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Gift of Water System Research

Experiments were conducted at Purdue University in 2013 to quantify the effectiveness of the systems to produce clean drinking water, including measurements of volumetric flow rate, bacterial inactivation, turbidity, free, total and combined residual chlorine concentrations, volatile disinfection by-products (DBPs), and UV absorbance at 254 nm. The clogging rates for the 1 μm string filters were measured to quantify their sustainability. The GOW system was also tested for human virus removal efficiency through inactivation assays using bacteriophage as surrogates for human viruses. Finally, source water quality data, including turbidity and viable Escherichia coli (E. Coli) concentrations, from communities where GOW systems are used were collected during a trip to Haiti.

  • Volumetric Flow Rate: The average flow rate through the Gift of Water systems proved to have little variability throughout the eight weeks of experimentation, implying that the clogging of the filters by colloidal particles from the source water was not sufficient enough to cause an obvious change in flow rate during that time. The average flow rate measurement was approximately 13 mL/s. The process, therefore takes approximately 25 minutes for the water to flow through the system.
  • Bacterial Inactivation: The Gift of Water system was successful in inactivating 100% of the E. Coli bacteria in the source water throughout the course of the experiments. This suggests that the combination of treatment methods used in the GOW system is effective for removal and/or inactivation of E. coli. The WHO regulates that there must be zero E. coli colonies in any 100 mL sample of drinking water. The MCLs, designated by the US EPA specify that there must be zero detectable E. coli colonies in a liter of sample. The GOW system successfully meets both of these objectives.
  • Turbidity: The Gift of Water system was able to remove a large fraction of the colloidal particles from the water.  The effluent turbidity values for the system consistently fell below 5 Nephelometric Turbidity Units (NTU), or the maximum turbidity limit for systems involving alternative filtration as defined by the US EPA, when the influent water was less than or equal to 12 NTU.
  • Free, Total and Combined Residual Chlorine: The prechlorination step in the Gift of Water system composes of a 67 mg tablet of free chlorine, resulting in a dose of 3.35 mg/L as Cl2. The post-chlorination step uses a 17 mg tablet of free chlorine, resulting in a dose of 0.85 mg/L as Cl2. The GAC was effective in removing most of the free and total chlorine from the first chlorine dose.  The average free and total chlorine concentrations in the final water samples were approximately 0.54 mg/L as Cl2 and 0.58 mg/L as Cl2, respectively. The combined chlorine concentration measurements were substantially less than the free chlorine concentration measurements, with an average concentration of 0.09 mg/L as Cl2 in the effluent water sample.
  • Volatile Disinfection By-Products: Chloroform (CHCl3) was the only DBP observed to be present above the detection limit in the chlorinated water samples.  The maximum average chloroform concentrations measured in the effluent water samples was 27 μg/L, which is well below the Maximum Contaminant Level of 80 μg/L for Total Trihalomethanes, as established by the US EPA.
  • UV Absorbance at 254 nm: The UV absorbance at 254 nm is indicative of the organic compounds present in the water that are associated with potential DBP formation. These measurements decreased an average of 38% from the raw water to the final water samples throughout the course of the experiment. This implies that the UV-absorbing compounds are successfully removed by the filtration or adsorption in the GAC, or by the reactions in the secondary chlorine dose.
  • Clogging Rate: The point of clogging was defined as when the filters reached a flow rate of 2 mL/s, corresponding to a filtration time of 2.8 hours. The string filters should be replaced once the flow rate slows to this point. The 1 μm polypropylene filter allowed an average of 4037 liters of water through the filter before clogging occurred. This corresponds to approximately 202 runs for the string filters. The turbidity in the raw water used throughout this experiment ranged from 0.4-35 NTU, so the lifespan of the filters recorded in this experiment is not likely identical to the lifespan of the filters in every situation.
  • Human Virus Removal: The US EPA requires 99.99% (4-log) removal of viruses in drinking water treatment processes. Two strains of bacteriophage (phage) were used as surrogates for human viruses in the inactivation assays; φS1, which infects the bacteria Pseudomonas fluorescens, and T4, which infects the bacteria E. coli. The GOW system achieved 99.99999% (7-log) removal for the φS1 phage suspension and 99.99% (4-logs) removal for the T4 phage suspension when used with Milli-Q water, an ultrapure water source that would not add excessive chlorine demand to the test water.

Source Water Quality in Haiti: Water quality data from six water sources were collected in Haiti. The E. coli concentrations in the samples ranged from 1.5 Most Probable Number (MPN) of E. coli per 100 mL of the sample to 48.3 MPN of E. coli per 100 mL of sample.  The experiments proved that the GOW systems can effectively inactivate these levels of E. coli concentrations. The turbidity measurements ranged from 0.19 NTU to 6.64 NTU. The experiments also proved that the GOW systems can meet the EPA turbidity regulations based on this data. This water was dramatically less turbid than the Wabash River water used for testing. The source water samples were also generally less turbid than the water used for the clogging rate experiments at the effluent contact chamber at the West Lafayette WWTP. Under the time periods studied, the water used in experiments at Purdue University in Spring 2013 were worse than what the GOW filter users would experience in Haiti.

Literature

Evaluation of Process Changes on Finished Water Quality for Gift of Water System

Amanda Costello
Purdue University, 2013

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Sodium Hypochlorite Generation for Household Water Disinfection in Haiti

Nadine van Zyl
Massachusetts Institute of Technology, 2001

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Trihalomethane Formation in Rural Household Water Filtration Systems in Haiti.

Daniele S. Lantagne
Massachusetts Institute of Technology, 2001

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11956 Bernardo Plaza Drive #231                  San Diego, CA 92128

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Gift of Water is a 501(c)(3) organization