Aparecido Nivaldo Módenes

Toxicity assessment from electro-coagulation treated-textile dye wastewaters by bioassays.

In this study the pollutant removal from a textile dyeing wastewater has been investigated by using the electro-coagulation technique with iron electrodes. In order to obtain optimal values of the system state variables, a 3(3) full factorial experimental design was applied. The electro-coagulation (EC) process response was evaluated on the basis of COD removal and decolourization values. The electrolysis time and density current were statistically significant for the COD removal and decolourization. Based on the lettuce seeds (Lactuca sativa) and brine shrimp (Artemia salina), the lowest toxicity level was achieved in 5 min of electrolysis time. Due to the remaining high toxicity level above 30 min of electrolysis time, the EC process is not adequate to be used in a single effluent treatment, suggesting that this electrochemical process of up to 5 min could be used as part of a complete effluent treatment system.

Performance evaluation of a photo-Fenton process applied to pollutant removal from textile effluents in a batch system.

In this work, the performance of a photo-Fenton process-based textile effluent treatment was investigated using both solar and artificial light sources. A full 3(3) factorial experimental design was applied for the optimisation with respect to three parameters: initial pH, amounts of Fe(2+) (0.01-0.09 g L(-1)) and H(2)O(2) (1-7 g L(-1)). The photo-Fenton process response was evaluated on the basis of chemical oxygen demand (COD) removal and decolourisation. The optimum conditions of the photo-Fenton process were attained at concentration values of 0.05 g Fe(2+) L(-1) and 6.0 g H(2)O(2) L(-1) and pH 3, for both solar and artificial light sources. The effects of initial pH, and Fe(2+) and H(2)O(2) concentrations were evaluated. From the monitoring of TOC, COD, turbidity and decolourisation over time, the progress of the mineralisation of dyes was analysed, forming nitrate, ammonia nitrogen and nitrite. Low amounts of residual peroxide and iron, which were below the limit allowed by Brazilian environmental legislation, were attained after 360 min of irradiation time for both artificial and solar sources. An operational cost of US

Optimised photocatalytic degradation of a mixture of azo dyes using a TiO2/H2O2/UV process

6.85 per m(3) of treated effluent was estimated using solar irradiation.

Application of high resolution X-ray emission spectroscopy on the study of Cr ion adsorption by activated carbon.

The aim of the present study was to optimise the photocatalytic degradation of a mixture of six commercial azo dyes, by exposure to UV radiation in an aqueous solution containing TiO(2)-P25. Response surface methodology, based on a 3(2) full factorial experimental design with three replicates was employed for process optimisation with respect to two parameters: TiO(2) (0.1-0.9 g/L) and H(2)O(2) (1-100 mmol/L). The optimum conditions for photocatalytic degradation were achieved at concentrations of 0.5 g TiO(2)/L and 50 mmol H(2)O(2)/L, respectively. Dye mineralisation was confirmed by monitoring TOC, conductivity, sulfate and nitrate ions, with a sulfate ion yield of 96% under optimal reactor conditions. Complete decolorisation was attained after 240 min irradiation time for all tested azo-dyes, in a process which followed a pseudo-first kinetic order model, with a kinetic rate constant of approximately 0.018 min(-1). Based on these results, this photocatalytic process has promise as an alternative for the treatment of textile effluents.

Determination of the mass transfer limiting step of dye adsorption onto commercial adsorbent by using mathematical models

In this work granular activated carbon has been chosen as an absorbent in order to investigate the Cr(VI) reduced by adsorption experiments. Several batch chromium-sorption experiments were carried out using 0.25 g of granular activated carbon in 50 mL aqueous solution containing approximately 70 and 140 mg L(-1) of Cr(VI) and Cr(III), respectively. Cr-Kbeta fluorescence spectra of Cr adsorbed in a carbon matrix and Cr reference materials were measured using a high-resolution Johann-type spectrometer. Based on evidence from the Cr-Kb satellite lines, the Cr(VI) reduction process has actually happened during metal adsorption by the activated carbon.

Analysis of Trace Elements in Groundwater Using ICP-OES and TXRF Techniques and Its Compliance with Brazilian Protection Standards

Reactive blue 5G dye removal in a fixed-bed column packed with Dowex Optipore SD-2 adsorbent was modelled. Three mathematical models were tested in order to determine the limiting step of the mass transfer of the dye adsorption process onto the adsorbent. The mass transfer resistance was considered to be a criterion for the determination of the difference between models. The models contained information about the external, internal, or surface adsorption limiting step. In the model development procedure, two hypotheses were applied to describe the internal mass transfer resistance. First, the mass transfer coefficient constant was considered. Second, the mass transfer coefficient was considered as a function of the dye concentration in the adsorbent. The experimental breakthrough curves were obtained for different particle diameters of the adsorbent, flow rates, and feed dye concentrations in order to evaluate the predictive power of the models. The values of the mass transfer parameters of the mathematical models were estimated by using the downhill simplex optimization method. The results showed that the model that considered internal resistance with a variable mass transfer coefficient was more flexible than the other ones and this model described the dynamics of the adsorption process of the dye in the fixed-bed column better. Hence, this model can be used for optimization and column design purposes for the investigated systems and similar ones.

