Water reclamation from anodizing wastewaters by removing reactive silica with adsorption and precipitation methods.

Water stress is a current environmental menace mainly driven by over exploitation of aquifers, which is triggering poor water quality with high concentration of minerals in extracted groundwater. Particularly, silica is widespread in natural water supplies due to weathering processes of silicates occurring in contact with water, light, air, and other factors. However, due to groundwater over extraction the concentration of silica has increased during the last years in aquifer reservoirs from Aguascalientes State (México). In this context, it is very important to note that the removal of silica compounds from water is challenging and different methods can be used to avoid embedding problems in different industries. In the present work, the removal of reactive silica from synthetic solutions as well as from real wastewaters from an industrial anodizing process was studied using adsorption and chemical precipitation methods. Twelve commercial materials of different nature were used for adsorption tests, while seven precipitant agents were applied in the precipitation experiments. Adsorption tests were performed in batch systems with constant stirring at 30 °C and at different pH values (7 and 9). Precipitation experiments were carried out in batch systems and the best conditions for silica removal were found using an L9 orthogonal array of the Taguchi method employing molar ratio, pH of wastewater, stirring time and temperature as experimental factors. Adsorption results showed that Ferrolox (Iron (III) hydroxide-base adsorbent) was the most efficient sorbent for reactive silica removal from synthetic solutions and the anodizing wastewater. Also, the reactive silica adsorption was higher at pH 9 as compared to that measured at pH 7 and the adsorbed quantity at pH 9 was 16.22 and 11.25 mg/g for the synthetic solution and anodizing wastewater, respectively. According to molecular simulation, the main interaction between Ferrolox and silica species was related to the formation of hydroxo-complexes and to the interaction of Fe with oxygen of silica species. Additionally, magnesium chloride was the best precipitating reagent for reactive silica achieving up to 87% removal. According to ANOVA analysis of Taguchi method, pH was the most influential factor during the precipitation of reactive silica with a variance value of 81.42, while values lower than 3 were obtained for the rest of parameters. Overall, the present work is reporting for the first time the removal of reactive silica from anodizing wastewaters with promising results that can be implemented at full scale for water reclamation, which may significantly contribute to manage water reservoir in the region sustainably.

Competitive adsorption of pollutants from anodizing wastewaters to promote water reuse.

Anodizing wastewater contains principally phosphate (PO43-) anions according to previous studies, but with the purpose to promote water reuse in this type of industry, a complete characterization of wastewater was made to remove other anions and cations also present in significant concentration. Particularly, the adsorption of sodium (Na+), potassium (K+), fluoride (F-), sulfate (SO42-) and phosphate (PO43-) was studied using different sorbents such as: coconut shell activated carbon, bone char, bituminous coal activated carbon, natural zeolite, silica, anionic and cationic exchange resins, a coated manganese-calcium zeolite, coconut shell activated carbon containing iron and iron hydroxide. All sorbents were characterized using FT-IR spectroscopy, potentiometric titration, nitrogen adsorption isotherms at 77 K, X-ray diffraction and SEM/EDX analysis to study the adsorption mechanism. The adsorption studies were performed in batch systems under constant agitation using both standard solutions of each ion and real anodizing wastewater. Results showed that, in general, the adsorption of all anions and cations is higher when mono-component standard solutions were used, since in the anodizing wastewater all species are competing for the active sites of the adsorbent. Na+ present in anodizing wastewater was efficiently adsorbed on coated manganese-calcium zeolite (20.55 mg/g) and natural zeolite (18.55 mg/g); while K+ was poorly adsorbed on all sorbents (less than 0.20 mg/g). Anions such as F-, SO42- and PO43-, were better adsorbed on the anionic resin (0.17, 45.38 and 2.92 mg/g, respectively), the iron hydroxide (0.14, 7.96 and 2.87 mg/g, respectively) and the bone char (0.34, 8.71 and 0.27 mg/g, respectively). All these results suggest that adsorption is a promising tertiary treatment method to achieve water reuse in the anodizing industry.

Adsorption of impurities from nickel-plating baths using commercial sorbents to reduce wastewater discharges.

