Nutrient recovery by microalgae in aqueous product of hydrothermal carbonization of dairy manure

Hydrothermal carbonization (HTC) is an emerging technology for energy recovery from wet biomass waste streams, including dairy manure. The HTC aqueous product (HAP) contains organic compounds and nutrients, requiring further treatment prior to environmental discharge. The goal of this study was to evaluate nutrient removal from dairy manure HAP using four species of microalgae: Chlamydomonas reinhardtii, Chlorella vulgaris, Arthrospira maxima, and Scenedesmus obliquus. The optimal HAP concentration for all species was 5% with little to no growth observed at lower dilutions. The highest nutrient removal occurred with A. maxima with > 93%, 33%, 81%, and 50% removal of NH3, NO3- , total nitrogen (TN), and total phosphorus (TP), respectively. Nutrient removal with the other species ranged from 35% to 82% of NH3, 29% to 35% of NO3- , 12% to 34% of TN, and 8% to78% of TP. Integrating HTC with microalgae cultivation is a promising treatment method for combined energy and nutrient recovery from dairy manure.