(146d) Utilizing Microalgae to Remove Phosphorus from Wastewater Effluent Streams through Hydrothermal Liquefaction

With the rise in human population and food consumption comes a high demand in the agriculture industry for phosphorus-rich fertilizers. Currently a majority of phosphorus is mined from a select few countries leaving no sustainable or renewable means to manufacture and produce phosphorus-rich fertilizers. Microalgae has shown great promise in removing phosphorus from wastewater effluent streams. Hydrothermal liquefaction (HTL) is a process that uses subcritical water to convert algae to four main products: a biocrude oil, a solid product, an aqueous co-product (ACP), and a small amount of gas that is primarily CO2. The HTL solids and ACP produced from this process contain varying levels of phosphorus. The objective of this work is to determine the parameters that maximize phosphorus recovery in the HTL solids. Calcite (CaCO3) was the primary inorganic structure observed by x-ray diffraction for both wastewater-cultivated and auto-flocculated algal solids. Thus, calcite and trisodium phosphate (Na3PO4) were loaded at calcium-to-phosphorus ratios ranging from 1 to 2.33 and reacted under conventional HTL conditions (350°C; 60 minutes). In addition, low-ash algae was added to the calcite and Na3PO4 reactions. The hypothesis was that the algae creates more CO2 during the reaction, thus allowing for great dissociation of CaCO3. This phenomenon creates more Ca2+ molecules, which the aqueous phosphorus can bond with and be recovered in the solid HTL product. The addition of algae caused a greater recovery of phosphorus in the HTL solid product at all major Ca:P molar ratio thus confirming our hypothesis.