Percorrer por autor "Vilar, Vítor J.P."
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- Accumulation and release of Pb(II) in aqueous solution by aquatic mosses (Fontinalis antipyretica)Publication . Martins, Ramiro; Freitas, Olga; Vilar, Vítor J.P.; Boaventura, RuiThe uptake and release of Pb(II) by Fontinalis antipyretica was studied in laboratory, by exposing the plants to different lead concentrations for 144 h and 335 h contamination and decontamination periods, respectively. A first order kinetic model was fitted to the experimental data to determine the uptake and release constants, k1 and k2, and other relevant parameters. The metal accumulation capacity, at equilibrium, follows the order: Pb(II) > Zn(II) > Cd(II) > Cr(VI). A Bioconcentration Factor (BCF) and a Biological Elimination Factor (BEF) were also determined; for 0.9–2.2 mg Pb l–1, BCF decreases from about 30748 to 21296.
- Aplicabilidade do musgo aquático fontinalis antipyretica na bioacumulaçãode iões metálicos (Cd2+)Publication . Martins, Ramiro; Vilar, Vítor J.P.; Boaventura, RuiCom este estudo pretende-se compreender quantitativa e qualitativamente a acumulação e a libertação de iões cádmio em solução aquosa, por uma briófita aquática - Fontinalis antipyretica – na perspectiva duma aplicação, quer na biomonitorização de cursos de água, quer na descontaminação de efluentes industriais. A acumulação de cádmio e posterior eliminação pelo musgo foi estudada em laboratório expondo as plantas a concentrações de cádmio na gama 0,5 – 2,5 mg l-1, durante um período de contaminação de 144 h, e depois a água isenta de metal durante um período de descontaminação de 192 h. Foi ajustado um modelo cinético de transferência de massa de primeira ordem aos dados experimentais.
- Cadmium uptake by algal biomass in batch and continuous (CSTR and packed bed column) adsorbersPublication . Vilar, Vítor J.P.; Santos, Sílvia; Martins, Ramiro; Botelho, Cidália; Boaventura, RuiIn this work, the properties of marine algae Gelidium, algal waste from agar extraction industry and a composite material were investigated for cadmium(II) biosorption. Equilibrium experiments were performed at three pH values (4, 5.3 and 6.5). Equilibrium data were well described by the Langmuir and Langmuir–Freundlich isotherms. Two models predicting the pH influence in the cadmium biosorption (discrete and continuous models) have been developed in order to better describe the equilibrium. The continuous model also considers a heterogeneous distribution of carboxylic groups, determined by potentiometric titration. The results of batch kinetic experiments performed at different pH values were well fitted by two mass transfer models and the homogeneous diffusion coefficients for the cadmium ions inside the biosorbentwere obtained. Continuous stirred tank reactor (CSTR) and packed bed column configurationswere also examined for the biosorption of cadmium ions. A strong acid (0.1MHNO3)was used as eluant to regenerate the biosorbents in the column. Several mass transfer models were applied with success to describe the biosorption process in batch mode, CSTR and fixed bed column.
- Continuous biosorption of single and binary metal solutions in a fixed-bed column using algae gelidium and granulated algal waste from agar extractionPublication . Vilar, Vítor J.P.; Botelho, Cidália; Martins, Ramiro; Boaventura, RuiThis paper describes the biosorption of single (Zn(II) and Cr(III)) and binary (Cd(II)/Zn(II) and Cu(II)/Cr(III)) metal solutions in a packed bed column using algae Gelidium and an algal waste from the agar extraction industry immobilized with polyacrylonitrile. In the sorption process, Zn(II) breaks through the column faster than Cd(II) due to its lower affinity for the biosorbent. An overshoot in the outlet Zn(II) concentration was observed and explained by competitive adsorption between Cd(II) and Zn(II), whereby the higher Cd(II) affinity for the biosorbent displaces bound Zn(II) ions. The same was verified for the binary system Cu(II)/Cr(III), where an overshoot in the outlet Cu(II) concentration also appeared. Metal desorption using 0.1 M HNO3 as eluant was 100% effective for Cd(II), Zn(II) and Cd(II)/Zn(II) systems. For Cr(III) and Cu(II)/Cr(III) systems, the elution of Cr(III) was not 100% effective. A mathematical model for a fixed-bed system considering film and intraparticle diffusion, equilibrium represented by single and binary Langmuir equations and desorption described by the mass action law, was developed. The uptake breakthrough and elution curves obtained in fixed-bed experiments were adequately predicted by the model.
