Recovery of Polyvinyl Alcohol from Desizing

830 Ankur Sarkar1 Debasish Sarkar2 Madhurima Gupta2 Chiranjib Bhattacharjee1 1

Department of Chemical Engineering, Jadavpur University, Kolkata, India 2 Department of Chemical Engineering, University of Calcutta, Kolkata, India

Clean – Soil, Air, Water 2012, 40 (8), 830–837

Research Article Recovery of Polyvinyl Alcohol from Desizing Wastewater Using a Novel High-Shear Ultrafiltration Module Polyvinyl alcohol (PVA), the major constituent of desizing water constituting 45% of the total BOD load has a significant environmental impact owing to its poor biodegradability. In order to prevent PVA from being discharged by the effluent stream, modern textile industries opt for membrane based separation techniques using ultrafiltration so that the recovery and recycle of PVA in tandem could be achieved. However, the process of ultrafiltration is still not widely accepted as expected due to the well-known non-idealities of concentration polarization and pore blockage. In this article, design and performance characterization of a lab-scale novel shear enhanced ultrafiltration unit, named as spinning basket membrane (SBM) module are discussed. The proposed module is unique in terms of its inbuilt cleaning facility eliminating the effects of polarization and subsequent periodic fouling leading to its uninterrupted production operation. The test fluid, necessarily a solution of PVA was treated in the proposed module under different parametric conditions with polyvinylidene fluoride (PVDF) membranes of two different molecular weight cut-off (50 and 100 kDa). After 2 h of continuous operation the permeate flux was observed to be within 95–97% of the respective initial fluxes. Such performance is rarely been attained in practice. Hence, the novelty of the present research is achieved. Considering the performance of the present module in terms of flux regeneration and product recovery, it may be regarded as an efficient device and can be potentially deployed for cleaning of other industrial wastewater. Keywords: Cleaning run; Permeate flux; Shear enhanced; Spinning basket membrane Received: September 23, 2011; revised: January 25, 2012; accepted: January 30, 2012 DOI: 10.1002/clen.201100527

1 Introduction Indian textile industry is one of the leading industries in the world contributing about 14% to the industrial production, 4% to gross domestic product (GDP), and 17% to the country’s export earnings, according to the Annual Report 2010–11 of the Ministry of Textiles [1]. Textile industries consume various chemicals and a large amount of water for wet/dry processing encompassing spinning, weaving, and finishing. In the weaving stage, high-speed looms are generally used for weaving the fibers. Prior to the weaving stage, sizing agents such as starch, polyvinyl alcohol (PVA) [2], and carboxymethyl cellulose (CMC) are added for smoothening the fibers and to enhance the thread tenacity [3]. Sizing agents need to be removed before the clothes are taken to the finishing stage following weaving operation. In the desizing operation, chemicals are removed by washing the

Correspondence: Dr. D. Sarkar, Department of Chemical Engineering, University of Calcutta, Kolkata 700 009, India E-mail: [email protected] Abbreviations: MWCO, molecular weight cut-off; PVA, polyvinyl alcohol; PVDF, polyvinylidene fluoride; RDM, rotating disk membrane; SBM, spinning basket membrane; SS, single stirred

ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

clothes with hot water. Water collected from this desizing operation attribute to a high biochemical oxygen demand (BOD) content, which is around 45% of the total BOD load from a textile industry [4]. There are various processes to treat this wastewater, like electrocoagulation [5], biological degradation, bio-elimination (adsorption by activated sludge), precipitation, and recycling by ultrafiltration, etc. [6–10]. One of the major components of wastewater collected from desizing operation is PVA, a valuable material that should be recovered for reusing it again as a sizing agent in the process. Among several treatment processes, ultrafiltration is one of the typical membrane separation processes to recover PVA from the waste stream followed by the recycling of water in a textile process [11]. Over the last two decades, membrane separation process has been widely applied in different effluent treatment processes [12–16]. However, the major disadvantage of such a process is the massive flux decline due to concentration polarization at the membrane surface [17, 18]. On the other hand, fouling is caused by irreversible solute adsorption on the membrane surface as well as inside the membrane pores. These two phenomena are mainly attributing to the decline of permeate flux from the time of start-up to steady state. Hitherto, the only way to regenerate the fouled membranes is by back flushing or by chemical cleaning [19], which not only interrupts the process but also enhances the economics of the same. www.clean-journal.com


