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

ABSTRACT

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 145 days, with a hydraulic retention time of 2 days. 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 µg L⁻¹) after 5 weeks of operation. In that case, the organic load rate was 0.343 kg COD m⁻³ d⁻¹. Furthermore, different steroidal compounds (e.g., testosterone propionate, stigmast-4-en-3-one, 5α-pregnan-12-one-20α-hydroxy, 5α-pregnane-3,11,20-trione and 3α-hydroxy-5α-androstane-11,17-dione were detected in the Kraft mill effluent as potential products of phytosterol biotransformation.

KEYWORDS:

• Biotransformation
• Kraft mill effluent
• moving bed biofilm reactor
• steroidal metabolites
• stigmasterol

Acknowledgments

The authors thank the Doctoral Network REDOC.CTA and the University of Concepción, Concepción, Chile.

Funding

This work is supported by MINEDUC Grant 270 UCO1202, FONDECYT 3120216, FONDECYT 1120664 and CONICYT/FONDAP/15130015.