CuO coated olive cake nanocomposites for rapid phenol removal and effective discoloration of high strength olive mill wastewater

Phenolic compounds removal in table olive processing wastewater by column adsorption: conditions' optimization

The annual production of wastewater from the olive table industry poses a serious problem owing to its high organic matter load, which is highly concentrated in phenolic compounds (PCs) and inorganic materials. This research used adsorption to recover PCs from table olive wastewater (TOWW). Activated carbon was employed as a novel adsorbent. The activated carbon was obtained from olive pomace (OP) and activated using a chemical agent (ZnCl2). Fourier transform infrared spectroscopy analysis (FTIR), Brunauer-Emmett-Teller analysis (BET), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were applied to characterize the activated carbon sample. To optimize the biosorption conditions of PCs (adsorbent dose (A), temperature (B), and time (C)), a central composite design (CCD) model was used. An adsorption capacity was 1952.34 mg g-1 for optimal conditions with an activated carbon dose of 0.569 g L-1, a temperature of 39 °C, and a contact time of 239 min. The pseudo-second-order and Langmuir models as kinetic and isothermal mathematical models were proved to be more appropriate for the interpretation of the adsorption phenomenon of PCs. PC recovery was performed in fixed-bed reactors. The results of the adsorption of PCs from TOWW by activated carbon could be an effective process at a low cost.

Optimization of preparation conditions of a novel low-cost natural bio-sorbent from olive pomace and column adsorption processes on the removal of phenolic compounds from olive oil mill wastewater

Olive oil mill wastewater (OMWW) poses an undeniable environmental problem due to its high organic loads and phenolic compound (PC) content. This study determined the optimal conditions for preparing a new bio-sorbent from olive pomace (OP) and the adsorptive treatment of OMWW by this bio-sorbent. The activation reaction was performed with hydrogen peroxide. The results of the combination effect optimization of the three preparation variables, the activation temperature (°C) X₁, the activation time (min) X₂, and the impregnation ratio X₃, are presented by the response surface methodology (RSM). The maximum adsorption capacity was obtained at an activation time of 240 min, a temperature of 80 °C, and a ratio equal to 6.2:1. The bio-sorbent was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD). The adsorption process performance of this bio-sorbent was examined in batch (phenol solution) and fixed-bed columns (real effluent of OMWW). An adsorption capacity of 789.28 mg g^-1 and 643.92 mg g^-1 has been achieved for 4000 mg L^-1 concentration of PCs, respectively, for batch and fixed-bed column essays. The adsorption isotherm and kinetics were consistent with the Langmuir and pseudo-second-order models. Therefore, the Thomas model best fits the fixed-bed column experimental data. The bio-sorbent gave a high desorption percentage of PCs, which was above 60% using HCl (0.1M).

In Situ-Formed Phenoxyl Radical on the CuO Surface Triggers Efficient Persulfate Activation for Phenol Degradation

Transition-metal oxide (M_xO_y)-based persulfate (PDS) activation processes have demonstrated enormous potential for pollutant degradation in water purification. However, the mechanistic insight of PDS activation by a M_xO_y catalyst concerning the mediate role of the organic substrate remains obscure. Here, we demonstrated that the in situ-formed phenoxyl radical on the CuO surface can trigger efficient persulfate activation for phenol degradation. The formation of the phenoxyl radical was an inner-sphere process, which involved the successive steps of chemisorption through surface hydroxyl group substitution and the subsequent spontaneous electron transfer reaction from adsorbed phenol to CuO. The organic substrate phenol can be oxidized by the PDS molecule and surface-bound SO₄^•- through the nonradical and free-radical pathways, respectively. Such a unique "half-radical" mechanism resulted in an extraordinarily high PDS utilization efficiency of 188.9%. More importantly, a general rule for phenoxyl radical formation was concluded; it can be formed in the cases of organic substrates with a Hammett constant σ⁺ lower than -0.02 and metal ion of a 3d subshell between half-filled and fully filled. This study clarifies the mediate role of the organic substrate for interfacial PDS activation on M_xO_y and also gives new insights into the rational design of a highly efficient M_xO_y catalyst for selective phenolic/aniline pollutant degradation in wastewater.