Regarding the prevention of concentration polarization, various type of shear enhanced module have been developed so far implying shear stress on the membrane surface resulting into a reduced solute accumulation in the vicinity of the surface [20–22]. Rotating disk/ single stirred (SS) module has been incorporated as a shear enhanced module at the initial period, but their uses are mostly limited within the scope of small-scale laboratory operation. The first commercialized shear enhanced membrane module was a Couette flow type device used for collecting plasma from human blood [23, 24]. Later, a modified rotating disk module was introduced by ABB Flowtek, the optifilter CR, and still being used for treating paper-pulp and dye effluents [25]. Several experiments and simulation works have been done so far to modify the existing design of rotating disk membrane (RDM) module [26, 27]. Consequently, extending the concept of shear enhanced rotating membrane module, multiple shaft disk (MSD) separator had been introduced and commercialized by Aaflowsystems [28]. Jaffrin et al. [21] studied the efficacy of the same with a modified MSD pilot equipped with overlapping ceramic membranes. In a separate study, Jaffrin [20] also proposed vibratory shear enhanced processing (VSEP) using oscillatory motion/vibration to intensify the shear stress on the membrane surface in order to alleviate the flux decline phenomena. However, adopting all the high-sheared membrane devices discussed so far, problems of permeate flux decline from the start-up to the steady state cannot be eliminated completely. In order to regain the reduced permeate flux, chemical cleaning of membrane is the only option that interrupts the normal operation periodically, and also this chemical cleaning may damage the membrane material and its selectivity resulting in the reduction of membrane life [29, 30]. Therefore, devising a unique high-shear membrane module is always a primary concern of different researchers that can effectively reduce the concentration polarization or fouling related to a membrane separation process imposing minimum washing cycle duration. Present study thus proposes a shear enhanced module, named as spinning basket membrane (SBM) module considering its inherent structural similarity with the well-known spinning basket reactor that articulates a self-cleaning technique. The proposed module does not only reduce the use of expensive chemicals for cleaning of the membrane but it also allows smooth operation of the separation process continuously for a longer period of time. The objective of this study is to characterize the proposed novel high-shear membrane module in order to recover PVA from desizing wastewater by conducting experiments using two polyvinylidene fluoride (PVDF) membranes of 50 and 100 kDa molecular weight cut-off (MWCO), respectively. Membrane performance (e.g., permeate flux and rejection rate) for the SBM module has been investigated as a function of various operating parameters, namely the basket rotational speed (V) and the applied transmembrane pressure (TMP). The use of two different PVDF membranes with different MWCO has helped in exploring the effects of membrane pore size on the overall performance of the module.

Recovery of Polyvinyl Alcohol from Desizing Wastewater

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adjacent radial arms, while the other side remains impermeable as shown in Fig. 1. The SBM pilot was made of SS316 manufactured by Gurpreet Engineering Works, Kanpur, UP (India) as per our specified design. The schematic of the complete filtration bench is shown in Fig. 2. The hollow basket with four radial arms (which may be increased in a scaled up module) was mounted on a central hollow shaft fitted with a pulley drive. The whole system with suitable sealing arrangement was placed in a stainless steel cylindrical tank fed by a triplex piston pump. In order to enhance the shear rate on the membrane surface, the basket was subjected to high-speed rotation in the direction of the membrane surface (outward normal to the membranes). The power requirement for the high-speed rotation was provided by a three-phase induction motor with a belt pulley drive connected to the central shaft of the SBM module. The induction motor was fitted with a variable speed drive and a reversing switch for efficient speed control and reversal of the rotational

Figure 1. Schematic of the spinning basket module (inset showing the photograph of the spinning basket).

2 Materials and methods 2.1 Experimental setup The proposed module, conceptualized like a spinning basket reactor, with flat membranes (each of dimension 65 145 mm2 with an effective area of 55 130 mm2) was fitted on alternate sides of


Figure 2. Schematic of the complete filtration bench.

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direction, respectively. The clearance between the tip of the radial arms and the cylindrical housing was 6 mm, which causes additional dynamic pressure built up on the membrane surface. As a result, the effective TMP becomes higher than the applied TMP developed by the pump. However, the primary advantage of small clearance can be explained from the perspective of vortex like circulation flow generated between two adjacent arms. Because of the high-velocity circulation of the feed solution accumulated solutes on the membrane surface were swept away leading to a reduced degree of polarization. With all its shear enhancement, still the proposed module may suffer from the drop of transient permeate flux from the start-up to the respective steady state as in the case of any membrane module irrespective of whether it is shear enhanced or not. In order to overcome this limitation, the operation of the system was designed in a unique fashion, which is explained here for better understanding. Once the flux reached its steady state, the basket was designed to be rotated in the reverse direction (i.e., in the direction normal to the impermeable side of the radial arms) after releasing the applied TMP to atmospheric pressure by operating the back pressure regulator (BPR) fitted in the retentate line. As a result, a local vacuum of ð1=2ÞrVu2 was created on the membrane surface, so that the effective absolute pressure on the retentate side became Patm ð1=2ÞrVu2 , whereas on the permeate side, it remained atmospheric. Because of the counter-rotation induced pressure difference, the accumulated solute was expected to be disengaged from the membrane thereby reducing the hydraulic resistance of the same. This has resulted in a recovered permeate flux in the next normal run.


