Sustainable integrated process for cogeneration of oxidants for VOCs removal.

This study upgrades the sustainability of environmental electrochemical technologies with a novel approach consisting of the in-situ cogeneration and use of two important oxidants, hydrogen peroxide (H2O2) and Caro's acid (H2SO5), manufactured with the same innovative cell. This reactor was equipped with a gas diffusion electrode (GDE) to generate cathodically H2O2, from oxygen reduction reaction, a boron doped diamond (BDD) electrode to obtain H2SO5, via anodic oxidation of dilute sulfuric acid, and a proton exchange membrane to separate the anodic and the cathodic compartment, preventing the scavenging effect of the interaction of oxidants. A special design of the inlet helps this cell to reach simultaneous efficiencies as high as 99% for H2O2 formation and 19.7% for Caro's acid formation, which means that the cogeneration reaches efficiencies over 100% in the uses of electric current to produce oxidants. The two oxidants' streams produced were used with different configurations for the degradation of three volatile organic compounds (benzene, toluene, and xylene) in a batch reactor equipped with a UVC-lamp. Among different alternatives studied, the combination H2SO5/H2O2 under UVC irradiation showed the best results in terms of degradation efficiency, demonstrating important synergisms as compared to the bare technologies.

Life cycle inventory for an organic swine waste treatment system.

The aim of this study was to analyze the efficiency of a system of treatment of organic swine waste as a management tool in the transformation of organic waste into products of value in the swine industry. The residues from the pig farm and the products obtained (compost, biol and biogas) were quantified and characterized, as were the energy used within the process and the distribution of the products. The negative impacts on the soil and adjacent river, as well as the efficiency of the compost as fertilizers and biol in grass and corn crops, were evaluated. The subsystems were: S1-slurry separation, S2-anaerobic digestion, S3-composting solid fraction of slurry, and S4-composting of dead tissues. S2 was not efficient in obtaining biol, with COD and TSS required. The process requires 31.1 kW/d of electrical energy and 3.22 L/d of diesel. The biogas (35,486.0 m3/d) is used for cooking food and heating houses, whilst the compost (82 kg/d) and biol (7.72 m3/d) replace inorganic fertilizers in crops. The system was adequate for the transformation of 38,109.0 kg/d of waste into valuable products. The biol needs further treatment time or to couple biodigesters-another treatment. The pig farm can be considered eco-efficient.

Sulfonated and gamma-irradiated waste expanded polystyrene with iron oxide nanoparticles, for removal of indigo carmine dye in textile wastewater.

In this work, waste expanded polystyrene (WEPS) was irradiated with gamma rays, ranging doses from 100 kGy to 1,000 kGy. After irradiation, the WEPS had decrease on its glass transition temperature (Tg), as consequence of the scissions of its polymer chains. Then, the irradiated WEPS was sulfonated, and its degree of sulfonation (DS) was measured. The highest DS value, 46.6%, was obtained for an irradiation dose of 200 kGy. The sulfonated and irradiated polystyrene (denominated as iS-WEPS), was used as a support of iron oxide nanoparticles. Such composite system was denominated (FeO-NPs + iS-WEPS). The results show nanoparticle sizes of 31.5 nm containing 21.97% iron oxide. The composites followed a pseudo-second order model, with a maximum adsorption capacity of 20 mg/g, and an equilibrium time of 30 min, according to the Langmuir model. Moreover, the optimal conditions followed by the Fenton process were: pH = 3.2, H2O2 concentration = 0.32 mM/L, composite concentration (FeO-NPs + iS-WEPS) = 2 g/L, and a reaction time 20 min. Finally, 99% removal of indigo carmine dye was achieved, and a reduction of 83% of COD in textile wastewater.

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

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.

Effective mercury(II) bioremoval from aqueous solution, and its electrochemical determination.

