Development of a novel biopolymer surrogate for studying Cryptosporidium parvum removal in sand media

<p dir="ltr">Understanding <i>Cryptosporidium</i> oocyst removal in porous media is important in water safety management. While studies have assessed <i>Cryptosporidium</i> transportation in different filtration media using oocyst-sized synthetic polystyrene microsphere surrogates, their applications are limited due to the lack of environmental biodegradability. Surrogates with biodegradable properties are needed for applications involving real operating systems and eco-sensitive environments. In this study, we developed a novel biopolymer surrogate for <i>C. parvum</i> oocysts using alginate-chitosan-layered carnauba wax microparticles. The surrogate closely resembled the size (surrogate diameter 4.2 ± 0.4 μm vs oocysts 5.3 ± 0.70 μm), shape, and surface hydrophobicity (14.4 % ±5.4 vs oocysts 16.8 % ± 1.8) of the oocysts but were more negatively charged (surrogate −52.7 ± 0.3 mV vs. oocysts −12.8 mV ±2.8). Surrogate microparticles were fluorescently stained with safranin to facilitate their enumeration. Filtration removal experiments in alluvial sand showed that the relative concentrations of the surrogate and <i>Cryptosporidium</i> oocysts were mostly in the same order of magnitude (2.0–3.5 log), and the surrogate's total mass recovery (3.2 %) was close to that of the oocysts (2.2 %). However, the surrogate was slightly conservative as its removal was 0.5–0.7 log lower than oocyst removal during the peak breakthrough, potentially due to its greater negative charge.</p>