Mass Production of Hydrogel Beads for the Sustainable Biological Treatment of Emerging Contaminants in Soil and Groundwater

Chlorinated solvents are commonly found in drinking water supply aquifers and groundwater plumes throughout the United States¹. The Centers for Disease Control and Prevention lists all chlorinated aliphatic hydrocarbons (CAHs) detected in groundwater samples as probable human carcinogens as well as having other hazardous health effects towards humans and the environment². A permeable reactive barrier system has shown to be an effective in situ bioremediation technology for treating chlorinated compounds found in groundwater with microorganisms immobilized in hydrogel beads with orthosilicates as slow-release compounds (SRCs) to support aerobic cometabolism³. Rhodococcus rhodochrous ATC 21198 bacteria strain has successfully treated common chlorinated solvents and can be used as a passive bioremediation method for treating contaminated groundwater plumes. Thus, a lab-scale bead generator was built to generate mass quantities of hydrogel beads. Laminar jet flow breakup in addition to coaxial air flow and a vibrating nozzle allowed for bead parameters such as size and circularity to be controlled. Different concentrations of sodium alginate were flown through the bead generator at varying Reynolds numbers to characterize the optimal flow parameters of the polymer fluid. A correlation between the Reynolds number (inertial forces/viscous forces) versus Ohnesorge number (viscous forces/inertial forces and surface tension) was generated to find the flow regime for a laminar jet stream, and found that different concentrations could be binned into different ranges of Reynolds numbers. Images were used to capture and measure the bead perimeter and circularity. Data collected was used to optimize the independent variables (Reynolds number, vibrational frequency, and coaxial air flow), on the dependent variables (bead perimeter and circularity) for each with a design of experiments approach.

(1) Grindstaff, M. Bioremediation of Chlorinated Solvent Contaminated Groundwater; 1998. https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=caddf817a... (accessed 2023-08-10).

(2) Organic Solvents | NIOSH | CDC. www.cdc.gov. https://www.cdc.gov/niosh/topics/organsolv/default.html.

(3) Rasmussen, M. T.; Saito, A. M.; Hyman, M. R.; Semprini, L. Co-Encapsulation of Slow Release Compounds and Rhodococcus Rhodochrous ATCC 21198 in Gellan Gum Beads to Promote the Long-Term Aerobic Cometabolic Transformation of 1,1,1-Trichloroethane, Cis-1,2-Dichloroethene and 1,4-Dioxane. Environmental Science: Processes & Impacts 2020, 22 (3). https://doi.org/10.1039/c9em00607a.