure their biomass, and assess their productivity and suitability for harvesting. For plantations, productivity and suitability for harvest can be monitored at fine spatial scale and with unprecedented precision. Whether the algae are in waterways or on land-based plantations, spectral images can be processed to retrieve the per-pixel concentration of suspended chlorophyll, which provides a quantitative measure of both total and dry algal biomass. Chlorophyll concentrations can be correlated with simultaneously retrieved concentrations of colored dissolved organic carbon to obtain a per-pixel estimate of productivity and maturity, and the corresponding estimate of productive biomass and best locations for harvesting.
In the figure below is shown the image-retrieved chlorophyll concentrations for an algal mass in a cove of an impaired water body. The image retrieved per-pixel concentrations of suspended chlorophyll are shown. Mean concentrations for the central algal mass (red arrow) are near 20mg/m-3, which corresponds to a dry algal biomass of 800mg/m-3 or total biomass of 8g/m-3.
In the next figure is shown the image-retrieved concentration of Colored Dissolved Organic Carbon (CDOC). Areas of enhanced CDOC within the algal mass concentration represent areas of algae decay, while areas of low to modest concentrations in the mass represent areas of algae growth. In the growth areas, the image-retrieved concentrations can be used in conjunction with image-retrieved visibilities (not shown) to determine areal productivity rates. In this case they correspond to ~19g m-2 day-1, which are generally considered commercially viable quantities for harvesting for biodiesel production, assuming even modest lipid contents of 20-30% for the mature algae. From the distribution of CDOC, the most mature and harvestable (lipid-rich) algae are generally in the peripheral portions of the mass, while primary production is generally concentrated in the central portion.
In the next figure is shown the concentration of suspended minerals, which reveals that the likely source of nutrients responsible for the primary production of the algae in this cove is agricultural runoff. This is an important source of information for predicting future behavior and developing harvesting strategies at this location.
