Characterization and evaluation of commercial biochar for surface water purification

Abstract

Biochar is a promising material for carbon storage and water purification, particularly for heavy metal removal. The transition from laboratory studies to real-world applications remains challenging due to variability in commercial biochar properties and lack of testing on multi-contaminant matrixes.

The study aims at bridging such a gap by characterizing and testing nine commercial biochar in the real case scenario of the area surrounding the decommissioned Malagrotta landfilling site (Latium region, central Italy). The area is notorious for legal, social, health and environmental issues. Periodic monitoring performed by local authorities classifies chemical water quality as scarce. In this context, the effect of environmental water-biochar interactions was tested on surface water samples. Biochar multi-method characterization was carried out through optical microscopy, SEM, EDX spectroscopy, X-ray diffraction, ICP-MS, pH-electric conductivity and FT-IR spectroscopy.

Biochar characterization allowed systematic comparison not possible trough commercial labels: bulk composition is carbonaceous (78–92 %); mineralization mostly consists of calcite (<8 % for most samples); heavy metal contaminants are present (up to >100 ppm for Chromium and Zinc); pH ranges from 8 to 12, bearing exponential relationship with electrical conductivity (EC230–2417 µS); FT-IR spectra testify high aromaticity and variability in oxygenated (≈1700 cm^-1) functional groups, less abundant in pyro-gasification-produced biochar compared to pyrolysis-produced ones.Contrary to expectations, trace pollutant concentrations in Malagrotta waters are within legal limits. Thus Malagrotta case study explores bottom thresholds for surface water treatment using biochar. Low trace contaminant concentrations hinder detection of adsorption phenomena. Moreover, leaching tests utilising drinking water and high biochar dosage (10 g/L) demonstrate biochar's safety, as leaching is limited to few μg/L. These results are instrumental in elaborating biochar specific water treatment regulations.