Danae Doulia

Adsorption of humic acid on acid-activated Greek bentonite.

The adsorption of humic acid on bentonite from Milos Island (Greece) acid-treated with dilute H(2)SO(4) solutions over a concentration range between 0.25 and 13M has been studied. Bentonite activated with 3M sulfuric acid (AAS) showed a higher efficiency in removing humic acid from aqueous solutions and was selected for further investigation. The specific surface area of acid-activated bentonite was estimated using the methylene blue adsorption method. The morphology of untreated, activated, and HA-sorbed bentonite was studied under scanning electron microscope (SEM). The effects of contact time, adsorbate concentration, adsorbent dose, and temperature on the adsorption of humic acid onto bentonite activated with 3M H(2)SO(4) were studied using a batch adsorption technique. Acidic pH and high ionic strength proved to be favorable for the adsorption efficiency. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to describe the kinetic data and the rate constants were evaluated. The experimental isotherm data were analyzed using Langmuir, Freundlich, and Temkin equations and the isotherm constants were determined. Thermodynamic parameters (DeltaH(o), DeltaS(o), and DeltaG(o)) of adsorption of humic acid onto acid-activated bentonite with 3M sulfuric acid were also evaluated.

Adsorption of Pesticides on Carbonaceous and Polymeric Materials from Aqueous Solutions: A Review

Abstract Carbonaceous and polymeric materials have been extensively used in adsorption processes for the removal of pesticides from aqueous solutions. The aim of this review is the systematic and comparative presentation of the possibilities of the above adsorbents, arising from the data reported in the literature for the period 1990–2004. A brief description of each article is given in tables. The data is divided into two groups, based on the chemical structure of adsorbent (carbonaceous or polymeric material) and is given in tables. In each table information on the type of adsorbent (powder, granular, fibers, cloths, resins, cartridges etc), pesticide structure, experimental conditions, aim and results of each work, is reported. In addition, data is included concerning single pesticides adsorption, competitive adsorption, parameters of adsorption isotherms (Langmuir, Freundlich, Dubinin–Radushkevich) and kinetic models parameters (homogeneous surface diffusion model‐HSDM, equivalent background compound‐EBC, Peel model), such as surface diffusion coefficients and mass transfer coefficients. Information on adsorption yields, effect of various factors on adsorption effectiveness, static or continuous operation, laboratory, pilot or industrial scale process and combination of adsorption with other methods, is also included.

Polymeric Ultrafiltration Membranes and Surfactants

Surfactants have been extensively used in ultrafiltration processes such as membrane cleaning,removal of surfactants or other organic toxic compounds and metal ions from solutions and estimation of interactions at surfactant and membrane interface. The aim of this review is to present the possibilities that arise from the data reported in the literature on the field of ultrafiltration (UF) membranes and surfactants. This data is classified into five groups and a brief description of each article is given. Pretreatment of membranes with surfactant solutions can lead to performance increase of UF process. By Micellar‐Enhanced Ultrafiltration the separation of low molecular weight toxic substances and heavy metals is possible, extending the applications of conventional UF (e.g. separation of proteins). Through estimation of the type of interactions on membrane surface with surfactants the prediction of retention and removal of small size substances, the prevention of fouling, the modification of surfactant‐membrane system, the design of new surfactant‐membrane system could be achieved. Finally economical aspects of UF‐surfactant processes are given.

Adsorption of Pesticides on Resins

The objective of this work was to assess the capability of organic hydrophobic polymeric resins Amberlite XAD‐4 and XAD‐7 to remove the pesticides alachlor and amitrole from water. The pesticides adsorption on the two different adsorbents was measured by batch equilibrium technique and isotherm types and parameters were estimated. Two theoretical models were applied based on a Freundlich and a Langmuir isotherms. The effect of pesticides chemical composition and structure as well as the nature of solid surface on the efficiency of adsorption was evaluated. The influence of pH also was studied. In low pH solutions adsorption of amitrole was higher upon the nonionic aliphatic acrylic ester copolymer XAD‐7 in comparison to the nonionic, crosslinked macroreticular copolymer of styrene divinylbenzene XAD‐4. In neutral and intermediate pH solutions the polar acrylic ester copolymer XAD‐7 was more effective to the retention of alachlor. The acrylic ester copolymer showed at pH 3 the lower effectiveness in alachlor removal from water. The data of the adsorption isotherms of pesticides upon the examined polymeric resins seemed to conform to both the Freundlich and the Langmuir isotherm models.

