Patricia Balderas-Hernández

Determination of pKa's for thymol blue in aqueous medium: evidence of dimer formation.

Formation constants for recrystallized thymol blue were determined in water, using the SQUAD and SUPERQUAD programs. The best model correlating spectrophotometric, potentiometric and conductimetric data was fitted with the dissociation of HL(-)=L(2-)+H(+)-log K=8.918+/-0.070 and H(3)L(2)(-)=2L(2-)+3H(+)-log K=29.806+/-0.133 with the SUPERQUAD program at variable low ionic strength (1.5x10(-4)-3.0x10(-4) M); and HL=L(2-)+H(+)-log K=8.9+/-0.000, H(3)L(2)(-) =2L(2-)+3H(+)-log K=30.730+/-0.032, H(4)L(2)=2L(2-)+4H(+)-log K=32.106+/-0.033 with SQUAD at 1.1 M ionic strength.

Comparison of Cd-Pb adsorption on commercial activated carbon and carbonaceous material from pyrolysed sewage sludge in column system.

The sorption behaviour of Cd and Pb from aqueous solutions in columns, using both commercial activated carbon and a carbonaceous material from pyrolysis of sewage sludge, was determined. The breakthrough data obtained for Cd and Pb sorption could be described by the linear form of the Thomas adsorption model. The breakthrough capacities found from column studies were different for each metal and the data reflect the order of metal affinity for the adsorbents materials. The adsorption capacity of the carbonaceous material was higher for cadmium than for lead in a single system and in binary systems, and, for activated carbon, the sorption capacities of lead and cadmium were similar in the binary system. The results indicated that the carbonaceous material from pyrolysis of sewage sludge is a better adsorbent than activated carbon of cadmium and lead.

Cr(VI) reduction in wastewater using a bimetallic galvanic reactor.

The electrochemical reduction of Cr(VI)-Cr(III) in wastewater by iron and copper-iron bimetallic plates was evaluated and optimized. Iron has been used as a reducing agent, but in this work a copper-iron galvanic system in the form of bimetallic plates is applied to reducing hexavalent chromium. The optimal pH (2) and ratio of copper to iron surface areas (3.5:1) were determined in batch studies, achieving a 100% reduction in about 25 min. The Cr(VI) reduction kinetics for the bimetallic system fit a first order mechanism with a correlation of 0.9935. Thermodynamic analysis shows that the Cr(VI) reduction is possible at any pH value. However, at pH values above 3.0 for iron and 5.5 for chromium insoluble species appear, indicating that the reaction will be hindered. Continuous column studies indicate that the bimetallic copper-iron galvanic system has a reduction capacity of 9.5890 mg Cr(VI) cm(-2) iron, whereas iron alone only has a capacity of 0.1269 mg Cr(VI) cm(-2). The bimetallic copper-iron galvanic system is much more effective in reducing hexavalent chromium than iron alone. The exhausted plates were analyzed by SEM, EDS, and XRD to determine the mechanism and the surface effects, especially surface fouling.

Inside the removal of lead(II) from aqueous solutions by De-Oiled Allspice Husk in batch and continuous processes

A new adsorbent material for removing lead ions from aqueous solutions has been investigated. The residue of the allspice extraction process (De-Oiled Allspice Husk) was used on the removal of Pb(II) from water solutions. The lead sorption capacity of De-Olied Allspice Husk (DOAH) was studied in batch and continuous processes. It was found that percentage removals of Pb(II) depend on the pH and the initial lead concentrations. The Pb(II) uptake process was maximum at pH 5 in a range concentrations of 5-25 mg L(-1). The overall sorption process was well described by the pseudo-second-order kinetic model under conditions of pH 5 (0.1 g adsorbent per 100 mL of contaminated solution) 0.001 mass/volume ratio and 25 degrees C. The sorption capacity of lead(II) onto DOAH in batch process was 5.00, 8.02, 11.59, 15.23 and 20.07 mg g(-1), when the concentration solutions were 5, 10, 15, 20 and 25 mg L(-1) respectively. These values are lower than obtained in continuous process, where lead was removed by 95% and the experimental results were appropriately fitted by the Yoon-Nelson model. X-ray photoelectron spectroscopy (XPS) provides information regarding the interactions between lead ions and the adsorbent surface indicating that the formation of 2 complexes depends on the functional groups associated.

