Iron uptake is essential for Escherichia coli survival in drinking water

Iron amendments minimize the first-flush release of pathogens from stormwater biofilters

First flush or the first pore volume of effluent eluted from biofilters at the start of rainfall contributes to most pollution downstream because it typically contains a high concentration of bacterial pathogens. Thus, it is critical to evaluate designs that could minimize the release of bacteria during a period of high risk. In this study, we test the hypothesis of whether an addition of iron-based media to biofilter could limit the leaching of Escherichia coli (E. coli), a pathogen indicator, during the first flush. We applied E. coli-contaminated stormwater intermittently in columns packed with a mixture of sand and compost (70:30 by volume, respectively) and iron filings at three concentrations: 0% (control), 3%, and 10% by weight. Columns packed with a mixture of sand and iron (3% or 10%) without compost were used to examine the maximum capacity of iron to remove E. coli. In columns with iron, particularly 10% by weight, the leaching of E. coli during the first flush was 32% lower than the leaching from compost columns, indicating that the addition of iron amendments could decrease first-flush leaching of E. coli. We attribute this result to the ability of iron to increase adsorption and decrease growth during antecedent drying periods. Although the addition of iron filings increased E. coli removal, the presence of compost decreased the adsorption capacity: exposure of 1 g of iron filings to 1 mg of DOC reduces E. coli removal by 8%. The result was attributed to the alteration of the surface charge of iron and blocking of adsorption sites shared by E. coli and DOC. Collectively, these results indicate that the addition of sufficient amounts of iron media could decrease pathogen leaching in the first flush effluent and increase the overall biofilter performance and protect downstream water quality.

Influence of sand depth and pause period on microbial removal in traditional and modified biosand filters

Three different-sized biosand filters (i.e., the center for Affordable Water and Sanitation Technology v10 concrete filter, a 5-gal bucket filter, and a 2-gal bucket filter with fine sand depths of 54, 15, and 10 cm, respectively), configured with and without the addition of iron nails to the diffuser basin, were evaluated for removal of bacteria, protozoa, and viruses over pause periods ranging from 1 to 72 hrs. Biosand filtration proved effective at all pause periods tested, and log10 removal of bacteria and protozoan cysts for all filter sizes and configurations ranged from 3 to 4. The addition of nails resulted in significantly better (p<0.05) bacteria removal for all filter sizes and significantly better (p<0.02) protozoan removal for the bucket-sized filters. Log10 virus removal for all filter types and sizes ranged from <1 to 6. Both the pause period and filter type (size/configuration) influenced virus removal, and the addition of nails to the filter improved virus removal at the shorter pause periods. Scaled-down biosand filters provide a viable household water treatment option for some of the millions of people that still lack access to an improved water source.

Assessment of an anti-scale low-frequency electromagnetic field device on drinking water biofilms

Low intensity and very low-frequency electromagnetic fields (EMF) used for preventing scaling in water distribution systems were tested for the first time for their potential impact on drinking water biofilms. The assays were carried out in laboratory-scale flow-through reactors that mimic water distribution systems. The drinking water biofilms were not directly exposed to the core of the EMF generator and only subjected to waterborne electromagnetic waves. The density and chlorine susceptibility of nascent or mature biofilms grown under exposure to EMF were evaluated in soft and hard water. This EMF treatment was able to modify CaCO₃ crystallization but it did not significantly affect biofilms. Indeed, over all the tested conditions, there was no significant change in cell number, or in the integrity of the cells (membrane, culturability), and no measurable effect of chlorine on the biofilm.

The association between water supply and inflammatory bowel disease based on a 1990-1993 cohort study in southeastern Norway

Inflammatory bowel disease refers to a group of chronic diseases of unknown etiology related to both genetic and environmental factors. In this 1990-1993 study, the authors investigated associations between the content and quality of drinking water and the incidence of inflammatory bowel disease. They used data from a population-based cohort recruited in southeastern Norway and a registry of water quality derived from Norwegian waterworks that contained measurements of iron, aluminum, acidity (pH), color, turbidity, and coliform bacteria. The authors found that risk of developing inflammatory bowel disease, including ulcerative colitis and Crohn's disease, was associated with high iron content. The relative risk of developing inflammatory bowel disease increased by 21% (95% confidence interval: 9, 34) when the iron content in the drinking water increased by 0.1 mg/L. They found no association between the diseases and aluminum in the water, color of the water, and turbidity of the water. The authors suggest that the observations can be explained by 2 mechanisms. First, high iron concentration works as a catalyst for oxidative stress, which will cause inflammation and/or increase the rate of cell mutations. Second, iron content stimulates the growth of bacteria and increases the likelihood of inappropriate immune responses in genetically predisposed individuals.

Effect of humic acid on the attachment of Escherichia coli in columns of goethite-coated sand

Though coliform bacteria are used worldwide to indicate faecal pollution of groundwater, the parameters determining the transport of Escherichia coli in aquifers are relatively unknown. To investigate the effect of dissolved organic carbon (DOC) on the attachment of E. coli to saturated goethite-coated sand, we carried out column experiments with E. coli with and without humic acid (HA) in monovalent and divalent salt solutions. To characterize sorption of DOC and attachment of E. coli, we measured the pH of the influent and effluent, the cation concentrations and the zeta potential of particles. Depending on the chemistry of the E. coli suspension, the normalized breakthrough concentrations were over 80 times higher in columns treated with HA compared with columns not treated with HA. However, this difference was not constant: there were time-dependent variations in attachment of E. coli to the collector surface, and in the chemical composition of the bacterial suspension. Reduction in removal occurred because HA altered the surface charge of the collector and also sterically hindered E. coli. In addition, reduction of removal in a CaCl(2) bacterial suspension was probably caused by site-blocking mechanisms between HA and Ca(2+) ions. Our results indicate that in the presence of DOC, the concept of geochemical heterogeneity in explaining attachment of biocolloids has limited relevance.