Use of the Solid By-Product of Anaerobic Digestion of Biomass to Remove Anthropogenic Organic Pollutants with Endocrine Disruptive Activity

Abstract

Anaerobic digestion of biomass has increasing implementation for bioenergy production. The solid by-product of this technology, i.e., the digestate, has relevant potential in agricultural and environmental applications. This study explored the capacity of a digestate from mixed feedstock to remove from water four endocrine-disrupting chemicals, namely the pesticides metribuzin (MET) and boscalid (BOS) and the xenoestrogens bisphenol A (BPA) and 4-tert-octylphenol (OP). The surface micromorphology and functional groups of the digestate were investigated using scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy, respectively. Results of sorption kinetics showed that all compounds reached the steady state in a few hours according to a pseudo-first-order model in the cases of MET and OP, a pseudo-second-order model for BOS and both models in the case of BPA. Data of adsorption isotherms were fitted to the Henry, Freundlich, Langmuir and Temkin equations. The adsorption of MET preferentially followed the non-linear Freundlich model, whereas the adsorption of the other compounds was properly described by both the linear and Freundlich models. The organic carbon partition coefficients, KOC, were 170, 1066, 256 and 2180 L kg−1 for MET, BOS, BPA and OP, respectively. The desorption of BOS, BPA and OP was slow and incomplete, indicating a phenomenon of hysteresis. In conclusion, the digestate showed a remarkable efficiency in the removal of the compounds, especially those with high hydrophobicity, thus behaving as a promising biosorbent for environmental remediation.

Recent Advances on Innovative Materials from Biowaste Recycling for the Removal of Environmental Estrogens from Water and Soil

“…DG has also been directed to bio-oxidative conversion processes such as composting and vermicomposting [ 60 ], used in the preparation of biofilters and biobeds in mixtures with other C-rich substrates [ 61 ] or converted thermically to produce BC [ 41 ]. However, recent studies have shown that some DG properties, such as the presence of surface reactive functional groups, porosity and a fairly large surface area, can make this material a good candidate for the removal of inorganic and organic contaminants by adsorption [ 12 , 62 ].…”

“…The surface area of BC has shown positive correlations with the removal of contaminants from soil and water [ 34 ]. The BC commonly exhibits diffuse microporosity with pores usually smaller than 1–1.5 nm in diameter, while porosity is less pronounced in HC [ 32 ] and much less in DG [ 12 ]. The extensive porosity of BC, besides allowing routes for the release of volatile compounds such as H 2 O, CO, CO 2 and CH 4 during pyrolysis and providing sites for contaminants, would be an adequate habitat for symbiotic microorganisms once BC is incorporated into soil [ 10 ].…”

“…Common features of SEM images of DG are rough surfaces with irregularly shaped ridges, sharp edges, microparticles, channels and cavities mostly smaller than 10 µm. The EDS spectrum of DG usually shows the presence on the surface of elements typical of the raw biomass used in the AD process [ 12 ].…”

“…In addition to the peak at 3420–3440 cm −1 (O-H and N-H stretching), FTIR spectra of HC usually feature peaks at ~2920 and 2850 cm −1 (asymmetric and symmetric stretching of aliphatic C-H, respectively); ~1620 cm −1 (aromatic C=C stretching); at 1310, 1160, 1110 and 1030 cm −1 (stretching vibrations of C-H in hydroxyl, ether or ester and bending vibrations of O-H in cellulose and hemicellulose); 670 (out-of-plane bending vibration of C-H); and 580 cm −1 (bending vibration of O-H) [ 32 ]. The main features of FTIR spectra of DG are the presence of a wide absorption band at ~3300–3400 cm −1 (O-H vibration of carboxylic and alcoholic groups and N-H stretching) and peaks at ~2920 and ~2850 cm −1 (aliphatic C-H stretching), ~1630–1600 cm −1 (various vibrations, including aromatic C=C stretching), 1385 cm −1 (various vibrations, including O-H deformation and C-O stretching of phenolic groups, COO - asymmetric stretching) and ~1040 cm −1 (C-O stretching of polysaccharide-like substances and Si-O vibration of silicate impurities) [ 12 ].…”

“…In general, these studies considered a broad context of pollutants, including dyes, pharmaceuticals, polycyclic aromatic hydrocarbons PAHs, heavy metals, antibiotics and single EDCs. Furthermore, DG has been studied so far almost exclusively for agricultural use, although recently it has shown an appreciable ability to retain hydrophobic compounds such as the EDCs bisphenol A (BPA) and 4-tert-octylphenol (OP) [ 12 ]. It is reasonable to believe that also DG could be used as a biosorbent, possibly after further studies and improvements.…”