Peter Collignon is a Professor in the School of Clinical Medicine at the Australian National University. He is also the Director of the Infectious Diseases Unit and Microbiology Department at the Canberra Hospital.
Prof. Collignon is opposed to current ACT Government plans for the development of an indirect potable water recycling scheme for Canberra. We have discussed his views here in some detail previously.
Today Prof. Collignon has asked me to post the following more detailed discussion of his point of view. I am very pleased to do so and, as always, welcome your response.
Recycled sewage; why put ourselves at needless risk in Canberra?
Prof Peter Collignon
April 27th, 2007
I have appreciated the various informative and balanced discussion that has occurred on this website on this issue.
I am not against treating and recycling sewage in some circumstances. I just believe that our health is best protected by trying to keep all human (and preferable animal) faecal material out of drinking water. We should not put treated sewage into our drinking water unless we have no other options (which I agree in many areas of the world is the case). If it is already in our drinking water (ie contaminated rivers) then we should use systems to make drinking water as safe as possible. We should only recycle sewage into drinking water when there are not alternate safer water (and cheaper) sources available.
A number of you have asked why I needed to asks questions about the size of membrane pores, Reverse osmosis performance etc. I am not a water expert but rather a practicing clinical microbiologist, Infectious Diseases physician and clinical academic and so asked these questions from first principles. The reason I had to ask these questions is that when I entered this debate, that type of information was not made available by the local authorities when they announced this proposal (and is still not readily available). It still appears to me that they (ACTEW) and our local government have already decided to proceed with recycling sewage but without allowing ready access to adequate and meaningful technical information on the proposed performance. This is especially important from a virus and drug extraction point of view plus also what will be the safety fail-safe and testing systems. I have found out a lot more information over the last few weeks form people such as yourselves (eg Dr Khan). However people in Canberra are not being given anywhere as much information as I believe should be made available for those interested.
My belief remains that in Canberra, the proposed recycling of about 9 GL per year (and rising to 18 GL) of sewage and then pumping this treated water back into our domestic water supply reservoirs is a needless human health hazard. In the ACT, in most years, there are large and excess volumes of water available in our rivers and streams and we have the ability to store this water in dams for a “rainy day” (or reality - “non-rainy days”!).
Numerous infectious diseases outbreaks related to drinking water are still common in many developed countries including the US, Canada and Europe, even though they have advanced water treatment systems. Outbreaks result from pathogens found in high numbers in human or animal faeces and include numerous viruses, bacteria and protozoans (eg giardia). I am also concerned about the viruses and other pathogen we have still not discovered. While I acknowledge that our “recycled sewage” will likely be treated so that it is “safe” to drink. However further information on the process I have received over the last weeks have done little to lessen my concerns if this water was to be used in drinking water here as it can never be 100% safe. Reverse osmosis only seems to remove about 99% of salts (a log 2 reduction). If it can’t remove all salts how can we be sure it will remove all viruses?
My belief remains we should not take the risk inherent in putting recycled sewage into our water supply, unless we have no other choices. No matter how good your system, things occasionally go wrong with both the performance of equipment and with the people running equipment. I remain convinced that Canberra has lots of other choices to find 9 GL of water that are safer, more economic and more environmentally friendly than this proposal. We still here are using “drinking” water released from the Googong dam to fill Lake Burley Griffin. Surely our current treated water could be used for this purpose and others that does not require potable water quality and thus lower the amounts of water we need to release from our dams which would then stay filled for longer.
