Melamine-Ceramic Membrane for Oily Wastewater Treatment

: Four distinctive Ceramic membranes have been synthesized using bentonite and Egyptian clay with the expansion of melamine. The addition of melamine (~ 1% by wt.) enhanced the porosity, density, the thermal stability and water permeability of the membranes made from bentonite or Egyptian clay while decreasing the chemical stability of either bentonite or Egyptian clay membranes. The most noteworthy level of decrease in COD (94.7%) is acquired for the concentration of 200ppm with saturating flux of 4.63 E-05 (m 3 /m 2 .s) utilizing (B+M) membrane. The cost of the four manufactured clay membranes was assessed based on raw materials used in the present investigation.


INTRODUCTION
Oily wastewaters are one of the significant contaminants of the aquatic environment. Oily wastewater emitted to the aquatic environment is ranging from 0.5 to 1 ton for every 1 ton of processed oil from refineries [1]. As indicated by insights, consistently somewhere around 500 to 1000 million ton of oil is released into the aquatic environment through different ways [2], which causes water contamination, as well as ends up being a misuse of oil assets. And since the shortage of water resources has become more and more serious and due to the large volumes of oily wastewater generated by the petroleum refineries, petrochemical plants and transportation; oily wastewater treatment has turned into a pressing issue [3,4].
During the previous years, different techniques have been reported in the literature for oily wastewater treatment, for example, adsorption [5,6], flotation, coagulation [7,8], chemical oxidation [9] and using of membranes [10]. Lately, regulations for the discharge of industrial wastewater has been changed. The new European regulations allow less than 10mg/L of suspended solids, which could be met only using membrane technology [11]. Membrane separation technology for oily wastewater treatment offers numerous advantages with respect to other strategies, for instance, small footprint, low cost for establishing or operating and high oil removal efficiency [11,12].
*Address correspondence to this author at the City for Scientific Research and Technological Applications SRTA City, Borg Elarab, Alexandria, Egypt; Tel: 20-1001392281; E-mail: mhr1410@hotmail.com The utilization of porous ceramic membranes using low-cost materials has attracted much interest. Organic ceramic membrane technology has many disadvantages such as poor stability, poor acid and alkali corrosion resistance and non-renewable while Inorganic membrane has been studied and used by researchers due to its high-temperature resistance, high permeate flux, chemical corrosion resistance and good mechanical strength [13]. Many materials have been reported in the literature for the manufacture of ceramic membranes such as alumina (Al 2 O 3 ) [14], zirconia (ZrO 2 ) [15], titania (TiO 2 ) [16], silicon carbide (SiC) [17], glass (SiO 2 ) [18], or a combination of these metal oxides, and composites or combinations of oxides and non-oxides [19], as well as clay minerals (e.g., kaolin [20], mullite [21], dolomite [22], etc.). The thermally stable membrane expands the utilization area of membrane especially in comparing some crucial conditions. Elevated operation temperature is ready to improve membrane flux and decrease membrane fouling, which is meaningful for energy recovery and cost reductions [23]. Thermally stable membranes can be used in the treatment of various hot fluid streams without strict temperature control.
Melamine with triazine ring structure showed low toxicity, low reactivity and can endow the membrane with an excellent thermal resistance [24,25]. The composite membrane prepared with melamine may show excellent thermal resistance and better chlorine resistance. Melamine is used for the first time to prepare TFC membranes with excellent thermal resistance and chlorine resistance and the composite NF membrane was successfully fabricated with the interfacial polymerization of melamine and TMC with the PEI UF membrane as substrate [24]. This research presented here focuses on preparing membranes from bentonite and Egyptian clay with the expansion of Melamine and study the effect of adding melamine on the thermal stability of the prepared membranes then apply the prepared membrane for efficient treatment of an oil-in-water emulsion. Then study the cost analysis for membranes based on raw materials.

Materials Used
Bentonite; the EDAX analysis for bentonite is presented in Table 1, Egyptian Clay collected from Behaira Governorate area; the EDAX analysis for Egyptian clay is presented in Table 1, sodium carbonate, calcium carbonate, boric acid, sodium metasilicate and melamine as raw materials. All raw materials used for membranes fabrication were graded at least 99.5% pure and were used without any further purification.

Preparation of the Membrane
For the membrane preparation, Egyptian Clay or bentonite (40.74g), sodium carbonate (7.4g), boric acid (3.71g), calcium carbonate (18.52g) and sodium metasilicate (5.52g) were blended together with 37.03g of distilled water to yield a paste. Furthermore, for preparation of melamine bentonite (B+M) and melamine clay (C+M); 1g of melamine were included. The pastes were then shaped like a round circle by utilizing a hardened steel 316 ring of 55mm interior diameter across and 5mm thickness. At that point, the circle compose shape was dried at room temperature for 24h, at 100°C for 12h and at 250°C for 2h for finish evacuation of moisture. In this manner, the membranes were sintered at 900°C for 5h with a warming rate of 2°C /min. Subsequent to sintering, membranes turned out to be hard and unbending and with a permeable surface. The four membranes structure is displayed in Table 2. The four membrane discs were cleaned with rough paper to acquire a smooth, flat surfaces with a diameter of 52.5mm and a thickness of 5mm.

