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Estrada-Arriaga E.B.,National Autonomous University of Mexico | Mijaylova P.N.,Mexican Institute of Water Technology
Environmental Science and Pollution Research | Year: 2011

Introduction: This paper deals with the removal of two natural estrogens, estrone (E1) and 17β-estradiol (E2) and a synthetic one 17α ethinylestradiol (EE2) from wastewater in a laboratory-scale membrane bioreactor (MBR). Materials and methods: The effects of both solid retention time (SRT) and hydraulic residence time (HRT) were studied using synthetic wastewater in the MBR. At 35, 45, 60, 75, and 95 days, SRT was studied. The HRT was varied in the range of 7-12 h. Results: The results showed that the increases in HRT and SRT enhanced the biodegradation process after adaptation to microorganisms. At HRT of 12 h, the estrogen removals were close to 100% in the MBR. The highest estrogen removals were obtained at SRT of 60 days. Continuous tests showed a linear relationship between nitrification and estrogen removal rates. Conclusions: The most biodegradable compound was the E2. The membrane fouling rates increased with the decreased of SRT and HRT. Optimal process conditions in this work was obtained at the SRT and HRT of 60 days and 12 h, respectively, with high efficient of estrogen removal, nitrification efficiencies, as well as a minimum membrane fouling rate. © 2011 Springer-Verlag. Source

Flores-Berrones R.,Mexican Institute of Water Technology | Ramirez-Reynaga M.,Mexican National Water Commission | Macari E.J.,California State University, Sacramento
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2010

This paper describes an earth-rock dam whose filters' characteristics did not comply with the design criterion. In addition, the degree of compaction and the water content in the impervious core consisted of highly plastic residual clay. Although Terzaghi's filter design criterion was used, the as-built grain size distribution did not comply with such criterion. Several problems arose right after the first filling of the dam, including the following: (1) water leak at a rate of 200 L/s was observed along the downstream slope, in the vicinity of the outlet pipeline; the dark color of the observed water implied that the core material was being eroded; (2) two sinkholes near the crest (20 m apart) were observed along the outlet axis, one on the upstream and the other on the downstream slopes; right after the occurrence of these two sinkholes, the water leakage decreases significantly, noticing a plugged effect of the material that falls down through the sinkholes. To avoid piping, a notch was installed on the spillway to quickly reduce the reservoir level. A site investigation around the affected zone was performed to find the causes of the observed seepage through the dam. The paper presents a detailed description of the site investigation. In addition, the paper presents the instrumentation, laboratory, and field tests employed as part of the site investigation. After analyzing the information produced in the site investigation, the following conclusions were derived: (1) large variation in the water content was used during the compaction of each lift of the impervious core which resulted in a highly heterogeneous core of the dam; (2) stress analysis of the zones around the outlet pipe demonstrated that the hydrostatic pressure in such zones exceeded the sum of the transverse normal and tensile stresses, inducing hydraulic fracturing; and (3) because of the grain size segregation during the placement of the filter material, the upstream and downstream filters did not satisfy the design criterion. Description of the stabilization of the damage zones through a grouting process, together with the construction of a diaphragm wall and an interface grouting, is presented. Finally, this paper reviews existing criteria for designing filters to protect earth and rockfill dams against internal erosion or piping and applies these criteria to the described dam. A special discussion on this topic is also presented. © 2011 ASCE. Source

Estrada-Arriaga E.B.,National Autonomous University of Mexico | Mijaylova P.,Mexican Institute of Water Technology
Water Science and Technology | Year: 2011

The purpose of this paper is to report the study of the fate and distribution of three endocrine disrupting compounds (estrogens); Estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2) in a laboratory scale submerged membrane bioreactor (SMBR). For this matter, both aqueous and solids phases were analyzed for the presence of E1, E2 and EE2. The outcome of this study was that three SMBRs showed enhanced elimination of estrogens in different operational conditions; the estrogen removal was close to 100% in SMBR. Additionally, E1, E2 and EE2 were detected in SMBR sludge at concentrations of up to 41.2, 37.3 and 36.9 ng g-1 dry weight, respectively. The estrogen removal in the SMBRs was directly influenced by a combination of simultaneous biodegradation-adsorption processes, indicating that the main removal mechanism of the estrogens in the SMBRs is the biodegradation process. The E1, E2 and EE2 were biologically degraded in the SMBR (87-100%). The sorption of estrogens onto activated sludge was from 2%. Therefore, a high potential for estrogen removal by biodegradation in the SMBR was observed, allowing less estrogen concentration in the dissolved phase available for the adsorption of these compounds onto biological flocs. Two different methods were carried out for mass balance calculations of estrogens in SMBR. For the first method, the measured data was used in both liquid and solid phases, whereas for the second one, it was in aqueous phase and solid-water distribution coefficients (Kd) value of E1, E2 and EE2. The purpose of these methodologies is to make easier the identification of the main mechanisms involved in the removal of E1, E2 and EE2 in a SMBR. Both methods can be applied in order to determine the mechanism, fate and distribution of estrogens in a SMBR. © IWA Publishing 2011. Source

Estrada-Arriaga E.B.,National Autonomous University of Mexico | Mijaylova N.P.,Mexican Institute of Water Technology
Water Science and Technology | Year: 2010

The biological degradation of estrone (E1), estradiol (E2) and ethinylestradiol (EE2) was studied in batch experiments at typical concentration levels using nitrifying activated sludge from a membrane bioreactor (MBR). Since first-order, pseudo first-order and Monod-type kinetics were observed. Pseudo first order kinetic was reformulated using only the soluble concentrations S and assuming adsorption coefficient KD of the estrogens. For the adsorption coefficients KD determination, activated sludge from MBR was spiked with the respective target compounds and stirred. Finally, the water was analyzed. The KD values of estrogens ranged from 0.323 to 0.474 L/g. Greater than 98% of E1, E2 and EE2 were found to be removed in batch reactors. The measured data were linearly regressed giving R2 values ranging from 0.748 to 0.990. According to these results, the biodegradation kinetics were adjusted to pseudo first-order assuming adsorption coefficient KD and Monod-type kinetic. The biodegradation rate constant k of the estrogens were: E1 and E2 > 78.52 L/gVSS d and 12.41 L/gVSS d for EE2. Monod-type kinetic indicates that these compounds are biodegradated by co-metabolism. E2 was oxidized into E1. © IWA Publishing 2010. Source

Garzon-Zuniga M.A.,Mexican Institute of Water Technology | Buelna G.,Quebec Industrial Research Center
Water Science and Technology | Year: 2011

Based on results obtained in the laboratory a WWTP composed of a septic tank and an aerated percolating filter packed with organic media was built for a school. The system can treat 18 m 3 d -1 and was operated with a hydraulic loading rate of 0.078 (m 3 m -2 d -1). For 360 days different operational conditions including start-up; stabilization; operation with aeration and non aeration; effect of rainy season, breaks from activities due to holidays and restart; were monitored and described in the article. Once stabilized, the system was able to remove, without the need for mechanical aeration, 97% of BOD 5, 71% of COD, 93% of TKN, 11% of PO 4 --P, 95% of TSS, 96% of VSS, in addition to having a removal efficiency of 4 log units of Faecal Coliforms (FC) and 100% helminthes eggs (HE). With this quality, the treated wastewater can be chlorinated and reused to irrigate green areas and/or in toilets. Although sanitary wastewater has a high concentration of Total-N (250 mg L -1) and a C/N ratio of less than 1, the system removed 65% of Total-N. Finally it was observed that after non activity periods, there was neither system failure nor the need to re-stabilize the system. © IWA Publishing 2011. Source

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