Investigation of chlorinated phenols sorption mechanisms on different layers of the Danube alluvial sediment

The adsorption-desorption behavior of chlorothalonil in the cuticles of apple and red jujube

The distribution fate of chlorothalonil (CHT) in the environment (soil and water) and fruits is controlled by the capacity of cuticles to adsorb and desorb CHT, which directly affects the safety of both the environment and fruits. Batch experiments were conducted to reveal the adsorption-desorption behaviors of CHT in the cuticles of apple and red jujube. The adsorption kinetics showed that both physisorption and chemisorption occurred during the adsorption process. Furthermore, the isothermal adsorption of CHT in the fruit cuticles followed the Freundlich model. The thermodynamic parameters (ΔG ≤ -26.16 kJ/mol, ΔH ≥ 31.05 kJ/mol, ΔS ≥ 0.20 kJ/(mol K) showed that the whole CHT adsorption process was spontaneous, and the hydrophobic interaction was predominant. The CHT adsorption capacity of the apple cuticle was higher than that of the red jujube cuticle, potentially due to the significantly higher alkanes content of apples than that of red jujubes. An appropriate ionic strength (0.01 moL/L) could induce a higher adsorption capacity. In addition, the desorption kinetics were shown to conform to a Quasi-first-order model, meaning that not all the adsorbed CHT could be easily desorbed. The desorption ratios in apple and red jujube cuticles were 41.38% and 35.64%, respectively. The results of Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy further confirmed that CHT could be adsorbed and retained in the fruit cuticles. Investigating the adsorption-desorption behavior of CHT in the apple and red jujube cuticles allowed to determine the ratio of its final distribution in the fruits and environment, providing a theoretical basis to evaluate the risk of residue pesticide.

Characterization and application of biochar-immobilized crude horseradish peroxidase for removal of phenol from water

Biochar (BC) has attracted much attention as an environmentally friendly material for application in wastewater treatment. In this study, a suitability of wood-derived BC as a support for covalent immobilization of horseradish peroxidase (HRP) across glutaraldehide as crosslinker, known for the capability to remove phenol from water, was investigated. The efficiency of the immobilized HRP in removal of phenol (2 mM) from water at different reaction conditions (varying dosages of polyethylene glycol (PEG300) 0-750 mg/L; H₂O₂ 1.5-3.5 mM, as well as reaction time 5-120 min) and the general toxicity of bio-treated water (Allium cepa test) were measured. All analyzes were performed for free enzyme as well. The immobilized enzyme showed the highest activity at temperature 30 °C and pH 7.0. The greatest efficiency of immobilized enzyme in phenol removing (90 %) was obtained by applying 2.5 mM H₂O₂ and 1.5 mg/L of PEG300 at pH 7.0 after 2 h of reaction period. After 4 washings, immobilized HRP retained more than 79 % activity with phenol removal of 64 %. Utilizing immobilized enzyme significantly reduces the toxicity of the tested water (80 %), which further suggested that it might be considered as an environmentally acceptable process for wastewater treatment. Possible degradation products remained in treated water were analyzed in water samples by liquid and gas chromatography with mass spectrometry, including also analysis of volatiles by solid phase microextraction technique; different phenol-base compounds were detected.