This work proposed mercury elimination using agricultural waste (Allium Cepa L.). The biomass removed 99.4% of mercury, following a pseudo-second order kinetics (r2 = 0.9999). The Langmuir model was adequately fitted to the adsorption isotherm, thereby obtaining the maximum mercury adsorption capacity of 111.1 ± 0.3 mg g-1. The biomass showed high density of strong mercury chelating groups, thus making it economically attractive. Also, the implementation of a mercury-selective electrode for continuous determination in real time is proposed; this electrode replaces techniques like atomic absorption spectroscopy, thus it can be applied to real time studies. This work therefore presents a new perspective for removing mercury(II) from contaminated water for environmental remediation.

Reduction of pollutants and disinfection of industrial wastewater by an integrated system of copper electrocoagulation and electrochemically generated hydrogen peroxide.

The objective of this study was to evaluate the effect of copper electrocoagulation and hydrogen peroxide on COD, color, turbidity, and bacterial activity in a mixed industry wastewater. The integrated system of copper electrocoagulation and hydrogen peroxide is effective at reducing the organic and bacterial content of industrial wastewater. The copper electrocoagulation alone reduces COD by 56% in 30 min at pH 2.8, but the combined system reduces COD by 78%, biochemical oxygen demand (BOD5) by 81%, and color by 97% under the same conditions. Colloidal particles are flocculated effectively, as shown by the reduction of zeta potential and the 84% reduction in turbidity and 99% reduction in total solids. Additionally, the total coliforms, fecal coliforms, and bacteria are all reduced by 99%. The integrated system is effective and practical for the reduction of both organic and bacterial content in industrial wastewater.

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 mg Nacl/L. This highly encouraging proof-of-concept offers a potentially alternative greener approach to COD analysis.

Tolerance of Myriophyllum aquaticum to exposure of industrial wastewater pretreatment with electrocoagulation and their efficiency in the removal of pollutants.

The wastewater used in this study was obtained from a treatment plant where it mixed with wastewater of 142 industries and was treated using electrocoagulation with iron electrode and phytoremediation with Myriophyllum aquaticum, likewise certain biomarkers of oxidative stress of the plant were evaluated to find out its resistance to contaminant exposure. Electrocoagulation was performed under optimum operating conditions at pH 8 and with a current density of 45.45 A m(-2) to reduce the COD by 42%, color 89% and turbidity 95%; the electrochemical method produces partial elimination of contaminants, though this was improved using phytoremediation. Thus the coupled treatment reduced the COD by 94%, color 97% and turbidity 98%. The exposure of M. aquaticum to electrocoagulated wastewater did not have an effect on the ratio of chlorophyll a/b (2.84 + 0.24); on the activity of SOD, CAT and lipoperoxidation. The results show the potential of M. aquaticum to remove contaminants from pretreated wastewater since the enzymatic system of the plants was not significantly affected.

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.

Enhancing the electrochemical Cr(VI) reduction in aqueous solution.

In this study we present the cathodic Cr(VI) reduction using electrodissolution of iron anode. In batch experiments we tested four different cathodic materials; the best conditions were found when copper was used. It is observed that when more current is applied into the electrochemical cell faster reduction rates are achieved. Continuous experiments also reveal that Cr(VI) reduction could be done in a very efficient way. To confirm the experimental data, cyclic voltammetry was used and it was found that the cathodic Cr(VI) reduction is taking place.

An integrated electrocoagulation-phytoremediation process for the treatment of mixed industrial wastewater.

The elimination of organic contaminants in highly complex wastewater was tested using a combination of the techniques: electrocoagulation with aluminum electrodes and phytoremediation with Myriophyllum aquaticum. Under optimal operating conditions at a pH of 8 and a current density of 45.45 A m(-2), the electrochemical method produces partial elimination of contaminants, which was improved using phytoremediation as a polishing technique. The combined treatment reduced chemical oxygen demand (COD) by 91%, color by 97% and turbidity by 98%. Initial and final values of contaminants in wastewaters were monitored using UV-vis spectrometry and cyclic voltammetry. Finally, the morphology and the elemental composition of the biomass were characterized with using scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). The presence of Al in the roots of plants in the system indicates that the aluminum present in the test solution could be absorbed.

