Abstract
Access to safe drinking water is still a distant dream to millions of people around the world. Especially, people from the low-income group in the developing countries remain deprived of this fundamental right and causes millions of death. There is an urgent need to develop affordable and easy to handle water filter which can provide desired drinking water quality without any electricity. In the present work, a simple and low-cost surface engineered particle (SEP) based filter is developed via alkali treatment of soda-lime-silica particle. The SEP based filter can be used as a portable, non-electric, gravity-driven Point-of-Use (POU) water disinfection system. The developed SEP-based filter is capable to arrest the 99.48% (~2 to 2.5 log10 reduction) of gram-negative bacteria Escherichia coli (E. coli OP50) on its surface from the water containing 3 × 108 cells/ml. No bacterial regrowth is observed in the purified water for 12 h. The performance of SEP bed filter is implicated to the nano-scale surface roughness, its distribution along with the surface charge and surface hydrophobicity which are favorable to attract and adhere the bacteria in the flowing water. The observation is consistent over multiple filtration cycles indicating the suitability of SEP based bed filter for POU water disinfection. The SEP surface with 0.05 mM Ag+ loading (SEP+) completely inactivated (>99.99999%) bacteria and protects any bacteria recontamination in the purified water for its long term usage. The strong and effective silver binding property of SEP surface enables very minimal silver loading and eliminates any health hazard due to low silver leaching (~50 ppb) which is well below the drinking water equivalent level (DWEL ≤ 100 ppb). In rural and urban slum areas of developing countries where no water purification system exists prior to consumption, the easy-to-implement and affordable SEP-based gravity-driven non-electric point-of-use water purifier (materials cost ~ 0.25 USD) can be used to protect millions of lives from water borne diseases.
Highlights
Peclet Number (Ratio of convective transport to diffusive transport) London-van der Waals Force number (Ratio of interaction energy to particle’s thermal energy) Dimensional number for aspect ratio Gravity Number (Ratio of stokes particle settling velocity to approach velocity of the fluid)
Experiments were performed to evaluate the E. coli removal capacity of filter bed made up of surface engineered particle (SEP)
No bacterial regrowth is observed for 12 h in the agar plate with SEP which implies that a number of E. coli cells www.nature.com/scientificreports are not sufficient enough to regrow for 12 h after passing through SEP bed (Fig. 2D)
Summary
Peclet Number (Ratio of convective transport to diffusive transport) London-van der Waals Force number (Ratio of interaction energy to particle’s thermal energy) Dimensional number for aspect ratio Gravity Number (Ratio of stokes particle settling velocity to approach velocity of the fluid). In many cases, the contact time (between the material surface and bacteria) is much higher (~3 h) for complete inactivation (>7-log reduction). It is worthy to note that none of these silver free filter materials (i.e. uncoated) is able to reduce the bacteria number not more than 1-log reduction[22] (~90%). The bacterial removal or inactivation efficiency of any filter material depends on the interaction between bacteria and the surface which can be calculated using colloid filtration theory (CFT)[23,24] using collector efficiency (η), collision efficiency (α) and bacterial deposition rate (kd). Where, As, NPe, NLo, NR, and NG are the dimensionless numbers (given in Table 1) that account for effects of neighboring particles, diffusion, London-van der Waals forces, interception, and sedimentation on particle collisions respectively[25]. The bacterial deposition rate (kd) is determined using the following equation: kd
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