Unai Iriarte-Velasco

The effect of mixed oxidants and powdered activated carbon on the removal of natural organic matter.

Present paper studies the influence of electrochemically generated mixed oxidants on the physicochemical properties of natural organic matter, and especially from the disinfection by-products formation point of view. The study was carried out in a full scale water treatment plant. Results indicate that mixed oxidants favor humic to non-humic conversion of natural organic matter. Primary treatment preferentially removes the more hydrophobic fraction. This converted the non-humic fraction in an important source of disinfection by-products with a 20% contribution to the final trihalomethane formation potential (THMFP(F)) of the finished water. Enhanced coagulation at 40 mg l(-1) of polyaluminium chloride with a moderate mixing intensity (80 rpm) and pH of 6.0 units doubled the removal efficiency of THMFP(F) achieved at full scale plant. However, gel permeation chromatography data revealed that low molecular weight fractions were still hardly removed. Addition of small amounts of powdered activated carbon, 50 mg l(-1), allowed reduction of coagulant dose by 50% whereas removal of THMFP(F) was maintained or even increased. In systems where mixed oxidants are used addition of powdered activated carbon allows complementary benefits by a further reduction in the THMFP(F) compared to the conventional only coagulation-flocculation-settling process.

Kinetics of Chloroform Formation from Humic and Fulvic Acid Chlorination

Chloroform formation from chlorination of aquatic humic and fulvic acid solutions was studied. Second order overall kinetic model was assumed, first order with respect to chlorine and precursor content. Rate constants have been measured, resulting in values that varied significantly with reaction conditions, in the range of 0.177–7.206 [L/ mmol h], mainly for fulvic acid. The activation energy deduced from experiments carried out at different temperatures also increased notably when decreasing pH from 8 to 7. Increases of up to 60% were computed, where highest values were measured for humic acid. It is noteworthy the dependence observed on reaction time: higher activation energy resulted for longest reaction periods. Differences in the range of 40% have been reported. This effect is attributed to the existence of simultaneous reactions, each with different activation energy, competing for trihalomethanes formation.

Conversion of waste animal bones into porous hydroxyapatite by alkaline treatment: effect of the impregnation ratio and investigation of the activation mechanism

Microporous biochars, mainly composed by hydroxyapatite (HAp), were prepared from animal waste bones. In this study, a three-step procedure including pre-pyrolysis, chemical treatment with NaOH, KOH and K2CO3, and pyrolysis was investigated. The effects of the activation agent and its concentration were analysed by N2 adsorption–desorption, SEM, EDX, FTIR, and XRD techniques. The activation mechanism was investigated by TG-MS. FTIR and XRD data confirm that the obtained biochars were mainly composed of HAp. K2CO3 was the most effective with porosity being increased by 30xa0% (up to 234xa0m2/g) compared to non-alkali-treated sample. New pores were generated mainly in the microporous range. Analysis of the pyrolysis gases by MS revealed that the main effect of the alkali treatment is the incorporation of OH− ions, which then react with bone matrix to generate porosity. Other gas-phase reactions, such as reverse WGS and methanation reactions, promoted by K2CO3, may be involved in the activation process. In contrast, KOH caused little modification of the HAp structure. Statistical analysis supported the relationship among the release of certain compounds during pyrolysis and the textural properties of the final material.

Preparation of carbon-based adsorbents from the pyrolysis of sewage sludge with CO2. Investigation of the acid washing procedure

AbstractCarbon-based adsorbents were prepared through the physical activation of sewage sludge with CO2. The effect of the acid treatment was investigated, either before or after the physical activation. The post-washing increases the porosity due to the removal of the inorganic fraction and the improvement in the accessibility of the carbon fraction. The post-washing is essential for high activation temperatures since the high reactivity of CO2 leads to a high pore blockage. In fact, the material activated at 900°C has a very low surface area (43xa0m2/g), while after washing it reaches 654xa0m2/g. The effect of the acid treatment prior to the physical activation depends on temperature: at 600°C, it results in a huge pore development (mainly macropores), while at 900°C, the microporosity increases. The adsorption capacity is not directly related to the BET surface area. For both adsorbates, the uptake ability depends on the textural properties (it is favoured by mesoporosity for methylene blue (MB) and microp...

Selective hydrogenation of sunflower oil over Ni catalysts

This work focuses on the influence of the support and the preparation method on the activity and selectivity of nickel catalysts in the hydrogenation of sunflower oil. Catalysts were prepared over silica and alumina supports following the incipient wetness impregnation and deposition-precipitation techniques. The activation process was followed by temperature-programmed reduction (TPR). Precipitation-deposition method allowed a stronger metal-support interaction than incipient wetness impregnation. A precipitation-deposition time of 14 h (which allowed a Ni loading of about 20wt%) was deemed as the most adequate from the standpoint of high specific surface area and strong Ni-support interaction. The selectivity to oleic acid was not affected by the preparation method, but it was significantly influenced by the type of support. In this regard, the catalysts prepared on silica are more active and produce less saturated fatty acids.

Application of Principal Component Analysis to the Adsorption of Natural Organic Matter by Modified Activated Carbons

Adsorption of natural organic matter by physically and chemiclally modified activated carbons was studied in this work. Principal component analysis (PCA) was applied to datasets gathering morphological, physical, chemical properties, and adsorption capacity information of the modified activated carbon samples. The PCA was used to identify the main effects by clustering the samples according to the modifications undergone. Results indicate that total and/or fractional pore volume, and the iron and oxygen content were sensitive enough to detect good adsorption potential even for “a priori” nonoptimal overall properties. Unexpectedly, low values of pHpzc not always correlated with poor adsorption performance. The sum of N and O content may also be a good indicator to select a carbon with good adsorption performance. Based on PCA results, a prediction equation was developed to estimate values for the equilibrium uptake capacity and was tested against five additional carbon samples.