Culture of Microalga Botryococcus in Livestock Wastewater

Botryococcus has been one of the most frequently and extensively studied algae in the world. Its potentially high hydrocarbon content and applicability for wastewater treatment have attracted increasing attention in recent years. This study aimed to produce oil from Botryococcus braunii using livestock wastewater for dual purposes of biofuel production and animal waste nutrient removal. B. braunii was batch-wise cultivated in the laboratory in livestock wastewater containing various nutrient concentrations. Optimal growth of B. braunii occurred in 50% autoclaved wastewater. Dry biomass concentration of up to 2.543 g L-1 was achieved with an oil content of 19.8%wt. The 30-day average biomass and oil productivities were 84.8 and 16.8 mg L-1 day-1, respectively. Growing B. braunii in livestock wastewater also effectively removed nutrients. On average, 88% of total nitrogen and 98% of total phosphorous in wastewater were removed in 14 days. B. braunii was found to be able to co-exist with a wild green alga, Chlorella sp.; the presence of either alga did not negatively affect growth of the other. Dry weights of B. braunii and Chlorella sp. were measured using a spectrophotometer by correlating dry weights of algae with their optical density values. Linear regression equations (R2 > 99.7%) for dry weight versus optical density for both algae were developed. These equations can be used to determine the dry-weight concentration of B. braunii and Chlorella sp. using readily obtained optical density values, regardless of wastewater concentration.