Personal Research Data

Sampling and Testing Sites

            All sample collection was done at the Ketchum/Sun Valley Water and Sewer District Treatment Facility, located near Elkhorn in Ketchum, Idaho. In the plant are a series of UV lights above a “tray” that the raw effluent flows through. The effluent is exposed to UV light sterilizing the effluent.  Typical pre-UV effluent has E-Coli ranging from 105-1300 MPN/100mL and Total Coliform ranging from 1380-3970 MPN/100mL. After UV treatment the E-Coli count typically is <1 MPN/100mL. This is the effluent that would be used for snow making at the Sun Valley Ski Resort. Each sample was first collected in a sterile container provided by the Treatment Facility. Control samples of effluent were taken directly from the outflow trays in the sterilization building at the same location within the trays that the submersible pump pulled effluent for the snow gun. The samples were of two types. The first samples were the effluent taken directly from the outflow trays in the effluent treatment building. The second set of samples was from the “snow” produce during the experiment. Once all samples were collected they were then shipped to Magic Valley Labs located in Twin Falls, Idaho to be tested for Escherichia coli, Fecal Coliform and Total Coliform matter in the effluent.

Snow/Effluent Production

            In order for the “effluent snow” to be collected as it would at a ski resort, in a frozen, snow-like form, a variation of a snow gun had to be designed. The model used was a modification of one used by Alan Pennay, a local bed and breakfast owner in the Wood River Valley who produces his own man-made snow. Figure 1 shows the snow gun used in this experiment. A Y-shaped nose fitting was used to in order to allow both the effluent and air, under high pressure, to combine in a mixing chamber before being released through the nozzle of the apparatus. In addition there was a separate branch of the piping allowing for an effluent return system which was used between sample collections. A submersible pump was placed within the outflow trays to pump effluent to the snow gun. A high-pressure compressor was used to produce pressurized air at a range of 80 psi to 100 psi, which is consistent with those pressures used in commercial portable snow guns. Effluent was circulated through the system prior to each test. All hoses and fittings were flushed with a chlorine solution then clean water at the end of each testing session. The collection curtain was sterilized with a sprayed chlorine solution and clean water after each session as well.

Figure 1 

Collecting and Testing Procedures

High-pressure air and effluent was mixed before being ejected out of the nozzle into the freezing outside temperatures. The snow effluent sample was captured by spraying it onto a device consisting of a sheet of Visqueen (thin sheet of polypropylene) stapled between two pieces of wood with a collecting basin located at the bottom of the Visqueen (Figure 2).

Figure 2 

Each sample was taken from the Visqueen collecting basin and placed into a sterile container provided by the Treatment Facility. All of the samples were then shipped to the lab where all of the appropriate microorganism tests were done.

Results

Table 1

Test #1 (12/21/2010) (7 F or -14 C)
	Sample Type	Time	E. Coli (MPN/100mL)
	Pre-UV Effluent	8:00 AM	1300
	1 Pre-UV Effluent	9:30 AM	186
	1 Pre-UV Effluent Snow Sample	9:30 AM	275
	2 Post-UV Effluent	8:50 AM	<1
	2 Post-UV Effluent Snow Sample	8:50 AM	<1
Test #2 (12/28/2010) (17 F or -8 C)
	Sample Type	Time	E. Coli (MPN/100mL)	Total Coliform (MPN/100mL)	Fecal Coliform (CFU/100mL)
	1 Pre-UV Effluent	8:45 AM	105	1380	471
	1 Pre-UV Effluent Snow Sample	8:50 AM	409	3970	498
	2 Pre-UV Effluent	9:03 AM	209	1840	415
	2 Pre-UV Effluent Snow Sample	9:04 AM	333	2590	6089

This experiment is to evaluate if the snow making process could/would decrease the <1 MPN/100mL to an even smaller amount. After test #1 it was determined that the lab could not test E-coli levels below the stated value of <1 MPN/100mL and I determined that I needed to test the bacterial levels prior to UV disinfection. Test #2 was done with effluent prior to UV disinfection because the higher levels of E-Coli present allowed the snow making bacterial counts to be tested. The larger number of bacteria present prior to snowmaking would allow for a more accurate quantitative analysis.

After all of the tests were concluded and the data was collected a trend was seen. Unlike our hypothesis that the combination of forcing the effluent through a high pressure and cold temperature device would decrease the number of microbes, the opposite in fact seemed to have occurred. In every one of the samples taken either the E. coli, total Coliform, fecal Coliform or all of the quantities increased after going through the snow gun. The one exception was Test #1 the Post-UV Effluent samples where the difference in results was negligible due to it being less than 1 MPN/100mL in both cases.

The first issue that needs to be discussed is the large differences seen in the pre-snow gun effluent values. In Test #2 the pre-snow gun E. coli values basically double in less than 20 minutes whereas the Total Coliform values increase almost 30% in the same amount of time. The most likely reason for these seemingly random jumps in values are the extreme fluctuations in microbe density going through the treatment plant at one time. The effluent flow at the Sun Valley Sewage Treatment Facility is usually ~1187 gallons/min. This very fast flow rate means that the bacterial count in the water can greatly fluctuate in just a matter of minutes.

The second issue that needs to be discussed is why the increase in microbe activity occurred after going through the snow gun. A study entitled “Repair of Injury Induced by Freezing Escherichia coli as Influenced by Recovery Medium” tested the results of E. coli survival due to freezing at different temperatures. Three of their freezing methods included Liquid nitrogen (-196 C), Dry ice-acetone (-78 C) and Ethylene glycol (-20 C). As the temperatures they used to freeze the E. coli got colder so did the percentage of death, ~49%, ~56% and ~38% respectively, among the bacteria. This study proved that extremely cold temperatures were able to kill/disable the E. coli bacterium, but the temperatures that caused significant E. coli death were much colder than are feasibly possible in normal snowmaking guns used in ski resorts. Therefore according to this research the E. coli in our study should have had a slight death rate due to freezing temperatures (-14 C and -8 C) when data was collected.

An increase in not only E. coli levels but also in Fecal Coliform and Total Coliform levels after going through the snow gun was not expected. By vaporizing the effluent, thereby increasing the exposure of the E-Coli to the freezing temperature and subjecting the bacteria to high pressure, I expected some to be killed/disabled. I do not know from this test if any bacteria were permanently “disabled”.

The process of making artificial snow using sewer effluent did not decrease the number of E-Coli, Total Coliform or Fecal Coliform. The results of this basic experiment validate the idea that freezing alone doesn't kill E. Coli, cooking them is the only proper way to decrease E. Coli density. This experiment also concluded that the extreme fluctuation in microbe density at the testing site hindered the overall experiment. Vaporization and high pressure didn’t seem to have any affect of the microbial density of any of the samples.
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