Evaluation of low-cost materials for sorption of hydrophobic organic pollutants in stormwater

Abstract

Conventional stormwater treatment techniques such as sedimentation and filtration are inefficient for removing the dissolved and colloidal phases of hydrophobic organic compounds (HOCs) present in stormwater. Adsorption could be a promising technique for removing colloidal and dissolved pollutants. Five low-cost sorbent materials were investigated in this project, including two minerals – vermiculite and perlite – and three waste products – two pine barks and a sawdust – as potential adsorbents for removal of polycyclic aromatic hydrocarbons (PAHs), alkylphenols and phthalates; HOCs commonly found in stormwater. Adsorption capacity and kinetics were studied through batch adsorption tests using synthetic stormwater spiked with a mixture of HOCs. Vermiculite and perlite exhibited insignificant removal of the organic contaminants. The three wood-based materials retained >80% of the initial HOC concentration (10-300 μg/L). The two barks exhibited slightly higher adsorption capacities of HOCs than the sawdust. For all compounds tested, maximum adsorption onto the wood-based media was reached in <10 min. The highest adsorption capacity was found for PAHs (up to 45 μg/g), followed by alkylphenols and phthalates. No correlation was found between adsorption capacity and physical-chemical parameters such as solubility and partition coefficients (log K(ow)). Agreement between empirical data and the pseudo-second order kinetic model suggest chemisorption of HOCs onto a monolayer on wood-based media. This could lead to early saturation of the materials and should be investigated in future studies through repeated adsorption of HOCs, for example in column studies.

Mechanisms of removal of three widespread pharmaceuticals by two clay materials

“…2). Removal efficiencies obtained in this work with vermiculite for two of the pharmaceuticals (GB and MA) are comparable with those obtained in other adsorption studies, where removal efficiencies on this clay mineral seem to be frequently around 10-40% also for a variety of other compounds [14,25]. The large efficiencies obtained with LECA are also consistent with previous studies of other compounds [26,28].…”

“…Adsorption processes have been regarded as a potentially interesting option to complement existing water and wastewater treatment systems aiming to improve the removal of many organic xenobiotic pollutants, including pharmaceuticals [10,[13][14][15][16][17][18][19]. However, the selection of the adsorbent materials is crucial, not solely from the perspective of the pollutants removal efficiency but also in regard to its cost.…”

Adsorption of organic stormwater pollutants onto activated carbon from sewage sludge

“…The high-molecular weight compounds needed time to diffuse into smaller and smaller pores and finally reach equilibrium. Similar trends in kinetic data were observed in a previous study on the adsorption of HOCs onto sawdust and pine bark (Björklund and Li 2015).…”

“…The procedure to extract organic compounds from water and the instrumentation used for analysis are described in detail elsewhere (Björklund and Li 2015) and are summarized in the Supplementary Material.…”

“…This can be compared to a similar study of HOC adsorption onto wood-based products, where adsorption capacities ranged from 0.5-1.3 µg/g (Cinitial=10 µg/L) to 38-45 µg/g (Cinitial=300 µg/L) (Björklund and Li 2015). The highest remaining concentrations (Ce) after 24 h of adsorption were found for DEHP (≤205 µg/L), followed by benzo[e]pyrene (≤72.5 µg/L).…”