Arsenic removal in continuous systems using zero-valent iron fixed beds

FERNANDO S. GARCÍA EINSCHLAG*; JUAN M. TRISZCZ

Arsenic: Sources, Toxicity and Environmental Impact

Nova Science Publishers

Lugar: New York; Año: 2011;

Nota 1: Capítulo aceptado para su publicación con fecha 21-11-2011. Nota 2:Fecha estimada de publicación 1er semestre de 2012. Abstract Many different technologies have been developed to remove arsenic from drinking water. In particular, the zero valent iron method (ZVI) has recently gained attention due to its applicability under different conditions, operational simplicity and low cost maintenance. Owing to the “in situ” formation of various iron corrosion products, the main mechanisms involved in arsenic removal include adsorption, surface complexation, surface precipitation and co-precipitation. The relative importance of each mechanism may strongly depend on reaction conditions. Many studies on arsenic removal by ZVI systems have been focused on batch studies. However, separation and purification processes that employ contaminant uptake technologies mainly use continuous flow system columns. This operating mode facilitates scale up and optimization of drinking water treatment plants. Therefore, sorption data obtained in batch experiments cannot be easily extrapolated and it is necessary to carry out fixed-bed continuous flow tests. It is worth noting that, due to the relatively short history of the reactive barrier technology, long-term performance data are relatively scarce. Breakthrough curves are usually employed for studying the dynamic behavior of reactive bed columns. Starting at the inlet, the zone of exhausted reactive material gradually progresses throughout the column, the pollutant eventually breaking through the column. The breakthrough curves usually show S-shaped profiles, the slope being related with the uptake capacity, mass transfer rates and macroscopic flow parameters. Column performance may be characterized by values such as the number of pore volumes before breakthrough and number of pore volumes before exhaustion. These values depend on both column design and operation parameters. The aim of the present work is to present a survey of the data reported on arsenic removal by means of ZVI-based fixed bed columns. The effects of column design parameters (i.e., column setup, composition of reactive media, packing characteristics, bed depth, initial porosity and hydraulic conductivity) and operation conditions (i.e., flow rate, empty bed contact time, influent arsenic concentration, pH, dissolved oxygen concentration and aqueous matrix composition) are discussed. Special emphasis is given to bed clogging effects and ZVI reactivity losses during long term tests. In addition, the results obtained using two continuous ZVI systems operated in our laboratory under very different dissolved oxygen concentrations are discussed.