The performance of a mesophilic UASB reactor was studied for the treatment of sugar cane mill wastewater previously pre-treated for solid separation. The experimental work was carried out in a reactor with 80 L total volume. Four organic loads were applied and the process performance was evaluated during two months for each experimental stage. Removal efficiencies higher than 90% were obtained with organic loads up to 16 kg COD m(-3) d(-1). Stable process performance and high biogas production were obtained. The COD removal rate increased substantially with the load increase to 24 kg COD m(-3) d(-1). However, the obtained removal was of only 78-82%, which can be attributed to the accumulation of volatile organic acids. The kinetic coefficients were obtained using first order model for the substrate removal rate and Monod's equation for bacteria specific growth rate. The UASB reactor is a good option for the biological treatment of pre-treated sugar cane mill wastewaters. The discharge requirements for COD concentration can be accomplished if the reactor is operated at a low organic load of 4 kg COD m(-3) d(-1). At higher loads, an additional biological treatment stage is needed.
The biodegradation of fluoxetine, mefenamic acid, and metoprolol using ammonium-nitrite-oxidizing consortium, nitrite-oxidizing consortium, and heterotrophic biomass was evaluated in batch tests applying different retention times. The ammonium-nitrite-oxidizing consortium presented the highest biodegradation percentages for mefenamic acid and metoprolol, of 85 and 64% respectively. This consortium was also capable to biodegrade 79% of fluoxetine. The heterotrophic consortium showed the highest ability to biodegrade fluoxetine reaching 85%, and it also had a high potential for biodegrading mefenamic acid and metoprolol, of 66 and 58% respectively. The nitrite-oxidizing consortium presented the lowest biodegradation of the three pharmaceuticals, of less than 48%. The determination of the selected pharmaceuticals in the dissolved phase and in the biomass indicated that biodegradation was the major removal mechanism of the three compounds. Based on the obtained results, the biodegradation kinetics was adjusted to pseudo-first-order for the three pharmaceuticals. The values of k for fluoxetine, mefenamic acid, and metoprolol determined with the three consortiums indicated that ammonium-nitrite-oxidizing and heterotrophic biomass allow a partial biodegradation of the compounds, while no substantial biodegradation can be expected using nitrite-oxidizing consortium. Metoprolol was the less biodegradable compound. The sorption of fluoxetine and mefenamic acid onto biomass had a significant contribution for their removal (6-14%). The lowest sorption coefficients were obtained for metoprolol indicating that the sorption onto biomass is poor (3-4%), and the contribution of this process to the global removal can be neglected.
Municipal wastewater was treated in 4 biofilters packed with a mix of endemic tropical woodchips and natural fibers to evaluate the removal efficiency of organic matter and pathogen microorganisms under tropical conditions. Biofilters were operated during 400 days, with a hydraulic rate of 0.3 m3/m2.d and an aeration rate of 0.68 m3air/m2 h-1. Raw municipal wastewater presented higher concentrations, of organic matter and pathogens, than those reported for municipal wastewaters in temperate countries. However, pollutants were successfully removed: <98.5% of the organic matter as BOD5 < 99.99% of Faecal Coliforms (FC) and Total Colony Forming Units (TCFU), and < 96.93% Helminth eggs (HE) were removed remaining only very low concentrations in the treated effluent (≤2.5 mg DBO5/L; ≤ 240 FC/100 mL; ≤ 240 TCFU /100 mL and < 1.0 HE/5L). According with Mexican regulations (Nom 001-SEMARNAT, 1996) and with the EPA suggested guidelines for water reuse (U.S. EPA, 1992a) treated effluents with this quality can be safely reused for three main activities: Nonfood crop irrigation, landscape impoundments and for construction activities. The high removal efficiency of TCFU and FC may be related with a predatory activity of testate amoebas which were detected growing into the biofilters and, the most plausible hypothesis concerning HE removal is that they are retained by filtration over the organic materials.
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