This research investigated the removal of heavy metal ions (Cd, Cu, Pb, and Zn) and metalloid (As) common to stormwater runoff onto biochar-based media arranged in multiple configurations. Laboratory scale column experiments were conducted to quantify heavy metal removal efficiencies using sand, biochar, and nZVI-modified biochar (BC-nZVI) in four media configurations: a homogeneous mixture of sand and biochar (BCM); biochar layered in sand (BCL); BC-nZVI layered in sand (BCZ); and sand as a control. An inverse modeling approach was implemented to measured moisture and experimental data to determine media hydraulic parameters (θ_r, θ_s, α, n and K_s) and adsorption coefficients. The experiment was conducted using laboratory synthesized stormwater over 200 days at a rate of 5 cm/day. BCZ exhibited an excellent removal (99%) of As due to the high attachment to nZVI, via surface complexations. Biochar with abundant surface oxygen functional groups exhibited a great (99%) removal of Cd and Zn in both BCL and BCM columns. Water contents were observed 66.0, 44.3, 41.4, and 7.2% for BCL, BCM, BCZ, and sand, respectively. The attachment coefficients varied from 21.5 to 44.9, 16.1 to 19.3, 18.8 to 26.0, and 9.6 to 19.9 L/kg for BCL, BCM, BCZ, and sand, respectively. This study’s output provides useful information for stormwater management practices.

Population growth and the associated increase in the use of Onsite Wastewater Treatment Systems (OWTS) in the Black Hills have been a reason for interest in nitrate contamination within the public water supply over the past few years. The main concern for the Black Hills is the presence of karst formation that all OWTS for wastewater travel faster, limiting the natural attenuation of wastewater contaminants. The treatment performance of common soils in the Black Hills and wood-based media was evaluated using soil column experiments and a numerical model, HYDRUS 2D. Nitrate treatment performances were evaluated using alluvial and cedar soils collected from the Black Hills, sand, woodchips (loose and dense), and biochar. This research investigated hydraulic and reaction parameters through a combination of experimental and inverse modeling approaches. A good agreement was obtained between the measured and model-predicted soil moisture content, with R² values ranging from 0.57 to 0.99. The model was calibrated using flow data and nitrate concentration data measured from leachate collected at the bottom of the experimental columns. Nitrate removal rates varied from 32.3% to 70%, with the highest removal rate in loose woodchips, followed by dense woodchip and biochar, and the lowest removal rate in alluvial materials. The biochar and loose woodchips removed an additional 20% compared to common soils, attributable to the enhanced denitrification rate due to higher water content and organic content. The use of woodchips and biochar should be implemented in OWTS, where there are known karst formations.

This study reports biochar (BC) as an effective filtration media to retain graphene oxide (GO) under the subsurface environment in fixed-bed column reactors. A comprehensive mass balance approach, coupled with column dissections, was used to examine the retention behavior of GO as a function of ionic strength (IS) and flowrate. The retention of GO in BC was 3.5-fold higher compared

Transport and retention behavior of Graphene Oxide (GO) is influenced by the physical and chemical properties of porous media under subsurface environmental conditions. Fixed-bed column studies using quartz sand and biochar (BC) in different configurations were conducted as a function of ionic strength and flowrate. Colloid filtration theory (CFT) was employed to develop mathematical models based on the one-dimensional convection-dispersion equation using experimental GO breakthrough curves (BTCs) and retention profiles (RPs) obtained from the experimental data. GO transport and retention behavior was modeled using BC and BC-nZVI (BC surface modified with nanoscale zero-valent iron) as filter media to understand the effect of media properties. It was demonstrated that the model can describe measured BTCs and RPs of GO in the sand, BC, and BC-nZVI. The inverse modeling approach was implemented to determine the attachment coefficient (Ka) and maximum solid-phase retention capacity (Smax) using GO BTCs for different experimental conditions. Higher Ka in BC at 10 mM IS indicated the influence of straining which agrees with the depth-dependent retention kinetics. Furthermore, pronounced GO aggregation at higher IS supports the higher Ka values at 10 mM compared to 0.1 mM. In contrast, higher Ka values were predicted in BC-nZVI at lower ionic strength (0.1 mM) primarily due to the attachment of GO onto nZVI where nZVI in BC pores was also favorable for the straining process. This study revealed that CFT including the attachment, straining, and blocking process can effectively describe the GO transport in BC and surface-modified BC-nZVI under subsurface environmental conditions.