By Dave Conklin on November 4, 2021
A month ago I wrote about the discrepancies between the lab test results from 2019 and the results from this year. We are still working to reconcile the differences between the two labs. In October, we asked Umpqua Research (URC) to repeat a test of hand-cranked operation, but with 90 seconds of cranking instead of 60 seconds. Umpqua Research had reported log reductions of 1.9 and 1.5 in 60 second hand-cranked operation from tests run in September.
We expected that increasing the duration from 60 seconds to 90 seconds would bump up the log reduction to 2.0 or greater, but URC reported a log reduction of only 1.1 for 90 seconds of hand-cranked operation, a poorer result than they had obtained under the same conditions with 60 seconds of operation. The URC test report, dated October 18, 2021, is available on this website at Water Box Anti-Viral Report_101821. I had a frank discussion with URC’s director, Tom Williams, on October 21st, about the inconsistency between the October results and the September results, and an earlier inconsistency within the September results themselves (lower log reduction in shallower water). We concluded that while the URC tests do not support the conclusion that hand-cranked operation achieves the target effectiveness, neither do they support the conclusion that hand-cranked operation is not effective. Because of the wide range of results (from 0.3 log reduction in the August test to 1.9 log reduction in the September test) and because of internal inconsistencies in the results (lower log reduction in shallower water in the September test, and lower log reduction at 90 seconds in the October test), the best we can say about the hand-cranked test results from URC is that the tests are inconclusive as regards the efficacy of hand-cranked operation.
Tom at URC told me that these assays of log reduction are generally reproducible only to within about 0.5 log units. On that basis, the counterintuitive difference in the September test between a log reduction of 1.5 for hand-cranked 3-liter operation and 1.9 for hand-cranked 4-liter operation is probably not significant. We have not found an explanation for the difference between 1.9 for 60 second 4-liter operation in the September test and 1.1 for 90 second 4-liter operation in the October test.
We at Oregon Freshwater concluded that we need a more repeatable testing method, and we have decided to focus on measuring the UV “dose” directly. We have built an apparatus which will allow us to measure the intensity of the UV after it passes through the water column at 5 second intervals during operation. Those intensity measurements can then be integrated over the duration of the operation to calculate a lower bound for the UV fluence, the UV energy delivered per unit area, at each level in the water column. There have been some setbacks – at one point the window in the water box leaked and soaked the UV sensor, at another time I severed the cord which connects the sensor to the UV light meter. But we are carrying on, and hope to have fluence estimates before the end of the year.
An entirely separate and independent set of tests is being conducted by our colleagues at EMI East Africa in Uganda. Results from those tests, when they become available, will be posted on www.dayzerointernational.org.