Phosphorous is an essential nutrient and a limited resource, meaning it cannot be replaced with other elements. While phosphorous is an important component of plant and livestock production, levels in agricultural runoff can accelerate growth of algae blooms and affect water quality in lakes and streams. Finding ways to effectively recover phosphorous from wastewater is the subject of a new paper in the Journal of Environmental Engineering. Researchers Yifan Ding, David A. Sabatini, and Elizabeth C. Butler examine whether recovered phosphorous could be used as fertilizer with the goal being to close the cycle of phosphorous recovery and reuse. An exhaustive literature review turned up a range of studies on the subject and variety of minerals that can aid with phosphate removal.
Agricultural waste, specifically corn cobs and rice husks, were combined with magnesium and bittern to create biochar, which the authors used to test phosphorous recovery from model animal wastewater. Their paper, “Effects of pH and Soil Minerals on Phosphorus Release from Agricultural Waste–Based Sorbents: A Continuous-Flow Column Study,” explores these new treatment methods that could help address sustainable food challenges. Learn more about how this research could lower environmental impacts and reduce costs for farmers at https://doi.org/10.1061/JOEEDU.EEENG-7102. The abstract is below.
Abstract
Effective methods for the recovery and reuse of phosphorus are needed for sustainable agriculture. In this study, magnesium-amended corn cob chars prepared with brucite and sea bittern and calcium silicate hydrate (CSH) synthesized with hydrated lime and rice husk ash were tested for phosphorus recovery from a model animal wastewater at pH 8.0. After phosphorus uptake from the model wastewater, the two Mg-chars had a phosphorus concentration of 182–198 mg P/g, and CSH had a phosphorus concentration of 46 mg P/g. In continuous-flow column release studies, in which these materials were mixed with sand after phosphorus uptake, Mg-chars released over 80% of the recovered phosphorus within five pore volumes at pH 5.5, 7.0, and 8.5. Post-P-exposure CSH, on the other hand, required 335 pore volumes to release 90% of the recovered phosphorus at pH 8.5. The more rapid release at pH 5.5 and 7.0 compared to pH 8.5 for the spent Mg-chars is attributed to the greater solubility of magnesium phosphate minerals at lower pH values. When goethite or kaolinite was added to the sand columns containing spent Mg-char, the rate and extent of phosphorus release slowed significantly, especially for goethite versus kaolinite, and especially at pH 5.5. and 7.0 versus pH 8.5 for both minerals. This trend is attributed to the greater electrostatic driving force for the adsorption of phosphate to the mineral surface below the mineral point of zero charge (pHpzc).
Learn more about the new way to recover phosphorus in the ASCE Library: https://doi.org/10.1061/JOEEDU.EEENG-7102.