parameters, namely the applied TMP (294.2, 392.3, and 490.3 kPa), and rotational speed (20.95, 31.4, and 41.9 rad s1) could be investigated. In a particular experimental run, one of the parameters was kept constant while the other was varied in order to obtain the independent influence of each of them on the performance of the module. A constant retentate flow rate of 1.33 104 m3 s1 was maintained throughout all the experiments. During the cleaning runs, the module was operated at 41.9 rad s1 (same as the maximum rotational speed of normal runs) in the reverse direction for 300 s only. The speed as well as the duration of cleaning was chosen arbitrarily. After each cleaning run, the module was again subjected to normal run with the same TMP and rotational speed as earlier. Each experimental run marked by a definite TMP and V consisted of two successive normal runs with an intermediate cleaning run. In order to compare the performance of SBM module with other units, experiments were performed in SS and RDM modules using the same membrane–solute combination (PVDF/PVA). The detailed specifications and the geometry of these two well known shear enhanced modules are described elsewhere [22]. For the RDM module, membrane speed was fixed at its highest permissible limit, i.e., at 62.5 rad s1 so as to obtain the highest possible permeate flux under a fixed condition of stirrer speed. For the purpose of comparison, the stirrer speed of SS and RDM modules was chosen to be equivalent to the basket rotation speed, V of the proposed SBM module. Experiments were conducted at TMP, V, feed concentration (1.14 kg m3) and temperature (808C) similar to that used in case of the proposed SBM module.

2.5 Experimental procedure 2.2 Material Polyvinyl alcohol (cold), soluble in water at ambient temperature with an average molecular weight 125 000 g mol1 was obtained from E. Merck, Mumbai, India. Moist semi-permeable, asymmetric PVDF membranes of two different pore size (MWCO: 50 and 100 kDa, respectively) were obtained from Koch Membrane Systems (USA). The rectangular flat sheet membrane was operable in the pH range of 2.5–10.5. Typical operating pressure for the membrane was 210– 830 kPa (maximum operating pressure: 970 kPa) with operating temperature range of 5–548C (Maximum operating temperature: 65.58C).

2.3 Analysis Polyvinyl alcohol concentration was measured with a hand held refractometer (Model PAL-85S, Atago Co. Ltd., Japan). The density and viscosity of PVA solution were measured by using pycnometer and Ostwald viscometer, respectively.

Before start-up, four rectangular membranes were fixed up on the radial arms of the module. In order to overcome the membrane compaction effect, the module was pressurized with distilled water for 5 h at a TMP of 600 kPa. For measuring the transient flux, 10 mL of permeate was collected in a measuring cylinder and the time of collection was recorded. A normal run was continued till at least two successive flux readings were nearly equal. Each normal run was followed by a cleaning run of 300 s as described earlier. Once an experiment of about 2 h duration was over, all the four rectangular membranes were thoroughly cleansed with deionized water to remove the deposits. The water flux was checked again to detect any variation in the hydraulic resistance of the membrane. The same procedure was repeated for each experiment with fixed TMP, V, and C0. Similar experimental procedure was followed for the other two shear enhanced modules as mentioned earlier [27].

3 Results and discussion

2.4 Design of experiment

3.1 Variation of permeate flux profile with transmembrane pressure (TMP)

The concentration of PVA in desizing wastewater was reported to be at about 1.14 kg m3 [9]. Thus, in this present investigation, a feed solution of the same concentration level was prepared and used throughout all experiments. The temperature of the feed solution was maintained at 808C (characteristic temperature of the desizing wastewater) throughout all experiments with the help of an efficient temperature controller fitted with the feed tank as shown in Fig. 2. In order to assess the performance of the proposed module, experiments were designed in such a way so that the effects of two process

At a constant TMP, the transient flux exhibits an initial decay spanning over the first 20 and 35 min of the normal run for 100 and 50 kDa membranes, respectively, after which it attained the respective steady state values. The variation of permeate flux with time for different TMP, but under identical condition of rotational speed is shown in Fig. 3. For two successive normal runs, (intervened by one cleaning run) the average drop of permeate flux from start-up to steady state was observed to be around 13% for 100 kDa membrane, whereas the same was 27% for 50 kDa membrane. In fact, the




Figure 3. Variation of the unsteady permeate flux with time under the condition of different TMP for 50 and 100 kDa membrane.