Physicochemical and biological combined treatment applied to a food industry wastewater for reuse.

The aim of this study was to improve the wastewater treatment plant (WWTP) efficiency of a food industry. Despite the anaerobic-aerobic treatment, the efficiency of the plant is poor because of the high pollutants load derived mainly from the use of disinfectants and sanitizers. These cleaning products are used in the production process. In order to achieve the main goal of the study, the pollutants load reduction was targeted and a physicochemical treatment was added for that purpose. For this effort, the tests were divided in three parts. The first consisted of performing coagulation-flocculation laboratory tests to select the best chemical reagent for reduction of the high load of pollutants present in the influent. The evaluated compounds were ferric chloride, aluminum sulphate, hydroxychloride of aluminum (AHC) and polyaluminum sulphate (PAS). The second was a pilot plant study in which physicochemical and biological treatment werecombined. Finally processes were verified in the WWTP characterizing the effluent and evaluating the process for compliance with standards for reuse water. The results showed that the best coagulant was hidroxichloride of aluminium. Improving the relationship Chemical Oxygen Demand/ Biological Oxygen Demand (COD/BOD(5)) of 0.27 to 0.45 and getting a dose of 1 to 5 mg L(- 1) in the laboratory, which improved to make scaling to plant 0.5 to 2 mg L(- 1) with efficiencies removal of contaminants 98% for COD, 95% for BOD(5), 99% for O&G, to 99% for TSS and helminth eggs were not detect. The wastewater was characterized with cyclic voltammetry and the sludge produced with AHC was analyzed by scanning electron microscopy (SEM) and energy-dispersion spectroscopy (EDS).

Experimental correlation between the pKa value of sulfonphthaleins with the nature of the substituents groups.

This work presents the results obtained from a spectrophotometry study performed on some indicators of the sulfonphtaleins like phenol red (PR), thymol blue (TB), bromothymol blue (BTB), xylenol orange (XO) and methylthymol blue (MTB). During the first stage the acidity constants of some of the indicators were determined using the data from spectrophotometry, potentiometry and with the use of the software SQUAD. These were as follows: for the equilibrium 2H+BTB<-->H(2)BTB, log beta(2)=15.069+/-0.046 and for H+BTB<-->HBTB, log beta(1)=8.311+/-0.044. For the XO and the MTB five values were calculated for each, namely, for MTB: log beta(5)=42.035, log beta(4)=38.567+/-0.058, log beta(3)=32.257+/-0.057, log beta(2)=23.785+/-0.057, and log beta(1)=12.974+/-0.045 while for XO: log beta(5)=40.120+/-0.102, log beta(4)=35.158+/-0.062, log beta(3)=29.102+/-0.053, log beta(2)=21.237+/-0.044, and log beta(1)=11.682+/-0.044. During the second stage, a study was conducted on the effect of the substituents present in the indicators to determine the effect of different functional groups on the pK(a) value corresponding to the last indicator's dissociation.

A combined electrocoagulation-sorption process applied to mixed industrial wastewater.

The removal of organic pollutants from a highly complex industrial wastewater by a aluminium electrocoagulation process coupled with biosorption was evaluated. Under optimal conditions of pH 8 and 45.45 Am(-2) current density, the electrochemical method yields a very effective reduction of all organic pollutants, this reduction was enhanced when the biosorption treatment was applied as a polishing step. Treatment reduced chemical oxygen demand (COD) by 84%, biochemical oxygen demand (BOD(5)) by 78%, color by 97%, turbidity by 98% and fecal coliforms by 99%. The chemical species formed in aqueous solution were determined. The initial and final pollutant levels in the wastewater were monitored using UV-vis spectrometry and cyclic voltammetry. Finally, the morphology and elemental composition of the biosorbent was characterized with scanning electron microscopy (SEM) and energy dispersion spectra (EDS).