Treatment of soft drink process wastewater by ozonation, ozonation-H2O2 and ozonation-coagulation processes

In this research, we studied the treatment of wastewater from the soft drink process using oxidation with ozone. A scheme composed of sequential ozonation-peroxide, ozonation-coagulation and coagulation-ozonation treatments to reduce the organic matter from the soft drink process was also used. The samples were taken from the conventional activated sludge treatment of the soft drink process, and the experiments using chemical oxidation with ozone were performed in a laboratory using a reactor through a porous plate glass diffuser with air as a feedstock for the generation of ozone. Once the sample was ozonated, the treatments were evaluated by considering the contact time, leading to greater efficiency in removing colour, turbidity and chemical oxygen demand (COD). The effect of ozonation and coagulant coupled with treatment efficiency was assessed under optimal conditions, and substantial colour and turbidity removal were found (90.52% and 93.33%, respectively). This was accompanied by a 16.78% reduction in COD (initial COD was 3410 mg/L). The absorbance spectra of the oxidised products were compared using UV-VIS spectroscopy to indicate the level of oxidation of the wastewater. We also determined the kinetics of decolouration and the removal of turbidity with the best treatment. The same treatment was applied to the sample taken from the final effluent of the activated sludge system, and a COD removal efficiency of 100% during the first minute of the reaction with ozone was achieved. As a general conclusion, we believe that the coagulant polyaluminum chloride - ozone (PAC- ozone) treatment of wastewater from the manufacturing of soft drinks is the most efficient for removing turbidity and colour and represents an advantageous option to remove these contaminants because their removal was performed in minutes compared to the duration of traditional physical, chemical and biological processes that require hours or days.

Replacing dichromate with hydrogen peroxide in the chemical oxygen demand (COD) test

The widely used standard method for chemical oxygen demand (COD) involves hazardous chromium species, and its two-hour heating protocol entails a substantial amount of energy expenditure. In the present work we report a proof of concept for a major modification of this method in the range 10-800 mgCOD/L, whereby H2O2 is proposed as a replacement oxidizer. This modification not only reduces the use of unsafe chromium species but also allows for the use of milder conditions that decrease the total energy outlay. The results are comparable with those obtained either with the standard method or with a commercial Hach® kit.

Downscaling the chemical oxygen demand test.

The usefulness of the standard chemical oxygen demand (COD) test for water characterization is offset to some extent by its requirement for highly toxic or expensive Cr, Ag, and Hg species. In addition, oxidation of the target samples by chromate requires a 2–3 h heating step. We have downscaled this method to obtain a reduction of up to ca. 80% in the use and generation of toxic residues and a time reduction of up to ca. 67%. This also translates into considerable energy savings by reducing the time required for heating as well as costly labour time. Such reductions can be especially important for analytical laboratories with heavy loads of COD analyses. Numerical results obtained with the standard COD method for laboratory KHP samples (potassium hydrogen phthalate) show an average relative error of 1.41% vs. an average of 2.14% obtained with the downsized or small-scale version. The average % standard deviation when using the former is 2.16% vs. 3.24% obtained with the latter. When analysing municipal wastewater samples, the relative error is smaller for the proposed small-scale method than for the standard method (0.05 vs. 0.58, respectively), and the % std. dev. is 1.25% vs. 1.06%. The results obtained with various industrial wastewaters show good agreement with those obtained using the standard method. Chloride ions do not interfere at concentrations below 2000 mgNaCl/L. This highly encouraging proof-of-concept offers a potentially alternative greener approach to COD analysis.

