(396d) Investigating Lead Biosorption Mechanisms at Trace Concentrations

Heavy metals are highly toxic and acutely hazardous for living organisms and human health, even at very low concentrations. Lead, in particular, is one of the most abundant and toxic heavy metals. 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 water/wastewater treatment processes either fail to completely remove dissolved lead ions, or result in significant energy consumption, increased operational and maintenance costs, and generation of undesirable by-products. Biosorption, i.e. adsorption of heavy metal ions by inactive biomass, can offer a promising, low-cost and environmentally friendly alternative to conventional treatment processes. Although biosorption of heavy metals using a wide variety of biomaterials, including microorganisms and plants, has been extensively studied at the parts per million (ppm) contaminants scale, limited research has been conducted, so far, at the challenging trace concentrations of parts per billion (ppb) and below.

In this presentation the lead adsorption mechanisms at the ppb scale will be discussed. Saccharomyces cerevisiae has been selected as the most suitable biosorbent, as it is inexpensive and easy to cultivate at large scales, while it has been proven a good lead biosorbent at the ppm scale. Kinetic and equilibrium experiments have been conducted, using synthetic lead-containing aquatic solutions, to measure and characterize the stoichiometry, equilibrium, and selectivity of biomass under different pH values, initial lead concentrations (at the range of 30 – 1000 ppb) and biosorbent dosages. Residual lead concentrations have been measured using inductively coupled plasma - mass spectrometry. In addition, advanced characterization techniques, including X-ray photoelectron spectroscopy, transmission electron microscopy and Fourier-transform infrared spectroscopy, have been used to examine the biomass, in an effort to identify the functional groups and biomass sites responsible for lead uptake. Through these experiments, the adsorption equilibrium has been quantified and the underlying mechanisms have been identified, paving the way for the development of novel, highly effective and sustainable treatment processes.