From Waste to Resource: Innovative Slow-Release Fertilizer Advances the Nitrogen Circular Economy

In the coming decades, humanity will be faced with the challenge of feeding 10 billion people and managing large quantities of solid waste. These issues can be mitigated through the development of sustainable fertilizers derived from electrochemically treated waste activated sludge (EWAS), while promoting a nitrogen circular economy. This study investigates the chemistry of novel fertilizers to determine their soil chemistry dynamics. Untreated waste activated sludge (WAS) and EWAS were applied to agricultural soil and potting mix and the resulting aqueous samples were analyzed to determine nitrogen, phosphorous, carbon, and micronutrient adsorption and release behaviors. Commercial inorganic and natural fertilizers were utilized for comparison. X-ray adsorption near edge structure spectroscopy (XANES) was performed to characterize phosphorus speciation in the solid phases of the novel fertilizers. Results indicated that EWAS and WAS samples released less total nitrogen into solution than other treatments due to organoclay complexation of biomolecules and differences in the solubility of the nitrogen species. Samples containing EWAS released a higher percentage of organic and total carbon into solution due to the deformation of the structure of the organic matter by the alkaline electrolysis process. The solubility of nitrogen and carbon in the sludge was increased by the electrochemical process. Solid-phase phosphorus in EWAS and WAS was characterized by XANES analysis as struvite, which is a novel finding with important implications for P management from waste-based fertilizers. These experimental findings suggest that fertilizing with EWAS could result in reduced runoff and improved soil health while facilitating domestic fertilizer production.