Effect of Macro- and Nano-Biosolid Fractions on Sorption Affinity and Transport of Pb in a Loamy Sand Soil

Applications of large amounts of biosolid to agricultural lands have raised the concern over its potential impact on co-transport of metal contaminants. In this study, bulk biosolid was fractioned into six macro- and nano-biosolid fraction sizes. We investigated variations in the physicochemical properties of the different biosolid fraction sizes, and assessed sorption affinity and transport of Pb in a loamy sand soil. Decreasing biosolid fraction size from macro to nano resulted in consistent increases in surface area, surface charge, and a decrease in pore size. Biosolid particles >1000 µm showed similar surface properties that differ from biosolid particles < 1000 µm. Sorption affinity for Pb was larger on nano-biosolid as compared to all macro-biosolid fraction sizes. This is mainly attributed to the larger surface area and zeta potential of nano-biosolid, leading to increased surface reactivity and greater stability. Total amount eluted of Pb was increased in the presence of macro- and nano-biosolid by 21.3% and 45.6%, respectively. Our findings suggest that the application of the >1000 µm biosolid fractions can help to minimize adverse effects of biosolid applied in areas susceptible to potential environmental risk of contamination by heavy metals. Further assessment of potential mobility of nano-biosolid at the field scale is needed before the recommendation of including such approach during land application of biosolid.