News from Dr. Brown’s Research Group

  • Investigation of Pore-Scale CaCO3 Distributions and Their Effects on Stiffness and Permeability of Sands Treated by Microbially Induced Carbonate Precipitation (MICP)

    Our paper on pore-scale distributions of CaCO3 during microbially-induced carbonate precipitation and their effects on sand permeability and stiffness has been accepted for publication in Soils and Foundations.


    Lin, H., Suleiman, M.T. and Brown, D.G. 2020 (In Press). “Investigation of Pore-Scale CaCO3 Distributions and Their Effects on Stiffness and Permeability of Sands Treated by Microbially Induced Carbonate Precipitation (MICP).” Soils and Foundations.


    Physical properties of MICP-treated sands are controlled by CaCO3 distributions in pore space, which remain relatively unexplored. CaCO3 can deposit at the particles’ contact area (contact-cementing), coat sand particles (grain-coating), or create a cementation bridge between soil grains (matrix-supporting). The objectives of this paper are to determine the dominant CaCO3 distributions in pore space and investigate the effects of CaCO3 distributions on the small-strain stiffness (measured by S-and P-wave velocities) and permeability of MICP-treated sands. To achieve these objectives, cemented-sand and uncemented-sand models combined with three ideal CaCO3 distributions (contact-cementing, grain-coating, and matrix-supporting) were used to estimate the S-and P-wave velocities. In order to determine the dominant CaCO3 distributions in pore space, the calculated values from the models were then compared with experimental data. It was concluded that the dominant CaCO3 distributions were a combination of grain-coating and matrix-supporting. The effects of CaCO3 distributions at pore space on the variation of permeability were estimated using Kozeny-Carman and Panda-Lake models with three pore-scale cement distributions (pore-lining, pore-filling, and pore-bridging). The comparison between laboratory-measured and calculated permeability from the pore-filling Panda-Lake model for seven types of sands demonstrated a relatively good match with a maximum difference of one order of magnitude. The comparison suggests the pore-filling Panda-Lake model can be used for estimating the permeability of the MICP-treated sands.

  • Characterization and modeling of charge-regulated surfaces

    Our paper on a method for obtaining parameters to allow charge-regulation modeling of natural and undefined surfaces has been accepted for publication in Langmuir.


    Brown, D.G., Zhu, H., Albert, L.S., Fox, J.T. 2019. “Rapid characterization and modeling of natural and undefined charge-regulated surfaces in aqueous systems.” Accepted for publication in Langmuir.


    The surfaces of most materials in aqueous systems are charged due to the ionization of surface functional groups. When these surfaces interact, the surface charge, electrostatic potential, and pH will vary as a function of separation distance, and this process is termed the charge-regulation effect. Charge regulation is a controlling factor in the adhesion and transport of colloids and microorganisms in aqueous systems and its modeling requires representation of the pH-charge response of the surfaces, typically provided as the equilibrium constants (K) and site densities (N) of the dominant surface functional groups. Existing methods for obtaining these parameters demonstrate shortcomings when applied to many natural and man-made materials, such as weathered materials, materials with undefined or complex surface structures, and permeable materials, and for materials that don’t provide the requisite high surface area in suspension due to small sample sizes. This hinders inclusion of the charge-regulation effect in colloid and microbial transport studies, and most studies of colloidal and microbial surface interactions use simplifying assumptions – a key example is the routine use of the constant potential assumption in DLVO modeling. Here, we present a robust method that overcomes these issues and provides a rapid means to characterize charge-regulated surfaces using zeta potential data, without requiring a priori knowledge of the material composition. Applying a combined charge-regulation and Gouy-Chapman model, K and N values are obtained that accurately represent the electrostatic response of a charge-regulated surface. This method is demonstrated using activated carbon, aluminum oxide, iron (hydr)oxide, feldspar and silica sand. The resulting K and N values are then used to show the variations in surface charge, electrostatic potential and pH that can occur as these charge-regulated surfaces interact. This method provides a readily-applied experimental approach for characterizing charge-regulated surfaces, with the overall goal to promote the inclusion of charge-regulated interactions into adhesion and transport studies with natural and undefined materials.

  • Our patent for stabilizing anaerobic digestors to upset has been issued

    In-situ, self-adjusting stability control of methane-producing anaerobic biological reactors through novel use of ion exchange fibers. U.S. Patent No.10,399,877. Filed 25 September 2017, Issued 3 September 2019. Assignee:Lehigh University. Inventors: Arup K . SenGupta, Derick G. Brown, and Yu Tian.

    If you are interested in details on the process, see our paper:

    Tian, Y., SenGupta, A.K., and Brown, D.G. 2017. “In-situ stability control of energy-producing anaerobic biological reactors through novel use of ion exchange fibers.” ACS Sustainable Chemistry & Engineering. 5(10):9380-9389.

  • Congratulations to our new Environmental Engineering Ph.D.s!

    Congratulations to Chelsey Shepsko and Hang Dong for earning their Ph.D.’s in 2019!

    Chelsey Shepsko

    Dissertation: “Advancement of the Hybrid Ion Exchange Nitrogen and Phosphate (HIX-NP) Recovery from Waste Water and a New Approach to Brine-Free Nitrate Removal”

    Hang Dong

    Dissertation: “Hybrid Ion Exchange Process Driven by Carbon Dioxide”