Effect of Three Dimensional Substratum Features on Benthic Algal Biomass Productivity

Abstract

Algae has emerged as a promising and valuable source for biofuels, waste water remediation and bio-products such as fertilizers, bioplastics and aquaculture feed. Algae’s emergence can be attributed to its high growth rates and the ability to use the cultivation of algae for the dual purposes of a biofuel source and as an agent for wastewater remediation. For cultivated algae, the yield is strongly dependent on the characteristics of the substratum used for cultivating algae. Substratum features such as topography and roughness affect algal attachment and colonization, thereby influencing the growth rate of algae grown on such substratum. Traditionally, two dimensional substrata have been the substratum of choice for algal cultivation, with significant effort being invested towards optimizing features such as the surface roughness. Recently, the suitability of three dimensional substrata has been tested, with results showing strong algal yield performances. However, how three dimensional substratum supports algal biomass yield is not fully understood. This study seeks to investigate the effect of three dimensional substratum features such as fiber density on algal biomass productivity, with the goal of understanding how such features impact algal cultivation. Additionally, the three dimensional substratum are deployed in both low and high nutrient concentration environments to explore their performance under different nutrient environments. Also, the importance of substratum base roughness is investigated. In two dimensional substrata, the substratum roughness feature is vital. However, for three dimensional substrata, the introduction of vertical structures to support algal attachment and colonization activities may minimize the need for optimizing the roughness of the substratum base. To carry out these experiments, bioreactor systems were designed, constructed and put to use. Also, experimental methods for growing, harvesting, drying and measuring algal biomass were developed and implemented. Findings obtained from the studies showed that three dimensional substratum features such as fiber density significantly affect algal biomass productivity, while features such fiber height may not have so much effect on algal yield. The introduction of three dimensional substrata also significantly increased algal yield under different nutrient concentration environments. Under low nutrient environments, the switch to three dimensional substratum led to a 174% increase in yield, while under high nutrient environments the yield increased by 89%. Finally, results suggest that when using three dimensional substrata for algal cultivation, the substratum base roughness may not be a significant factor for algal biomass productivity.