Too Much of a Good Thing? The Effect of High Urea Concentrations on Microalgae Growth

Residing in the first trophic level of its food chain, photosynthetic algae takes in energy from the sun to create food for its ecosystem. Beyond the absorption of sunlight, this process involves the consumption of a complex balance of nutrients. Batches of wastewater can be an environment filled with the nutrients necessary for algal growth, and often contain large algae populations. In this experiment, we conducted an investigation on the effects of one specific nutrient, nitrogen, on the microalgae Chlorella sp. To guide our research, we questioned whether high concentrations of urea, a nitrogen source, would kill off the algae. By first growing algae in photobioreactors containing only a standard growth media and then growing a new group of algae with the addition of a high concentration of urea, we were able to gather data relevant to our question. By the conclusion of the experiment, we found that urea concentrations of 1500mg/L was sufficient to kill some of the algae. These findings suggest that, while urea is a vital nutrient in algal growth, it can be deadly if it is not at optimal concentrations. This is of particular relevance to those seeking to use algae in wastewater management and in biofuels production as it gives a guideline for what is useful in cleaning wastewater systems and what constitutes dangerous levels of urea in commercial production.