Thursday, November 06, 2008

Water comes from rivers

I was mildly amused by today's installment in The Australian.

It points out that much of the Thames River drinking water supply is sourced from discharged treated effluent. Apparently Stuart Khan reckons this is an example of indirect potable water recycling (albeit with much lower levels of treatment and management compared to SEQ).

However, as Prof Peter Collignon points out, places like London “don't use sewage as a primary source of water… they use rivers as water sources”.

Okay, well, then, excuse me sir, but, um, by that criterion, wouldn’t it be reasonable to say that Brisbane doesn’t (and wont) use “sewage as a primary source of water” either? Brisbane uses a river as its drinking water source. Brisbane takes its drinking water from the Brisbane River at Mt Crosby.

We can all close our eyes to what happens upstream if we want to… but its not the way that I would want to manage a drinking water supply for a large city like London or Brisbane.

Researchers Debate London's Lesson on Reuse of Water
Greg Roberts
The Australian
November 06, 2008

EXPERTS are divided on whether the drinking of recycled water from rivers in London and elsewhere is comparable with what is proposed for southeast Queensland.

University of NSW Water Research Centre contaminants researcher Stuart Khan said experience overseas had demonstrated the safety of drinking recycled water.

"London gets its water from the Thames River and there are 380 sewage treatment plants upstream from London which are putting effluent into the river," Dr Khan said.

"Despite more than 40 years' experience, no clear deleterious health effects from the deliberate recycling of purified water to a dam or river source of an urban water supply system have been observed."

Dr Khan said treatment processes being used in Queensland, including reverse osmosis and oxidation, were highly effective barriers to potential contaminants.

Australian National University microbiologist Peter Collignon said London and other centres that used recycled water from rivers for drinking -- such as Richmond in NSW -- could not be compared with what was planned for southeast Queensland.

"These places don't use sewage as a primary source of water," Professor Collignon said. "They use rivers as water sources, and rivers have much lower levels of potentially dangerous microbes and drugs than sewage.

"Sewage put into the rivers upstream has been in the rivers a long time and it's been heavily diluted by the time it gets to the people who drink the water after it is put through a filtering process. That is a long way from what will be happening in Queensland."


Anonymous said...

Hi Stuart. Thanks for all the updates and advice on this site. I was wondering about possible toxins, prions, hormones etc - that may not be removed when recycling sewage? Couldn't these harmful substances build up in our drinking water over time, as sewage is recycled - not once - not twice - not three times - but over - and over - and over - and over - and over - well you get the idea - again - in a closed system? Isn't that the type of recycled water system SEQ is scheduled to get? Toilet - to treatment - to dam - to tap - to toilet - to treatment - to dam - to tap - etc? I would imagine that in London - using water from a free flowing river - even using the example of the 7 sets of kidneys - there is not the same potential for harmful substances to build up in the drinking water supply over time. How can any - potentially harmful substances - trapped in a closed recycled water system - EVER escape down stream? I don't see how the London example put forward, can be used to show a closed looped sewage system is safe to use over long periods of time. Has a closed "toilet to tap" system been operating for decades anywhere in the world? I hate to think what could happen if the science gets this wrong. Am I worrying over nothing?

Stuart Khan said...

Hi Anonymous,

Thanks for your comment and question.

I really do not believe that there is any such contaminant that will not be effectively removed by the multiple barrier process that the SEQ system will use. Biological treatment (at the sewage treatment plant), reverse osmosis and advanced oxidation applied in sequence really doesn't leave much opportunity for contaminants to slip through.

However, to address your basic question, if we had a hypothetical totally conservative chemical that was:

- entirely resistant to oxidative biodegradation
- non-volatile
- small and neutrally charged so as to be poorly rejected by reverse osmosis membranes
- resistant to advanced oxidation (no carbon-carbon bonds)
- hydrophilic (so as not to be partitioned from water when in the reservoir)
- resistant to environmental biodegradation
- not removed during conventional drinking water treatment...

then we would have a very unusual chemical with some quite contradictory properties. However, most of our drinking water is not available for recycling. Usually only about half of it makes it to the sewage treatment plant (the remainder waters our plants and washes our windows etc, although this figure is obviously reduced during tight water restrictions!). More water will be lost during processes like reverse osmosis (around 20%). Then, in SEQ, a large proportion of what is produced by advanced water treatment processes will go to the Swanbank and Tarong power stations (about 60%, -I think?). After the water has been mixed in Lake Wivenhoe, it will travel 40 km or so downstream to the Mount Crosby water filtration plant. Presumably the Brisbane River will not be allowed to run completely dry at this point and only a fraction of the water will be re-collected for drinking, while the remainder continues to travel downstream.