effective thickness of the polarized layer was increased from zero to some steady value over the same duration and due to this increased thickness, the osmotic pressure differential across the membrane (Dp ¼ pm pp) was bound to increase leading to a reduced driving force (TMP – Dp). The phenomenon observed here is in good agreement with the well known osmotic pressure model of membrane filtration [31]. For a 50 kDa membrane, as the solute rejection was much higher than the 100 kDa membrane, the polarized layer thickness and hence the convective resistance towards permeation was much higher than the 100 kDa membrane. Accordingly, under the same set of parametric conditions, the permeate flux was always higher for the latter. On the other hand, as the thickness of the polarized layer was smaller for 100 kDa membrane, the duration of the normal run required to reach the steady state must be smaller than that of 50 kDa membrane. Figure 3 also reveals that the transient as well as the steady permeate flux was increased progressively with TMP. A closer investigation reveals enhancement of steady flux by 10% and 20% for 100 and 50 kDa membranes, respectively, due to a change of TMP from 294.2 to 490.3 kPa. Once the system was in steady state, marked by constant flux reading, the module was depressurized and the basket was rotated in the reverse direction for an arbitrary duration of 5 min. This marks the cleaning run as mentioned earlier. After the first cleaning run, the average % recovery of permeate flux (defined as ðJrecovered Jsteady Þ=ðJsteady Þ 100) was nearly 13% for 100 kDa membrane, whereas the same was 30% for 50 kDa membrane. This indicates that on an average, the regenerated flux was >95% of the initial flux (i.e., the flux at the beginning of the first normal run) for two different membranes operated under different conditions of TMP. This marks a unique feature of the proposed module and probably, no existing module can restrict the drop of permeate flux within 10% of the initial value for total runtime duration of 1.5 h. During a cleaning run high-speed reverse rotation of the basket was expected to generate a local vacuum of ð1=2ÞrVu2 on the retentate side of the membrane, which triggers the solute disengaging action. As the ratio of regenerated to initial permeate flux values was nearly same for both the membranes, it may be concluded that generated local vacuum was sufficient enough to disengage the accumulated solutes from the surfaces of both membranes.



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Figure 4. Variation of the unsteady permeate flux with time under the condition of different rotational speed (V) for 50 and 100 kDa membrane.

3.2 Variation of permeate flux profile with the rotational speed of the basket Variation of permeate flux with time for different rotational speed (V) is shown in Fig. 4. The permeate flux was observed to decay over the initial period of time until it attains the respective steady state. It can be seen from the figure that the permeate flux was increased with the rotational speed of the basket. The reason is twofold. Firstly, the increased rotational speed has intensified the dynamic pressure ð1=2ÞrVu2 on the membrane surface resulting an increased effective TMP (applied TMP þ dynamic pressure) and hence the permeate flux. On the other hand the membrane shear was expected to increase with rotational speed. In any shear enhanced filtration unit solute disengagement rate from the membrane surface was reported to enhance with shear stress [20]. Similarly in the present study the increased disengagement rate with increasing V was expected to result a reduced mass transfer resistance of the polarized layer and thereby increased the rate of permeation. In the first normal run, 23% enhancement of the steady flux was observed for a change of rotational speed from 20.95 to 41.9 rad s1 for 50 kDa membrane, which in turn was 19% only for 100 kDa membrane. During the second normal run, similar trend was maintained by both membranes. This observation indicates that the effect of rotational speed on flux was practically independent of the number of normal run at least for the first two successive runs. Additionally, Fig. 4 once again reveals the efficient characteristics of the cleaning run. It can also be observed from the figure that the average recovery of the permeate flux was around 32% for 50 kDa membrane, whereas it was restricted within 18% for 100 kDa membrane. The average regenerated fluxes for both membranes were close to 96% of the corresponding initial values.

3.3 Variation of the ‘‘observed rejection’’ ‘‘Observed rejection’’, defined as Robs 1 ðCp =C0 Þ, may be regarded as an important parameter to characterize the performance of a membrane separation process in general. Figure 5 shows the variation of the steady ‘‘observed rejection’’ with TMP at different rotational speed for the present study. The figure clearly indicates an increasing trend of Robs, which was nearly linear with TMP (average correlation coefficient ¼ 0.98). This can be explained in www.clean-journal.com

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Figure 5. Variation of steady state observed rejection (Robs) with TMP at different rotational speed (V) for 50 and 100 kDa MWCO (inset showing the same variation with (V) at different TMP).

