Elaboration of novel tubular ceramic membrane from inexpensive raw materials by extrusion method and its performance in microfiltration of synthetic oily wastewater treatment
Introduction
In recent years, the potential utilization of ceramic membranes has greatly improved, especially in a broad range of industrial processes and pollution treatment technologies. Ceramic membranes can be applied in extreme aggressive environments due to their distinct advantages, including good thermal stability, mechanical strength, chemical resistance, long lifetime and defouling properties. While organic polymer membranes cannot be applied owing to their restricted stability [1], [2], [3]. In general, most of the commercialized ceramic membranes available in the market are produced from alumina, silica, zirconia and titania materials. However, these ceramic membranes are severely restricted in large scale application due to the higher cost of starting materials and sintering processes [4], [5]. Therefore, the preparation of ceramic membranes with lower cost and excellent characteristics are the challenging tasks for the upcoming development of ceramic membranes for treatment of a large volume of waste matters contaminated liquids. Tubular ceramic membranes are especially suitable in applications where the feed stream contains a relatively high proportion of large particles, and where the membranes are exposed to extreme pH and temperature conditions. In general, the size of the feed flow channels in tubular ceramic membranes is larger than other membrane modules. This type of open channel geometry reduces the risk of the blockage of the feed channels and also the requirement of costly pretreatment before microfiltration [6]. Generally, ceramic membranes comprise of multi-layer formation with the substrate (support), intermediate layer and skin layer (separating layer). The substrate of membranes can be produced by various techniques, including isostatic pressing, extrusion, slip casting, etc., [7], [8]. The fabrication of porous ceramic membrane with the tubular configuration needs the expertise on choosing appropriate starting materials and methods. Shaping by extrusion is achievable only if the paste created from starting materials has rheological characteristics similar to those of clays [9]. As a consequence, currently many researches targeted on the development of ceramic membranes with utilization of less expensive materials such as apatite powder, dolomite, pyrophylite, Moroccan clay and kaolin, etc,. [10], [11], [12], [13]. Talidi et al. [10] prepared the tubular macroporous membrane using pyrophylite clay via extrusion and followed by a sintering process. The properties of the porous pyrophyllite membrane were discussed as a function of sintering temperature in order to optimize the preparation conditions. Saffaj et al. [11] prepared membrane support using Moroccan clay as a raw material by extrusion of the clay paste. The structural and mechanical properties of fabricated low cost membrane support were found suitable for membrane applications. Masmoudi et al. [12] produced tubular porous support using natural apatite powder and suggested for ultrafiltration (UF) and microfiltration (MF) applications. Bouzerara et al. [13] constructed membrane support from mixtures of doloma and kaolin. They strongly recommended that prepared support can be utilized for MF and UF processes.
A huge volume of oily wastewater was created from different process industries, including petrochemical, petroleum refineries, transportation and metallurgical industries [14]. Discharging of this effluent causes environmental pollution as well as decreases the yield of oil. Therefore, the treatment of oily wastewater is compulsorily required before discharging. As per environment (protection) rules (1986, India), the central pollution control board framed the discharge limit of oil into surface water as 10 (mg/L), public sewers as 20 (mg/L), irrigation water as 10 (mg/L) and coastal water as 20 (mg/L) from various industries [15]. Several conventional techniques have been used for oily wastewater treatment that includes electrostatic coalesce, heating treatment, filter coalesce, centrifugal settling, gravity settling, pH adjustment and chemical emulsification. All of these methods have some advantages and disadvantages [16], [17]. Hence, membrane technology comes into sight as a best competent technique for treatment of oily wastewater amongst the various conventional techniques. In addition, it is very attractive due to the advantages, such as compact design, lower energy requirement and higher separation efficiency as compared to other existing treatment processes [18]. However, the treatment cost can be further lowered by choosing microfiltration (MF) membranes since they do not require so high trans-membrane pressures and have higher flux than ultrafiltration membranes [19]. Numerous authors have evaluated the potential aspects of ceramic membranes in oily wastewater treatment. Mohammadi et al. [20] formulated a kaolin based tubular ceramic membrane with a pore diameter of 10 µm for the treatment of oily wastewater emulsions. The prepared membrane provided a good separation performance on various operating conditions. Zhong et al. [21] examined the efficiency of ZrO2 ceramic membrane (average pore diameter of 0.2 μm) in oily wastewater treatment. The prepared zirconia membrane displayed the oil removal of 99.4–99.9%. Yang et al. [22] attained 99.8% of oil rejection utilizing the commercial tubular (ZrO2/α-alumina) membrane with an average pore diameter of 0.2 μm. In another study, Cui et al. [17] obtained 99% of oil rejection employing the zeolite membrane having the pore size of 1.2 μm in microfiltration of oily wastewater. Amongst many research perceptions, the development and employment of the ceramic membranes derived from inexpensive raw materials for oily wastewater treatment are getting interest in recent days.
Considering such research trends, the study presented here focuses on the preparation of the novel tubular ceramic membrane by an extrusion method and evaluation of separation performance in treatment of oily wastewater emulsion. Contemplation on reducing the price of the membrane and to assess our natural resources, the local clay materials: kaolin, quartz, ball clay, pyrophyllite, feldspar and calcium carbonate are utilized as raw materials. The performance of the membrane is investigated through microfiltration of synthetic oily wastewater emulsions on various operating parameters, such as applied pressure, feed concentration and cross flow rate with respect to rejection and permeate flux. The fouling mechanisms are examined using obtained flux data during the microfiltration.
Section snippets
Materials and methods
The starting materials utilized for elaboration of the membrane (kaolin, quartz, ball clay, pyrophyllite, and feldspar) were of mineral grade and obtained in the vicinity (Kanpur). Crude oil was procured from Guwahati Refinery, IOCL (Assam). Calcium carbonate, hydrochloric acid and sodium hydroxide were supplied by Merck (I) Ltd, Mumbai.
Description of the pore blocking model for flux decline analysis
To identify the presentable microfiltration flux decline profile of oily wastewater emulsion, four fouling models, such as (a) complete, (b) standard, (c) intermediate pore blocking and (d) cake filtration model, have been analyzed [23].
(a). Complete pore blocking takes place when the size of the solute particles is bigger than the pores of the membrane. It causes the pore blocking on the surface of the membrane and does not cause inside pores of the membrane. (b). Standard pore blocking occurs
Characteristics of tubular ceramic membrane
The phase transformation activities of the membrane before and after sintering were analyzed through XRD patterns as depicted in Fig. 3. The sintering process generates various phase transformations and reactions, which initiates the creation of new phases. This gives the absence as well as transfer of the position of the XRD peaks. The perfect crystalline phase is observed for the sintered membrane and the mainly identified phases for the membrane (after sintering) are mullite (3Al2O3·2SiO2),
Conclusions
Low cost novel tubular ceramic membrane has been effectively fabricated using inexpensive clay mixtures by the extrusion technique. The prepared membrane offers better porosity (53%), lower average pore size (0.309 µm), strong mechanical strength (12 MPa) and excellent corrosion resistant. Moreover, the elaborated membrane is highly fulfilled in oily wastewater treatment. Microfiltration studies demonstrate that the permeate flux increases and the rejection decreases when the applied pressure
Acknowledgments
We would like to thank the Central Instruments Facility at IIT Guwahati for helping us to perform FESEM analysis.
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