Effect of the anode material, applied current and reactor configuration on the atenolol toxicity during an electrooxidation process.

Atenolol (ATL) is a beta-blocker pharmaceutical product which is excreted mainly unchanged and may represent a long-term risk for organisms present in the sea and in fresh water. Due to its low biodegradation rate, electrochemical advanced oxidation processes (EAOPs) can be used to remove this compound. In this work, ATL ecotoxicity was analyzed in the presence of sodium sulfate (Na2SO4), which is widely used as supporting electrolyte in EAOPs. Ecotoxicity values were expressed as the pollutant concentration that leads to a 50% inhibition of the root elongation of Lactuca sativa seeds in relation to the control (EC50(5 days)). The obtained values for ATL showed an EC50(5 days) of 1377 mg L-1 towards Lactuca sativa. When Na2SO4 was added, the toxicity of the sample increased but no synergy was detected between both compounds. With 2 g L-1 Na2SO4, ATL showed an EC50(5 days) of 972 mg L-1; and with 4 g L-1 Na2SO4 and higher concentrations, EC50 value for ATL was 0 mg L-1. Statistical tools were used to obtain the zones of the [ATL]-[Na2SO4] plane which are toxic towards Lactuca sativa. Solutions containing ATL and Na2SO4 were treated by electrooxidation. Two anode materials (a boron-doped diamond electrode and a microporous Sb-doped SnO2 ceramic one); three operation currents (0.4, 0.6 and 1 A); and two reactor configurations (one-compartment reactor and two-compartment reactor separated by a cation exchange membrane) were used. Lactuca sativa seeds and Vibrio fischeri bacterium tests were employed to evaluate the toxicity of the solutions before and after applying the electrooxidation process. In all the tests, the ecotoxicity of the treated sample increased. This fact is owing to the persulfate presence in the solution due to the sulfate electrochemical oxidation. Nevertheless, none of the final samples were toxic towards Vibrio fischeri because ecotoxicity values were lower than 10 TU; and, in the case of the one-compartment reactor, practically all of them were also non-toxic towards Lactuca sativa. The toxicity of the treated samples increased when using the two-compartment reactor in the presence of the BDD anode, and when the operation current was increased. This is attributed to the highest formation of persulfates. Amongst all the tests performed in this work, the lowest toxicity value (i.e., 3 TU) together with the complete mineralization and degradation degrees was achieved with the two-compartment reactor using the BDD anode and operating at 0.6 A.

Study of the chlorfenvinphos pesticide removal under different anodic materials and different reactor configuration.

The present manuscript focuses on the study of the electrochemical oxidation of the insecticide Chlorfenvinphos (CVP). The assays were carried out under galvanostatic conditions using boron-doped diamond (BDD) and low-cost tin dioxide doped with antimony (Sb-doped SnO2) as anodes. The influence of the operating variables, such as applied current density, presence or absence of a cation-exchange membrane and concentration of supporting electrolyte, was discussed. The results revealed that the higher applied current density the higher degradation and mineralization of the insecticide for both anodes. The presence of the membrane and the highest concentration of Na2SO4 studied (0.1 M) as a supporting electrolyte benefited the oxidation process of CVP using the BDD electrode, while with the ceramic anode the elimination of CVP was lower under these experimental conditions. Although the BDD electrode showed the best performance, ceramic anodes appear as an interesting alternative as they were able to degrade CVP completely for the highest applied current density values. Toxicity tests revealed that the initial solution of CVP was more toxic than the samples treated with the ceramic electrode, while using the BDD electrode the toxicity of the sample increased.

Microencapsulation of zinc plating waste using silicone polymers.

This paper deals with the treatment of hazardous zinc-bearing waste using hydraulic binders and silicone polymers, with the aim to allow its safe disposal into landfill. The waste was solidified using hydraulic binders in the first step and then encapsulated using silicone polymers. Samples were characterised using x-ray fluorescence, x-ray diffraction, and scanning electron microscopy. The effectiveness of the process was evaluated by leaching tests in distilled water and in an acidic environment according to Toxicity Characteristic Leaching Procedure. The effect of porosity and pH on the release of pollutants was also studied. Zinc and chloride were identified as the most significant pollutants in the waste. Portland cement did not stabilize them efficiently. The two-step treatment with Portland cement and silicone binders decreased, in the best case, the concentration of zinc and chloride in acidic extracts from 12,400 mg/L and 38,300 mg/L to 21.9 mg/L and 74 mg/L, respectively, and the treated waste complied with regulatory requirements for hazardous waste disposal into landfills. The two-step treatment was also found as a more effective method than microencapsulation using a silicone binder alone. The factor that most affects leachability appears to be the porosity of the encapsulated waste.

