R. Ibáñez

State of the art and review on the treatment technologies of water reverse osmosis concentrates.

The growing demand for fresh water is partially satisfied by desalination plants that increasingly use membrane technologies and among them reverse osmosis to produce purified water. Operating with water recoveries from 35% to 85% RO plants generate huge volumes of concentrates containing all the retained compounds that are commonly discharged to water bodies and constitute a potentially serious threat to marine ecosystems; therefore there is an urgent need for environmentally friendly management options of RO brines. This paper gives an overview on the potential treatments to overcome the environmental problems associated to the direct discharge of RO concentrates. The treatment options have been classified according to the source of RO concentrates and the maturity of the technologies. For the sake of clarity three different sources of RO concentrates are differentiated i) desalination plants, ii) tertiary processes in WWTP, and iii) mining industries. Starting with traditional treatments such as evaporation and crystallization other technologies that have emerged in last years to reduce the volume of the concentrate before disposal and with the objective of achieving zero liquid discharge and recovery of valuable compounds from these effluents are also reviewed. Most of these emerging technologies have been developed at laboratory or pilot plant scale (see Table 1). With regard to RO concentrates from WWTP, the manuscript addresses recent studies that are mainly focused on reducing the organic pollutant load through the application of innovative advanced oxidation technologies. Finally, works that report the treatment of RO concentrates from industrial sources are analyzed as well.

Kinetics of electro-oxidation of ammonia-N, nitrites and COD from a recirculating aquaculture saline water system using BDD anodes

The viability of the electro-oxidation technology provided with boron doped diamond (BDD) electrodes for the treatment and reuse of the seawater used in a Recirculating Aquaculture System (RAS) was evaluated in this work. The influence of the applied current density (5-50 A m(-2)) in the removal of Total Ammonia Nitrogen (TAN), nitrite and chemical oxygen demand (COD) was analyzed observing that complete TAN removal together with important reductions of the other considered contaminants could be achieved, thus meeting the requirements for reuse of seawater in RAS systems. TAN removal, mainly due to an indirect oxidation mechanism was described by a second order kinetics while COD and nitrite removal followed zero-th order kinetics. The values of the kinetic constants for the anodic oxidation of each compound were obtained as a function of the applied current density (k(TAN) = 7.86 × 10(-5) · exp(6.30 × 10(-2) J); kNO2 = 3.43 × 10(-2) J; k(COD) = 1.35 × 10(-2) J). The formation of free chlorine and oxidation by-products, i.e., trihalomethanes (THMs) was followed along the electro-oxidation process. Although a maximum concentration of 1.7 mg l(-1) of total trihalomethanes was detected an integrated process combining electrochemical oxidation in order to eliminate TAN, nitrite and COD and adsorption onto activated carbon to remove the residual chlorine and THMs is proposed, as an efficient alternative to treat and reuse the seawater in fish culture systems. Finally, the energy consumption of the treatment has been evaluated.

Assessment of the formation of inorganic oxidation by-products during the electrocatalytic treatment of ammonium from landfill leachates

This work investigates the formation of oxidation by-products during the electrochemical removal of ammonium using BDD electrodes from wastewaters containing chlorides. The influence of the initial chloride concentration has been experimentally analyzed first, working with model solutions with variable ammonium concentration and second, with municipal landfill leachates. Two different levels of chloride concentration were studied, i) low chloride concentrations ranging between 0 and 2000 mg/L and, ii) high chloride concentrations ranging between 5000 and 20,000 mg/L. Ammonium removal took place mainly via indirect oxidation leading to the formation of nitrogen gas and nitrate as the main oxidation products; at high chloride concentration the formation of nitrogen gas and the rate of ammonium removal were both favored. However, chloride was also oxidized during the electrochemical treatment leading to the formation of free chlorine responsible of the ammonium oxidation, together with undesirable products such as chloramines, chlorate and perchlorate. Chloramines appeared during the treatment but they reached a maximum and then started decreasing, being totally removed when high chloride concentrations were used. With regard to the formation of chlorate and perchlorate once again the concentration of chloride exerted a strong influence on the formation kinetics of the oxidation by-products and whereas at low chloride concentrations, chlorate appeared like an intermediate compound leading to the formation of perchlorate, at high chloride concentrations chlorate formation was delayed significantly and perchlorate was not detected during the experimental time. Thus this work contributes first to the knowledge of the potential hazards of applying the electro-oxidation technology as an environmental technology to deal with ammonium oxidation under the presence of chloride and second it reports efficient conditions that minimize or even avoid the formation of undesirable by-products.

