Wednesday, April 04, 2018

Workshop: Applying Water Quality and Filtration (supported by Lifelong Learning Council & Singapore Red Cross)

Figure: SETA water filtration unit for use in humanitarian assitance/ disaster relief
Date: 13 May 2018 (Sun) / 20 May 2018 (Sun)
[The 2 sessions are similar so you only need to sign up for one unless you feel like you need a revision.]
Time: 1 - 5p.m.
Venue: Red Cross House, 15 Penang Lane
No. of places for each session: 40 pax
Workshop Description
Water quality is a constant challenge for disaster relief and developmental work in developing countries. You may find sufficient water sources but how do you know whether the water is drinkable? When the lives and welfare of your beneficiaries are dependent on your judgement, it is imperative you make the right decision.
Often, the staff or volunteer responsible for such work is in need of useful and concise information on water quality and filtration to act effectively in the field.
At the end of this workshop, the learner should be able to:
  1. Identify critical water quality parameters to consider in the provision of drinking water
  2. Decide on the water contaminants of significance
  3. Apply the correct type of water filtration (if any) in the provision of drinking water
This workshop emphasises hands-on work by the learners in literature search and water quality testing.
Workshop Fees: $7 per pax
  • The fees will contribute to the purchase of consummables in the workshop.
  • Any leftover will be donated to Singapore Red Cross.
  • Regrettably, all fees are non-refundable.
  • Only participants who have paid their fees will be admitted to the workshop.
  • Registration closes once the class size has been reached for each session.
  • You can register and pay (PayPal) via the links here.

Figure: Chemical testing of water quality

A project supported by the LearnSG Seed Fund:
Every Day, A Learning Day

Also supported by
Singapore Red Cross

Wednesday, March 28, 2018

What good is testing for ORP (oxidation reduction potential)?

Personally, I hardly have a need to test for ORP (oxidation reduction potential). But recently, a supplier mentioned this water quality paramter in our discussion so I thought of writing a bit about it.

It is supposed to measure the redox (reduction-oxidation) state of a water sample. Usually in units of mV, it indicates whether the water is more likely to support oxidation (positive values of ORP) or reduction (negative values of ORP).

For those unfamiliar with chemistry, a very simple (perhaps overly so) explanation: oxidation is the process of chemical compounds reacting with oxygen (think combustion) while reduction happens when chemical compounds lose oxygen to become something else. (Yes, I know this explanation is woefully inadequate but it will have to do for this post. If anyone is inclined to find out more, please feel free to search for through the numerous chemistry websites.)

An alternative perspective through a biological lens:
  1. positive potential means the water is in an aerobic state
  2. negative potential indicates an anaerobic state
This can obviously apply to natural waters and wastewater treatment. In wastewater treatment, ORP can be easily and continuously monitored for feedback and control. But in the case of natural waters, I prefer to simply test for dissolved oxygen (DO) level if I am interested in how aerobic or anaerobic it is. I like DO being a direct measure of an important chemical species (i.e. oxygen) which directly affects aquatic organisms and biochemical processes.

Technically, an ORP probe is a circuit containing a reference electrode (immersed in a reference electrolyte) and an indicating electrode (immersed in the water sample). A salt bridge links the reference electrolyte and the water sample, allowing flow of ions but not mixing. The other ends of the 2 electrodes are linked to a voltmeter which shows the potential difference between the 2 electrodes - this is the ORP reading. Relatively simple and cheap, it can provide continuous monitoring in process control.

