Fixed-bed adsorption study with brewer’s spent grain for the removal of heavy metals in model waters

Abstract

Heavy metals are toxic water contaminants that require a clean-up treatment. Adsorption is a widely used treatment method which is easy to implement and operate, while being constrained by the high cost of adsorbents. Biosorbents made from industrial organic residual materials are inexpensive with an inherent ability to adsorb heavy metals trough functional groups. In this study the ability of brewer’s spent grain (BSG) as a biosorbent for heavy metal waste water remediation was evaluated with a fixed-bed adsorber and a batch experiment. BSG was able to specifically adsorb nickel(II), cadmium(II), and lead(II) ions from fresh and brackish model waters without affecting the concentrations of sodium, calcium, or magnesium ions. Multi-solute batch experiments showed a competition between the heavy metal ions for adsorption sites and long equilibration times. The affinity for lead(II) was the highest, as shown by the removal rate in the batch process and the amount of breakthrough volume in the fixed-bed adsorber. The esterification of BSG could increase the maximum Langmuir loading for lead(II) to 65.83 g kg−1 BSG dry weight, of which 5% could be reached until filter breakthrough. A surface complexation of lead(II) ions with natural occurring phytate to form water insoluble lead(II) phytate in a spontaneous reaction at room temperature is proposed to explain the adsorption mechanism. Therefore, a high potential is seen for BSG as a low cost biosorbent for the remediation of contaminated waste waters.