Membrane Density and Porosity Measurements
The Ceramic membrane discs were submerged in de-ionised water for 24 h. Abundance water was wiped with tissue paper. The wet membrane discs were weighed. From that point onward, membrane discs were vacuum dried in an oven at 100°C once more. Membrane density was calculated using equation (1).
Where, ρ is defined as density (g/cm 3 ), m dry as the weight of the dry ceramic disc, d diameter of the membrane disc (g) and l is the thickness of membrane disc. membrane porosity, ξ (%) has been characterized as the volume of the pores over the aggregate volume of the permeable membrane disc. It typically is dictated by  gravimetric strategy, considering the weight of water contained in the membrane pores, and it tends to be depicted by equation (2).

Water Permeability of the Membrane
The permeation test (clean water flux) was done in a dead-end filtration setup. The permeability of the membrane, WP, was assessed from the inclines of the water flow through the membrane versus pressure diagram, as per the Hagen -Poiseuille equation,

Acid and Base Corrosion Test
The chemical stability test of the membrane discs was tried in an acidic and alkaline arrangement. The orchestrated membrane discs were set independently in HCl and NaOH media for seven days. Toward the finish of test, the membranes were taken out from the solution (acid and alkaline), washed with distilled water, pruned with tissue paper to somewhat dry the discs, lastly dried in an oven at 100°C for around 60 minutes. From the distinction in the weight (previously, then after the treatment), the base and acid corrosion were determined.

SEM Study
The texture of the prepared ceramic membrane discs was investigated by SEM (Scanning Electron Microscope) to think about the surface morphology. SEM pictures from various segments of the membrane (and in various amplification) were contemplated.

"Energy Dispersive X-Ray" EDAX Analysis for Ceramic Membranes Prepared
EDX analysis of the membrane was carried out to verify the elemental composition of the membranes after adding melamine.

FTIR Spectra of the Ceramic Membranes
The surface functional groups and structure were studied by Fourier transform infrared spectroscopy (FTIR). The FTIR spectra of C, C+M, B and B+M ceramic membranes were recorded between 300 and 4,000 cm−1 using FTIR-8400S (Shimadzu Corporation, Nakagyo-Ku, Kyoto, Japan).

Thermal Gravimetric Analysis (TGA) for the Ceramic Membranes
Thermal Gravimetric Analysis or Thermogravimetric Analysis (TGA) were performed to measure the change of weight with respect to the increase in temperature in a controlled atmosphere to predict the thermal stability of the ceramic membranes.

Microfiltration of Oil -in-Water Emulsion
The oil filtration analyze was led with a simulated oil in water emulsion (O/W) of various oil concentrations (100, 150 and 200mg/l) blended at 2000rpm. The initial 10ml of the permeate was disposed of and time taken for the accumulation of the second 10 ml of permeate was estimated for permeate flux calculations Figure 1. Every trial was conducted at room temperature (25°C) and the rejection (R) was assessed by the accompanying articulations which represent the % decrease in the COD esteem.
Where C f and C p are the oil concentration in the feed and permeate respectively.
The oil concentration in feed and permeated were evaluated using COD analysis.

SEM Micrographs
The SEM micrographs for the membrane are shown in Figures 2 and 3. Each membrane demonstrated a  surface with rough morphological structure. A shallow perception of the SEM demonstrates that the membrane discs have extensively huge pore distance across and did not have any pinholes breaks or cracks. It tends to be observed that both bentonite and Egyptian clay membrane discs show an inhomogeneous surface. Truth be told it presents a few areas that don't contain any porosity and the obtained pores are not connected which would prompt a low penetrability of the membrane discs (C and B only). But with the utilization of melamine, it was clear the growth of the porosity (for either B+M or C+M). Likewise, the acquired pores were associated with one another. This clarifies the growth of the permeability for either bentonite with melamine membrane (B+M) or Egyptian clay with melamine membrane (C+M).

EDAX Analysis for Ceramic Membranes Prepared
To determine the composition of the membrane surface; the prepared membranes were analyzed using EDX analysis. The results of the ceramic membranes surfaces compositions can be seen in Table 3. By comparing the composition of ceramic membranes prepared and the composition of raw materials used (showed in Table 1), it was found that new elements have appeared which are carbon (C) and Nitrogen (N) in the melamine bentonite (B+M) and the % of C increased in melamine clay (M+C) membranes due to adding 1 g melamine which is converted to carbon nitride C 3 N 4 after heating to 900°C.

