Ana I. Leal

The role of hydroxyl radicals for the decomposition of p-hydroxy phenylacetic acid in aqueous solutions.

The chemical decomposition of p-hydroxyphenylacetic acid, a priority phenolic pollutant present in wastewaters from some agro-industrial plants, is studied by means of a single photochemical process produced by a polychromatic UV radiation and by hydroxyl radicals generated by the combination of UV radiation plus hydrogen peroxide and by the Fentons reagent (hydrogen peroxide plus ferrous salts). Batch experiments were conducted to establish the degradation levels obtained and the quantum yields in the single photodecomposition process. An improvement in the decomposition of the phenolic acid in the combined UV/H2O2 oxidation is observed, due to the generation of OH radicals, and the contribution of the radical reaction to the global process is determined. In the Fentons reagent oxidation, the effects of the operating variables (H2O2 and Fe2+ initial concentrations, pH, type of buffer used) are established and the rate constant for the reaction of p-hydroxyphenylacetic acid with OH radicals is evaluated from a kinetic model, its value being 7.02 x 10(8) M-1 s-1 at 20 degrees C.

Membrane filtration technologies applied to municipal secondary effluents for potential reuse.

Four UF membranes (denoted GH, GK, PT and PW with MWCO of 1000, 2000, 5000 and 20,000Da, respectively) and four NF membranes (denoted DL, CK, DK and HL, with an approximate MWCO of 150-300Da in all cases) were used for the filtration of an effluent generated in a municipal wastewater plant after a secondary treatment. The influence of the most important operating variables (nature and MWCO of the membranes, transmembrane pressure, tangential velocity, and temperature) on the permeate flux was widely discussed, and the resistances to the permeate flux were determined following the resistances in series model. Rejection coefficients for parameters that measure the global pollutant content of the effluent (chemical oxygen demand, total organic carbon, absorbance at 254nm, turbidity, total nitrogen and total phosphorus) were also evaluated, and the results revealed that both UF and NF are feasible options for the treatment of this effluent, yielding a permeate stream that can be reused in several applications. Finally, 28 pharmaceutical compounds were initially detected in this effluent, and their respective rejection coefficients were determined, with eliminations higher than 75% in the case of NF with the HL membrane. Therefore, it is concluded that NF is an excellent option for the removal of toxic pharmaceuticals in municipal wastewaters.

The use of ultrafiltration and nanofiltration membranes for the purification of cork processing wastewater

Filtration experiments in batch concentration mode (with recycling of the retentate stream) of the cork processing wastewater were performed in laboratory filtration membrane equipment, by using four commercial membranes: two UF membranes with MWCO of 20,000 and 5000 Da, and two NF membranes with an approximate MWCO of 150-300 Da. The filtration experiments of the selected wastewater were performed by modifying the most important operating variables: transmembrane pressure, tangential velocity, temperature, and the nature and MWCO of the membranes. The evolution of the cumulative permeate volumes and permeate fluxes with processing time were analysed, and it was established that the steady-state permeate flux was reached for a volume retention factor of 2. The effect of the mentioned operating conditions on this steady-state permeate flux was discussed. The effectiveness of the filtration treatments was determined by the evaluation of the rejection coefficients for several parameters, which measure the global pollutant content of the effluent: COD, absorbance at 254 nm, tannic content, color, and ellagic acid. Finally, the resistances in series model was used for the evaluation of the resistances to the permeate flux, and it was concluded that the contribution to the total resistance of the fouling resistance (combined external plus internal) was higher than the inherent resistance of the clean membrane.

Purification of cork processing wastewaters by ozone, by activated sludge, and by their two sequential applications.

Wastewaters generated in the cork processing industry were treated in continuous reactors by means of single treatments separately-a chemical ozonation and an activated sludge system-and then by both sequential processes-ozonation followed by aerobic degradation, and aerobic degradation followed by ozonation. The removals obtained in the ozonation alone were 12-54%, 65-81%, and 55-89% for the COD, total phenolics, and absorbance at 254 nm, respectively, while the consumed ozone yield ranged from 40% to 61%, and the biodegradability (BOD(5)/COD) varied from an initial 0.60 to final values between 0.68 and 0.93. The optimum hydraulic retention time and ozone partial pressure were 3 h and 3 kPa, respectively. The stoichiometric ratio was 0.56 g of organic substrate degraded per g of ozone consumed, while the rate constants obtained for the ozone disappearance and for the organic matter degradation were 4490 L g COD(-1) h(-1) and 1970 L g O(3)(-1)h(-1) respectively. The presence of hydrogen peroxide or UV radiation in addition to ozone increased the values of organic matter removal as well as the stoichiometric ratio and the rate constants. The aerobic treatment by the activated sludge system yielded COD removals between 13% and 37% for hydraulic retention times between 24 and 96 h, and the Contois model gave values of q(max)=0.14 g COD g VSS(-1)h(-1) and K(1)=22.6 g COD g VSS(-1) for the main kinetic parameters. The sequential processes increased the substrate removal efficiencies in comparison with the individual processes. These enhancements were greater in the aerobic degradation-ozonation sequence than in the ozonation-aerobic degradation sequence.

