Novel protein nanofibril–carbon hybrid adsorbent efficiently removes As(iii), As(v) and other toxic elements from synthetic and natural waters in batch and rapid small-scale column tests

Abstract

Novel adsorbents produced from β-lactoglobulin, a low-cost milk protein, have shown a high affinity to inorganic As(III) and As(V). Here, we report an application-oriented investigation of As-removal from synthetic and spiked natural groundwaters with a protein nanofibril carbon composite adsorbent. In batch experiments, removal of both As(V) and As(III) was efficient and not strongly affected by variations in Mg²⁺, Ca²⁺, and HCO₃⁻, while phosphate exerted a negative influence. 50–500 mg L⁻¹ of adsorbent was sufficient to reduce As-concentrations from 50–500 μg L⁻¹ to less than 10 μg L⁻¹. Adsorption kinetics were well-described by a second-order rate law. In rapid small scale column tests (RSSCTs) with 1.0 g sieved adsorbent, 100 μg L⁻¹ As(III) and As(V) in spiked tap water could be reduced to <1 μg L⁻¹ for over 40 000 bed volumes (BVs) and to <10 μg L⁻¹ for 50 000–70 000 BVs. Heavy metal ions (Cu, Zn, Pb) were also removed, but not nutrient ions such as Na⁺, Mg²⁺, Ca²⁺, Cl⁻, SO₄²⁻. With 1000 μg L⁻¹ As(III,V) and P (phosphate), As and P were removed to <10 μg L⁻¹ over more than 5800 BVs. After regeneration with 10 mM NaOH, 2400 more BVs could be treated. The composites are an alternative to established Fe(III)(hydr)oxide-based adsorbents. Distinct advantages are high efficiencies for removal of As(III) and As(V), low effluent concentrations, and regenerability. The activated carbon carrier can also potentially remove organic compounds and unpleasant odors and tastes.