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.

The uptake of organic pollutants by agricultural plants and their accumulation in edible parts cause serious health problems to animals and humans. In this study, we used carbon-rich materials, such as biochar (BC), hydrochar (HC), and green compost (GC), to reduce the absorption and accumulation of three pesticides, imidacloprid (IMI), boscalid (BOS), and metribuzin (MET) and two endocrine disruptors, 4-tert-octylphenol (OP) and bisphenol A (BPA), in rocket salad plants (Eruca vesicaria L.). After an experimental period of 35 days, compared to unamended soil, the addition of BC, HC, and GC significantly reduced chemical phytotoxicity, increasing the elongation of the aerial plant parts by 26, 25, and 39%, respectively, whereas GC increased the fresh biomass by 21%. The assessment of residual chemicals in both soil and plant tissues indicated that any amendment was very effective in enhancing the retention of all compounds in soil, thus reducing their uptake by plants. Averagely for the five compounds, the reduction of plant absorption followed the trend BC > HC > GC. In particular, the presence of BC decreased the chemical residues in the plants from a minimum of 71% (IMI) to a maximum of 91% (OP). The overall results obtained encourage the incorporation in soil of C-rich materials, especially BC, to protect leafy food plants from the absorption and toxicity of organic pollutants of a wide range of hydrophobicity, with relevant benefits for consumers.

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In this study, a biochar obtained from poplar wood gasification at a temperature of 850 °C was used to adsorb the xenoestrogens 4-tert-octylphenol (OP) and bisphenol A (BPA) and the herbicide metribuzin from water. Scanning electron microscopy (SEM-EDX) and Fourier-transform infrared (FTIR) spectroscopy were employed to investigate the surface micromorphology and functional groups composition of biochar, respectively. The study of sorption kinetics showed that all compounds achieved the steady state in less than 2 h, according to a pseudo-second order model, which denoted the formation of strong bonds (chemisorption) between biochar and the compounds. Adsorption isotherms data were described by the Henry, Freundlich, Langmuir and Temkin equations. At temperatures of 10 and 30 °C, the equilibrium data of the compounds were generally better described by the Freundlich model, although, in some cases, high correlation coefficients (r ≥ 0.98) were obtained for more than one model. Freundlich constants, KF, for OP, BPA and metribuzin were, respectively, 218, 138 and 4 L g−1 at 10 °C and 295, 243 and 225 L g−1 at 30 °C, indicating a general increase of adsorption at higher temperature. Desorption of all compounds, especially OP and BPA, from biochar was slow and very scarce, denoting an irreversible and hysteretic process. Comparing the results of this study with those reported in the literature, we can conclude that the present biochar has a surprising ability to retain organic compounds almost permanently, thus behaving as an excellent low-cost biosorbent.