So regardless of the fact that we like to think of recycling as a "closed system", its actually a very leaky system and we will always lose more water than we actually recapture and reuse. In the case of multiple subsequent water users on a river, the opportunities for concentration build-up of recalcitrant chemicals is, I think, much greater. This is largely because the treatment processes are much less intensive, but also because there are fewer water losses from the system between one user and the next (e.g. generally no Swanbank or Tarong Power stations and no reverse osmosis separation). For example, part of Berlin's water supply comes from the Spree River, -which can be comprised of up to 70% discharged effluent during dry periods. You could never achieve that with a system like Western Corridor.

Anonymous said...

Thanks Stuart - your comments provide some great points to think about - So the water used and released by the Power Stations is not recycled back into the system?

Stuart Khan said...

Hi Anonymous,

That’s a good question. I’m no expert on power generation, but I assume that the majority of the water use at the power stations is to create steam, which is subsequently released to the atmosphere. However, I expect that some cooling water must be released somewhere. I’m not sure whether any such released water becomes part of the Wivenhoe catchment, but if so, I personally would be more concerned about pollutants introduced during the industrial processes than anything that may have been present in the source water. If anyone can shed any light on water management at Swanbank and Tarong power stations, I’d be grateful.

Daqtaoge( said...

Hi Stuart,

About the contaminants, I would like to use an analogy of a subway system. Individual persons can enter the subway system, but cars cannot, lorries cannot, 20 ton trucks cannot.

Individual ions can go through the multiple barriers as they probably do, but bacteria and pathogens do not.

However, if we were to make an opening in the train, we could possibly load a car in. If there is a tear in the membrane, small bacteria could go in.

As an academic, you may not be exposed to wear and tear and live in a shiny bright cosy environment. But were you a car owner, as probably you are, you would have been advised to change your car tyres when they have aged and hardened. But did you maintain your tyres. If you did not, do you think a Water Authority which might comprise of someone like you or lesser, would know how and when to change the membranes? These sort of issues, financial suicide for the RO membranes manufacturers, are they being brought up? If not, it may be the start of a trend of sudden cardiac deaths in Queensland soon and be prepared to start installing Automated External Defribillators at every 500 m interval to prevent young athletes collapsing and dying. Young healthy males have been reported to have died whilst exercising in Singapore, the last few years.

Stuart Khan said...

Hi Daqtaoge,

Thanks for your insightful comment.

I like your analogy and I appreciate your point regarding larger species being able to fit through an RO membrane if it is severely compromised. Your point regarding maintenance is also perfectly reasonable and valid. I certainly share your conviction that maintenance at (any) water treatment plant needs to be more vigilant than my own personal history with changing car tyres! Tight regulation and careful management is always required to ensure safe drinking water in any location.

Hopefully installing "automated external defibrillators" at every 500 m interval will not prove to be necessary.

Anonymous said...

more in the Australian today .. "Gold Coast Mayor Ron Clarke said a staff member was believed to have been responsible for mixing up waste-water lines at the plant in September.
A pipeline was disconnected on Friday when the problem was uncovered. Up to 240 employees and visitors who may have drunk water that was not fit for consumption are being contacted to determine if they had suffered any ill effects.
"Somebody has stuffed up and it should have been cross-checked before it happened," Mr Clarke said. "If it had happened in the public works, it would have been disastrous...."

Anonymous said...

Article to illustrate the car maintenance point -link to the Australian: Recycle sewage 'as a last resort',24897,24626801-601,00.html

Anonymous said...

I suppose the issue about compromised membranes is resolved by the fact that there is not just one membrane. The water has to go through several membranes, each filtering for different sizes of contaminant particles. There would need to be simultaneous failure at all points through the process.
Moreover, the control systems check and measure the quality of the water at each stage, so as well as failure in the process itself, the control systems would also have to fail, at the same time.
It all starts to seem a little unlikely.
And that is before we go back and acknowledge - again - that we are not talking about a closed system. PRW is not put into the domestic supply, it is put into the Wivenhoe. From there it goes down the Brisbane River, gets sucked up 40 KM downstream, goes through another treatment plant and only then gets into the domestic supply.
I have to speak of course as a born Londoner, who grew up drinking Oxford's treated sewage. What goes into the Thames is of far lower quality than will be produced by the treatment plants at Gibson Island, Luggage Poitn and Bundamba.

bedroom foods said...

We can all close our eyes to what happens upstream if we want to…

breast fibrocystic said...

Brisbane takes its drinking water from the Brisbane River at Mt Crosby.

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