Tolerance and hyperaccumulation of a mixture heavy metals (Cu, Pb, Hg and Zn) by four aquatic macrophytes.

ABSTRACT In the present investigation, four macrophytes, namely Typha latifolia (L.), Lemna minor (L.), Eichhornia crassipes (Mart.) Solms-Laubach, and Myriophyllum aquaticum (Vell.) Verdc, were evaluated for their heavy metal (Cu, Pb, Hg, and Zn) hyperaccumulation potential under laboratory conditions. Tolerance analyses were performed for 7 days of exposure at five different treatments of the metals mixture (Cu+2, Hg+2, Pb+2, and Zn+2). The production of chlorophyll and carotenoids was determined at the end of each treatment. L. minor revealed to be sensitive, because it did not survive in all the tested concentrations after 72 hours of exposure. E. crassipes and M. aquaticum displayed the highest tolerance to the metals mixture. For the most tolerant species of aquatic macrophytes, The removal kinetics of E. crassipes and M. aquaticum was carried out, using the following mixture of metals: Cu (0.5 mg/L) and Hg, Pb, and Zn 0.25 mg/L. The obtained results revealed that E. crassipes can remove 99.80% of Cu, 97.88% of Pb, 99.53% of Hg, and 94.37% of Zn. M. aquaticum withdraws 95.2% of Cu, 94.28% of Pb, 99.19% of Hg, and 91.91% of Zn. The obtained results suggest that these two species of macrophytes could be used for the phytoremediation of this mixture of heavy metals from the polluted water bodies.

Ozonation of Indigo Carmine Enhanced by Fe/Pimenta dioica L. Merrill Particles

Green synthesis of metallic particles has become an economic way to improve and protect the environment by decreasing the use of toxic chemicals and eliminating dyes. The synthesis of metal particles is gaining more importance due to its simplicity, rapid rate of synthesis of particles, and environmentally friendly. The present work aims to report a novel and environmentally friendly method for the synthesis of iron particles using deoiled Pimenta dioica L. Merrill husk as support. The indigo carmine removal efficiency by ozonation and catalyzed ozonation is also presented. Synthesized materials were characterized by N2 physisorption and scanning electron microscopy (SEM/EDS). By UV-Vis spectrophotometry the removal efficiency of indigo carmine was found to be nearly 100% after only 20 minutes of treatment under pH 3 and with a catalyst loading of 1000 mgL−1. Analytical techniques such as determination of the total organic carbon content (TOC) and chemical oxygen demand (COD) showed that iron particles supported on deoiled Pimenta dioica L. Merrill husk can be efficiently employed to degrade indigo carmine and achieved a partial mineralization (conversion to CO2 and H2O) of the molecule. From the results can be inferred that the prepared biocomposite increases the hydroxyl radicals generation.

Pb(II) Removal Process in a Packed Column System with Xanthation-Modified Deoiled Allspice Husk

The present research dealt with lead removal using modified Pimenta dioica L. Merrill as biosorbent in a batch and in continuous flow column systems, respectively. The allspice husk residues were modified first with a treatment through the xanthation reaction. For the adsorption tests, the atomic adsorption spectrophotometry method was used to determine the lead concentrations in the liquid samples. In the kinetic batch study (10 mg of sorbent in 10 mL of 25 mg L−1 lead solution), the removal efficiency was 99% (adsorption capacity of 25.8 mg g−1). The kinetic data followed the pseudo-second-order model. The adsorption isotherm was fitted to the Freundlich model, where constants were and (8.06 mg  g−1 L and 0.52), corresponding to adsorption capacities of 8 and 62 mg g−1, at liquid equilibrium concentration of 1 and 50 mg L−1, respectively. In the continuous flow systems where lead solution of 50 mg L−1 was treated in 2 columns of 5 cm (4.45 g) and 10 cm (9.07 g) bed heights, the dynamic adsorption capacity obtained by fitting the Thomas model was 29.114 mg g−1 and 45.322 mg g−1, respectively.