Metal sorption with struvite, and intersections with community engagement and science policy
Creators: name: Goswami, Omanjana
Publisher: name: No Publisher Supplied
Year: 2021

description: Nutrient pollution through excess application of phosphorus (P) and nitrogen (N) fertilizers, and subsequent detrimental impact on environmental water quality is a persistent environmental problem. To mitigate the issue of P-runoff and establish an alternate source of fertilizer-grade phosphate, struvite (MgNH4PO4·6H2O) recovery is being encouraged. However, wastewaters feasible for recovering struvite often contain elevated concentration of heavy metals, and metal association with struvite can affect the quality of recovered product. This dissertation combines laboratory with field research and evaluates geochemical and science policy challenges to struvite recovery and use.The sorption of heavy metals cadmium, cobalt, copper, nickel, lead, and zinc, on struvite was evaluated using a combined macroscopic and spectroscopic approach. It was hypothesized that aqueous geochemical conditions such as metal concentration, pH, and the presence of organic ligands dictates the extent of metal sorption with struvite. Both sorption and desorption processes were evaluated. In organic-free systems, metal loadings ranged from 2-493 mg kg-1, and increased with pH from 7-10 and initial metal concentration from 1-5 μM. Reversibility of sorption ranged from 10-85%. Acetic and benzoic acid had no significant impact on metal sorption, whereas humic acid complexed metals, inhibiting sorption. Spectroscopic analysis indicated that metals sorb as mono- or bidentate complexes in common coordination environments, and the binding environment remains unchanged in the presence of organics. Organics also sorbed with struvite at loadings of 493-1364 mg kg-1, and primarily impacted the thermal stability of the mineral, with key thermal indicators and release of volatile components shifted to lower temperatures.The concentration and speciation of metals in urban farm soils was evaluated to determine the potential impact of metal-bearing struvite fertilizer on soil contaminant content. Soils were sampled from urban farms across the city of Newark, New Jersey. Using soil extraction techniques and spectroscopic analysis, lead was found to be the dominant metal, with concentrations highest adjacent to buildings and parking lots, and lowest in raised bed soils. Lead was sequestered in the low-mobility fraction of the soil and speciated with phosphate minerals, and iron and manganese oxides. As a community-engaged research project, dissemination of results supported the local farming community in understanding the potential of exposure to soil lead and in developing robust farming practices to reduce exposure.Furthermore, this dissertation also discusses science policy experiences in Washington DC and elucidates the establishment of a national framework to promote P recovery policy and reuse in the United States, required to popularize struvite use in agroecosystems. Overall, findings of this dissertation demonstrated that combined geochemistry research, community-engagement, and science policy approaches can help address scientific challenges and inform practices in society.