Characterisation and management of incinerator wastes

Management of municipal and hospital wastes by means of incineration processes generates solid residues, such as bottom and fly ashes and air pollution control residues with high content of heavy metals, inorganic salts and other organic compounds. Characterisation of 24 ash samples, collected from four municipal solid waste incinerators (MSWI) and six hospital medical waste incinerators (HMWI) located in the Basque Country Region (Northern Spain), were carried out at the request of Spanish Regulations and European Economic Community guidelines. The ecotoxicity values, EC(50), of the TCLP leachates show a high variability ranging from 12,967 to 1,000,000mgl(-1) in MSWI samples and from 2917 to 333,150mgl(-1) in HMWI samples. Results from chemical characterisation of DIN 38414-S4 leachates show a high concentration of lead, sulphate and chloride in MSWI samples and chromium in HMWI samples.

Assessment of soil pollution based on total petroleum hydrocarbons and individual oil substances

Different oil products like gasoline, diesel or heavy oils can cause soil contamination. The assessment of soils exposed to oil products can be conducted through the comparison between a measured concentration and an intervention value (IV). Several national policies include the IV based on the so called total petroleum hydrocarbons (TPH) measure. However, the TPH assessment does not indicate the individual substances that may produce contamination. The soil quality assessment can be improved by including common hazardous compounds as polycyclic aromatic hydrocarbons (PAHs) and aromatic volatile hydrocarbons like benzene, toluene, ethylbenzene and xylenes (BTEX). This study, focused on 62 samples collected from different sites throughout The Netherlands, evaluates TPH, PAH and BTEX concentrations in soils. Several indices of pollution are defined for the assessment of individual variables (TPH, PAH, B, T, E, and X) and multivariables (MV, BTEX), allowing us to group the pollutants and simplify the methodology. TPH and PAH concentrations above the IV are mainly found in medium and heavy oil products such as diesel and heavy oil. On the other hand, unacceptable BTEX concentrations are reached in soils contaminated with gasoline and kerosene. The TPH assessment suggests the need for further action to include lighter products. The application of multivariable indices allows us to include these products in the soil quality assessment without changing the IV for TPH. This work provides useful information about the soil quality assessment methodology of oil products in soils, focussing the analysis into the substances that mainly cause the risk.

Experimental study of the waste binder anhydrite in the solidification/ stabilization process of heavy metal sludges

Abstract An experimental study of the use of an industrial byproduct, anhydrite (CaSO 4 ), as inorganic binder in the solidification/stabilization (S/S) process of heavy metal sludges has been performed. The influence of the variables: binder:waste ratio, anhydrite particle size and water amount on the S/S process of a synthetic sludge containing Cd, Cr and Pb has been studied. Leaching of stabilized products using the Toxicity Characterization Leaching Procedure was used to evaluate the behaviour of heavy metals after treatment with anhydrite. Significant reductions of leached metal concentrations were achieved depending on the experimental variables. Therefore, it has been shown the possibility to use anhydrite as binder in S/S processes of wastes containing heavy metals and the influence of the main variables in the S/S process, in order to satisfy landfill disposal regulations.

Electrochemical disinfection of secondary wastewater treatment plant (WWTP) effluent.

