Improvement of the Bag-Mediated Filtration System for Sampling Wastewater and Wastewater-Impacted Waters

Abstract

Environmental surveillance of poliovirus (PV) plays an important role in the global program for eradication of wild PV. The bag-mediated filtration system (BMFS) was first developed in 2014 and enhances PV surveillance when compared to the two-phase grab method currently recommended by the World Health Organization (WHO). In this study, the BMFS design was improved and tested for its usability in wastewater and wastewater-impacted surface waters in Nairobi, Kenya. Modifications made to the BMFS included the size, color, and shape of the collection bags, the filter housing used, and the device used to elute the samples from the filters. The modified BMFS concentrated 3-10 L down to 10 mL, which resulted in an effective volume assayed (900-3000 mL) that was 6-20 times greater than the effective volume assayed for samples processed by the WHO algorithm (150 mL). The system developed allows for sampling and in-field virus concentration, followed by transportation of the filter for further analysis with simpler logistics than the current methods. This may ultimately reduce the likelihood of false-negative samples by increasing the effective volume assayed compared to samples processed by the WHO algorithm, making the BMFS a valuable sampling system for wastewater and wastewater-impacted surface waters.

Keywords: BMFS; Enterovirus; Environmental surveillance; Pathogens; Poliovirus; Wastewater.

Fig. 1

Schematic of collection bag. a First-generation yellow, 10-L bag. Bag outlet was located 4 cm above the bag’s bottom. b Second-generation drab green, 10-L bag. Bag outlet was located 10 cm above the bag’s bottom. 0.5-L volume increments were demarcated on the bag. c Third-generation drab green, 6-L bag. Bag outlet was located at the bag’s bottom, and a 15.5° slope was heat sealed onto the bottom of the bag. 0.25-L volume increments were demarcated on the bag

Fig. 2

BMFS sample filtration. a Collection bag hangs on tripod stand by hooks and holes in the side seams; b after the collection bag is hung, the ViroCap filter attaches via a tubing adapter; c ViroCap filtrate drains to the source water

Fig. 3

Schematic of elution device. a Syringe to inject the eluent; b hole in injection tubing allows air flow during eluent injection and prevents liquid lock; c ViroCap filter receives the eluent and viruses adsorbed to the filter are released to the eluate; d collection cup encloses the eluate during final collection, reducing the potential for cross-contamination by aerosolization of pathogens from popping bubbles; e hydrophobic filter prevents aerosols from entering the bilge pump; f manual bilge pump drives the eluate movement from the ViroCap filter to the collection cup by vacuum pressure

Fig. 4

Time required to filter samples at the Kibera site in Nairobi. Total volume filtered ranged from 2.9 to 4.0 L. n = 2 for disposable housing, n = 6 for reusable housing. Error bars represent standard deviation

Fig. 5

Schematic of filter housing. a Disposable housing: flow enters the filter housing, passes through the filter, and then exits the filter housing on a vertical plane. The semi-flexible tubing creates a 0.2-m lost head from the flow exit. b Reusable housing: flow enters the filter housing, passes through the filter, and then exits the filter housing on a flat horizontal plane

Fig. 6

Liquid and air flow in the reusable filter housing. a Foam/bubble formation caused by the introduction of air into the liquid phase. b Outlet extension tube forces the formation of an air barrier, which reduces foam formation

Fig. 7

Average volumes filtered through ViroCap disposable housings at sites in Nairobi. For Kibera, Eastleigh A, and Eastleigh B sites, n = 13. For the Mathare site, n = 15. Error bars represent standard deviation