- Cr(III) uptake by marine algal biomass: equilibrium and kineticsPublication . Vilar, Vítor J.P.; Freitas, Olga; Costa, Pedro; Botelho, Cidália; Martins, Ramiro; Boaventura, RuiIn this work, biosorption of trivalent chromium by the marine brown algae Sargassum muticum was 37 studied in a batch system. The effect of the solution pH on Cr(III) uptake by Sargassum was 38 investigated. Kinetics and equilibrium experiments were conducted at different pH values (3.0, 4.0 and 39 5.0). Equilibrium data are well described by the Langmuir and Langmuir-Freundlich isotherms and 40 kinetics follows the pseudo-second-order model, at different pH values. The two mass transfer models 41 give comparable results, but they did not provide a perfect representation of the sorption data. The 42 homogeneous diffusivity, Dh, was found to be around 1.6´10-8 cm2 s-1 for 100 mg l-1 Cr(III) 43 concentration. 44 Sargassum muticum was compared with the brown algae Laminaria hyperborean and the red algae 45 Gelidium sesquipedale in terms of uptake capacity. The maximum uptake capacities for Sargassum, 46 Laminaria and Gelidium were, respectively, 56 ± 3, 70 ± 4 and 18 ± 1 mg Cr(III) g-1, at pH = 5.
- Enhancing methane yield from crude glycerol anaerobic digestion by coupling with ultrasound or A. niger/E. coli biodegradationPublication . Paulista, Larissa Oliveira; Boaventura, Rui; Vilar, Vítor J.P.; Pinheiro, Alexei; Martins, RamiroAnaerobic digestion of crude glycerol from biodiesel production is a feasible way for methane production. However, crude glycerol (CG) contains impurities, such as long-chain fatty acids (LCFA) that can inhibit methanogenic microorganisms. Ultrasound promotes the hydrolysis of LCFA and deagglomerates the microorganisms in biological flocs. Furthermore, Aspergillus niger and Escherichia coli produce lipases capable of degrading LCFA. This study aims at improving the methane yield from anaerobic digestion by coupling with ultrasound or E. coli/A. niger biodegradation. The effect of the different treatments was first assessed in a perfectly mixed batch reactor (PMBR), using diluted CG at concentrations of 0.2%, 1.7%, and 3.2% (v/v). Later, the best conditions were replicated in an upflow anaerobic sludge blanket (UASB) reactor to simulate full-scale practical applications. Experiments in the PMBR showed that ultrasound or A. niger biodegradation steps improved methane yield up to 11% for 0.2% CG and 99% for 1.7% CG, respectively. CG biodegradation by E. coli inhibited the subsequent anaerobic digestion for all concentrations tested. Using a UASB digester, ultrasonic treatment of CG led to an average increase of 29% in methane production. The application of ultrasound led to a lower accumulation of propionic acid in the digested material and increased biogas production. On the other hand, an average 77% increase in methane production was achieved using a preliminary CG biodegradation step by A. niger, when operated at a loading rate of 2.9 kg COD m-3 day-1. Under these conditions, an energy gain of 0.48 kWh day-1, with the production of the 0.434 m3 CH4 kg-1 CODremoval and 0.573 m3 CH4 kg-1 VS, and a biogas quality of 73% in methane were obtained. The digested material was analyzed for the detection and quantification of added-value by-products in order to obtain a broad assessment of the CG valorization through anaerobic digestion. In some experiments, propionic and oxalic acid were detected. However, the accumulation of propionic caused the inhibition of the acetogenic and methanogenic microorganisms.
- Finding a suitable treatment solution for a leachate from a non-hazardous industrial solid waste landfillPublication . Barbosa Segundo, Inalmar D.; Martins, Ramiro; Boaventura, Rui; Silva, Tânia F.C.V.; Moreira, Francisca C.; Vilar, Vítor J.P.The current study aimed at tackling the lack of effective treatment solutions for leachates from industrial solid waste landfills (ISWLs) through the development of a treatment train for a non-hazardous ISWL (NHISWL) leachate with low/moderate content of organics and salts and low biodegradability. The following technologies were tested: (i) coagulation using ferric chloride (FeCl3) or aluminium sulphate (Al2(SO4)3), (ii) biological oxidation, and (iii) chemical and electrochemical advanced oxidation processes (AOPs/EAOPs), including photo-Fenton oxidation using ultraviolet C (UVC) or ultraviolet A (UVA) radiation (PF-UVC or PF-UVA), anodic oxidation (AO), ozonation process and ozone (O3)-based processes. The best multistage treatment strategy included: (i) coagulation with FeCl3 for partial removal of organics (with direct impact on colour, odour and turbidity removal and biodegradability enhancement) and phosphorous, (ii) PF-UVC process for recalcitrant organics oxidation (with direct impact on colour and odour removal and biodegradability enhancement) coupled to a clarification step for removal of suspended solids, turbidity, iron and phosphorous, and (iii) biological process for removal of the generated biodegradable organics and of nitrogen compounds. Upon treatment, the NHISWL leachate fulfilled European and Portuguese requirements for discharge into aquatic systems, except for ammonium (and consequently for total nitrogen), pointing to the need to change the biological process conditions or add an air stripping step. The application of coagulation before the PF-UVC process has proved to be crucial for the fulfilment of the legislation requirements.