The presence of moderate concentrations of impurities in the nickel-plating baths generates failures on the coated pieces. This situation entails the necessity of replacing the electroplating bath, which implies the generation of large volumes of wastewater with metallic species and high quantity of sludge. For this reason, the adsorption of the principal impurities of nickel-plating baths of an industry was analyzed in this work. Particularly, the removal of Zn2+ was studied in more detail since the presence of this metal in the baths generates black spots on the coated pieces. Different commercial materials were used as adsorbents and Zn2+ adsorption studies were carried out using both standard solutions and industrial water from the nickel-plating baths. All the adsorption tests were performed in batch systems under constant agitation and the quantification of the impurities was made by ICP-MS analysis. The bone char (BC) was an efficient adsorbent for the removal of the principal impurities of nickel-plating baths. The use of molecular simulation tools helped to understand the preferences of the hydroxyapatite (the principal component of bone char) for different metallic ions present in the industrial waters. According to both the experimental adsorption and molecular simulation results, hydroxyl and phosphate groups of bone char are responsible of the adsorption of impurities of nickel-plating baths.

Bone char with antibacterial properties for fluoride removal: Preparation, characterization and water treatment.

In the present work, it was established a new method for the preparation of bone chars with a double purpose, i.e., the removal of fluoride from water and the antibacterial character. These adsorbents were obtained by doping a commercial bone char with Ag using different reagents. The optimal conditions for the enrichment with silver were established by following the Taguchi method and using as response variable the removal of fluoride from water. Optimal bone chars were thus prepared and they were characterized using FT-IR spectroscopy, SEM/EDX analysis, adsorption isotherms of N2 at -196 °C and X-ray diffraction. All adsorbents were used in the removal of fluoride from water and the antibacterial character was assessed using the technique of total viable count employing standard solutions of Escherichia coli and drinking water. Results clearly indicated that doping of bone chars with silver provides with suitable antibacterial properties, however the fluoride adsorption capacity was not affected by the presence of Ag° on the carbon surface.

Efficient anaerobic treatment of synthetic textile wastewater in a UASB reactor with granular sludge enriched with humic acids supported on alumina nanoparticles.

A novel technique to co-immobilize humus-reducing microorganisms and humic substances (HS), supported on γ-Al2O3 nanoparticles (NP), by a granulation process in an upflow anaerobic sludge bed (UASB) reactor is reported in the present work. Larger granules (predominantly between 1 and 1.7 mm) were produced using NP coated with HS compared to those obtained with uncoated NP (mostly between 0.25 and 0.5 mm). The HS-enriched granular biomass was then tested for its capacity to achieve the reductive decolorization of the recalcitrant azo dye, reactive red 2 (RR2), in the same UASB reactor operated with a hydraulic residence time of 12 h and with glucose as electron donor. HS-enriched granules achieved higher decolorization and COD removal efficiencies, as compared to the control reactor operated in the absence of HS, in long term operation and applying high concentrations of RR2 (40-400 mg/L). This co-immobilizing technique could be attractive for its application in UASB reactors for the reductive biotransformation of several contaminants, such as nitroaromatics, poly-halogenated compounds, metalloids, among others.

Correlation between mesopore volume of carbon supports and the immobilization of laccase from Trametes versicolor for the decolorization of Acid Orange 7.

Immobilization of laccase from Trametes versicolor was carried out using carbon supports prepared from different lignocellulosic wastes. Enzymes were immobilized by physical adsorption. Taguchi methodology was selected for the design of experiments regarding the preparation of the carbon materials, which included the use of activating agents for the promotion of mesoporosity. A good correlation between the mesopore volumes of the carbon supports and the corresponding laccase loadings attained was observed. Specifically, the chemical activation of pecan nut shell with FeCl3 led to a highly mesoporous material that also behaved as the most efficient support for the immobilization of laccase. This particular laccase/carbon support system was used as biocatalyst for the decolorization of aqueous solutions containing Acid Orange 7. Mass spectrometry coupled to a liquid chromatograph allowed us to identify the products of the dye degradation.

Green and simple approach for low-cost bioproducts preparation and CO2 capture.

This study has demonstrated, for the first time, a simple, fast and flexible microwave processing method for the simultaneous preparation of bio-products (bio-oil, bio-gas and biochar) using a methodology that avoids any form of catalyst or chemical activation. The dielectric properties of biomass and physicochemical characterisation such as TGA, elemental and proximate analysis, XRD, SEM/EDX and textural properties, showed that 8 kJ g-1 of microwave energy can produce superior biochars for applications in CO2 capture. The maximum CO2 uptake capacity for biochar produced was 2.5 mmol g-1 and 2.0 mmol g-1 at 0 and 25 °C and 1 bar, which and also exhibited high gas selectivity compared with N2, fast kinetics of adsorption (<10 min) and desirable reusability (>95%) after 20 cycles. GC-MS analysis of generated bio-oil products revealed that higher microwave energies (>8 kJ g-1) significantly enhanced the amount of bio-oil produced (39%) and specifically the formation of levoglucosan, furfural and phenolics compounds, and bio-gas analysis identified trace levels of H2 and CH4. The results from this study confirm a green, inexpensive and efficient approach for biomass valorisation which can easily be embedded within bio-refinery process, and also demonstrates the potential of biochars for post-combustion CO2 uptake.

