Sepia ink as a surrogate for colloid transport tests in porous media
Diego Soto-Gómez, Paula Pérez-Rodríguez, J.Eugenio López-Periago, Marcos Paradelo
Available online 06 June 2016. Published by Elsevier B.V.
We examined the suitability of the ink of Sepia officinalis as a surrogate for transport studies of
microorganisms and microparticles in porous media. Sepia ink is an organic pigment consisted on
a suspension of eumelanin, and that has several advantages for its use as a promising material for
introducing the frugal-innovation in the fields of public health and environmental research: very
low cost, non-toxic, spherical shape, moderate polydispersivity, size near large viruses, nonanomalous
electrokinetic behavior, low retention in the soil, and high stability.
Electrokinetic determinations and transport experiments in quartz sand columns and soil
columns were done with purified suspensions of sepia ink. Influence of ionic strength on the
electrophoretic mobility of ink particles showed the typical behavior of polystyrene latex spheres.
Breakthrough curve (BTC) and retention profile (RP) in quartz sand columns showed a depth
dependent and blocking adsorption model with an increase in adsorption rates with the ionic
strength. Partially saturated transport through undisturbed soil showed less retention than in
quartz sand, and matrix exclusionwas also observed. Quantification of ink in leachate fractions by
light absorbance is direct, but quantification in the soil profile with moderate to high organic
matter content was rather cumbersome.
We concluded that sepia ink is a suitable cheap surrogate for exploring transport of pathogenic
viruses, bacteria and particulate contaminants in groundwater, and could be used for developing
frugal-innovation related with the assessment of soil and aquifer filtration function, and
monitoring of water filtration systems in low-income regions.