Treatment of Wastewater by Nanofiltration

In recent years, some countries have implemented regulations governing aqueous discharges. With a view to sustainable development, manufacturers are looking for wastewater treatment technologies to control their discharges. Nanofiltration seems particularly suitable for the separation characteristics that it allows with regard to the size of the target molecules. Pollution by rare earths and heavy metals affects groundwater and surface water. This changed the quality of the water and made it unsafe to use. Water pollution is a big problem, given the diversity of sources and characteristics of polluting species, the main ones being industrial, urban and agricultural discharges, generated by human activity. The great difficulty being that heavy metals are not biodegradable and tend to accumulate in living organisms (fish, mollusks, vegetables, etc.) consumed by humans. For these concerns, environmental laws have become more severe. For this, the treatment of aqueous effluents has become important. It can be concluded that separation and purification chemistry is an area of topical research. The discharges coming from the industry contain heavy metals (chromium, copper, zinc, nickel, iron, cobalt, cadmium, lead, …) which are harmful for the human health, the fauna and flora. It is necessary to be well controlled. This chapter presents a study of nanofiltration for industrial wastewater treatment.

Application of the Zimm-Bragg Model to the Removal of Azo Dyes with Pectin

In this work, the ability of pectin (Pec) to remove direct red 80 (DR80), Congo red (CR), methyl orange (MO), and methyl red (MR) was studied. The removal percentages under adequate pH and ionic strength conditions were as follows: DR80 (99.5%), CR (99.8%), MO (88.6%), and MR (68%), showing that this methodology is efficient to remove azo dyes. The proposed method included the addition of native Pec to the dye aqueous solution and the formation of a gel that occurred when a calcium salt solution was added. This gel retains the molecules adsorbed onto the molecular surface of Pec through hydrogen bonds and electrostatic and hydrophobic interactions. To our knowledge, it is the first time that the Zimm-Bragg model is used to describe the removal of azo dyes with native Pec. This model includes two parameters: K u (nucleation constant), which is related to the tendency exerted by a dye molecule attached to the Pec to bind to other molecules present in the aqueous phase, and U (cooperativity parameter), which determines the aggregation capacity of the dye molecules already attached to the Pec. This model fits the experimental isotherms very well, suggesting that Pec binds single molecules and dye aggregates. The obtained results in the values of K u ranged from 922 mol/kg (MR) to 1,157,462 mol/kg (CR), and U varied from 2.51 (MR) to 169.19 (MO). These results suggest that the use of Pec is a viable option to remove azo dyes from aqueous effluents and that the Zimm-Bragg model fits adequately the isotherms of dyes that have a high tendency to form aggregates.

Remediation of Diethyl Phthalate in Aqueous Effluents with TiO2-Supported Rh0 Nanoparticles as Multicatalytic Materials

An innovative “domino” process, based on an arene hydrogenation followed by a photocatalytic step, was designed for the remediation of endocrine disrupting compounds, in highly concentrated aqueous effluents. The novelty relies on the use of TiO2-supported zerovalent Rh nanoparticles as multicatalytic materials (MCMs) for this two-step treatment, applied on diethyl phthalate, which is a model aromatic pollutant frequently present in aquatic environments. This nanocomposite advanced material, which was easily prepared by a green, wet impregnation methodology, proved to be active in the successive reactions, the reduction in the aromatic ring, and the photodegradation step. This sustainable approach offers promising alternatives in the case of photoresistive compounds.

Study of the effect of the LDH cations precursors in the removal of arsenic in aqueous solution

Layered double hydroxides (LDH) are anionic clays, mainly used as adsorbents, ion exchange material, and catalysts. Generally, they present high specific surface areas, alkaline character, high metallic dispersion, and high thermal stability. If they contain a transitional element in their structure, the solid may present redox properties. LDH were synthesized with the following combinations: MgAl, MgFe, and ZnMgFe, aiming to determine the effect of cationic nature in the structure and the functionality of the synthesized clay as adsorbents in polluted aqueous effluents. The textural properties were determined by nitrogen adsorption isotherms. Crystalline structure was studied by XRD and the presence of the anions of the interlayer was determined by FTIR spectroscopy. The studies of removal of As(III) and As(V) from aqueous solutions, using the LDH, show that after 24 h the solids reach a high removal efficiency. ZnMgFe solid removed both species of arsenic with values of 95 and 98% for As(II) and As(V), respectively. The MgFe solid showed some selectivity to the uptake of As(V), while the MgAl only removed As(V). This selective behaviour can be beneficial in studies of arsenic speciation.

Adsorption Studies of Volatile Organic Compound (Naphthalene) from Aqueous Effluents: Chemical Activation Process Using Weak Lewis Acid, Equilibrium Kinetics and Isotherm Modelling

This study deals with the preparation of activated carbon (CDSP) from date seed powder (DSP) by chemical activation to eliminate polyaromatic hydrocarbon—PAHs (naphthalene—C10H8) from synthetic wastewater. The chemical activation process was carried out using a weak Lewis acid of zinc acetate dihydrate salt (Zn(CH3CO2)2·2H2O). The equilibrium isotherm and kinetics analysis was carried out using DSP and CDSP samples, and their performances were compared for the removal of a volatile organic compound—naphthalene (C10H8)—from synthetic aqueous effluents or wastewater. The equilibrium isotherm data was analyzed using the linear regression model of the Langmuir, Freundlich and Temkin equations. The R2 values for the Langmuir isotherm were 0.93 and 0.99 for naphthalene (C10H8) adsorption using DSP and CDSP, respectively. CDSP showed a higher equilibrium sorption capacity (qe) of 379.64 µg/g. DSP had an equilibrium sorption capacity of 369.06 µg/g for C10H8. The rate of reaction was estimated for C10H8 adsorption using a pseudo-first order, pseudo-second order and Elovich kinetic equation. The reaction mechanism for both the sorbents (CDSP and DSP) was studied using the intraparticle diffusion model. The equilibrium data was well-fitted with the pseudo-second order kinetics model showing the chemisorption nature of the equilibrium system. CDSP showed a higher sorption performance than DSP due to its higher BET surface area and carbon content. Physiochemical characterizations of the DSP and CDSP samples were carried out using the BET surface area analysis, Fourier-scanning microscopic analysis (FSEM), energy-dispersive X-ray (EDX) analysis and Fourier-transform spectroscopic analysis (FTIR). A thermogravimetric and ultimate analysis was also carried out to determine the carbon content in both the sorbents (DSP and CDSP) here. This study confirms the potential of DSP and CDSP to remove C10H8 from lab-scale synthetic wastewater.