FTIR Spectra of the Prepared Ceramic Membranes
The observed bands showed in Figure 4 Figure 5 represents the TGA analysis for the prepared membranes. It merits referencing that the thermal analysis was carried out up to 1099°C. During the main period of warming the mass loss of membranes (B and B+M) up to 552°C and 622°C was 1.4% and 2.16% respectively while by increasing the temperatures up to 1099°C, the B and B+M membranes had indicated a mass loss of 6% and 5.8%, respectively.  For C and C+M membranes up to 1099°C the mass loss of 16% and 13% respectively. These mass losses can be explained to the loss of loosely bound water molecules and the presence of some absorbent substances (like Na metasilicate, boric acid). The results exhibit that the four types of membranes (B, B+M, C and C+M) are thermally stable up to 1099°C and the membranes made of B and B+M are more thermal stable than that made of C and C+M up to 1099°C. The results also show that adding melamine increased the thermal stability for bentonite and Egyptian clay membranes. Table 4 shows the density and porosity for the four fabricate membranes.

Membrane Density and Porosity
The data shown in Table 4 indicate that the membrane discs fabricated from Egyptian clay have higher density and porosity than the membrane disc fabricated from bentonite. Adding under 1% by weight to the blend used to fabricate either the bentonite or Egyptian clay membrane discs have expanded the density and porosity of the membrane discs. Table 5 shows the effect of treating the four fabricated membrane discs (B, B+M, C, and C+M) to either acid or alkaline media to clarify the substance steadiness of the delivered membrane discs. The test is displayed by ascertaining weight reduction % after subject the membrane discs to acid or alkaline media.   Table 5 indicated that the membrane discs manufactured from either bentonite or Egyptian clay are stable in corrosive acid media. The membrane discs manufactured from either bentonite or Egyptian clay are marginally influenced by base media while the discs prepared from bentonite is higher influenced by base media than that prepared from Egyptian clay. Adding melamine to either Egyptian clay or bentonite will lessen the chemical stability of the membrane discs in either corrosive acid or base media.

Water Permeability of the Membrane
The four fabricated membrane discs were characterized by the assurance of water permeability. It tends to be seen that the water flux increases with increasing the applied pressure (Figures 6-9). Water permeability was resolved by the slope of the linear variation of flux (m 3 /m.s) versus the applied pressure. Table 6 demonstrates the water permeability for the four fabricated membrane discs. The outcomes demonstrated that including melamine for either bentonite or Egyptian clay will upgrade the water permeability of the membrane discs.

Application to the Treatment of Oily Wastewater
The four fabricated ceramic membranes (B, B+M, C, and C+M) were connected for the treatment of simulated oily wastewater emulsions. Applied pressure, feed oil concentration and cross flow rates are the imperative factors that influence the treatment procedure as far as penetrate flux and dismissal.  Figures 10-13 show the % reductions in COD with time for various oil concentration (100, 150, and 200 ppm) for Bentonite (B), Bentonite with melamine (B+M), Clay (C) and Clay with melamine (C+M) respectively. From the above-mentioned figures, it is clear that the % reduction in COD increases with increasing time and also the % reduction in COD increases with increasing concentration. From the percentage of reduction in COD for the four fabricated membranes shown in Table 7 and Figure 14        extent of oil droplets is higher than the pore distance across of the membrane at higher concentrations which agree with literature [28].   The results showed that adding melamine for the membrane composition enhance both the % reduction in COD and the permeate flux as shown in Figures 19,  20, and Table 7.   Figure 21 shows the effect of backwashing on permeation flux decline, for the first 120min of a longterm operation. Permeate flux was plotted as a function of time for 100ppm oil concentration at 1bar. As watched, permeation flux was essentially reestablished by backwashing [29,30]. It may be seen that the backwash of the ceramic membranes with hot water is adequate to keep up its exhibition good for a long term activity. As appeared, it is conceivable to recuperate over 95%, 92%, 79%, 65%, and 60% of the original flux by backwashing of C+M, B+M, C and B membranes respectively. It means that utilizing continuous backwashing expels oil and particulates that block the membrane pores and lessens penetrate permeate flux decline.

Cost Analysis for Membranes Based on Raw Materials
The cost of the four fabricated ceramic membranes was evaluated on the basis of raw materials utilized in    [22]. Therefore, it can be concluded from the cost estimation that the prepared membrane is inexpensive as compared to alumina membranes.

CONCLUSIONS
Four Low-cost dead-end ceramic membranes have been effectively fabricated using inexpensive bentonite and Egyptian clay with the expansion of Melamine (adding less than 1% by weight melamine). The prepared membranes have been characterized by SEM, FTIR, EDAX, acid and base corrosion tests, water permeability and measuring density and porosity. The results indicating that utilization of melamine increasing the porosity, density, the thermal stability and water permeability of the membranes made from bentonite or Egyptian clay while decreasing the chemical stability of either bentonite or Egyptian clay membranes. The four membranes have been tested in the removal of oil from industrial water and the results showed that the highest percentage of reduction in COD (94.7%) is obtained for the feed concentration of 200ppm with permeate flux of 0.000128m/s using (B+M) membrane. An increase in the oil concentration results in declines in permeate flux. The cost of the four fabricated ceramic membranes was evaluated on the basis of raw materials utilized in the present study. It can be concluded from the cost estimation that the prepared membranes are inexpensive as compared to alumina membranes. Overall, the presented work suggests the competency of the elaborated membranes in the direction of utilization towards the treatment of oily wastewater emulsion.