terms of increased convective flow towards the membrane leading to a higher Robs at higher TMP. Further, in any standard ultrafiltration process, the rejected solute forms an additional mass transfer resistance that acts like a secondary membrane in series with the actual one, promoting higher rejection. Trend of Robs with V for different TMP is also included in the inset of Fig. 5. Robs was observed to decrease, once again in linear fashion (average correlation coefficient ¼ 0.97) with increasing V. For an increase of rotational speed from 20.95 to 41.9 rad s1 the average reduction of Robs was about 7%. This could be attributed to a reduced polarized layer thickness at a higher rotational speed. The phenomenon clearly establishes the shear enhancing character of the proposed module and indicates that the shear enhancement mechanism is purely dynamic as it is completely independent of the feed flow rate. In general, Robs was always found to be higher for 50 kDa membrane as expected because membranes with smaller pore size always promote higher polarization hence lower permeate concentration (Cp). In the present study, 15 to 25% enhancement of Robs was observed over the change of membrane pore size from 100 to 50 kDa. Additionally, a closer investigation reveals that, the rate of change of ‘‘observed rejection’’ with respect to the applied TMP was practically same for different rotational speeds. For example, under different rotational speed, Robs was observed to increase by 12–14% for a change of TMP from 294.2 to 490.3 kPa for 50 kDa membrane, whereas it was about 10–12% for 100 kDa membrane. Similarly, the rate of decrease of Robs with V was independent of TMP. It was due to the fact that, Robs was observed to decrease by 6–7% for a change of rotational speed from 20.95 to 41.9 rad s1 for 50 kDa membrane, whereas it was 9–10% for 100 kDa membrane. Considering the functionality between Robs and TMP as well as Robs and V, as shown in Fig. 5 and its inset, Robs may be identified to be a strong, nearly linear, monotonic function of TMP as well as V with ð@Robs =@TMPÞ > 0 and ð@Robs =@VÞ < 0. Accordingly, Robs may be expressed as: Robs ¼ a1 ðVÞ þ b1 ðVÞTMP

(1)

Robs ¼ a2 ðTMPÞ þ b2 ðTMPÞV

(2)

with b1(V) > 0 and b2(TMP) < 0. As the rate of change of Robs with respect to one parameter is nearly independent of the other ½ð@2 Robs =@ðTMPÞ@VÞ 0, b1 and b2 may be considered to be simple


Figure 6. Variation of average power consumption rate ðE_ Þ with rotational speed (V) at different TMP (inset showing the same variation with TMP at different (V)).

numerical constants specific to the module, which means that the ‘‘observed rejection’’ of the proposed module is purely a linear function TMP and V, at least within the framework of the present experimentation. From this observation, it can be concluded that both TMP and V can independently act as a manipulated variable for the purpose of controlling the ‘‘observed rejection’’ and subsequently the overall performance of the module.

3.4 Characterization of the SBM module performance in terms of power consumption The total electrical power consumed, which is a sum of power supplied to the feed pump and to the induction motor was measured with a wattmeter. The variation of average power consumption of the module with rotational speed and TMP is shown in Fig. 6 along with its inset. The figures clearly indicate nearly a linear trend of power with TMP as well as with V (the correlation coefficients were found to be 0.99 and 0.98, respectively). It is well known that for an induction motor, the power consumption is proportional to the rotational speed, and hence for the present case E_motor ¼ kV, where k is a constant. On the other hand, for a triplex piston pump, the power requirement ðE_pump Þ can be expressed as E_pump ¼ ðgQ TMPÞ=h, where h is the pump efficiency and Q is the feed flow rate. Accordingly, the total power requirement becomes: gQ TMP E_ ¼ E_motor þ E_ pump ¼ kV þ h

(3)

From Eq. (3) it becomes evident that the power consumed by the present module must vary with both TMP and V linearly, provided h and Q remain unchanged. In the present study, as mentioned earlier, the retentate flow rate was fixed at 1.33 104 m3 s1, whereas the maximum permeate flow rate was 3.32 107 m3 s1, negligible in comparison to the retentate flow. Thus, the feed flow rate (Q) may be considered constant for all the experimental runs. Accordingly, the power consumption becomes linear, as per Eq. (3), with respect to both TMP and V, consistent with the trend shown in Fig. 6. www.clean-journal.com


3.5 Comparison of the performance of the proposed module with other modules Extensive literature survey revealed that application of membrane technology in desizing wastewater treatment was mostly limited to cross flow type modules. However, the performance of shear enhanced module does not seem to be available in the existing literature. Thus direct comparison of the performance of the proposed module with the available systems is not possible. In order to compare the performance in such a situation, performances of other shear enhanced modules are being considered here, for instance, two standard modules of shear enhanced class, namely (i) SS and (ii) RDM. Experiments with SS and RDM modules were performed in the present investigation in such a manner that the parametric conditions and membrane–solute combination matched well within those reported in the literature. In a standard SS module a highspeed stirrer was placed in the close vicinity of a stationary membrane to promote disengagement of the solutes and hence the permeate flux. The polarization effect could be further diminished in a RDM module where the membrane was also subjected to rotation, necessarily in the opposite direction with respect to the stirrer. Accordingly, the permeate flux obtained from a RDM module was expected to be higher than a SS module with similar operating conditions. The detailed description and performance analysis of these two modules were reported elsewhere [27]. In this comparison, it was assumed that the stirrer speeds of SS and RDM modules were equivalent to the basket rotational speed of the proposed SBM module. The RDM module was operated at its highest possible membrane speed of 62.5 rad s1 in order to obtain maximum permeate flux at a constant stirrer speed. The effect of TMP on steady permeate flux obtained at the end of the first normal run for the SS, RDM, and the proposed SBM module at fixed V, for the two different PVDF membranes (50 and 100 kDa) is shown in Fig. 7. It can be seen from the figure that the steady permeate flux of the proposed module for different TMP was 170– 210% higher than that of RDM, while it was 390–530% enhanced compared to the SS module. It might be attributed due to different velocity fields prevalent in the different modules. In the proposed SBM module the large tangential component (with respect to the

Figure 7. Steady permeate flux (as obtained at the end of first normal run) at different TMP for (i) SS (ii) RDM (membrane speed ¼ 62.5 rad s1) and (iii) SBM module for 50 kDa MWCO membrane (inset showing the same with 100 kDa MWCO membrane).



