Removal of stigmasterol from Kraft mill effluent by aerobic biological treatment with steroidal metabolite detection

Stigmasterol is a phytosterol contained in Kraft mill effluent that is able to increase over 100% after aerobic biological treatment. This compound can act as an endocrine disrupter as its structure is similar to that of cholesterol. The aim of this study was to evaluate the removal of stigmasterol from Kraft mill effluents treated by a moving bed biofilm reactor (MBBR) with steroidal metabolite detection. The MBBR was operated for 145days, with a hydraulic retention time of 2days. Stigmasterol and steroidal metabolites were detected by gas chromatography with a flame ionization detector during MBBR operation. The results show that the MBBR removed 87.4% of biological oxygen demand (BOD5), 61.5% of chemical oxygen demand (COD), 24.5% of phenol and 31.5% of lignin, expressed in average values. The MBBR system successfully removed 100% of the stigmasterol contained in the influent (33 mu g L-1) after 5weeks of operation. In that case, the organic load rate was 0.343kg COD m(-3) d(-1). Furthermore, different steroidal compounds (e.g., testosterone propionate, stigmast-4-en-3-one, 5-pregnan-12-one-20-hydroxy, 5-pregnane-3,11,20-trione and 3-hydroxy-5-androstane-11,17-dione were detected in the Kraft mill effluent as potential products of phytosterol biotransformation.