Public statements from ACTEW show that they are planning for a worse case scenario where there is a sustained 90% reduction in the water inflows into our dams over many continuous years (and thus the need for recycled sewage). I don't believe CSIRO or any other group are saying this is very likely scenario. The 10 year long-term moving average rainfalls from the Bureau of Meteorology (BOM) website, show no sustained drop over the last 120 years in South East Australia rainfall despite this recent severe drought. 2006 was one of our worst years on record with a 90% reduction in inflows to our dams, but there have been numerous other severe drought years in the past. Despite and despite this our dams are still now 33% full. Australia will continue to be a land of droughts followed by floods
Mr Michael Costello, Managing Director, ACTEW Corporation, in a recent letter has stated “the balance of probability is that the extremely severe conditions of 2006 will not be repeated, and that there will be sufficient water to meet our needs without having to use recycled water.” However he went onto say we cannot rely on long-term averages and we may face extreme inflow problems. Even though the risk is small “we cannot afford not to take out insurance against it. And that is how we should see the recycled water project – as essential insurance which we hope will seldom, if ever, have to call upon.” This seem to me to clearly say we will only use this recycled sewage water in very dry years and I presume also only when our dams are also very low (<10%). Obviously if we don’t use any recycled water from sewage there cannot be an increased risk to the Canberra community and so from an Infectious Disease point of view I can hardly raise any objections. However this is likely to mean, that this $150+ million facility may only be used once every 30 years - or probably not at all. This is potentially very expensive "insurance". The cost of this facility is likely to be over $1,000 per Canberra household and this cost I presume will be borne by householders.
In Canberra, if we include the Cotter dam catchments, then there is normally about 210 GL of water that inflows into our dams on average per year which we could use use for domestic water supplies. The small Cotter dam is the lower of the 3 dams on the Cotter river, (others are the Corin and Bendora) and thus the only dam on that river where any releases and “spills”, means the water is then lost from the domestic water supply. With the water restrictions we now have in place, about 50 GL of water is removed for domestic use (and we return about 35 GL after recycling to the Murrumbidgee) and about 9 GL is used as legislated environmental flows as releases from the Cotter and Googong Dams (5.5 and 3.5 GL respectively). Thus from what I can see, we are only in big trouble if we consistently receive less that 60 GL per year into our dams (ie a 66% continuous drop in inflows). As far as I am aware no major scientific group is predicting that as a likely long-term scenario. Except for 2006, in every other year during our prolonged drought since 2001, we had inflows into our dams of more than this.
Even if we do recycle 9 GL per year of our sewage into our water supplies, this water will be put into the very small Cotter dam (only 4 GL capacity). However in 2006 (one of our driest years ever) this dam was full or overflowing for 5 months of 2006 (July to November). Hence unless a new and bigger Cotter dam is built, any "recycled" sewage will be "wasted" water from a domestic consumption point of view unless we can pump it out faster than we put it in, which we appeared incapable of doing in 2006. Most of this recycled water will likely to just flow over the top of the dam. In 2006 we did not manage to avoid major spills from the Cotter dam. It is difficult to find figures but if 13.5 GL was released from the Cotter dam in 2006 (ACTEW figures) and only 5.5 GL as environmental releases, I presume that 8 GL spilt over the top of the dam. It would be very useful for ACTEW to release their figures for both mandated environmental releases as well as their estimates of yearly “spills” over the top of the Cotter dam for the last 10 years. This dam can apparently not be allowed to fall below 90% capacity as otherwise some native fish in the Cotter dam become endangered. However this means that frequently this dam will overflow.
Thus irrespective of the health risks, I can't see how it is sensible to consider starting this proposed sewage recycling project until we have a bigger Cotter dam to receive the recycled water - yet the stated plan is to have this sewage recycling system operating 3 years before any new dam is constructed. If a bigger Cotter dam is built as planned presumably that will fix this water shortage problem and without the need to recycle 9 GL of treated sewage into our drinking water. The bigger dam will presumably help store for future years the large volumes of "pristine" catchment water currently lost as “spills" over the smaller Cotter dam.
My view remains that this proposal to recycle sewage should not proceed in Canberra. We have ample flows of much safer water that could be stored and used for human consumption. If we proceed and put this water into our drinking water when we have other options, we will be creating a human health hazard needlessly for our population. It will also be at great financial cost and without any obvious benefits to our environment.
Prof Peter Collignon.
Infectious Diseases Physician and Microbiologist
Director Infectious Diseases Unit and Microbiology Department, The Canberra Hospital.
