Decolorization of tanning house effluent by Aspergillus niger in tannery industries for biological removal of chromium

Introduction. Color is conside red as one of the major water resource pollut ants and other parts of the environment. In tannery industries the application of trivalent chromium salts in tanning of leath er produces a hazardous color whic being disposed directly to environment and it is likely to change to hazard ous hexavalent form in the oxidation conditions of the receiving environments. During the last few years, studies have shown the potent ial of fungi in removing the color of wastewaters in appropriate conditions.The aim of this research was to study deco lorizat ion of tanning house effluent by Aspergillus niger in tann ery indust ries for bio logical removal of chromium. Materials and Methods. The first, qu ality of tanning house effluent was st udied. Afte r adjusting of carbon to nitro gen ration in th e effluent, A. nigar was inoculated in the different size into the eflluent with different dillution s. The samples for 24 h. put in the shaker incubator. Then, the absorbance rate in the wavelength of 565 nm and biomass growth was estimated. Results. In this research Aspergillus niger was selecte d as the species of fungi for removing color from tanning house eflluent. Resu lts showed that Aspergillus niger is able to grow effectively in th e tanning house effl uent with dillution percentages of 10% and 20% (or chromium con centration 122.5 and 245 mg/l), with C/N ratio of 10 and pH= 3; and can reduce the color, 94.5% and 93.4%, respectively. According to th e experiments in this study, th e best size of inocculum was det ermined as 10 rnl, The percen tage of decolorization was increased due to the increase of dry weight of fungal mass to the conce ntra tion of chromium (1.7-23.7 mg dry weight of mass/mg trivalent choromium). The highest chromium rem oval percentage, 94.5%, was obtained in the 23.7 mg/mg ratio. The meaningful rel ationship of th ese par ameters is confirmed according to the multi ple regression coefficient of 0.8836. Conclusion. This study showed that Aspergillus niger can grow in tanning effl uent and remove about 95 % of color caused by trivalent chromiu m. Therefore, can be removed efficiently during the decolori zation process.