Packing List #1

Christmas Eve. Ten days until departure. Most of the large problems worked out well enough for comfort. Plane reservations for the group and hotel acommodations for me and Gail are all made. Its a little too early to actually start packing but its a good idea to be getting things ready. My biggest contribution to the group is a very well provisioned first aid kit and the ability to use it. I replaced and expanded the kit after return last time so that is pretty much set. All it needs is a quick recheck to make sure nothing is outdated. There are a few items that experience taught me is good to have along and I will periodically share them over the next week.

1. Cheap, light plastic rain ponchos. 2 or 3 of them; keep one in my backpack
2. Small nautical pulleys (3). Useful for raising items.
3. Thin nylon cord for #2
4. AAA batteries
5. Freeze dried ice cream - treat for students. Last years group had never heard of it and didn't believe me
    until I gave them some.
6. Spoon/knife eating utensil
7. Crazy glue
8. Assorted zip lock plastic bags

I will post more as I think of things.

Had a nice train ride Tuesday with Frank Sokolowski. He was heading home to Philadelphia from Rensselaer so I boarded the train in Rhinecliff and traveled down to New York City with him. We tested the Hach colorimeter that he got from the campus store room. It is quite a bit more sophisticated than my unit and can measure numerous different analytes whereas mine is exclusively for chlorine.We actually sat on board the train measuring water samples. The two meters agreed nicely and are both easy to use. All in all it was a fun trip. We hung out in Penn Station for a half hour then I boarded the next northbound train and headed back home.

Answers - Finally!

With the arrival of the Hach Colorimeter I was finally able to get good quality data and make some solid conclusions. Here's what it looks like: The meter itself is the black device that looks like a TV remote clicker. To it's right is a container of 5-in-1 test strips.

I did some practice runs on tap water from my home which is well derived and free of any baseline chlorine by making a 1:10 bleach dilution which allowed me use much smaller source volumes, everything scaled back by factors of 10: instead of 6 ml of undiluted bleach in 55 gallons I could do 0.6 ml of the 1:10 dilution into 0.55 gallons of water and get the same concentrations. Using the test strips I could get an idea if we really were in the ballpark range. Here are the results:

5 in 1 Dipstick Measurements done on well water using 1:10 bleach dilution in 0.55 gallons water
Bleach (0.825%) ml			Total Cl (ppm)		Free Cl (ppm)
Trial 1
0.5			1		0
0.6			2		0.5
0.7			4		0.5
0.8			4 to 10		1 to 2
0.9			4		0.5
1			4		1
Trial 2
0.5			2		0.5
0.6			4		1
0.7			4		1
0.8			4		1
0.9			4 to 10		1 to 2
1			<10		4

So, based on dipstick values we are pretty good in terms of being in the range. The problem with the dipstick is that they are a "blunt instrument". Rather than giving you a reliable numerical measurement the strips basically tell you one of three things: "none/not enough", "enough" or "too much". A good start for estimating but lacking in finesse. Enter the colorimeter. It works by detecting the absorption of light at a wavelength of 528nm. To perform the test water is mixed with a small pre-measured packet of DPD (dietheyl-phenylenediamene) powder; if chlorine is present it reacts to turn the solution pink.

The meter then reads the strength of absorption proportional to the amount of chlorine present. We get a number. A real quantitative value that can be used to generate data, produce equations and make predictions.

 

The challenge with the meter is that, as usual, the devil lies in the details. Every time you draw up a sample from a different source or strength, everything has to be thoroughly cleaned with tap water (sample cups, measuring tubes, syringes for drawing up, etc). So, even a few relatively simple measurements can chew up an hour or too pretty easily. Now add in going in and out to add increments of bleach to the barrel, letting it mix for 20-30 minutes with the occasional stir, siphoning out samples, labeling the jars plus doing the measurements and you can lose an entire afternoon really fast! Anyways, I was able to squeeze a few hours together yesterday and did just that. Here are the results:

Colorimeter Measurements			55 Gallon Barrel		Dipstick Measurements			55 Gallon Barrel
Bleach (8.25%) ml			Total Cl (ppm)		Total Cl (ppm)		Free Cl (ppm)
Trial 1
0			0.01		0		0
5	0.85		0.85		0		0
6	1.4		1.4		0.5		0
7	1.77		1.77		0.5		0
8	1.58	*	1.58	*	0	*	0	*
9	2.2		2.2		0.5		0
10	2.2		2.2		0.5		0
11	2.2		2.2		1		0.5
12	2.2		2.2		1		0.5

 

However, note that the value for 8 ml is a statistical outlier leading to some inaccuracy in the linear equation. If we drop that value we get a better estimate of the line and a different equation.