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membrane surface) of the velocity vector was responsible for disengaging the solutes. In case of SS and RDM modules, being typical dead-end types, the axial velocity component was primarily responsible for similar action. In general, a tangential momentum flux more effective than its axial counterpart in scraping a surface was present in the proposed SBM module, and hence the permeate flux was enhanced in the SBM module compared to its SS or RDM counterpart. The similar trend was observed in the variation of steady permeate flux with V but at fixed TMP and C0 as shown in Fig. 8. It can be seen from the figure that over the same change of V, the steady flux of the SBM module was 175–215% higher than its RDM counterpart, while it was 390–560% enhanced compared to that in SS. A legion of studies on cross flow modules regarding the treatment of desizing wastewater was reported. The performances of some of them are reviewed here in comparison to the proposed SBM module and are presented in Tab. 1 [32–37]. It can be seen from the table that the highest permeate flux reported was 2.7 105 m3 m2 s1 [35]. However, the corresponding TMP was several times higher than the present study. In terms of PVA recovery, the present module was also comparable with the other cross flow units. Additionally, for the flux recovery, all the cross-flow units would require either chemical cleaning or periodic back washing. Generally, in order recover the permeate flux; the backwashing in a standard wastewater treatment plant is performed at a frequency of 30 min to 1 h [38]. On the contrary, in the proposed module, the flux recovery was achieved by an inbuilt mechanism and membrane cleaning was accomplished without the frequent use of cleaning agents or washing liquid. From the foregoing discussion, it is clear that the proposed SBM module can perform efficiently than the existing cross-flow units. Further, the system can be operated so as to recycle desizing effluent back into the process leading to a zero effluent discharge plant. The module developed could also be applied for cleaning of other wastewater generated from different industries. Considering the concept of sustainability in the use of water (a natural resource), and discharge of wastewater, the present invention would be an economic proposition in today’s market place for various water intensive industrial applications.

Figure 8. Steady permeate flux (as obtained at the end of first normal run) at different V for (i) SS (ii) RDM (membrane speed ¼ 62.5 rad s1) and (iii) SBM module for 50 kDa MWCO membrane (inset showing the same with 100 kDa MWCO membrane).


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Table 1. Comparison of the proposed SBM module with the reported cross flow units in terms of permeate flux

Membrane specification

TMP (kPa)

Permeate flux (m3 m2 s1)

Reference

Polysulfonamide membrane (MWCO: not reported) Flat sheet membrane (MWCO: 10 kDa) PVDF membrane (MWCO: 70 kDa) ˚) Polyvinyl sulfone membrane (pore size: 5000 A PVDF membrane (MWCO: not reported) Polysulfone membrane (MWCO: 30 kDa) PVDF membrane (MWCO: 100 kDa)

100 100 220 1200 300 200 294.2

0.11 105 0.72 105 0.59 105 2.7 105 0.44 105 0.41 105 4.85 105

[32] [33] [34] [35] [36] [37] Present study

Module Hollow fiber module Cross flow module Spiral-wound module Spiral-wound module Tangential UF pilot Bench scale hollow fiber module SBM

density of feed solution (kg m3) rotational speed of the basket (rad s1)

4 Conclusions

r V

A shear enhanced membrane module with inbuilt cleaning facility for desizing wastewater reclamation has been proposed and tested to investigate the possibility of replacing current membrane based units. The module has been named as SBM module considering its inherent structural similarity with the well known spinning basket reactor. Experiments under different parametric conditions of TMP and basket rotational speed were conducted with PVDF membranes of two different pore sizes (50 and 100 kDa). The results showed that the flux decline could be restricted within 2% of its initial value after 2 h of continuous operation. The module could be periodically cleaned simply by the reverse rotation of the basket with released TMP avoiding use of any chemical agent or complex backflushing technique adopted in conventional ultrafiltration units. The comparison of performances between the proposed module and existing cross-flow units and other shear enhanced modules revealed that the permeate flux of the proposed module was enhanced by 170–210% under similar operating condition. Hence, the novelty of the proposed module was investigated. Considering the novelty of the system developed it was concluded that this module could be scaled up for continuous recycling of desizing wastewater leading to a zeroeffluent plant. The operation of this system could further reduce process water consumption and in that the overall operation would become more economic than the system being used at present.