Professor, School of Clinical Medicine, Australian National University.
- Stuart Khan
- Sydney, New South Wales, Australia
- I am a water researcher in an Environmental Engineering Department. Topics on which I work include: • Analysis of trace chemical contaminants in aquatic environments • Analytical method development (gas chromatography, mass spectrometry, etc) • Environmental and public health risk assessment of chemicals in the environment • Environmental chemical modelling techniques • Evaluation of water and wastewater treatment processes in terms of chemical fate • Water recycling practices in Australia and internationally • Guidelines for the management of chemicals in water.
16 comments:
At around 10 pm Friday night I accidentally chopped off about the last third of Prof Collignon’s post. I noticed my mistake at 10 am Saturday morning. So if you read this post during that window, you might want to take another look. Apologies for the blunder...
If the Prof. had raised his views during the Toowoomba debate, he would have been vilified as a non-believer.
I thought I’d provide a quick answer to the one question that was posed by Prof Collignon in this post:
“Reverse osmosis only seems to remove about 99% of salts (a log 2 reduction). If it can’t remove all salts how can we be sure it will remove all viruses?”
The comparison of salt rejection by RO membranes to virus rejection is not a very good one since quite different mechanisms are involved.
Ions that form ‘salts’, like sodium and chloride are actually smaller than reverse osmosis ‘pores’. While the geometry of such ions is quite different to that of a water molecule, it’s a reasonable estimation to say that they are much the same size. So why should they be rejected by an RO membrane at all? The reason is that RO membranes, depending on the chemical properties of the polymers from which they are made, tend to have negative charges on their surface. This negative charge makes it very difficult for anions such as chloride to get close enough to the membrane to pass through it. The fact that anions are restricted from passing means that cations such as sodium are also retained since significant charge separation of cations and anions is a highly energy-unfavourable situation and thus physically prevented.
Viruses also tend to be negatively charged and thus are also effectively rejected by the electrostatic forces described above for salts. However, if some viruses are able to overcome the electrostatic repulsion and approach the membrane surface, unlike sodium or chloride ions, they will find that they are simply too large to physically fit through the available ‘passageways’ through the RO membrane. Viruses are at least 40 times larger than typical RO porosity. As a result, viruses have been shown to be rejected by RO membranes many times more effectively than small inorganic salts.
The fact that 30mg/litre of somthing is in the 'purified water' after treatment has always been a sticking point with me.
Those 30mg have been variously described as "organic substances" "NaCl", "CaCO3" "other compounds". Salts in the output seems at odds with your explanation, Stuart.
To then say that some complex compounds exist at 'undetectable levels' might say more about our ability to detect them rather than their existence. Their long term effect - totally unexplored.
Also the ability of membranes to prevent 'prions' passing through needs an explanation.
Prof Collington,
As a man of science you must know the importance of semantics when communicating facts. Your response contains very reasonable and interesting points, however you are grammatically incorrect using the term "recycled sewerage".
It's the water that is being recycled not the sewerage. The sewerage is what is treated and contains among other things, water. In case I'm not being clear;
When we recycle paper its not text or the pictures (in essence, the ink) we end up re-using, its the paper fibres...
It may be simple ignorance of the workings of our language but such usage (or should I say, abusage) often marks the speaker out as someone who wishes to coerce others into irrational fear or disgust.
It seems trivial but such errors self-propigate and are detrimental to rational and truthful discussion.
thankyou.
Anonymous: Bore water comes from bores, dam water from dams, sea water from the sea, rainwater from rain, riverwater from rivers and sewage water from sewers.
PRW (purified recycled water)is the new euphemism for sewage water in the hope to avoid honest debate on the issues of making it clean and acceptable for human consumption.
Your pedantic stance on language really doesn't add constructively to the debate.
This water debate has more than its fair share of really weird suggestions. For example this one I just came across: Recycled waste water will be so pure (so they say) that it could be used for kidney dialysis.