Analysis of norfloxacin ecotoxicity and the relation with its degradation by means of electrochemical oxidation using different anodes.

In this work, ecotoxicological bioassays based on Lactuca sativa seeds and bioluminescent bacterium (Vibrio fischeri) have been carried out in order to quantify the toxicity of Norfloxacin (NOR) and sodium sulfate solutions, before and after treating them using electrochemical advanced oxidation. The effect of some process variables (anode material, reactor configuration and applied current) on the toxicity evolution of the treated solution has been studied. A NOR solution shows an EC50(5 days) of 336 mg L-1towards Lactuca sativa. This threshold NOR concentration decreases with sodium sulfate concentration, in solutions that contain simultaneously Norfloxacin and sodium sulfate. In every case considered in this work, the electrochemical advanced oxidation process increased the toxicity (towards both Lactuca sativa and Vibrio fischeri) of the solution. This toxicity increase is mainly due to the persulfate formation during the electrochemical treatment. From a final solution toxicity point of view, the best results were obtained using a BDD anode in a divided reactor applying the lowest current intensity.

Stabilization/solidification of hot dip galvanizing ash using different binders.

This study focuses on solidification of hot dip-galvanizing ash with a high content of zinc and soluble substances. The main purpose of this paper is to immobilize these pollutants into a matrix and allow a safer way for landfill disposal of that waste. Three different binders (Portland cement, fly ash and coal fluidized-bed combustion ash) were used for the waste solidification. Effectiveness of the process was evaluated using leaching test according to EN 12457-4 and by using the variance analysis and the categorical multifactorial test. In the leaching test, four parameters were observed: pH, zinc concentration in leachate, and concentration of chlorides and dissolved substances in leachate. The acquired data was then processed using statistical software to find an optimal solidifying ratio of the addition of binder, water, and waste to the mixture, with the aim to fulfil the requirement for landfill disposal set by the Council Decision 2003/33/EC. The influence on the main observed parameters (relative amount of water and a binder) on the effectiveness of the used method and their influence of measured parameters was also studied.

The effectiveness of the stabilization/solidification process on the leachability and toxicity of the tannery sludge chromium.

A stabilization/solidification (S/S) process by using cement was applied to tannery sludge in order to find a safer way of landfilling this waste. The effects of three parameters on the process effectiveness were analysed in terms of leachate toxicity and chromium retention (%). The parameters studied were the relative amount of added water (30-50 wt.%), cement (10-60 wt.% in the solid components), and the use of three different types of cement (clinker with additions of limestone, with additions of limestone and fly ashes, and with additions of pozzolans). Statistical analysis performed by variance analysis and categorical multifactorial tests reveals that all the studied parameters significantly influence the effectiveness of the process. Results showed that chromium retention decreases as the relative amount of cement and water increases, probably due to additional chromium provided by cement and increased in the porosity of the mixtures. Leachate toxicity showed the same minimum value for mixtures with 30% or 40% cement, depending on the type of cement, showing that clinker is the main material responsible for the process effectiveness, and additives (pozzolans or fly ashes) do not improve it. The volume increase is lower as less sludge is replaced by cement and the relative amount of water decreases, and for the cement without additions of fly ashes or pozzolans. Therefore, the latter seems to be the most appropriate cement in spite of being more expensive. This is due to the fact that the minimum toxicity value is achieved with a lower amount of cement; and moreover, the volume increase in the mixtures is lower, minimizing the disposal cost to a landfill.

Effect of pH and chloride concentration on the removal of hexavalent chromium in a batch electrocoagulation reactor.

In this work, the effect of pH and chloride ions concentration on the removal of Cr(VI) from wastewater by batch electrocoagulation using iron plate electrodes has been investigated. The initial solution pH was adjusted with different concentrations of H(2)SO(4). The presence of chloride ions enhances the anode dissolution due to pitting corrosion. Fe(2+) ions formed during the anode dissolution cause the reduction of Cr(VI) to form Cr(III), which are co-precipitated with Fe(3+) ions at relatively low pH. The reduction degree of Cr(VI) to Cr(III) and the solubility of metal hydroxide species (both chromic and iron hydroxides) depend on pH. At higher concentrations of H(2)SO(4), the reduction of Cr(VI) to Cr(III) by Fe(2+) ions is preferred, but the coagulation of Fe(3+) and Cr(III) is favoured at the lower H(2)SO(4) concentrations.