Recycled water not worth risks ...

Excerpt from Canberra Times:

Recycled water not worth risks

30 March 2007

It is proposed in Canberra that we will recycle about 9GL (nine billion litres) of waste-water and then pump this treated water back into our reservoirs.

It will then be used as part of our domestic water supply, which includes drinking water.

One of our most significant public health improvements was removing sewage from water supplies. Human waste contains numerous viruses, bacteria, protozoans and other microbes that frequently cause disease if ingested.

While our sewage will be treated so that it is "safe" to drink, the mechanisms being proposed for this all have potential problems with performance.

Thus there is a strong possibility that at times we will contaminate our water supply with disease-causing micro-organisms.

Worldwide there are localities where there is no alternative but to accept the risks associated with using recycled sewage.

However, whenever possible when we can avoid placing treated sewage into drinking water this hazard is obviously desirable to avoid.

In Canberra there is no reason to take this risk.

The ACT has large volumes of unused water. Indeed it is a very large net exporter of water to NSW (about 471GL per year). We also currently have one of the best water supplies in Australia (and probably worldwide) from a safety point of view.

Currently no human sewage enters our drinking water in our catchments.

We are also very fortunate (and unique) in that minimal domestic animal waste enters the water supply because few farms are in our catchments. Most of our current Canberra water is good enough to bottle!

A number of methods are purposed to make this recycled sewage "safe" but how many systems work perfectly all the time?

If membrane technology is used, how can we be sure that these membranes will be able to accommodate the planned 24 million litres of recycled water that they need to filter each day?

How will we know when there are small tears in parts of the membranes? Bacteria are very small and unless the pore size of these membranes is 0.2 microns it is unlikely that all bacteria will be removed.

However, if the pore size is so small, I find it difficult to see how these membranes can satisfactorily work without being frequently blocked by larger waste material. Even if such small pore sizes are used, this will still not remove viruses, which are much smaller.

Membranes will also not remove drugs passed in urine and faeces that are not broken down (such as oestrogens).

A "reverse osmosis" process is also going to be used. But there is a lack of details available to Canberra residents to see how effective this system may be in removing viruses (and drugs).

Ultraviolet light will also be used as an additional sterilising agent. However, this is far from an ideal disinfectant.

There are many issues such as time of exposure, susceptibly of different microbes, and so on, for it to work. How can we be sure that this can handle 24 million litres of waste-water per day?

Safety monitoring is planned, presumably by culturing the water and looking at coliform counts. If coliforms (eg E. coli) are present in the treated water this implies faecal contamination (and thus a failure of the system).

However, this type of monitoring has problems.

Around the world numerous outbreaks with water contaminated with viruses and Cryptosporidiosis have occurred despite low or zero coliform counts. In addition these indicator bacteria take one or two days to grow and identify. There does not appear to be a plan for storing two or three days of recycled water in a temporary reservoir.

Presumably the water will be pumped directly back into our dams after treatment. This will mean that even when we detect a failure with our treatment system, there will be little we can do about it because the contaminated water will already be in our dams.

How often will this coliform testing be done? Every half hour, hourly, daily or just weekly?

In Canberra we do not need to recycle our waste-water back into our drinking water supply.

The current proposal is for initially 9GL of water per year to be recycled into our dams. On average, however, about 120GL per year has been released from our dams into the rivers as environmental flows (46GL) and as spills (75GL). Spills are when dams overflow which has occurred frequently, even in droughts, with the Cotter dam, because of is low storage capacity.

This released water is relatively "pristine" from an infection point of view.

Why not find ways to withhold 9GL of this water?

Is this not a better option than pumping 9GL of very expensively treated waste-water upstream into our reservoirs when we cannot be assured it will always be free of harmful microbes?

In February 2006, the Chief Minister announced the start of a transfer scheme commencing in December 2006 of 12GL per year from the Cotter reservoirs to the Googong Dam.

"This scheme takes water that would otherwise spill over our dam walls, and makes it available for consumption in the Canberra region".

This amount is larger than the proposed 9GL volume of recycled water. Can't more water from the Cotter dams be transferred if we still have a shortage of water in the Googong dam?
Given on average 75GL of water "spills" per year from our dams, surely the amount transferred could be increased to say 20GL per year and avoid the costs and risks of recycling sewage into our water supply.

This current proposal to recycle sewage also does not seem to make environmental sense.

Effectively this will be putting 9GL less water into our waterways. This is because 9GL of water will be pumped back into our reservoirs instead of being released into our rivers as occurs currently. We could remedy this by letting an extra 9GL out of our dams and into the rivers.

That, however, would effectively mean that there is no net increase in the water supply for human use. If we did that we will have spent maybe $100 million or more to process and pump water back into our dams, just to let the same amount of water out again!

It makes neither environmental nor economic sense.

Nearly all of the water that is released from ACT Dams as environmental flows plus natural flows, move into the Murrumbidgee River where it is then captured in the Burrinjuck Dam (capacity 1025GL) near Yass. Nearly all the water in the Burrinjuck Dam is for irrigation purposes, when it is let out for downstream users. One of the major uses of this water is for rice cultivation.

In 2001 (Australian Bureau of Statistics), 1924GL was used for rice production in NSW/ACT. There is no rice production in the ACT, which means all this water is being used further downstream in the Murrumbidgee river system. If the rice growers down river from Canberra decreased their water usage by just 1 per cent, that would mean that there would be another 19GL available for the rivers. This is more than double the amount that is proposed to be saved by recycling our waste-water in Canberra.

It does not appear to make sense to spend huge amounts of money recycling waste water and putting this water back into our Canberra drinking water, when at the same time we are releasing "pristine" water from these same dams for environmental flows especially when this released water is effectively being used mainly for irrigation purposes downstream to produce water intensive crops such as rice.

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 we will be creating a human health hazard needlessly for our population at great financial cost and without any obvious benefits to our environment.

Professor Collignon is director of the Infectious Diseases Unit and Microbiology Department at the Canberra Hospital, and Professor at the School of Clinical Medicine, Australian National University.