Kraft mill effluents were biologically treated in an aerated lagoon (AL) (3.4 L) to evaluate the behavior of aromatic compounds by UV-vis spectroscopy. Under aerobic conditions, biological oxygen demand (BOD(5)) removal was between 84% and 95%, whereas soluble chemical oxygen demand (COD(s)) removal ranged between 40% and 60%. A slight increase was observed in the VIS(436)/COD(s) relationship (0.101-0.110), indicating that color reduction was less than the total organic matter reduction expressed by COD(s). Additionally, low values of UV(254)/UV(280) (1.23-1.12) indicate the presence of lignin-derived compounds in the aerobic effluent relationship. Ultrafiltration (UF) analysis shows that color was concentrated in the molecular weight fraction larger than 10,000 Da. The recalcitrant fraction was found to be resistant to further biodegradation, even under optimized microbiological conditions.

Estrogenic activity of kraft pulp mill effluents (P. radiata, E. globulus and mixed -50% E. globulus and 50% P. radiata) was evaluated by the yeast estrogen screen assay. The estrogenic activity values were relatively low, ranking between 1.475 and 0.383 ng/L of EE2 eq. (Estrogenic equivalent of 17 alpha-ethynylestradiol), where the highest value corresponds to the E. globulus effluent and the lowest value to the P. radiata effluent. Analysis by solid phase extraction (SPE) and gas chromatography-mass spectrometry (GC-MS) of chemical compounds present in all three effluents detected at least five major groups of organic compounds, corresponding to fatty acids, hydrocarbons, phenols, sterols and triterpenes. Comparison of analytical and biological data suggests that sterols could be the cause of the estrogenic activity in the evaluated effluent.

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Kraft mill effluent, due to its organic matter content and acute toxicity, must be treated. A primary treatment followed by a secondary treatment is the most common system. Aerated lagoon is also considered an effective biological treatment, although this technology has some drawbacks related with operation parameters and land extension space. Moreover, the recovery efficiency for micropollutants contained in kraft mill effluent is questioned due to the anoxic zone in the *Corresponding author system. The goal of this work is to evaluate the performance of the aerated lagoon to remove stigmasterol contained in kraft mill effluents. Kraft mill effluent was treated by an aerated lagoon (AL), which was operated with three different stigmasterol load rates (SLR = 0.2, 0.6 and 1.1 mg/L x d) and a hydraulic retention time of 1 day. The AL's maximum Chemical Oxygen Demand (COD) removal was 65%, whereas the Biological Oxygen Demand (BOD 5 ) was around 95%.Chamorro, S. et al. 2The removal efficiency of stigmasterol removal was 96% when SLR 1.1 mg/L x d, although an accumulation of stigmasterol was detected for lower SLR.Estrogenic endocrine disruption could be produced by extractive compounds coming from the kraft pulp. High concentrations of extractive compounds (and in particular sterols) are contained in black liquor from the digestion processes, and these are generally recovered by evaporation and combustion . However, there is a small part of black liquor that remains in the fiber and is dragged into the washing processes. Thus, in the discharged kraft mill effluents, concentrations ranging from 0.3 to 3.4 mg/L for sterols and 0.28 to 1.21 mg/L for resin acids can be found (Vidal et al. 2007 where the whitening process consisted in elementary chlorine free processes, finding that a phytosterol reduction process was produced in all cases except in the case of stigmasterol, where it could increase between 192% and 367%. In the activated sludge system, an 88% increase in stigmasterol was observed, and is probably due to the chemical or biological transformation in the precursor treatment system where it was converted into stigmasterol (Cook et al. 1997). However, few studies present results with respect to EDC behavior in aerated lagoons.The goal of this work is to evaluate the performance of aerated lagoon in removing stigmasterol contained in kraft mill effluents. MATERIALS AND METHODS WastewaterThe effluent was obtained from a modern kraft mill that bleaches softwood pulp and is located in Southern Chile. Pinus radiata is the raw material used in the process. The kraft mill effluent was obtained after primary treatment. Table 1 shows the main physicochemical characteristics of this effluent. The effluent was supplemented with 0.022 g/L of NH 4 Cl as nitrogen source and 0.169 g/L of K 2 PO 4 as phosphorus source (BOD 5 :N:P = 100:5:1). InoculumThe aerobic lagoon was inoculated using an aerobic microbial consortium (5 g/L of volatile suspended solid (VSS), 9 g/L of total suspended solid (TSS)) that was obtained from ...