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Membrane Treatment of Pharmaceutical Wastewater

Author reviews wastewater treatment technology to treat toxic pharmaceutical wastewater. Review by Chitra Gowda

The pharmaceutical industry generates process wastewaters containing various pollutants, which depend on the nature of processes by which the products are produced. Most pharmaceutical substances are manufactured utilizing batch processes; at the end of a manufacturing batch, another pharmaceutical intermediate or substance is made, thus generating different waste streams. For specific pollutants that do not get removed by physico-chemical and biological treatment, such as recalcitrant toxics such as volatile organic compounds (VOCs) and for bioinhibiting substances such as sulfur and cyanide, other advanced treatment technologies have been developed. The suitability of each to a particular pharmaceutical wastewater is assessed by treatability studies, many of which are recorded in literature.

Studies on the feasibility of membrane treatment for pharmaceutical effluents describe how this technology could eliminate typical activated sludge process (ASP) problems by accomplishing liquid-solid separation and biodegradation within the reactor (avoiding secondary clarification), having a control on F/M ratio (less sludge produced), doing away with recycle pumps (consuming less power), and removing almost all suspended solids (SS) with the microporous membrane (Benitez, et al., 1995, and Freitas dos Santos and Biundo, 1999).

Extractive membrane bioreactors (EMB) are documented extensively for destroying toxic VOCs by a combined step of membrane extraction and biodegradation of the permeate by specially cultured biomedium in a mixed and aerated reactor (Livingston et al., 1998). A typical EMB employs hollow fibre membranes consisting of many tubular membranes encased in a cylindrical shell; rarely are flat plate membranes used. Freitas dos Santos and Biundo (1999) conducted treatability studies on pharmaceutical wastewater contaminated with dichloromethane (DCM) with no pre-treatment or dilution. Their laboratory-scale EMB removed 95% of DCM, which is indeed impressive. Freitas dos Santos and Livingston (1995) have reported similar removal success of 1,2 dichloroethane (DCE) from synthetic wastewater, and mathematically analysed mass transfer and biofilm diffusion and reaction.

Hollow fiber membrane reactors (HFMR) themselves are used to remove pollutants from pharmaceutical wastewaters. Aziz et al. (1995) conducted studies on an HFMR to treat wastewater contaminated with trichloroethane (TCE). At influent concentrations between 120 to 709 µg/L, 81.0 to 95.3% TCE was removed from the lumen (inner) side of the membrane and passed to the biomedium on the shell side where 77 to 88% TCE was biodegraded. In a similar study on pharmaceutical wastewater with high COD (more than 1000 mg/L) Benitez et al. (1995) used a bench scale HFMR. Wastewater was filtered through the membrane radially by suction in, interestingly, intermittent cycles and average COD removal efficiency was only 68%.

Before reiterating that membrane bioreactors could be the answer to ASP difficulties, it is necessary to assess their method, performance and costs. From literature, it is clear that the membrane performance depends on the mass transfer coefficient and membrane-aqueous partition coefficient; different operating parameters and applications result in varying coefficients (Gabelman and Hwang, 1999, and Semmens and Gantzer, 1994) and membrane performances (Min and Hwang, 1999). Reported membrane-aqueous partition coefficients are greater than 1 and according to Brookes and Livingston (1995), they are amenable to extraction. However, mass transfer coefficients reported are low compared to economically optimum values of, according to Livingston et al. (1998), 1 to 5 *10-5m/s. Mathematical modeling by Freitas dos Santos and Livingston (1995) helped pinpoint the cause of limited mass transfer as being the accumulation of pollutant at the membrane-biofilm interface, while Aziz et al. (1995) construed from their modeling exercise that the film resistance on both sides of the membrane are equal and strongly affect mass transfer rate while the membrane resistance itself is negligible. Thus mathematical modeling of the mass transfer as well as biodegradation processes proves useful to improving the process efficiency.

Extractive membrane bioreactors hold great promise in destroying VOCs but very high capital costs seem to hinder practical application. The gap between bench scale studies and actual application has to be bridged by corroborating the small-scale results with scale up pilot plant studies. Given the highly variable nature of the pharmaceutical effluent, it is not possible to come up with a common treatment plant design. However, with more investigations being done into the treatment of various types of pharmaceutical industry effluents, the prospects of arriving at technologically acceptable and economically feasible treatment alternatives seems good, given time and extensive research.

References

*Aziz, C.E., Fitch, M.W., Linquist, L.K., Pressman, J.G., Georgiou, G., and Speitel, Jr. G.E. 1995. Methanotrophic biodegradation of trichloroethylene in a hollow fiber membrane bioreactor. Environmental Science and Technology. 29, pp. 2574–2583.

*Benitez et al. 1995. Stabilization and dewatering of wastewater using hollow fiber membranes. Water Research, 10, 2281-2286.

*Brookes, P. R. and Livingston, A. G. 1995. Auqeous-aqueous extraction of organic pollutants through tubular silicone rubber membranes. Journal of Membrane Science, 104, 119.

*Frietos dos Santos, L. M., and Biundo G. L.1999. Treatment of pharmaceutical industry process wastewater using the extractive membrane bioreactor. Environmental Progress, 18, 34-39.

*Frietos dos Santos, L. M., and Livingston, A. G. 1995. Novel membrane bioreactors for detoxification of Voc wastewaters: biodegradation of 1,2-dichloroethane. Water Research, 29, 179-194.

*Gabelman and Hwang, 1999. Hollow fiber membrane contactors. Journal of Membrane Science, 159 (1-2), 61-106.

*Livingston, Arcangeli, Boam, Zhang, Marangon, Freitas dos Santos, 1998. Extractive membrane bioreactors for detoxification of chemical industry wastes: process development. Journal of Membrane Science, 151, 29-44.

*Min, L., and Hwang, S. K., 1999. Correlation of concentration polarization and hydrodynamic parameters in hollow fibe r modules. Journal of Membrane Science, 159 (1-2)143-165.

*Semmens, M.J., Gantzer, C.J. 1994. Gas transfer without bubbles, Proceedings of the ASME Fluids Engineering Division Summer Meeting, Pt. 9, Lake Tahoe, NV, 51–58

Posted by Moderator on January 16th, 2006 filed in review Discuss now »