Adsorption of MIB by activated carbons produced using several activation techniques

Abstract

Water treatment authorities use activated carbon as the best available technology to remove low molecular weight organic compounds from potable water. In Australia, pollutants of concern include secondary metabolites from bacterial and cyanobacterial blooms which are highly odorous and, in some cases, toxic. Of these compounds, 2-methylisoborneol (MIB) is one of the most common and its unpleasant musty earthy odour can be detected at or above approximately 10 ng/L. Difficulties in using activated carbon to target such small organic compounds arise when the water has high concentrations of natural organic matter (NOM), as these compounds also adsorb on activated carbon. The adsorption of NOM on activated carbon increases the cost of using this material in water treatment due to competition with the target organic compounds, reducing the capacity of the activated carbon for the latter. The surface of activated carbon can be tailored during production to provide physical and chemical characteristics that can either aid or hinder the adsorption of particular compounds. One source of activated carbon currently under investigation at RMIT University is brown coal char waste from power stations. This waste, currently disposed of to landfill, is potentially an option for activated carbon production. This material has the advantage that it has already been carbonised at around 500°C in the power generation process. This means that less energy is required to produce activated carbon from power station char compared to coal, making the final product cheaper to produce. Previous work at RMIT has shown that steam activated power station char can remove organic compounds from water. Production of a range of activated carbons from power station char (PSC) was undertaken using different activation methods, including steam activation, steam activation with acid pre-treatment, alkali heat treatment, and Lewis acid heat treatment. The different activation methods produced activated carbons with different pore size distributions, in particular, the acid pre-treatment increased the surface area and porosity significantly compared with steam activation, and the alkali treatment increased the microporosity. Adsorption of MIB on these activated carbons was evaluated to determine the relationship between physical and chemical interactions of the activated carbon and adsorption. Adsorption of MIB on these activated carbons was found to be dependent on the secondary micropore volume. Lewis acid treatment and alkali treatment was not involved in the generation of many of these secondary pores, hence carbons from these treatments did not perform well in adsorption tests. The best adsorption results were achieved with steam activated or acid treated steam activated samples which performed comparably to commercial products. Initial results showed that competition from NOM adsorption was lowest with the PSC activated carbons, allowing greater adsorption of MIB, compared with the commercial activated carbons.