Effects of Temperature and pH on Reduction of Bacteria in a Point-of-Use Drinking Water Treatment Product for Emergency Relief

Abstract

The effects of temperature and pH on the water treatment performance of a point-of-use (POU) coagulant/disinfectant product were evaluated. Cold temperatures (ϳ5°C) reduced the bactericidal efficiency of the product with regard to Escherichia coli and total coliform log 10 reductions. There is evidence that point-of-use (POU) water treatment and safe storage techniques can be effective interventions to prevent diarrheal diseases in humanitarian emergency contexts (1). Water quality objectives for humanitarian relief (2) consist of no Escherichia coli per 100 ml, a free chlorine residual (FCR) of 0.5 mg/liter (30 min contact time and pH Ͻ 8), and turbidity of less than 5 nephelometric turbidity units (NTU).Coagulant/disinfection products (CDPs) are a POU water treatment option that provide microbial quality improvements, turbidity reductions, and a posttreatment FCR. Most commercially available CDPs are sachets containing a coagulant (e.g., ferric sulfate) and a disinfectant (e.g., calcium hypochlorite) along with other chemical components (e.g., oxidizing agents, flocculant aids, etc.) for a predetermined treatment volume. Cold temperatures (Ͻ5°C) can affect coagulant-assisted treatment processes (3), and alkaline pH levels (Ͼ8) can render free residual chlorination less effective (4). Thus, the effects of pH and temperature (under extreme conditions) should be an important part of the evaluation of the treatment efficiency of CDPs and were the objective of this study.Treatment efficiencies (i.e., bacterial removal, turbidity reductions, and FCR levels) were evaluated against current humanitarian water treatment objectives (2) and recent quantitative microbial risk assessment (QMRA)-based criteria for the evaluation of POU treatment options (5). This study focused on bacterial water quality improvements (i.e., E. coli removal), the microbial quality criterion in relief situations.Treatment steps of a CDP (PUR; Procter & Gamble Co., Pakistan) were adapted to a laboratory setup, namely, mixing (for 5 min), settling (for 5 min), cloth filtration, and continued disinfection (for 20 min). A Kemwater Flocculator 2000 (Kemira, Sweden) stirring paddle was set at 250 rpm to provide uniform mixing. A commercially available cloth (J-Cloth; Associated Brands, Canada) was used as the filtration material to simulate a worstcase scenario for this step. This was in line with the objective of evaluating the CDP's performance under simulated extreme conditions.The test water was a 1:5 dilution of primary settled wastewater (Station d'epuration Est, Québec) in dechlorinated tap water (5). Treatment efficiencies were tested under different conditions, namely, "reference" (pH 7, 20°C), "extreme pH" (pH 9, 20°C), and "cold temperature" (pH 7, 5°C). When needed, pH was adjusted with NaOH and H 2 SO 4 . A crushed ice jacket around the mixing vessel kept test water at 5 Ϯ 1°C. Turbidity was adjusted to approximately 100 NTU using a kaolin clay slurry. In order to further examine the temperature and pH effect on the different underpinnin...

Laboratory evaluation of a new coagulant/disinfectant point-of-use water treatment product for emergencies

“…The E. coli LRs of this study are in line with the results of another CDP tested previously (Marois‐Fiset et al . ) under similar conditions.…”

“…Such a property has been previously shown to mitigate effects of alkaline pH on disinfection efficiencies (Marois‐Fiset et al . ). The lowest LRs and highest post‐treatment bacterial (total coliform) concentrations occurred at alkaline treatment pH coupled with cold temperature conditions.…”

“…Similar trends were observed in trials of another CDP (without a quenching agent) tested under similar conditions (Marois‐Fiset et al . ). Although this test water composition recommendation (WHO ) may not be representative of typical surface waters on which the product would be used, it does test the product under very challenging conditions with regard to microbial removal.…”

“…The bacterial removal that could be potentially attributable to coagulation and settling (between 1–2 LRs) has been previously characterized (Marois‐Fiset et al . ) for a different CDP product and was also shown to be negatively affected by reduced temperatures.…”

Laboratory Efficacy and Disinfection by-Product Formation of a Coagulant/Disinfectant Tablet for Point-of-Use Water Treatment

“…Laboratory efficacy testing can serve to highlight the performance envelopes of this type of POU water treatment product [9,15]. This type of testing can also serve to highlight other relevant issues such as the product's capability of maintaining adequate FCR levels and can indicate possible levels of DBPs that could be generated by its use.…”