- Intensification of heterogeneous photocatalysis by applying a kenics® static mixer as catalyst supportPublication . Vilar, Vítor J.P.; Diez, A.M.; Moreira, F.; Marinho, B.; Espínola, J.; Martins, Ramiro; Sanromán, M.; Pazos, M.; Boaventura, RuiDespite scientific community’s efforts, overcoming mass and photon transfer limitations remain a main challenge for heterogeneous photocatalysis with immobilized catalysts. Here, a Kenics® static mixer was used for the first time as catalyst support for heterogeneous photocatalysis in tubular reactors. This permitted not only to take advantage of the enhanced mass transfer supplied by the intense mixing, but also to provide a total illumination of the photocatalyst surface area with front-irradiation mechanism by using sunlight combined with compound parabolic collectors. Stainless steel Kenics® static mixers were coated with TiO2 or Fe2O3 photocatalyst and applied for oxytetracycline (OTC) degradation in aqueous solutions. The photocatalytic efficiency was evaluated as a function of different parameters: (i) catalyst deposition technique (dip coating or spray coating), (ii) photocatalyst film thickness, (iii) oxidant (H2O2) concentration, and (iv) number of static mixing elements.
- Kinetic modelling of cadmium and lead removal by aquatic mossesPublication . Martins, Ramiro; Vilar, Vítor J.P.; Boaventura, RuiBecause biosorption is a low cost and effective method for treating metal-bearing wastewaters, understanding the process kinetics is relevant for design purposes. In the present study, the performance of the aquatic moss Fontinalis antipyretica for removing cadmium and lead from simulated wastewaters has been evaluated. Five kinetic models (first-order, pseudo-first-order, Elovich, modified Ritchie second-order and pseudo-second-order) were fitted to the experimental data and compared. Previously, the effect of parameters such as the initial solution pH, contact time, and initial metal ion concentration on biosorption was investigated. The initial pH of the solution was found to have an optimum value in the range of 4.0-6.0. The equilibrium sorption capacity of cadmium and lead by Fontinalis antipyretica increased with the initial metal concentration. For an initial metal concentration of 10 mg L-1, the uptake capacity of the moss, at equilibrium, is the same for both metals (4.8 mg g-1). Nevertheless, when the initial concentration increases up to 100 mg L-1, the uptake of Pb(II) was higher than 78%. The pseudo-second order biosorption kinetics provided the better correlation with the experimental data (R2 ≥ 0.999).
- Multistage treatment for olive mill wastewater: Assessing legal compliance and operational costsPublication . Vuppala, Srikanth; Paulista, Larissa Oliveira; Morais, Daniela F.S.; Pinho, Inês L.; Martins, Ramiro; Gomes, Ana I.; Moreira, Francisca C.; Vilar, Vítor J.P.A treatment train for the remediation of a raw olive mill wastewater (OMW) was investigated, aiming to comply with the emission limit values (ELVs) for direct discharge into water bodies. The following stages were proposed: (i) pre-treatment (filtration and sedimentation), (ii) coagulation, (iii) biological oxidation, and (iv) advanced oxidation process (AOP). Under the best-operating conditions for coagulation (0.8 g L- 1 of Al2(SO4)3, pH = 4.5), high removal of total suspended solids (TSS) (97%), turbidity (98%), and phenols (57%) was achieved, along with a decrease in the inhibition of the biological activity. A subsequent biological oxidation stage provided a high removal of organic matter (chemical oxygen demand (COD) removal of 73%). For the third stage, three AOPs were applied and compared – photo-Fenton with UVA radiation (PF-UVA), anodic oxidation (AO), and ozonation (O3). After 3 h of treatment, the PF-UVA process (pH = 2.8, [H2O2] = 400–500 mg L- 1, [Total dissolved iron]0 = 100 mg L- 1) allowed to meet the ELV for COD, but the other parameters exceeded the threshold, while O3 process (inlet concentration = 100 mg O3 Ndm- 3, gas flow = 0.2 Ndm3 min- 1) allowed to comply with phenols, TSS, and sulfate limits. The AO process (current density up to 200 mA cm- 2) was the least efficient AOP for all studied parameters. The operational costs for the coagulation and biological oxidation stages were estimated at 1.20 € m- 3. Regarding the most effective AOPs, ozonation presented an estimated cost 2.3-fold higher than PF-UVA (11.9 € m- 3 vs. 5.2 € m- 3).
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