Graphene oxide triggers mass transfer limitations on the methanogenic activity of an anaerobic consortium with a particulate substrate.

Graphene oxide (GO) is an emerging nanomaterial widely used in many manufacturing applications, which is frequently discharged in many industrial effluents eventually reaching biological wastewater treatment systems (WWTS). Anaerobic WWTS are promising technologies for renewable energy production through biogas generation; however, the effects of GO on anaerobic digestion are poorly understood. Thus, it is of paramount relevance to generate more knowledge on these issues to prevent that anaerobic WWTS lose their effectiveness for the removal of pollutants and for biogas production. The aim of this work was to assess the effects of GO on the methanogenic activity of an anaerobic consortium using a particulate biopolymer (starch) and a readily fermentable soluble substrate (glucose) as electron donors. The obtained results revealed that the methanogenic activity of the anaerobic consortium supplemented with starch decreased up to 23-fold in the presence of GO compared to the control incubated in the absence of GO. In contrast, we observed a modest improvement on methane production (>10% compared to the control lacking GO) using 5 mg of GO L-1 in glucose-amended incubations. The decrease in the methanogenic activity is mainly explained by wrapping of starch granules by GO, which caused mass transfer limitation during the incubation. It is suggested that wrapping is driven by electrostatic interactions between negatively charged oxygenated groups in GO and positively charged hydroxyl groups in starch. These results imply that GO could seriously hamper the removal of particulate organic matter, such as starch, as well as methane production in anaerobic WWTS.

Removal of acid orange 7 by guava seed carbon: a four parameter optimization study.

The preparation of carbon from waste materials is a recent and economic alternative for the removal of dyes. In this study four samples of carbon were obtained by thermal treatment at 1000 degrees C using as precursor the guava seed with different particle sizes. The Taguchi method was applied as an experimental design to establish the optimum conditions for the removal of acid orange 7 in batch experiments. The chosen experimental factors and their ranges were: pH (2-12), temperature (15-35 degrees C), specific surface area (50-600 m(2)g(-1)) and adsorbent dosage (16-50 mg ml(-1)). The orthogonal array L(9) and the larger the better response category were selected to determine the optimum removal conditions: pH 2, temperature 15 degrees C, S(esp) 600 m(2)g(-1) and dosage 30 mg ml(-1). Under these conditions a total removal of acid orange 7 was achieved. Moreover, the most significant factors were the carbon specific surface area and the pH. The influence of the different factors on the adsorption of acid orange 7 from solution is explained in terms of electrostatic interactions by considering the dye species and the character of the surface.

Guava seed as an adsorbent and as a precursor of carbon for the adsorption of acid dyes.

The guava seed (SEGUVE) was characterized by ultimate and proximate analysis. In SEGUVE the principal thermal effect occurred at 363 degrees C and this can be attributed to the cellulose degradation, which was the main component ( approximately 61%). The guava seed has an acidic character with a high content of bulk functional groups (CO) and these characteristics were affected by carbonization. Two samples of carbon were prepared from the seeds at 600 and 1000 degrees C without chemical activation. Adsorption of eight acid dyes belonging to the monoazo and anthraquinone class was studied at 25 degrees C. The non-carbonized SEGUVE adsorbed the acid dyes more efficiently than SEGUVE-C600 and SEGUVE-C1000 although the specific surface of the raw material SEGUVE was low.

Performance of mango seed adsorbents in the adsorption of anthraquinone and azo acid dyes in single and binary aqueous solutions.

In this study the husk of mango seed and two carbonaceous adsorbents prepared from it were used to study the adsorption behavior of eight acid dyes. The adsorbed amount in mmol m(-2) decayed asymptotically as the molecular volume and area increased. The interaction between the studied dyes and the mesoporous carbon was governed by the ionic species in solution and the acidic/basic groups on the surface. Less than 50% of the external surface of the microporous carbon became covered with the dyes molecules, though monolayer formation demonstrating specific interactions only with active sites on the surface and the adsorption magnitudes correlated with the shape parameter of the molecule within a particular dye group. The adsorption behavior in mixtures was determined by the molecular volume of the constituents; the greater the molecular volume difference, the greater the effect on the adsorbed amount. We also demonstrated that the raw husk of the mango seed can be used to remove up to 50% from model 50 mg l(-1) solutions of the studied acid dyes.