Biobased & Biodegradable Materials for Advanced Water Treatment: Removal of Trace Lead by Yeast-Laden Hydrogel Capsules

Traces of heavy metals in water resources, due to mining activities and e-waste discharge, pose a global threat, with lead being one of the most abundant and toxic trace contaminants. As a result of various incidents of lead-contaminated drinking water, relevant water regulations are being revised, while according to the US Environmental Protection Agency, no level of lead in drinking water is considered safe. Conventional treatment processes fail to remove trace lead from drinking water in a resource-efficient manner. We have previously shown that by using the yeast <i>Saccharomyces cerevisiae</i> we can effectively remove trace lead from water <i>via</i> a rapid mass transfer process, called biosorption, achieving an uptake of up to twelve mg lead per gram of biomass in solutions with initial lead concentrations below 1 part per million. We have also found that equilibrium is achieved within the first five minutes of contact. The rapid and high lead uptake is advantageous for the large-scale application of this inexpensive and abundant biomaterial for the removal of trace heavy metals from water.<br/><br/>The main limitation for scaling up the developed water treatment approach is the requirement for additional treatment steps to remove the added yeast. In this presentation, we demonstrate the development of a sustainable material by encapsulating yeast cells in hydrogel microparticles to overcome this limitation. Yeast-containing poly(ethylene glycol) diacrylate (PEGDA) biobased and biodegradable hydrogel capsules are synthesized using an off-the-shelf microfluidic device through a scalable approach. Scanning electron microscopy and confocal fluorescence imaging have been used to measure the capsules’ porosity and assess the distribution of yeast cells inside the capsules. Through kinetic and equilibrium experiments we characterize the stoichiometry, equilibrium, and selectivity of the hydrogel capsules under different initial lead concentrations (in the range of 30 – 1000 ppb). Residual lead concentrations have been measured using inductively coupled plasma-mass spectrometry. Data shows that hydrogel capsules are highly effective vehicles for holding yeast cells, being sufficiently large to be easily separated from water under the effect of gravity, as well as sufficiently porous to not limit the adsorption capacity of the yeast or the kinetics of lead removal. Furthermore, we perform biomechanical static and dynamic compression tests to assess the mechanical robustness of the capsules and guide the design of a cm scale, packed-bed bioreactor operated as a flow-through filter to serve as a proof-of-concept of our approach. Finally, through a life cycle approach (LCA) we compare our proof-of-concept water treatment approach with physicochemical state-of-the-art counterparts and assess its environmental and economic benefits. Our work overcomes separation and structural stability issues that limit biosorption scalability, opening a new generation of environmentally friendly, highly effective, and sustainable biosorbents targeting emerging contaminants.