The design and usage of a portable incubator for inexpensive in-field water analysis
Humanitarian engineers need an inexpensive, fast, visually compelling way to assess bacterial water quality in remote locations. One way to do this is with 3M Petrifilm E. coli/Coliform (EC) Count Plates to detect E. coli in water samples. These require incubation at close to body temperature. To meet this need, we provide a free, open-source design of a battery-powered incubator capable of maintaining 35Â°C Â± 1Â°C for up to 65 hours in ambient temperature of 25Â°C. Our incubator, called the Armadillo, can be replicated by an ordinarily skilled person in five hours for under USD $200.00 in materials cost. This paper summarises the reference documentation for construction, sample handling, inoculation, and incubation using Petrifilms and the Armadillo. Colony-forming unit (CFU) counts generated by the Armadillo are compared side-by-side with a laboratory-grade incubator. Incubation performance at ambient temperatures of 25Â°C and 4Â°C shows that a single battery charge reliably powers a full incubation period of 48 hours under normal ambient temperatures.
M 2018, E. coli/Coliform Count Plate Interpretation Guide, viewed 18 April 2018, https://multimedia.3m.com/mws/media/1388591O/petrifilm-e-coli-coliform-count-plate-interpretation-guide.pdf
Adegbite A 2015, â€˜Comparative assessment of field methods for microbiological water quality testing in emergencies, International Journal of Development Research, Vol. 5, No. 7, pp. 4908-4915, viewed 10 December 2018, https://www.researchgate.net/publication/299461356_COMPARATIVE_ASSESSMENT_OF_FIELD_METHODS_FOR_MICROBIOLOGICAL_WATER_QUALITY_TESTING_IN_EMERGENCIES
Allen, M, Edberg, S, Clancy, J & Hrudey, S, 2015, â€˜Drinking water microbial mythsâ€™, Critical Reviews in Microbiology, vol. 41, no. 3, pp. 366-373, viewed 10 December 2018, https://www.tandfonline.com/doi/abs/10.3109/1040841X.2013.849655
Bain, R, Bartram, J, Elliott, M, Matthews, R, McMahan, L, Tung, R, Chuang, P & Gundry, S, 2012, â€˜A summary catalogue of microbial drinking water tests for low and medium resource settingsâ€™, International Journal of EnvironmentalRresearch and Public Health, vol. 9, no.5, pp. 1609-1625, viewed 10 December 2018, http://www.mdpi.com/1660-4601/9/5/1609
Brown, J, Stauber, C, Murphy, J, Khan, A, Mu, T, Elliott, M. & Sobsey, M, 2011, â€˜Ambientâ€temperature incubation for the field detection of Escherichia coli in drinking waterâ€™, Journal of Applied Microbiology, vol. 110, no. 4, pp. 915-923, viewed 10 December 2018, https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2672.2011.04940.x
Edberg, S, Rice, E, Karlin, R & Allen, M 2000, â€˜Escherichia coli: the best biological drinking water indicator for public health protectionâ€™, Journal of Applied Microbiology, vol. 88, no. S1, viewed 10 December 2018, https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2672.2000.tb05338.x
EPA 2016, Quick Guide to Drinking Water Sample Collection, United States Environmental Protection Agency, pp. 7-8, viewed 18 April 2018, https://www.epa.gov/sites/production/files/2015 11/documents/drinking_water_sample_collection.pdf
EWB-USA-Austin 2017, Portable Petrifilm Incubator for Inexpensive In-field Analysis of Water Quality. Instructables.com, viewed 10 December 2018, http://www.instructables.com/id/Portable-Petrifilm-Incubator-for-Inexpensive-In-Fi/.
EWB-Austin-Github 2017a, Construction of Armadillo V1.0: A Low-Cost Incubator for Off-Grid Water Quality Analysis, viewed 10 December 2018,https://github.com/EWB-Austin/petrifilm-incubator/blob/master/doc/ConstructionManual.pdf.
EWB-Austin-Github 2017b, User-Guide, viewed 10 December 2018, https://github.com/EWB-Austin/petrifilm-incubator/blob/master/doc/UserGuide.pdf
EWB-Austin-Github 2018, Petrifilm-incubator, viewed 10 December 2018, https://github.com/EWB-Austin/petrifilm-incubator
Geissmann, Q 2013, â€˜OpenCFU, a new free and open-source software to count cell colonies and other circular objectsâ€™ Public Library of Science (PLoS) ONE, vol. 8, no. 2, viewed 10 December 2018, http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0054072
Schwartz, M & Ward, A 2015, â€˜Portable incubator design, construction, validation and case studyâ€™, Unpublished Draft Paper, Engineers Without Borders USA, viewed 10 Decembert 2018, http://www.ewb-usa.org//files/2015/05/PortableIncubator.pdf
Thaemert, D & Andrews, D 2014, â€˜Bacterial testing plate incubation in developing regionsâ€™, World Environmental and Water Resources Congress 2014, pp. 1608-1616, viewed 10 December 2018, https://ascelibrary.org/doi/abs/10.1061/9780784413548.159
Vail, J Morgan, R, Merino, C, Gonzales, F, Miller, R & Ram, J L 2003, â€˜Enumeration of waterborne Escherichia coli with Petrifilm platesâ€™, Journal of Environmental Quality, vol. 32, no. 1, pp. 368-373, viewed 10 December 2018, https://dl.sciencesocieties.org/publications/jeq/abstracts/32/1/368
Wohlsen, T, Bates, J, Vesey, G, Robinson, WA & Katouli, M 2006, â€˜Evaluation of the methods for enumerating coliform bacteria from water samples using precise reference standardsâ€™, Letters in Applied Microbiology, vol. 42, no. 4, pp. 350-356, viewed 10 December 2018, https://onlinelibrary.wiley.com/doi/full/10.1111/j.1472-765X.2006.01854.x
World Health Organization 1996, Guidelines for drinking-water quality. Vol. 2, Health criteria and other supporting information, pg. 95, viewed 10 December 2018, http://www.who.int/water_sanitation_health/publications/gdwq2v1/en/index1.html