Effect of electrolytes on the simultaneous electrochemical oxidation of sulfamethoxazole, propranolol and carbamazepine: behaviors, by-products and acute toxicity.

In this work, the effect of supporting electrolytes on the simultaneous electrochemical oxidation of the pharmaceuticals sulfamethoxazole (SMX), propranolol (PRO), and carbamazepine (CBZ) in aqueous solutions has been studied. Based on the identified by-products, the degradation mechanisms were proposed and the acute toxicity was evaluated for each electrolyte. Assays were carried out in batch mode in a 2 L undivided reactor using a niobium coated with boron-doped diamond (Nb/BDD) mesh anode and Ti cathode at 2.5 A in presence of different supporting electrolytes (Na2SO4, NaCl, or NaBr) at the same concentration of 7 mM. The degradation rates were higher in the assays with NaCl and NaBr. Reaction by-products were identified by gas chromatography-mass spectrometry. Indirect oxidation by electrogenerated reactive halogen species (RHS) was the main mechanism when halide ions were used as electrolytes. Ten by-products were detected using Na2SO4 as electrolyte, while 19 (12 non-halogenated and 7 halogenated) and 20 (10 non-halogenated and 10 halogenated) using NaCl and NaBr respectively. The proposed degradation pathways involve transformation (hydroxylation, deamination, desulfonation, and halogenation) and bond rupture to produce less molecular weight compounds and their further transformation until total degradation. Chlorinated and brominated by-products confirm halogenation reactions. The electrogenerated RHS presented a significant inhibition effect on Vibrio fischeri; nevertheless, acute toxicity was not presented using Na2SO4 as electrolyte and a pharmaceutical concentration of 5 µg/L. In this view, the role of the supporting electrolyte in electrochemical oxidation process is crucial since it strongly influence degradation rate, by-products, and acute toxicity.

Electrochemical carbamazepine degradation: Effect of the generated active chlorine, transformation pathways and toxicity.

Carbamazepine (CBZ) is a biorecalcitrant pharmaceutical compound frequently detected in wastewater and water bodies which has numerous negative effects on living organisms. In this investigation the effect of electrocatalytically generated active chlorine on CBZ degradation was studied using Nb/BDD or Ti/IrO2 anodes. Subsequently, a response surface methodology based on a factorial plan and central composite design was carried out to determine the contribution of individual factors and to obtain the optimal experimental parameters for CBZ abatement. Electric current and treatment time were found to be the pivotal parameters influencing the degradation efficiency with respective contributions of 45.19% and 35.44%. The anode material had lower influence on the response, however, using an Nb/BDD anode, the oxidation was more effective due to the increased production of OH radicals as well as HClO, Cl and ClO- species. Considering CBZ degradation and energetic consumption, the percentage of degraded CBZ was 88.70 ± 0.35% consuming 1.07 kWh m-3 (at 1.0 A, NaCl concentration of 14 mM after 12.45 min, using Nb/BDD anode). First order kinetic constant (k) value of 0.189 min-1 was obtained at optimal conditions when demineralized water was used for the NaCl supporting electrolyte, while k was lower when tap water or treated wastewaters were used for this purpose. Oxidation of CBZ yielded six aromatic intermediates, identified by gas chromatography - mass spectrometry technique and degradation pathways were proposed. The performed acute toxicity tests indicated an increase during the treatment, which was demonstrated to be mainly attributed to the remnant active chlorine.

Removal of naphthalene and phenanthrene using aerobic membrane bioreactor.

The removal of polycyclic aromatic hydrocarbons by membrane bioreactor (MBR) under aerobic conditions had been studied using naphthalene (NAP) and phenanthrene (PHE) as model compounds. Three MBRs with submerged ultra-filtration hollow fiber membranes were operated applying different operational conditions during 6.5 months. Complete NAP and PHE removal was obtained applying loads of 7 gNAP kgTSS(-1) day(-1) and 0.5 gPHE kgTSS(-1) day(-1), while the organic loading rate was adjusted to 0.26 kgCOD kgTSS(-1) day(-1), with the biomass concentration being 6000 mgTSS L(-1), the hydraulic retention time (HRT) 8 h and the solids retention time (SRT) 30 days. Load increases, as well as HRT and SRT reductions, affected the NAP and PHE removals. Biodegradation was found to be the major NAP and PHE removal mechanism. There was no NAP accumulation in the biomass. Low PHE quantities remain sorbed in the biomass and the contribution of the sorption in the removal of this compound was estimated to be less than 0.01 %. The volatilization does not contribute to the PHE removal in MBRs, but the contribution of NAP volatilization can reach up to 0.6 % when HRT of 8 h is applied.

Criterios de diseño para un sistema de composteo de lodos residuales

Si bien se ve un auge en el tratamiento de aguas residuales municipales e industriales en toda Latinoamérica no es lo mismo con el manejo y disposición adecuada para los lodos residuales generados. En este trabajo se presentan los principales aspectos para la planeación de un sistema de composteo con base en los diseños de dos plantas de tratamiento de aguas residuales. Se proporcionan los costos de inversión inicial y algunos aspectos para la comercialización del producto

El control de la contaminación del agua en México

Se presenta un panorama del desarrollo del derecho ambiental mexicano, la nueva política y legislación referente a la calidad de las aguas nacionales. Se aclaran las atribuciones para la elaboración de la normatividad, las verificaciones normativas y las responsabilidades por el incumplimiento de las disposiciones ambientales