Activated sludge versus aerated lagoon treatment of kraft mill effluents containing β-sitosterol and stigmasterol

Abstract

In the present study the performance of an activated sludge system (AS) and an aerated lagoon (AL) are compared for the treatment of kraft cellulose effluents. Both reactors were operated at organic loading rates (OLR) up to 9 g COD/L· d. The activated sludge system presented better performance at high OLR than the aerated lagoon with removal percentages of 57–67% and 95% of COD and BOD₅, respectively. The removal percentages of specific compounds were always slightly higher in the case of the AS than in the AL with exception of the total phenolic compounds which concentration increased in the former. Furthermore the analyzed fractions from the effluents indicated that in the AS the compounds were fully removed while in the case of the aerated lagoon were transformed into compound with low molecular weight P2 (5 kD < MW < 10 kD). In the case of the AS system the increase of the total phenolic compounds concentrations was corroborated with the increase of the fractions P2, P3 and P4.

The studied phytosterol were removed from the effluent at concentrations up to 2 mg/L in percentages close to 100% mainly by adsorption in the case of the AL and by a combining adsorption and mainly degradation in the AS. The BOD₅ concentration in the effluent of both systems fulfilled the requirements of the Chilean regulations for effluent discharge indicating the feasibility of aerobic treatment of this kind of effluents.

Keywords:

• Activated sludge
• aerated lagoon
• kraft mill effluents
• β-sitosterol
• stigmasterol

Acknowledgments

This work was partially supported by Fondecyt 1070509. Anuska Mosquera-Corral thanks to the European ALFA N° II-0311-FA-FCD-FI-FC by supporting her stay at the Environmental Science Center EULA-Chile, Universidad de Concepción (Chile).

Notes

¹Estimated amount of adsorbed phytosterols on the biomass by batch experiments.