Fabrication and properties of low cost ceramic microfiltration membranes for separation of oil and bacteria from its solution

Abstract

This work addresses the development of low cost ceramic microfiltration membrane from inexpensive raw materials such as kaolin, quartz, calcium carbonate using uniaxial dry compaction method. The prepared membranes were sintered at different temperatures ranging between 900 and 1000 °C. The raw materials and the prepared membranes were characterized with thermogravimetric analysis (TGA), particle size distribution (PSD), X-ray diffraction and scanning electron microscope analysis. Subsequently, the effect of sintering temperature on the membrane properties such as porosity, flexural strength, chemical stability and pure water permeability was investigated and optimized for the sintering temperature. It is observed that with increasing sintering temperature, the porosity of the membranes decreases and the flexural strength, chemical stability and pure water permeability of the membranes increases. The flexural strength and chemical stability of the membranes are found to be excellent. Based on these results, the membrane sintered at 900 °C (porosity of 30%, flexural strength of 34 MPa, average pore size of 1.30 μm) is inferred as an optimum membrane for microfiltration applications. Solvent permeation studies have also been carried out for the membrane sintered at 900 °C and the results infer that the membrane is hydrophobic in nature. Further, the membrane is subjected to oil–water emulsion and bacteria separation experiments. The observed rejection decreased with an increase in the applied pressure and increased with an increase in the concentration of oil and bacteria, respectively. The results show a maximum rejection of 85% and 99% for oil (feed oil concentration of 250 mg/L) and bacteria (feed bacteria concentration of 6 × 10⁵ CFU/mL), respectively.

Introduction

During the last few decades, the applications of ceramic membrane have increased due to its excellent chemical, thermal and mechanical stability and higher separation efficiency [1], [2], [3], [4], [5]. In the near future, the exploitation of new type of the ceramic materials and simple fabrication techniques could play a significant role for the preparation of low cost membranes. The alumina-based ceramic membrane for industrial application is limited due to its higher cost and sintering temperature [6], [7]. Therefore, the clay-based low cost ceramic membranes would be further applicable to the industries. Many researchers have used low cost clays such as raw clay, moroccan clay, tunisian clay, sepiolite clay, algerian clay, dolomite and kaolin [8], [9], [10], [11], [12], [13]. Kaolin is one of the cheapest membrane raw materials easily available in India. Various researchers have reported the use of kaolin as a starting material with other additives for membrane applications [14], [15]. Recently, Neelakandan et al. have used the low cost clays available in India (kaolin, feldspar, ballclay, quartz, pyrophyllite and calcium carbonate) for the preparation of ultrafiltration membranes [16].

Large quantities of oily wastewater generated from various process industries, particularly refinery and metallurgical industries need to be treated before discharge to a sewage system. Discharging these effluents pollute the environment and also reduce the yield of oil. Amongst various processes for treatment of oily effluent, membrane separation process appears to be a most competent process. It has many advantages such as high oil removal efficiency, low energy cost and compact design compared with other conventional treatment process including mechanical separation, filtration, skimming, and gravity settling [17]. Nowadays, ceramic membranes are increasingly being applied for treating oily wastewater due to their excellent properties. Many researchers have reported the oily wastewater treatment using ultrafiltration (UF) and microfiltration (MF) with polymeric and ceramic membranes [18], [19], [20], [21]. Zhong et al. have used the zirconia membrane for the treatment of oily wastewater produced from refinery process [22]. Mueller et al. have investigated the performance of both ceramic and polymeric MF membranes for the treatment of oily wastewater using heavy crude oil with concentration of 250–1000 mg/L and oil droplets size of 1–10 μm [23]. Cui et al. have reported the microfiltration of oily wastewater using zeolite membrane with a pore size of 1.2 μm and achieved 99% rejection for a feed concentration of 100 mg/L [24]. Nandi et al. have used a ceramic membrane for treatment of oily wastewater and investigated the effect of concentration oil-in-water and operating pressure on the rejection performance of the membrane [25].

The removal of microorganism is a major concern for the production of high quality medical and drinking water. Membrane separation processes including microfiltration (MF) and ultrafiltration (UF), have received a great deal of attention for the removal of microbes [26], [27]. Kobayashi et al. have reported the cutoff performance of Escherichia coli using charged and uncharged polyacrylonitrile (PAN) ultrafiltration membranes with a feed concentration of 10⁷ (CFU/mL) [28]. The role of cell-wall structure for the retention of bacteria using polycarbonate track-etched microfiltration membranes with a pore size of 0.4 μm was investigated by Lebleu et al. [29]. Karim et al. have used the polysulfone membrane possessing an average pore size of 0.1 μm for the separation of E. coli lysate by flocculation enhanced microfiltration and achieved complete removal of E. coli [30]. The removal of microorganism for the production of drinking water using different types of UF and MF membrane having different pore size was studied by Mavrov et al. and the results indicated a significant reduction of microbes [31]. There are several reports for the removal of microbial cell adopting polymeric membranes for microfiltration (MF) and ultrafiltration (UF) [32], [33]. In the case of ceramic membrane, few literatures are available for bacteria removal. Due to this reason, we focus to prepare ceramic membranes for the removal of bacteria from water.

The objective of this article is to study the influence of sintering temperature on the properties of low cost ceramic microfiltration membrane derived from inexpensive raw materials and evaluate its separation performance for the treatment of oil–water emulsion and bacteria solution. The structural characteristics, mechanical and chemical stability of the prepared membranes were examined. Pure water and solvent permeation experiments were also carried out to estimate the membrane performance. Microfiltration experiment of synthetic oil–water emulsion and bacterial solution was carried out to evaluate the separation capability of the prepared ceramic membrane.