Experimental and Numerical Modeling Studies of Arsenic Removal with Wood Ash from Aqueous Streams

Abstract

Arsenic, a toxic element, is found all over the earth's crust. It comes in contact with water through the dissolution of minerals and ores. This raises the concentration of arsenic in ground water. Long-term exposure to arsenic through drinking water has proved to be catastrophic for the human body. That is why the US EPA has lowered the allowable concentration of arsenic in drinking water to 5 ppb. The people of the affected area need a cost-effective simple process to combat arsenic problem.

While many processes have been proposed in the past, most of them are not cost-effective and/or not efficient to remove As (III), one of the two inorganic species, and ten times more toxic than As (V). In this research, it is found that wood ash has the potential to adsorb both As (III) and As (V) from contaminated water at low concentration levels without any chemical treatment.

Wood ash is the inorganic and organic residue remaining after the combustion of wood or unbleached wood fiber. Wood ash is usually found as a disposed waste. Consequently, it can be used as one of the cheapest adsorbent materials- in household level treatment. Maple wood ash was used both for static batch tests and dynamic column tests. Static batch tests with the sodium arsenite (NaAs02) and sodium arsenate (Na2HAs04) solutions of different concentration were conducted. The Langmuir and Freundlich adsorption model have been developed for all the inorganic species that are present in aqueous streams.

In dynamic column tests, aqueous streams that were contaminated with arsenic were passed through the column containing ash, which lowered the arsenic concentration to less than 5ppb. Six runs were conducted to show the efficacy of wood ash column. The ash column was modeled using surface excess theory and has been successfully matched with experimental results.