In this work the electrochemical disinfection of the effluent of a secondary wastewater treatment plant is investigated. In the experimental work, performed on-site with real effluents of the WWTP located in Vuelta Ostrera (Cantabria, Spain), boron-doped diamond (BDD) electrodes were employed. The initial concentration of E. coli in the effluent of the WWTP varied in the range 1.3 x 10⁴-5.2 x 10⁵ cfu/mL. The influence of two operation variables on the kinetics of E. coli deactivation was investigated: i) The applied current density was varied in the range J=40-120 mA/cm², showing first order kinetics, and linear dependency of the apparent kinetic constant with the applied current density; and ii) the chloride concentration was varied in the range 60-1,050 mg/L, showing that increasing chloride content also enhanced the kinetics of the E. coli deactivation. The latter parameter is particularly important in coastal areas, as in the case of the present study. The formation of disinfection by-products (DBPs) was followed by measuring the content of trihalomethanes (THMs) that nevertheless was maintained below 100 μg/L, so it can be concluded that the formation of DBPs is not a disadvantage of electrochemical disinfection of secondary effluents of WWTP.

Characterization of metal finishing sludges: influence of the pH

Metal finishing sludges are classified as metal hydroxide hazardous wastes due to the heavy metal release to the environment. This release, commonly determined by compliance lixiviation tests based on the equilibrium conditions at the end of the leaching experiment, is mainly dependent on the pH of the solution. In this work, the leaching behaviour of Cd, Cr, Cu, Fe, Ni, Pb and Zn, of the 32 metal finishing sludges coming from 16 European industrial facilities, and using the distilled water compliance test DIN 38414-S4, have been studied. The concentrations of chromium and copper in the leachates do not follow the solubility evolution of their hydroxide with the pH. The simple assumption of a heavy metal concentration in the leachate directly related to the solubility of the hydroxide is not in good agreement with the experimental results of the distilled water leaching test, probably due to the presence of different species, which can contribute to the metal mobility depending on the sludge composition. An experimental evaluation of the easily available amount of metals in real wastes seems to be necessary for disposal assessment. This paper contains valuable information, from orderly handling metal finishing wastes to the statistical studies of production and management of wastes suggested recently by the Commission of the European Community.

Pervaporation Technology for the Dehydration of Solvents and Raw Materials in the Process Industry

Pervaporation (PV) is a membrane process used to separate liquid mixtures. In the dehydration application, water is removed from its mixtures with organic components by selective permeation through a dense hydrophilic membrane. The most relevant application of PV is the separation of liquid azeotropes and close boiling point solvent-water mixtures. In the present article, the research work developed in the field of hydrophilic pervaporation by the Advanced Separation Processes group of the University of Cantabria (Spain) will be reviewed. Special attention will be devoted to the applications related to the recovery by dehydration of organic solvents employed in different industrial processes. A brief description of the theoretical background and design basis of hydrophilic pervaporation will be followed by the presentation of a series of case studies: (i) Valorization of an industrial ketonic waste; (ii) recovery of tetrahydrofuran; (iii) isopropanol recovery from a pharmaceutical waste stream; and (iv) drying of cyclohexane in the chemical manufacturing of synthetic rubbers.

Modeling of pervaporation processes controlled by concentration polarization

Pervaporation is considered a clean and energetically efficient process used for a wide range of applications, working separately or integrated into a hybrid process. In this work, a mathematical model has been developed accounting for the mass transport phenomena under non-isothermal conditions with strong contribution of polarization concentration that prevail in pervaporation systems. The mathematical model incorporates characteristics of the module geometry, mass and heat transfer correlations and estimation of the system physicochemical properties. The equation-oriented simulation software g-PROMS® was used in the solution of the final problem. Finally, the model was tested against a representative case study, pervaporative dehydration of cyclohexane, the solvent used in the manufacture of synthetic rubber. Model simulated curves described satisfactorily well the kinetic data of cyclohexane dehydration obtained in a pilot plant set-up.