1390 Research Article Received: 10 February 2009 Revised: 16 March 2009 Accepted: 16 March 2009 Published online in Wiley Interscience: 30 April 2009 (www.interscience.wiley.com) DOI 10.1002/jctb.2194 Optimized reuse and bioconversion from retentate of pre-filtered palm oil mill effluent (POME) into microbial protease by Aspergillus terreus using response surface methodology Ta Yeong Wu, a Abdul Wahab Mohammad, b,c∗ Jamaliah Md. Jahim b and Nurina Anuar b Abstract BACKGROUND: The membrane filtration process enables the treatment of wastewater, producing permeate which is less polluted. However, disposal is usually required for the retentate, which is produced as a concentrated constituent along with the permeate. In this study, the authors explored the possibility of reusing, rather than disposing of, the retentate of pre-filtered palm oil mill effluent (POME) as a fermentation substrate in protease production by a wild type strain of Aspergillus terreus IMI 282743. In addition, the quantitative and interactive effects of the concentration factor for retentate, temperature, inoculum concentration, and fermentation time on the optimization of protease production were investigated using response surface methodology (RSM). RESULTS: Using RSM, the optimum conditions were found to be a concentration factor of 7.27, temperature of 37.95 ◦ C, inoculum concentration of 1.30% (v/v) and fermentation time of 3.83 days. The protease production was increased 4.37-fold in comparison with the results obtained under non-optimized conditions. CONCLUSION: To a certain extent, protease production could be enhanced with an increase in concentration factor and temperature, and a decrease of inoculum concentration and fermentation time. Also, POME retentate was found to be a good substrate for protease production with high product activity and without nutrient supplementation. c  2009 Society of Chemical Industry Keywords: Aspergillus terreus; palm oil mill effluent (POME); protease; response surface methodology (RSM); retentate; ultrafiltration INTRODUCTION The disposal of retentate or concentrate generated from mem- brane filtration processes is rapidly becoming a major environ- mental concern. This is because the retentate usually contains a high degree of organic loading and solids content in comparison with municipal sewage. Until now, no conclusive management concept has been available for the disposal of retentate. However, the retentate might offer excellent potential for reuse purposes in different ways, depending on prevailing local conditions. For example, Wu et al. 1,2 found that after the ultrafiltration process of palm oil mill effluent (POME), the retentate contained a lot of bioresources that could possibly be reused as fermentation substrates without the addition of other nutrients. Proteases are a commercially important group of microbial enzymes that are widely used in several industries, particularly the detergent, food, pharmaceutical, chemical, leather and silk industries, as well as in waste treatment. 4 The microbial proteases of Aspergillus species have been studied in detail, since they are known to be secreted at high levels in a suitable growth environment. The possibility of producing proteases by Aspergillus strains in effluent or waste has been reported. For example, proteases were successfully produced by Aspergillus sp. in shochu distillery wastewater, 5 ‘thin stillage’ from a rice-spirit distillery, 6 wheat bran, 7 shrimp and crab shell powder medium, 8 brewery and meat processing wastewater, 9 retentate from POME, 1 fish scale powder medium 10 and silk degumming waste solution. 11 In view of the many industrial applications of proteases 12 and the statistical methodologies applied in bioprocesses, a worthwhile technique to identify the variables in the system is response surface methodology (RSM). 13,14 RSM can be used to evaluate the relative significance of several factors and reveal the possible interactions between variables, rather than a ‘one-factor-at-a-time’ ∗ Correspondence to: Abdul Wahab Mohammad, Dean’s Office, Universiti Ke- bangsaan Malaysia, 43600 Bangi, Selangor Darul Ehsan, Malaysia. E- mail: wahabm@eng.ukm.my a School of Engineering, Monash University, Jalan Lagoon Selatan, 46150 Bandar Sunway, Selangor Darul Ehsan, Malaysia b Department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Darul Ehsan, Malaysia c Dean’s Office, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Darul Ehsan, Malaysia J Chem Technol Biotechnol 2009; 84: 1390–1396 www.soci.org c  2009 Society of Chemical Industry