Removal of amino acids from water by adsorption on polystyrene resins

The adsorption of eight amino acids, L-asparagine, D,L-threonine, L-lysine, L-leucine D,L-methionine, L-tyrosine, L-phenylalanine and D,L-tryptophan, on the non-polar macroporous adsorbents Amberlite XAD-2 and XAD-4 (polystyrene–divinylbenzene copolymers) was studied. Equilibrium adsorption experiments were conducted to estimate the types of isotherm and their parameters. The effect the chemical composition and structure of the amino acids on the efficiency of adsorption was evaluated. The influence of pH and ionic strength was also studied. The data of adsorption isotherms of the examined amino acids seemed generally to approach the Freundlich isotherm model. Tryptophan isotherm adsorption data could match in some cases the Langmuir model. The majority of the adsorption isotherms were almost linear. In terms of adsorbed amino acid on both resin surfaces, the amino acids can be ranked thus: D,L-tryptophan > L-phenylalanine > D,L-methionine, L-tyrosine > L-leucine > L-lysine > D,L-threonine > L-asparagine. In low pH solution, adsorption was generally higher than that at intermediate and high pH values. Generally, as the ionic strength increases, the adsorption of the amino acids increases. © 2001 Society of Chemical Industry

Effect of ionic strength and pH on the adsorption of selected herbicides on Amberlite

The effect of ionic strength on the adsorption of alachlor, trifluralin, and prometryn on Amberlite XAD-4 polymeric resin is studied. Static adsorption experiments are carried out at pH 3–6.5 and ionic strength 0.01–2 M at 20°C. By increasing the ionic strength, the adsorption of herbicides can be significantly increased. The electrolyte addition affects both the effectiveness and efficiency of adsorption, leading eventually to a saturation of the resin surface. An explanation of the alteration of adsorption mechanisms, caused by ionic strength, is given, based mainly on the reduction in repulsive forces at the resin–herbicide interface and between adsorbing herbicide molecules, since both resin and herbicides have a polar ring as part of their structure.

Removal of atrazine from water by use of nonionic polymeric resins

Abstract The objective of this work was to assess the capability of organic hydrophobic polymeric resins Amberlite XAD‐2, ‐4, and ‐XAD‐7 to remove atrazine from water. The atrazine adsorption on the three different adsorbents was measured by batch equilibrium technique and isotherm types and parameters were estimated. Two theoretical models were applied based on a Freundlich and a Langmuir isotherms. The effect of atrazine chemical composition and structure as well as the nature of solid surface on the efficiency of adsorption was evaluated. The influence of pH and ionic strength also was studied. Retention changes in the order XAD‐7> XAD‐4 > XAD‐2 in intermediate and high pH solutions and in the order XAD‐4> XAD‐7> XAD‐2 in low pH solutions. The more polar Amberlite XAD‐7 was proved the more effective for atrazine removal from water. Generally, as the ionic strength increases, the adsorption of atrazine decreases.

Pseudomonas, Pantoea and Cupriavidus isolates induce calcium carbonate precipitation for biorestoration of ornamental stone

Bacterially induced calcium carbonate precipitation from various isolates was investigated aiming at developing an environmentally friendly technique for ornamental stone protection and restoration.

Adsorption of Cationic Dyes onto Bentonite

The removal of dyes from wastewater effluents is a challenging issue in environmental engineering. Among the techniques employed, adsorption technology is generally considered highly efficient and industrial bentonite clay has been extensively used for this purpose. The aim of this study is the systematic and comparative presentation of the available information on the adsorption of cationic dyes from aqueous solution onto raw or modified bentonites. The review outlines the bentonite modification methods and presents a list of isotherm and kinetic models used for the interpretation of adsorption. A brief description of each article and information on the type and the characteristics of the adsorbent are given in tables. In addition, data is included concerning single and competitive adsorption of basic dyes on bentonite. Experimental conditions are outlined and the kinetic and isotherm parameter values of proposed models are listed in tables. The effect of various factors on the adsorption efficiency is discussed and the most important aspects referring to adsorption thermodynamics are reviewed.

Multiparametric investigation of mould‐free shelf life of bread via factorial design

Abstract The investigation of a complex process, such as the bread making process, can be greatly favored by the approach of statistical design of experiments. Using simple first order factorial designs, reliable models were constructed investigating the effects of salt, sugar, sorbic acid, calcium propionate, vegetable fibers, fat and emulsifier on the shelf life of bread (optimization parameter). These effects were in general linear. An exception was observed in the case of use of calcium propionate where an interaction between salt and sugar was determined. The effects of all significant factors on optimization parameter were reasonable. Sorbic acid and calcium propionate proved to be more effective preservatives than salt and sugar by an order of magnitude. Antifungal efficiency of sorbic acid was found to be about three times that of calcium propionate. Prolongation of shelf life reached 117% for sorbic acid and 63 % for calcium propionate, when salt and sugar were fixed to their basic levels. Vegetable fibers had a detrimental effect on shelf life greatly decreasing it by as much as 65 % of the control samples (without fibers). Addition of fat and emulsifier in the dough showed a slightly negative effect on the mould‐free shelf life of bread.