Increasing Phosphorus Concentration in Anaerobic Digesters Utilizing Wastewater Grown Algae

Abstract

The sequestration, recovery and recycling of phosphorus from both environmental and industrial processes is of great importance due to its high demand in fertilizer production. Additionally, high concentrations of phosphorus from agriculture runoff cause eutrophication of lakes disrupting eco-systems. Microalgae has been identified as an ideal concentrating agent of phosphorus by capturing dissolved phosphorus for growth. The high in phosphorus microalgae must then be harvested and degraded for phosphorus recovery using methods such as anaerobic digestion. This thesis looked to identify ideal conditions for dissolved phosphorus recovery from anaerobic digesters utilizing wastewater grown microalgae. Firstly, we identified stable substrate load rates (15g/L) and growing conditions (35ⴰC, 10rpm) for our anaerobic bacterial inoculum of 500mL. We analyzed volatile solid removal and organic acid and biogas production to determine the level of digestion of the substrate. Secondly, we operated several digesters at different retention times, analyzing most notably pH and dissolved phosphorus concentrations. The results of this thesis showed anaerobic digesters with lower retention times maintained a lower pH and higher levels of dissolved phosphorus. However the retention time must also be high enough to prevent washing out of anaerobic bacteria. Therefore, there exists an optimal retention time for dissolved phosphorus recovery which can be identified with further experimentation. Future work would also include optimization of a two-stage anaerobic digester process with both dissolved and precipitated phosphorus recovery points.