Removal of phenolic compounds in water by ultrafiltration membrane treatments

The ultrafiltration (UF) of aqueous solutions containing mixtures of three phenolic compounds (gallic acid, acetovanillone, and esculetin) was studied in a tangential UF laboratory system. These substances were selected as model pollutants present in the tannic fraction of the cork processing wastewaters. The two membranes used were a polyethersulfone membrane (Biomax5KTM) and a regenerated cellulose membrane (Ultracel5KTM), both with a molecular weight cut-off (MWCO) of 5000 Da. Previous experiments for the characterization of the membranes led to values for the water hydraulic permeability of 70.3 and 18.1 L/h · m2 · bar for the Biomax5K and Ultracel5K membranes, respectively. During the UF experiments, the permeate flow rate remained almost constant with processing time and the evolution of the pollutants concentrations varied depending on the nature of the membranes and the substances. The influence of the main operating variables (tansmembrane pressure and feed flow rate) on the permeate flux was established, and values for the apparent and intrinsic rejection coefficients were evaluated. Cork processing wastewater UF experiments were also conducted under similar operating conditions to those applied to the ultrapure water solutions. Removals of chemical oxygen demand, aromatic and tannic contents, and color were determined in these experiments, and the elimination of the three model compounds in the wastewater was also followed, with the evaluation of their apparent rejection coefficients.

Oxidation of Acetovanillone by Photochemical Processes and Hydroxyl Radicals

Acetovanillone [Ethanone, 1-(4-hydroxy-3-metoxyphenyl)] is one of the major pollutants that is present in the wastewater produced during the boiling of raw material in the cork industry. The oxidation of its aqueous solutions by monochromatic UV radiation alone and combined with hydrogen peroxide, Fentons reagent and the photo-Fenton system has been investigated. In the single UV radiation process, the apparent rate constants and the quantum yields are determined, and in the UV/H2O2combination, the additional efficiency in the oxidation process due to the presence of hydrogen peroxide is established. The influence of some operating variables, such as initial concentrations of H2O2 and Fe(II), as well as the pH, is discussed in the Fenton and photo-Fenton systems, and the partial contribution of the radical pathways to the global oxidation rates are evaluated. The rate constant for the reaction of acetovanillone with hydroxyl radicals is also determined by means of a competition kinetics model, its value being 5.62× 109 M−1s−1. Finally, chemical oxidation experiments of wastewaters generated in this industry were carried out by using the same advanced oxidation processes. Specifically, the elimination of acetovanillone in these effluents was determined, and the removal of the global organic pollutant content was also evaluated.

Purification of storage brines from the preservation of table olives

The chemical oxidation of the wastewaters generated during storage of table olives in NaCl brines, prior to their manufacturing process, was studied. Ozone alone produced COD removals in the range 14-23%, and a higher average removal of 73% of the aromatic compounds. The additional presence of hydrogen peroxide and UV radiation increased these values to 39% for COD and 86% for aromatics. However, UV radiation alone only gave a removal of 9% for COD and 27% for aromatics, and the additional presence of 0.5M H(2)O(2) led to 13% for COD and 38% for aromatics, respectively. The Fentons reagent oxidation achieved a COD removal of 24% for the higher concentrations of Fe(2+) and H(2)O(2). The most effective process was the combination O(3)/UV/H(2)O(2) with total removals of 65 and 92% for the COD and aromatics, respectively. The aerobic treatment of these effluents gave a 66% removal regardless of the initial biomass concentration used, and a rate constant of 0.19 per day was obtained for the process by using the Contois model. Finally, the aerobic treatment of the wastewaters previously ozonated alone, and ozonated with UV radiation, gave increases in the COD removal and a final rate constant of 0.44 per day. The enhancements were due to the chemical oxidations, these procedures being suitable technologies as pre-treatments to subsequent biological processes for the purification of these residues.

Oxidation of Esculetin, a Model Pollutant Present in Cork Processing Wastewaters, by Chemical Methods

The ozonation of esculetin (6,7-dihydroxycoumarin), a major pollutant present in the wastewater generated in the cork industry, was accelerated at high pH, with apparent second-order rate constants in the range from 3.3 × 104 L/(mol·s) at pH=2 to 8.4 × 107 L/(mol·s) at pH=9. The acid-base equilibrium of esculetin was studied, resulting in a pKa value of 7.37. Taking into account this pKa, the rate constants for the reaction between ozone and the un dissociated and dissociated forms of esculetin were 3.0 × 104 and L/(mol·s) 6.67 × 108 L/(mol·s), respectively. Apparent first-order rate constants for the photolysis by UV irradiation were also evaluated, with values between 0.12 × 10−2 min−1 at pH=2 and 1.15 × 10−2 min−1 at pH=9, while the quantum yields for this photo-degradation reaction varied from 0.99 × 10−2 mol/Eins to 11.1 × 10−2 mol/Eins at these pHs. The Fentons reagent system was used for the generation of hydroxyl radicals, and the rate constant for the reaction between esculetin and these radicals was determined to be 1.06 × 1010 L/(mol·s). Finally, several chemical oxidation systems were used in the degradation of this pollutant: single oxidants (ozone, UV irradiation) and advanced oxidation processes (Fentons reagent, UV/H2O2, O3/H2O2, O3/UV, O3/H2O2 /UV, and photo-Fenton system). The results revealed that the most efficient methods in terms of esculetin removal were ozonation among the single oxidants, and the photo-Fenton system among the combined processes.