Subscript

5 Notations a1 a2 b1 b2 C0 Cp E_ E_motor E_pump g k Q Robs TMP Vu

parameter used in Eq. (1) (dimensionless) parameter used in Eq. (2) (dimensionless) parameter used in Eq. (1) (Pa1) parameter used in Eq. (2) (rad1 s) feed concentration (kg m3) permeate concentration (kg m3) total power consumption (W) power consumption by motor (W) power consumption by feed pump (W) acceleration due to gravity (9.8 m s2) constant used in Eq. (1) (W s rad1) feed flow rate (m3 s1) observed rejection (dimensionless) transmembrane pressure (Pa) tangential velocity of the basket (m s1)

Greek letters h pump efficiency (dimensionless) p osmotic pressure (Pa) Dp osmotic pressure differential across the membrane (Pa)


M membrane p permeate obs observed

Acknowledgments The financial assistance provided under SERC scheme (SR/S3/CE/058/ 2009) by The Department of Science & Technology (DST), Govt. of India, is gratefully acknowledged. The authors have declared no conflict of interest.

References [1] Annual Report 2010–11, Ministry of Textiles, Government of India, New Delhi 2011. [2] C. Ozdemir, M. K. Oden, S. Sahinkaya, E. Kalipci, Color Removal from Synthetic Textile Wastewater by Sono-Fenton Process, Clean – Soil Air Water 2011, 39 (1), 60–67. [3] S. W. Lee, S. J. Haam, J. H. Jang, Y. C. Lee, Ultrafiltration of Desizing Wastewater Containing PVA in Bench Scale Test, Environ. Technol. 1999, 20, 277–283. [4] J. J. Porter, D. W. Lyons, W. F. Nolan, Water Uses and Wastes in the Textile Industry, Environ. Sci. Technol. 1972, 6 (1), 36–41. [5] A. Dalvand, M. Gholami, A. Joneidi, N. M. Mahmoodi, Dye Removal, Energy Consumption and Operating Cost of Electrocoagulation of Textile Wastewater as a Clean Process, Clean – Soil Air Water 2011, 39 (7), 665–672. [6] E. Balanosky, F. Herrera, A. Lopez, J. Kiwi, Oxidative Degradation of Textile Wastewater. Modeling Reactor Performance, Water Res. 2000, 4, 582–596. [7] G. Ciardelli, N. Ranieri, The Treatment and Reuse of Wastewater in the Textile Industry by Means of Ozonation and Electroflocculation, Water Res. 2001, 35, 567–572. [8] G. R. Groves, C. A. Buckley, R. H. Turnbull, Closed Looped Recycle Systems for Textile Effluents, J. Water Pollut. Control Fed. 1979, 51 (3), 499–517. [9] G. M. Walker, L. R. Weatherly, Textile Wastewater Treatment Using Granular Activated Carbon Adsorption in Fixed Beds, Sep. Sci. Technol. 2000, 35, 1329–1341. ´ stria Teˆxtil e o Meio Ambiente, Quı´m. Teˆxtil 1996, [10] A. S. Pacheco, A Indu 20 (46), 13–34. [11] S. H. Lin, W. J. Lan, Polyvinyl Alcohol Recovery by Ultrafiltration: Effects of Membrane Type and Operating Conditions, Sep. Technol. 1995, 5, 97–103. [12] S. You, C. Tsai, Using Chlorine Dioxide to Remove the Fouling of Ultrafiltration Membrane and Control Disinfection By-Products, Clean – Soil Air Water 2011, 39 (4), 351–355.