Biodegradability and toxicity assessment of a real textile wastewater effluent treated by an optimized electrocoagulation process.

In this work, an assessment of groundwater quality and its compliance with Brazilian environmental protection standards was carried out. Ground waters from the Serra Geral aquifer are currently used for human consumption at the western region of the Brazilian state of Paraná. Ground water samples from 10 wells covering the entire Toledo municipality rural region were collected and analysed by two highly accurate and sensitive spectrometric techniques: inductively coupled plasma–optical emission spectrometry (ICP-OES) and total reflection X-ray spectrometry (TXRF). Among all detected elements, 18 elements (As, Ba, Br, Ca, Pb, Cl, Co, Cu, Cr, Fe, P, S, Mn, Ni, K, Ti, V and Zn) were measured by the TXRF technique while three elements (B, Mg and Na) were measured by ICP-OES. Trace element concentration levels were then compared with Brazilian environmental legislation (BEL). From the results obtained, concentrations of chromium, iron, arsenic, selenium, manganese and barium were detectable in some wells at slightly above the maximum limits allowed by the BEL.

The evaluation of benzene and phenol biodegradation kinetics by applying non-structured models.

In this work, the application of an iron electrode-based electrocoagulation (EC) process on the treatment of a real textile wastewater (RTW) was investigated. In order to perform an efficient integration of the EC process with a biological oxidation one, an enhancement in the biodegradability and low toxicity of final compounds was sought. Optimal values of EC reactor operation parameters (pH, current density and electrolysis time) were achieved by applying a full factorial 33 experimental design. Biodegradability and toxicity assays were performed on treated RTW samples obtained at the optimal values of: pH of the solution (7.0), current density (142.9 A m−2) and different electrolysis times. As response variables for the biodegradability and toxicity assessment, the Zahn–Wellens test (Dt), the ratio values of dissolved organic carbon (DOC) relative to low-molecular-weight carboxylates anions (LMCA) and lethal concentration 50 (LC50) were used. According to the Dt, the DOC/LMCA ratio and LC50, an electrolysis time of 15 min along with the optimal values of pH and current density were suggested as suitable for a next stage of treatment based on a biological oxidation process.

Toxicity assessment of tannery effluent treated by an optimized photo-Fenton process

The biodegradation kinetics of the aromatic hydrocarbons benzene and phenol as single substrates and as a mixture were investigated through non-structured model analysis. The material balance equations involving the models of Monod and Andrews and representing the biodegradation kinetics of individual substrates in batch mode were numerically solved. Further, utilization of a benzene-phenol mixture was described by applying more sophisticated mathematical forms of competitive, noncompetitive and uncompetitive inhibition models as well as the sum kinetic interactions parameters (SKIP) model. In order to improve the performance of the studied models, some modifications were also proposed. The Particle Swarm Global Optimization method, coded in Maple, was applied to the parameter identification procedure of each model, where the least square method was used as a search statistical criterion. The description of the biodegradation kinetics of a benzene-phenol mixture by the competitive inhibition model was based on the information that the compounds could be catabolized via one metabolic pathway of Pseudomonas putida F1. Simulation results were in good agreement with the experimental data and proved the robustness of the applied methods and models. The developed knowledge database could be very useful in the optimization of the biodegradation processes of different bioreactor types and operational conditions.

Assessment of the banana pseudostem as a low-cost biosorbent for the removal of reactive blue 5G dye.

In this work, an optimized photo-Fenton process was applied to remove pollutants from tannery industrial effluent (TIE) with its final toxicity level being assessed by a lettuce-seed-based bioassay test. A full 33 factorial design was applied for the optimization of long-term photo-Fenton experiments. The optimum conditions of the photo-Fenton process were attained at concentration values of 0.3 g Fe2+ L−1 and 20 g H2O2 L−1 and pH 3, for 120 min UV irradiation time. Reactor operating parameter (ROP) effects on the removal of chemical oxygen demand, colour, turbidity, total suspended solids and total volatile solids were evaluated, suggesting that a broad range of ROP values are also suitable to give results very near to those of the photo-Fenton experiments under optimal conditions. Based on the low calculated median lethal dose (LD50) values from a lettuce-seed-based bioassay test, we suggest that recalcitrant substances are present in treated TIE samples. A possible cause of the high toxicity level could partly be attributed to the nitrate concentration, which was not completely abated by the photo-Fenton process. Apart from this, the photo-Fenton process can be used as a part of an industrial effluent treatment system in order to abate high organic pollutant loads.