Performance and dynamic modeling of a continuously operated pomace olive packed bed for olive mill wastewater treatment and phenol recovery

The solid waste of olive oil extraction processes (olive pomace, OP) was converted into activated carbon (AC) by treating it with NaOH and then encapsulating it within sodium alginate (SA) in beads by crosslinking (SA-AC beads). The prepared SA-AC beads were utilized as an adsorbent for the elimination and recovery of phenolic compounds (PCs) from olive mill wastewater (OMWW) following a zero liquid and waste discharge approach to implement and promote the circular economy concept. The novel AC and SA-AC beads were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and Brunauer, Emmett and Teller (BET) analysis. The adsorption performance of these beads was evaluated in batch and fixed-bed reactors operated in a concurrent flow system. The results revealed that an adsorption capacity of 68 mg g^-1 was attained for 4000 mg L^-1 phenolic compounds. The kinetics of the adsorption process of the PCs fit a pseudo second-order model, and the most likely mechanism took place in two stages. The adsorption isotherm conformed to the Langmuir model, representing the monolayer adsorption of the phenolic compounds. The dynamic models were used, and they accurately represented the breakthrough curves. Considering PC recovery and process reusability, a regeneration experiment of SA-AC beads was carried out in fixed-bed reactors. SA-AC beads showed a high percentage desorption >40% using ethanol and were efficient after several cycles of OMWW treatment and phenol recovery.

NiP/CuO composites: Electroless plating synthesis, antibiotic photodegradation and antibacterial properties

This work reports a simple method to prepare nickel-phosphorus (Ni-P) alloy modified CuO (Ni-P/CuO) composite, which shows excellent performance in terms of photodegradation antibiotics, particularly regarding the antibacterial properties. The Ni-P/CuO composites were prepared via two steps. The first step was to produce CuO by the hydrothermal method and the second step was to grow Ni-P in-situ on the surface of CuO through electroless plating. After loading of Ni-P, the photocatalytic activity of CuO for the decomposition of antibiotics is significantly increased under visible light irradiation. The photocatalytic activity of Ni-P/CuO with 4 wt% Ni-P loading is 25 times higher than that of CuO. Compared with CuO, the antibacterial activity of Ni-P/CuO with 4 wt% Ni-P loading against Escherichia coli is strongly increased. Based on the photoluminescence and photocurrent measurements of CuO and Ni-P/CuO, Ni-P cocatalyst improves the separation and transfer of the photogenerated charge in CuO, and enhances the photocatalytic activity of antibacterial performance. This work reveals that using Ni-P as the cocatalyst can strengthen the photocatalytic performance of CuO, which has great application potential in water purification and antibacterial treatments.

CuCr2O4@CaFe-LDO photocatalyst for remarkable removal of COD from high-strength olive mill wastewater

Wastewater from the olive mill constitutes a serious environmental concern, as it is characterized by a high inorganic and organic load. Here, a hybrid photocatalyst based on calcined Ca-Fe-LDH was successfully synthesized for the degradation of phenolic compounds and the removal of chemical oxygen demand (COD) from the high-strength olive mill wastewater (OMW). The catalyst (CuCr₂O₄@CaFe-LDO) displayed a stable ~4.48 µA cm^-2 photocurrent response, a 2.56 eV bandgap and a wide variety of pores with an average size of 12.51 nm. 1.0 g CuCr₂O₄@CaFe-LDO achieved 66% COD removal after 300 mins without an oxidant in the dark, while after 180 mins of reaction, CuCr₂O₄@CaFe-LDO/K₂S₂O₈/sunlight system resulted in ~99% and 98.3% COD and colour removal. Seven phenolic compounds were found in the crude OMW, with hydroxytyrosol (76.84%) and tyrosol (15.14%) being the main ones. The final pH of the sample treated increased from 4.3 to 7.3, which confirmed the degradation of phenolics and fatty acids in the OMW. OH, SO₄^-, h⁺ and O₂^- contributed notably to the degradation of polyphenols and the spent catalyst was easily and rapidly recovered from the bulk solution due to its saturation magnetization of 54.7 emu g^-1.