Clean – Soil, Air, Water 2012, 40 (8), 830–837 [13] P. G. Oduor, X. Santos, J. Abwawo, J. Dunham, Permselective Membrane Fouling during Azo Dye Wastewater Treatment, Clean – Soil Air Water 2008, 36 (2), 171–179. [14] H. Wichmann, T. Sahlabji, M. Ohnesorge, R. Vogt, M. Bahadir, Feasibility Study on Membrane-Aided Cleanup and Fractionation of Fatty Acid Esters Produced from Waste Fats, Clean – Soil Air Water 2008, 36 (10–11), 840–844. [15] Y. Oztekin, Z. Yazicigil, N. Ata, N. Karadayi, The Comparison of two Different Electro-Membrane Processes’ Performance for Industrial Applications, Clean – Soil Air Water 2010, 38 (5–6), 478–484. [16] M. Soylak, Y. E. Unsal, A. Aydin, N. Kizil, Membrane Filtration of Nickel(II) on Cellulose Acetate Filters for Its Preconcentration, Separation, and Flame Atomic Absorption Spectrometric Determination, Clean – Soil Air Water 2010, 38, 91–95. [17] G. Belfort, R. H. Davis, A. L. Zydney, The Behavior of Suspensions and Macromolecular Solutions in Cross Flow Microfiltration, J. Membr. Sci. 1994, 96, 1–58. [18] S. S. Sablani, M. F. A. Goosen, R. Al-Belushi, M. Wilf, Concentration Polarization in Ultrafiltration and Reverse Osmosis: A Critical Review, Desalination 2001, 141, 269–289. [19] M. Kazemimoghadam, T. Mohammadi, Chemical Cleaning of Ultrafiltration Membranes in the Milk Industry, Desalination 2007, 204, 213–218. [20] M. Y. Jaffrin, Dynamic Shear-Enhanced Membrane Filtration: A Review of Rotating Disks, Rotating Membranes and Vibrating Systems, J. Membr. Sci. 2008, 324, 7–25. [21] M. Y. Jaffrin, G. He, L. H. Ding, P. Paullier, Effect of Membrane Overlapping on Performance of Multishaft Rotating Ceramic Disk Membranes, Desalination 2006, 200, 269–271. [22] D. Sen, W. Roy, L. Das, S. Sadhu, C. Bhattacharjee, Ultrafiltration of Macromolecules Using Rotating Disc Membrane Module (RDMM) Equipped with Vanes: Effects of Turbulence Promoter, J. Membr. Sci. 2010, 360, 40–47. [23] K. H. Kroner, V. Nissingen, Dynamic Filtration of Microbial Suspensions Using an Axially Rotating Filter, J. Membr. Sci. 1988, 36, 85–100. [24] U. B. Holeschovsky, C. L. Cooney, Quantitative Description of Ultrafiltration in a Rotating Filtration Device, AIChE J. 1991, 37, 1219–1226. [25] S. S. Lee, B. G. Russoti, B. Buckland, Microfiltration of Recombinant Yeast Cells Using a Rotating Disk Dynamic Filtration System, Biotechnol. Bioeng. 1995, 48, 386–400.



837

[26] C. Bhattacharjee, P. K. Bhattacharya, Ultrafiltration of Black Liquor Using Rotating Disk Membrane Module, Sep. Purif. Technol. 2006, 49, 281–290. [27] D. Sarkar, C. Bhattacharjee, Modeling and Analytical Simulation of Rotating Disk Ultrafiltration Module, J. Membr. Sci. 2008, 320, 344– 355. [28] H. P. Feuerpeil, D. Blase, H. Olapinski, Aaflowsystems GmbH, German Patent DE 102 39 247 C1 2003. [29] M. H. Tran-Ha, D. E. Wiley, N. D. Lawrence, M. Iyer, Development of a Standard Cleaning Protocol to Evaluate the Effect of Cleaning on Membrane Performance, Aust. J. Dairy Technol. 2002, 57, 20– 29. [30] P. Blanpain-Avet, J. F. Migdal, T. Be´ne´zech, Chemical Cleaning of a Tubular Ceramic Microfiltration Membrane Fouled with a Whey Protein Concentrate Suspension – Characterization of Hydraulic and Chemical Cleanliness, J. Membr. Sci. 2009, 337, 153– 174. [31] O. Kedem, A. Katchalsky, The Physical Interpretation of Phenomenological Coefficients of Membrane Permeability, J. Gen. Physiol. 1961, 45, 143–179. [32] J. Hao, Q. Zhao, The Development of Membrane Technology for Wastewater Treatment in the Textile Industry in China, Desalination 1994, 98, 353–360. [33] S. Barredo-Damas, M. I. Alcaina-Miranda, M. I. Iborra-Clar, A. Bes-Pia´, J. A. Mendoza Roca, A. Iborra-Clar, Study of the UF Process as Pretreatment of NF Membranes for Textile Wastewater Reuse, Desalination 2006, 200, 745–746. [34] M. Marcucci, I. Ciabatti, A. Matteucci, G. Vernaglione, Membrane Technologies Applied to Textile Wastewater Treatment, Ann. N.Y. Acad. Sci. 2003, 984, 53–64. [35] J. J. Porter, Recovery of Polyvinyl Alcohol and Hot Water from the Textile Wastewater Using Thermally Stable Membranes, J. Membr. Sci. 1998, 151, 45–53. [36] F. J. Bassetti, L. Peres, J. C. C. Petrus, Recuperation of Polyvinyl Alcohol (PVA) through Microporous Membranes, Lat. Am. Appl. Res. 2001, 31, 547–550. [37] S. W. Lee, S. J. Haam, J. W. Kwak, J. H. Jang, Y. C. Lee, Ultrafiltration of Desizing Wastewater Containing PVA in Bench Scale Test, Environ. Technol. 1999, 20, 277–283. [38] E. Arkhangelsky, D. Kuzmenko, N. V. Gitis, M. Vinogradov, S. Kuiry, V. Gitis, Hypochlorite Cleaning Causes Degradation of Polymer Membranes, Tribol. Lett. 2007, 28, 109–116.
