Jon I. Álvarez-Uriarte

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.

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.