Inhibition of biofilm formation on the surface of water storage containers using biosand zeolite silver-impregnated clay granular and silver impregnated porous pot filtration systems.

Development of biofilms occurring on the inner surface of storage vessels offers a suitable medium for the growth of microorganisms and consequently contributes to the deterioration of treated drinking water quality in homes. The aim of this study was to determine whether the two point-of-use technologies (biosand zeolite silver-impregnated clay granular (BSZ-SICG) filter and silver-impregnated porous pot (SIPP) filter) deployed in a rural community of South Africa could inhibit the formation of biofilm on the surface of plastic-based containers generally used by rural households for the storage of their drinking water. Culture-based methods and molecular techniques were used to detect the indicator bacteria (Total coliforms, faecal coliform, E. coli) and pathogenic bacteria (Salmonella spp., Shigella spp. and Vibrio cholerae) in intake water and on the surface of storage vessels containing treated water. Scanning electron microscopy was also used to visualize the development of biofilm. Results revealed that the surface water source used by the Makwane community was heavily contaminated and harboured unacceptably high counts of bacteria (heterotrophic plate count: 4.4-4.3 Log10 CFU/100mL, total coliforms: 2.2 Log10 CFU/100 mL-2.1 Log10 CFU/100 mL, faecal coliforms: 1.9 Log10 CFU/100 mL-1.8 Log10 CFU/100 mL, E. coli: 1.7 Log10 CFU/100 mL-1.6 Log10 CFU/100 mL, Salmonella spp.: 3 Log10 CFU/100 mL -8 CFU/100 mL; Shigella spp. and Vibrio cholerae had 1.0 Log10 CFU/100 mL and 0.8 Log10 CFU/100 mL respectively). Biofilm formation was apparent on the surface of the storage containers with untreated water within 24 h. The silver nanoparticles embedded in the clay of the filtration systems provided an effective barrier for the inhibition of biofilm formation on the surface of household water storage containers. Biofilm formation occurred on the surface of storage plastic vessels containing drinking water treated with the SIPP filter between 14 and 21 days, and on those containing drinking water treated with the BSZ-SICG filter between 3 and 14 days. The attachment of target bacteria on the surface of the coupons inoculated in storage containers ranged from (0.07 CFU/cm2-227.8 CFU/cm2). To effectively prevent the development of biofilms on the surface of container-stored water, which can lead to the recontamination of treated water, plastic storage containers should be washed within 14 days for water treated with the SIPP filter and within 3 days for water treated with the BSZ-SICG filter

Oligonucleotides used in this study for amplification of pathogenic genes of <i>E</i>. <i>coli</i> strains [30].

<p>Oligonucleotides used in this study for amplification of pathogenic genes of <i>E</i>. <i>coli</i> strains [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194715#pone.0194715.ref030" target="_blank">30</a>].</p

Schematic representation of the SIPP filter—A: silver-impregnated porous pot; B: 10 L bucket with clay pot inside; C: 20 L bucket for the collection of treated water; D: a complete SIPP filter.

<p>Schematic representation of the SIPP filter—A: silver-impregnated porous pot; B: 10 L bucket with clay pot inside; C: 20 L bucket for the collection of treated water; D: a complete SIPP filter.</p

Schematic representation of modified HWTS—(1) BSZ-SICG; (2) modified BSF with zeolite and silver-impregnated granular clay; (3) layers of the modified BSF (A—7 mm gravel; B—0.95 mm coarse sand; C—3 mm natural zeolite; D—silver-impregnated granular clay; E—diffusion plate; and F—0.15 mm fine sand); (4) a complete BSZ-SICG.

<p>Schematic representation of modified HWTS—(1) BSZ-SICG; (2) modified BSF with zeolite and silver-impregnated granular clay; (3) layers of the modified BSF (A—7 mm gravel; B—0.95 mm coarse sand; C—3 mm natural zeolite; D—silver-impregnated granular clay; E—diffusion plate; and F—0.15 mm fine sand); (4) a complete BSZ-SICG.</p

Monthly observations on prevalence of indicator and presumptive pathogenic bacteria in surface water that serves as a drinking water source in Makwane community.

<p>Monthly observations on prevalence of indicator and presumptive pathogenic bacteria in surface water that serves as a drinking water source in Makwane community.</p

Amount of silver leached from BSZ-SICG, SIPP-H and SIPP-L filters.

<p>Amount of silver leached from BSZ-SICG, SIPP-H and SIPP-L filters.</p

SEM images depicting attachment of microorganisms on the surface of the coupons inoculated in treated water produced by BSZ filter (filter without silver).

<p>SEM images depicting attachment of microorganisms on the surface of the coupons inoculated in treated water produced by BSZ filter (filter without silver).</p

Average physicochemical analysis values of untreated and treated water samples (D = days).

<p>Average physicochemical analysis values of untreated and treated water samples (D = days).</p

Indicator bacteria and pathogenic presumptive bacteria attached on the surfaces of coupons inoculated in untreated water and treated water produced by various household drinking water treatment systems during the storage period—A: heterotrophic plate count; B: faecal coliforms; C: total coliforms; D: <i>Salmonella</i>; and E: <i>E</i>. <i>coli</i>.

<p>Indicator bacteria and pathogenic presumptive bacteria attached on the surfaces of coupons inoculated in untreated water and treated water produced by various household drinking water treatment systems during the storage period—A: heterotrophic plate count; B: faecal coliforms; C: total coliforms; D: <i>Salmonella</i>; and E: <i>E</i>. <i>coli</i>.</p

Pearson’s correlation values showing relationship between the attached microorganisms from the coupons inoculated in different sources (untreated water, water treated with SIPP, water treated with BSZ and water treated with BSZ-SICG) and the length of storage (Days 1–3, Day 7, Day 14 and Day 21).

<p>Pearson’s correlation values showing relationship between the attached microorganisms from the coupons inoculated in different sources (untreated water, water treated with SIPP, water treated with BSZ and water treated with BSZ-SICG) and the length of storage (Days 1–3, Day 7, Day 14 and Day 21).</p