I was wondering if Professor Collignon could be sporting enough to do a "Mythbusters" on this? No need for actual human patient trials - just a professional opinion "Confirmed" or "Busted" would be great.
Cheers,
Hello W.F.,
I would be interested to know where the figure of 30 mg/L ‘Total Dissolved Solids’ (TDS) came from.
In reality, water quality is very scheme-specific. What you end up with depends on many factors such as the original composition of the water, the various treatment processes that are used and exactly how you operate them. For example in the case of reverse osmosis, the TDS of the product water will vary depending how hard you push the membranes to achieve a particular water recovery. The configuration of various membrane modules (in parallel and in sequence) will also have an impact, as will the precise type of RO membrane that you choose to use
All of these factors (source water, plant design, and plant operation) will also influence the overall composition of the final TDS. So its not as simple as being able to say that the TDS is composed primarily of substances x, y and z. Nonetheless, we do have some good understanding of which chemicals are well removed by RO and which are not.
The least well retained chemicals are generally small uncharged organics (eg NDMA, trihalomethanes). However, many of these wont show up as ‘TDS’ since they are highly volatile. On the other hand, small charged species (cations and anions) are usually quite well removed, but not completely (depending on the electrostatic-repulsion mechanism described above). Since these start out at quite high concentrations in conventionally treated effluent (1-2 g/L is typical), even a small proportion passing through can lead to say 10-30 mg/L in the RO permeate.
To put this in context, it would be very difficult to find any natural drinking water source in the world with less than 10-30 mg/L TDS. The Australian drinking water guidelines don’t provide a health-based guideline value for TDS, but they state that “<500 mg/L is regarded as good quality drinking water based on taste”.
Water with very low TDS tends to be corrosive to many types of pipes (and it also doesn’t taste very nice). For this reason, most advanced water treatment plants will include a ‘stabilisation’ process subsequent to RO treatment. This involves re-adding minerals, usually lime (calcium carbonate). One effect of this is a substantial increase in TDS.
Your comment that to “say that some complex compounds exist at 'undetectable levels' might say more about our ability to detect them rather than their existence” is correct. However, this is intentional. It simply means that when we undertake a test for a substance in water and we get a reading of “zero”, instead of saying “the chemical is not present” we acknowledge the fact that every test as a detection limit and any chemical may be present at a lower level. Thus we say that “the chemical was at levels less than the analytical detection limit” or it was “not present at a detectable concentration”. I tend to go with the assumption that every possible chemical will be present at any possible location and that we would see them all if we had infinitely low detection limits. However, regardless of what our detection capabilities are, this is a fundamental concept that will remain constant even if detection limits improve a billion-fold.
There was a useful article about prions in the journal ‘Nature’ not too long ago (Vol 437, 8 Sep 2005, p 257-261). It showed that for a prion to be infective, it needs to have a particle size diameter of at least around 20 nanometres. This means that it would be about the same size as the smallest known virus and thus would be expected to be very effectively removed from water by reverse osmosis.
Regarding the terminology of “recycled water” vs “recycled sewage” or “recycled sewerage”, I’m personally very happy for people to use which ever term they prefer. Their meaning is usually quite clear from the context. I would suggest that “recycled sewerage” is technically incorrect (“sewerage” is the term that describes the components that a sewer is constructed of –ie. pipes etc, while “sewage” describes the contents of the sewer). I think “recycled drinking water” is a fine description because we are talking about taking what was drinking water and making it drinking water again. But “recycled sewage” works too since we are also talking about taking sewage and making it sewage again. These two terms are essentially equivalent since they simply refer to different stages in the same cycle. I personally prefer to use “recycled water” or simply “water”.
Thanks, by the way, for your kind blog post about this blog post!
The 30mg/L comes from the Mass Balance options prepared by CH2M Hill in the TCC submission to the NWC with supporting text discussion that states quite clearly "RO produces water at 30mg/L TDS" and goes on to say that to increase this by bypassing a portion of the stream would jeopardise the integrity of the "barrier" treatment concept.