  1. Unlike DO or pH, ORP does not measure any specific chemical species since it reflects the various reactions occuring on the indicating electrode to produce a "mixed potential". This gives rise to a "black box" effect - you have an output but you have no idea what processes are involved.
  2. The "black box" effect becomes an impediment to interpreting ORP values across different water systems. Actually, they probably make no sense beyond a very broad qualitative kind of conclusion. The ideal use of ORP is to make comparisons within the same system in which it can indicate a disturbance in the process.
  3. Being an electrode system, the ORP can suffer from polarisation and poisoning of the indicator electrode surface, further affecting the accuracy of the reading.
Uses of ORP
  1. Chemical disinfection seems to have found a use for ORP as it can give an idea of the disinfectant strength. Chemistry tech talk: most chemical disinfectants (ozone, chlorine, chloramine etc.) are oxidising agents (chemicals that promote oxidation) so the greater the disinfectant concentration, the more positive the ORP value. Nevetheless, it is a good idea to correlate the ORP to other tests that measure the actual chemical species e.g. ozone.
  2. With the craze in alkaline water, hydrogen water etc. in recent years, it seems customary to measure the ORP to showcase the water's "anti-oxidant" properties. Of course, in this case, the more negative value, the stronger its anti-oxidant power. The health benefits are controversial and you can read a bit more in a previous post.
Figure: My ORP meter. Simple to measure but hardly used

Wednesday, February 07, 2018

If you only want to test one drinking water parameter, this is the one... and how to do it

If you have been reading my blog, you will no doubt find that I have touched upon quite a number of water quality parameters e.g. COD (chemical oxygen demand), pH, electrical conductivity. Yet, when it comes to drinking water, the number one parameter to check is:

Bacterial count

And not just any bacteria, the favourite in the water industry seems to be E. coli though Enterococcus seems to be a strong contender. Essentially, the idea is to find an indicator microbe to "indicate" recent faecal pollution which implies possible presence of human pathogens. In addition, this microbe has to be:
  • Always present in faeces of humans 
  • Present in high numbers
  • Easy to detect by simple and inexpensive methods
  • Unable to multiply after they have left the body and entered the water supply
  • Not a pathogen itself
Obviously, no microbe can satisfy all the above criteria perfectly but E. coli (and Enterococcus) comes as close as you can get.

How to measure it?

In 1 of my previous posts - How do I test my own tap water: a DIY guide (part 2) , I recommended this product for E. coli.
Industrial Test Systems 487197 WaterWorks EZ Cult Bacteria Test. USD9.77
Thanks to Victor who provided 2 test bottles, I finally have a chance to test it out. Personally, I still find this product rather pricey, especially when you factored in the shipping costs. But as mentioned in my previous post, this product is as idiot-proof as you can get.

Anyway, with Victor's help, we set up 1 bottle to be the sample with live faecal pollution and the 2nd bottle to be the blank with deionised water.

I also took the chance to try out Aquagenx CBT (compartment bag test) specifically to quantify E. coli in MPN (most probable number). The setup is similar to the above - 1 live sample and 1 blank.

Important: WaterWorks EZ Test is qualitative - either YES or NO for the presence of coliform (and E. coli under UV light) while Aquagenx CBT is a semi-quantitative test that provides a numeral in MPN for E. coli count.

Though Aquagenx CBT allows for "incubation" at ambient temperature provided it does not fluctuate too much, we nevertheless incubate all tests in a mini-incubator that I dug out. (Personally, I find the requirement for incubation at a steady temperature e.g. 35C to be the most formidable technical challenge for anyone engaging in DIY bacterail testing, more so if under field conditions.)


Figure: Before incubation. Left - live sample, right - blank.

Figure: Preparing for incubationl Notice the leftmost bottle for live sample has already turned green, indicating the presence of coliform. And this is only at most half an hour after inoculation. The Aquagenx CBT (rightmost) is the live sample.

Figure: After 1 day of incubation. The CBT blank (white clip) still remains brownish while the CBT sample (red clip) has fully turned green, indicating E. coli and also translating to > 1000 MPN/100mL or very high risk. Unfortunately, my UV light was not working so I could not confirm the presence of E. coli in the EZ Test sample as under UV light, E. coli will display fluorescence.

Ok, that's it, folks! Hope the discussion above is helpful to those doing testing of drinking water, especially in the field. Oh, the price of Aquagenx CBT: including shipping cost --> ~USD150 for 10 tests.