A new ceramic microfiltration membrane based on olive seeds: development and characterization

Membrane technology is gaining a lot of interest due to its possible uses in various production processes (Fatni et al. 2021; Addich et al. 2022a). It offers several advantages, such as a changeable microstructure, pore size distribution, low environmental pollution, and reduced energy consumption at gentler conditions (Agarwalla & Mohanty 2022; Gu et al. 2022). Consequently, numerous researchers are currently working toward the development of novel membrane types and application procedures (Lagdali et al. 2023). Microfiltration is a widely adopted technique for the separation of particles, microorganisms, and colloidal species from suspensions (Najid et al. 2022). It involves the use of a selectively permeable membrane that selectively retains the target species while allowing the desired filtrate to pass through. The process is suitable for numerous uses across multiple sectors (Teow et al. 2022), including biotechnology, pharmaceuticals, food, and beverage (Poli et al. 2022), and wastewater treatment (Safaee et al. 2022), among others (Addich et al. 2022a, 2022b). The effectiveness of the microfiltration process is primarily determined by the size and composition of the microorganisms and particles to be removed, the membrane's pore size, and operating conditions such as pressure, flow rate, and temperature. Overall, microfiltration is a reliable and efficient solution for the separation and purification of suspensions, and its versatility and flexibility make it a popular choice in many applications (Omar et al. 2024).

Ceramic membranes have significant industrial potential. As such, a lot of effort has gone into developing nature-based ceramic membranes using clay materials like sand (Aloulou et al. 2017; Addich et al. 2022a, 2022b), clay (Ouaddari et al. 2019), and phosphate (Mouiya et al. 2018). Membrane processes used for separating oil-in-water emulsions often face the issue of membrane fouling caused by the accumulation of oil phase near the membrane surface (Alftessi et al. 2021; Naseer et al. 2024). This poses a major challenge to increase the efficiency of membrane permeate flux and cleaning procedures during operation. During oil-in-water emulsion filtration, convective permeation flow transports oil droplets near the membrane surface, which can then accumulate on it. The burgeoning expansion of various industries such as oil and gas, petrochemicals, food processing, pharmaceuticals, and metallurgical sectors results in the generation of substantial volumes of oily wastewater effluents. The standard concentration of oil and grease in the produced water from oil fields typically falls within the range of 100–1,000 mg/L or may even exceed these levels, contingent upon the characteristics of the crude oil (Chakrabarty et al. 2008). Substituting conventional polymeric membranes with ceramic microfiltration membranes proves highly efficient owing to their hydrophilic properties and precise, narrow pore size distribution.

The objective of this project is to utilize the extrusion technique for the production and characterization of a ceramic tubular membrane using olive seeds as a raw material. The selection of this particular raw material is justified by the requirement for the development of hybrid ceramic membranes possessing exceptional surface properties and demonstrating effective and sustainable anti-fouling characteristics during cleaning and filtration cycles.

In this study, we utilized olive seeds obtained from Taroudant, Morocco, to manufacture tubular microfiltration membranes. We ground 50 g of the powder using a mortar crusher (Retsch, France) for 20 min. After drying the powder, we sifted it through a 125 μm sieve to obtain the desired structure for the membrane.

The production of tube-shaped supports involves the use of 125 μm particle size powder and organic additives, including Amijel derived from starch, starch, and methocel. After several tests, the ideal paste composition comprised 82% olive seed powder, 10% Amidon as a porosity agent, 4% plasticizer (methocel), and 4% binder (Amijel). Homogenization of the blend was performed using an electric mixer at 250 (tr/min) for 20 min. Distilled water (28.4% by weight) was progressively added to the solid mixture to achieve the desired plastic paste. The mixture was sealed and aged for 24 h to guarantee full dispersion of organic ingredients and water.

The developed membrane was subjected to a comprehensive characterization process involving several analytical techniques, including X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The XRD analysis provided insights into the crystalline structure of the olive seed powder, while FTIR spectroscopy revealed the functional groups. TGA/DTA analyses provide information on the thermal stability and decomposition behavior of the membrane. Finally, SEM analysis was used to evaluate the morphology and the membrane surface. The combination of these techniques provides a comprehensive understanding of the physicochemical properties of the developed membrane.

In addition, the three-point bending method of the Shimadzu EZ-LX was used to measure resistance to mechanical force.

The process of sintering temperature determines the porosity of a ceramic membrane. During this process, organic additives are combusted, which creates pores in the membrane. The microstructure of the membrane is considerably affected by the sintering temperature. Sintering begins at 200 °C, causing small fragments to agglomerate. At 250 °C, the duration of the piece is predominately portrayed in Figure 6(b). Analysis of the membrane revealed that 200 °C is the ideal temperature for sintering to create a ceramic membrane from olive seeds. Figure 6(c) illustrates the advancement of porosity and flexural strength of the membrane prepared at both sintering temperatures. The mechanical resistance increases from 0.5 to 0.7 MPa. However, these values are inadequate when compared to the literature. In addition, fritting over 350 °C is not recommended according to TGA/DTA analysis; nonetheless, oils can be filtered by gravitation without applying high pressure. Furthermore, the next study project will focus on incorporating a particular amount of clay to improve the mechanical strength of this membrane.

The researchers utilized ImageJ software to assess the features of the pores in the membranes based on the SEM images acquired (Achiou et al. 2018; Addich et al. 2022a, 2022b). The software was able to measure the diameters of almost 100 pores, and a careful sampling process was necessary to determine the pore size distribution. These values represent the actual porous shape of the support material. From Figure 6(d), it is evident that the ceramic membrane contains pores with diameters ranging from 2 to 15 μm in 75–89% of the support pores.

Oil-in-water emulsion test solutions were prepared using virgin-grade olive oil in deionized (DI) water with 0.01 wt% Tween 80 as the surfactant. Two different oil concentrations, 500 and 1,000 mg/L, were utilized. The oil, surfactant, and DI water were combined in Pyrex glass bottles and subjected to mechanical shearing using a homogenizer (Ultra turax) at 14,000 rpm for 30 min. Subsequently, the obtained emulsion was left to stabilize for 24 h.

Figure 9(b) illustrates the variation of permeate flux over time during the filtration process of both emulsions under 1 bar pressure. It is observed that the flux experiences a significant initial decrease, eventually stabilizing at nearly constant values. Initially, water flows easily through the membrane pores, resulting in high flux values. However, as filtration progresses, oil droplets obstruct the pores, leading to a reduction in flux values until reaching a steady state. This rapid decline in flux during the early stages of filtration is analyzed by examining the flux using various membrane fouling models.

The photographs of the feed and the filtrate water samples are shown in Figure 9(c). An SEM image of the filtered membrane sample surface is shown in Figure 9(d). The turbidity values of the water sample before and after the filtration experiments are given in Table 1.

The concentration of oil in the permeate water was determined using UV–visible spectroscopy, and the results are presented in Table 1. It was observed that an increase in the oil concentration in the feed resulted in enhanced oil rejection, consistent with findings reported by Ebrahimi et al. (2010). Oil rejection rates of up to 97.6% were achieved for the 1,000 mg/L sample. When the oil content in the feed is high, the accumulation of oily particles gradually blocks the larger pore channels through which tiny oily particles could penetrate, thereby affecting the rejection performance over time.

This study describes the elaboration of an innovative microfiltration membrane made from olive seeds. The membrane's support was evaluated with various characterization techniques, including SEM. The study findings indicate that the membrane holds significant potential for use in various applications where microfiltration is required. The cost-effectiveness of the membrane production process and its efficient separation capabilities make it an attractive alternative to existing technologies.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.