I understand 'hungry water' and also understand that 30mg/L is a tiny amount - however it is coming from the most toxic water source on the planet, so we need a thorough knowledge of what it is and what tiny amounts ingested over a lifetime may do to future generations.
I know - 'scaremongering'. But I think the issue needs to be properly addressed and not dismissed lightly (or rudely).
The previous paragraph (3.7) contained the oft quoted "Thus, the recyled water would represent 26% of the total yield or 29% of the water supply to Mt Kynoch. This ratio of water is high by international standards and will need detailed review and further studies." which wasn't very reassuring.
Much debate ensued on the exact nature of that 30mg/L and why CH2M Hill issued a cautionary comment about TCC's proposal.
Your view would be interesting.
Thanks to Professor Collignon for his detailed response. I believe that an open debate relies on a range of opinions being expressed and the more “sane” critics of IPU participating in the discussion on water recycling can only be a positive, ensuring the best possible water supply system. I also think it is important to consider the impact of comments on public opinion and the course of the debate. I hope that the Canberra Times publishes a response from an independent expert in advanced water treatment.
I agree with Professor Collignon, that detailed information on the advanced water treatment technology needs to be made accessible. Singapore seems to have done a pretty good job at providing the community with information and opportunity to ask detailed questions about their IPU system. The Public Utility Board's “NEWater” website is worth a visit (www.pub.gov.sg/NEWater).
Thanks for the information, W.F.
Clearly CH2M Hill had a particular scheme in mind (ie a potential Toowoomba scheme) with some clear assumptions regarding how it would be designed and operated. I personally don't think it is appropriate to assume that the figure of 30 mg/L TDS automatically applies to all schemes.
Trying to understand the exact chemical composition of a tiny amount of residue in an RO permeate is a worthy ambition. However, its not likely to ever be fully achieved and even if it were, it would not necessarily tell us the full story regarding toxicity since mixtures can have complex interactions.
In my opinion, a more satisfactory approach is to test the toxicity of the 'whole effluent mixture'. Typically you would need to concentrate it a few hundred or few thousand times to be able to do this. A good example of where this has been undertaken is at the San Diego Total Resources Recovery Project during the 1990s. Genetic toxicity and carcinogenic testing of the concentrated effluent indicated lower levels than the already very low levels in the city's traditional drinking water source. When the two sources would be mixed together (prior to drinking water treatment and distribution to customers), the proportion of contaminants that would have come from the advanced water treatment plant would have been insignificant.
I hope you don't think that I tend to dismiss issues such that you raise lightly (or rudely). However, I do have to be realistic about how much time I can devote to this blog before breakfast. In any case, I see it as an on-going discussion and we do tend to re-visit subjects in further details as time goes on.
blah blah blah!
The simple fact is that nobody shoud be forced to drink there own effluent. Period. Is that so hard to understand???
right on man
but you're not going to be drinking your own effluent, g.o.i.!, rather you'll be drinking water that has been purified from your effluent.
funnily, stuart decried an early comment on pedantry, but really, i think the point of anonymous' post was in this generic spirit - the debate is clouded by perjorative terms that can serve to misrepresent the issues to a mindset public. it is worth being clear in any discussion, especially so when it comes to eating our own shit, or not...
I certainly wouldn’t argue with Samuel Coleridge about the importance of well constructed language. But as far as pedantry goes, I do think that “recycled sewage” is a pedantically acceptable term (as explained above).
Nonetheless, I admit that as far as I am concerned, the clear communication of a person’s intended meaning is more important than technical accuracy. Furthermore, a person’s choice of terms between “recycled sewage” “recycled water”, “purified recycled water” or other more-or-less sanitised variations quite often provides more insight to their opinion on the general subject area than what would be communicated if we all used the same term. Some people choose to be quite subtle about their precise choice of words and others are very very unsubtle.
How subtle or unsubtle is the choice of the misleading coined label called Newater then? Recycled water is water, only it is recycled water, showing where it comes from. Newater suggests it is New water and has no allusion to its source. Tell me, which is more misleading?
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