(18c) Nutrient Recovery from Hydrothermally-Treated Dairy Manure Using Algae Cultivation

Increased demand for dairy products has led to intensification of farms, resulting in significant environmental impacts. Manure management is one of the most significant contributors to environmental impacts through greenhouse gas emissions (GHGs) and contamination of water resources by nitrogen (N) and phosphorus (P). As such, innovative treatment methods are needed to handle large quantities of manure and mitigate the environmental impacts within this food-energy-water system. Recent work has focused on energy and nutrient recovery of the organic matter and nutrients found in manure. Hydrothermal carbonization (HTC) is an emerging thermochemical treatment that converts organic waste into a carbon-rich solid fuel and a nutrient-rich aqueous product (HAP). The solid fuel can be used for energy production as a substitute for fossil coal. However, the HAP requires further treatment to capture nutrients and mitigate environmental impacts. In this research, algae species commonly used for nutrient removal in wastewater are evaluated for cultivation in HAP: Spirulina maxima, Chlorella vulgaris, Scendesmus obliquus, and Chlamydomonas reinhardtii. Species performance is quantified using growth rate, total biomass production, and removal of nitrate, ammonia, total nitrogen, and total phosphorus from various concentrations of HAP. Preliminary results show all species are capable of growth in HAP at low (<10%) concentrations and S. maxima shows high nutrient removal (>94% total nitrogen and total phosphorus removed) in low concentrations of HAP, improving water quality of the effluent. In addition, microalgae biomass is rich in protein and can be utilized as a food source for dairy cattle, directly recycling nutrients on-farm. Integration of algae production with HTC can help recover valuable nutrients from manure and improve water quality, alongside renewable energy production.