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

Understanding Cryptosporidium oocyst removal in porous media is important in water safety management. While studies have assessed Cryptosporidium 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 C. parvum 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 Cryptosporidium 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.