Microwave activated and iron engineered biochar for arsenic adsorption: Life cycle assessment and cost analysis

Humans are exposed to arsenic (As) from various sources such as food, drinking water, and air, thus, treatment of water matrices contaminated with As is a worldwide challenge. In this work, H3PO4 and FeCl3 treated canola straw biochar (CSB) was assessed for its adsorption efficiency for arsenite, As(III), and arsenate, As(V), in water. The main factors in determination of an optimal CSB (OCSB) included microwave (MW) power for the creation of the biochar and FeCl3 modification. For both As(III) and As(V), the highest performing biochar was found to be at the highest MW power (1000 W) and lowest FeCl3 concentration (0.1 M). It was found that biochar surface area was enhanced by biomass activation using FeCl3 and no crystalline phases of FeCl3 were identified, potentially a consequence of the low iron concentrations considered. Modification parameters were studied and showed that pH 7 was more favorable for As(V) adsorption, while pH 10 favored As(III) adsorption. Additionally, isotherm and kinetic analysis indicated that a physical adsorption mechanism took place for As(III) and As(V) which may have resulted from surface complexation. Life cycle assessment (LCA) results showed that OCSB production is environmentally friendly, generating - 0.298 kg CO2 eq/kg of biochar. For an economic perspective, a life cycle cost analysis (LCCA) of OCSB found a cost of $5.14/kg (USD) of biochar that is mainly impacted by materials. Overall, OCSB shows potential for As adsorption and environmental evaluation shows promising results for consideration of this biochar as an adsorbent.