This improved data and equation now allow us to confidently plug in any amount or volume of bleach we may want to add to the 55 gallon drum and come up with a reliable concentration of chlorine remaining in the water, and it should stand up to measurement with the colorimeter. Here is a table of such a prediction. So, if the WHO established chlorine level is 2.5 mg/L (PPM) then a dose of somewhere between 9 and 10 ml of 8.25% bleach will reliably produce that level. But, there is a catch: Every different source water will have it's own unique chlorine requirement so that the values I have established for rainwater in Hurley, NY may be very different, from say, water taken from the Gowanus Canal in Brooklyn, NY. This is called "chlorine demand" and means that one of the first things we will need to do in Panama, in tandem with installing the new tanks, is to set up a barrel and starting testing to establish what the chlorine demand is for their source water (rain) and make up a table for them to use once the system is up and running. Still, this gives us a good idea of the variability of chlorine dosing and the fact that untested calculations alone are not enough. Very satisfying.

Table based on equation Y=0.3263x-0.6474 5 0.9841 6 1.3104 7 1.6367 8 1.963 9 2.2893 10 2.6156 11 2.9419 12 3.2682 13 3.5945 14 3.9208 15 4.2471

Things Are Never as Easy as They Seem

Less than three and a half weeks until we leave and we still have not established the correct bleach dose. I have been using 60 ml plastic specimen containers to collect the water and then bringing it up to the lab at RPI. I have usually done the dosing and sampling the day before so that the samples have sat for 24 or more hours in the containers before being tested. Last week I had done the bleach dosing on Tuesday then went up to campus on Wednesday night and we ran the levels using dipsticks. The effective dose seemed between 12 and 15 ml per barrel and we were hoping to confirm this using a colorimeter. Chip and Frank found the one in the basement and I ordered a used on on Ebay (as well as reagent kits for it and several bottles of 5-in-1 test strips). Frank went back a couple of days later and rechecked the levels. The previously robust sample ranges (12-15 ml) were now reading zero. This can be explained by either adsorption of chlorine to the plastic or reactivity of the chlorine (oxidation) with the plastic itself. Given the 24 hour delay between sampling time and testing, this calls into question the validity of these ranges. It may be much lower bleach dose is needed and that means we need to do more testing.

The new plan involves a two-arm experimental plan: One is a real time dose-titration, the other a time-stability study. Now that I have all of the necessary equipment at my house I can test immediately after I have made each dose titration. I will start at the 6 ml of 8.25% bleach, do a fresh sample using both dipstick and colorimeter and then pull off two samples - one stored in plastic and the other stored in glass (these are for the time-stability portion). I can add bleach in any increment I choose then add smaller increments as I start to get readings on either dipstick or colorimeter until I get overshoot. Hopefully, once and for all, this will give us the best correct bleach dose. Once that portion is complete I can then do a daily check on the stored plastic and glass container samples to see if the chlorine degrades faster in the plastic containers.If there is degradation of chlorine level I don't know if this data will be sufficient to distinguish the mechanism between adsorption to the sides of the container versus oxidation of the plastic by the chlorine. That would be a function of the reaction rate kinetics. Chip can hopefully shed some light on that aspect.

I have picked up two more 55 gallon drums to hook to the downgutters so I have enough water to repeat tests if I need to. Fortunately, I don't anticipate much packing as most stuff is all packed up neatly from last year. As soon as I get some of the testing done (hopefully Sunday afternoon) I will post the results here. Lastly, it looks like my loyal reading base in South Korea has been looking in. I wish you all gyejeol-ui insa. I am trying to say "Seasons Greetings" and I am totally depending on Google Translate for this. If am wrong, please, someone correct me and let me know the correct way to say it. Also, there seems to be a bunch of folks in Russia reading; to all of you I send sezony privetstviya. Again, if wrong, please me a comment and correct me.

Third Times a Charm

Following the first two sets of rainwater tests, we really did not have a great sense of the correct bleach dose for a 55 gallon barrel. The calculated amount of 5.8 ml (let's just call it 6 ml, please) was insufficient and did not register on the chlorine test strips at all; the 58 ml (a 10x strength) overshot the mark by a bit; and the 580 ml (100x) was way off the scale. A crude series of 50%-50% volume dilutions indicated that the correct dose lay somewhere between, say, 9 ml (1.5x) and 18 ml (3x). We needed at least one more trial to fine tune the dosing and my concern was that, with little more than a month until we travel, we would not get sufficient rain for one more refill of the barrel before winter and snow set in. Fortunately, the weather is cooperating. The barrel is full and I am in the process of making a series of chlorine solutions  starting with our calculated 6 ml dose and increasing it by 3 ml increments through 18 ml. I have collected samples up through 12 ml; the 15 ml dose is equilibrating and is due to be sampled in 5 minutes. Then the last solution will be 18 ml of bleach and that range of specimens ought to capture the final free chlorine target dose of 2.5 mg/L (or ppm) as specified by the World Health Organization. I will bring the samples up to campus tomorrow during the weekly meeting and Frank, Kyra and Jonathan can test them. We are also looking at a small Hach colorimeter that would provide more accurate measurements and I have located one on Ebay at a reasonable price.