Recycled drinking water

Recycling waste water for drinking could help with water shortages but is it safe?
 
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  • Updated:27 Jan 2008
 

03.Are the myths true?

There's a lot of conflicting information circulating about the pros and cons of recycling water for drinking. Here, we sort the myths from the facts.

"Adding it to the environment improves it."

Overseas, Namibia is unique in directly reusing its recycled water — meaning that the recycled water is put directly into the drinking water pipes. Most schemes add recycled water to a river, underground aquifer or reservoir (in Queensland’s case the Wivenhoe dam). This step’s been dubbed 'the miracle mile' and 'shandying' — but it works and it’s how indirect potable reuse will occur in Australia.

It might simply be because of the obvious dilution it receives, but Australians are much more comfortable with recycling if the process includes a natural environmental stage combined with the thorough treatment given to the rest of the water supply.

There’s a less obvious reason too. Authorities tweak water treatment operations for our existing water supply, depending on the particular qualities of the water coming downstream. So putting the recycled water into the main water supply adds another safety buffer, because it provides time to identify and respond to blips in water quality.

"It’s not clean: you’d be drinking sewage."

The yuck factor is a key reason people oppose recycling wastewater for drinking. However, experts say the perception simply doesn’t match reality. By the time recycled water has passed through all the treatment processes it’s in fact cleaner than regular drinking water and has less 'taste', because it has fewer impurities. In fact, it’s of such a high standard that, theoretically, it could be used in hospitals for kidney dialysis.

Schemes under consideration in Australia would treat the wastewater at regular sewage treatment plants before it arrives at the recycling plant (see diagram of the recycling process). So treated domestic and industrial wastewater going into the recycling plants would already be more than 99% water.

Some experts have raised legitimate concerns about the fact that wastewater also contains contaminants of organic material (poo), viruses and bacteria, detergents, grease and oil, salts, nutrients, organic chemicals, metals and other inorganic chemicals.

Where we do recycle our wastewater, it’s clearly important that these health risks are managed well. The recycled water guidelines are being developed with this front-of-mind, so that recycling processes are designed to remove these contaminants.

The multi-barrier approach used in producing recycled drinking water means that sewage contamination of the end product is unlikely. The idea is that even if there’s a fault at one stage, the next will be there to remove the contaminants.

For example, if there’s a fault with one of the membranes in the reverse osmosis process and unwanted molecules slip through, many will be removed or destroyed by the hydrogen peroxide and ultraviolet light used in the next stage of the process. The likelihood of contamination is further reduced by having a series of membranes, conducting frequent maintenance, and a set of extra barriers when the water reaches the regular drinking water treatment plant (for example, lime is often added to reduce trace amounts of metals).

"It turns men into women."

Micro pollutants are a legitimate concern, because we’re putting an increasing mix of chemicals into our water systems. These include nasties such as detergents, personal care products, antibiotics, hormones, insecticides and chemicals that make plastic soft (plasticisers). The Toowoomba and southeast Queensland campaigns against the introduction of recycled water argued that it had the ability to change the sex of fish.

But experts say that evidence of harm to human health — let alone sex change — isn’t supported by strong scientific evidence. The fear of feminisation comes from studies of fish swimming in sewage that hadn’t been completely treated, and can’t be simply translated to humans and highly treated recycled water. Experts say there’s no evidence that recycled water contains dangerous levels of hormones.

Conventional sewage treatment processes in Australia remove 95-99% of hormones and the potable recycling process, particularly the reverse osmosis stage, can then remove the remainder of trace hormones to below the limit of detection.

All this emphasises the importance of caution: multiple barriers in the treatment process, water quality testing, monitoring and research. The draft recycled water guidelines include quality criteria for pharmaceuticals and other chemicals of concern.

"It’s cheaper so it must be poor quality."

In fact, a lot of Singapore’s recycled water gets used for electronic chip manufacturing that demands higher-quality water than drinking water. It’s true that when recycled water is provided for non-drinking purposes it’s sometimes offered at a discount, but quality isn’t the chief reason.

The price was set lower when these schemes were introduced, to encourage people to use recycled water. But as with any water, recycled supplies can’t be regarded as an unlimited resource; they need demand management too. It costs money to produce recycled water, so in future its price is likely to more closely reflect this cost.

"It uses a lot of energy."

This is no myth. It does take a lot of energy to make each litre of recycled water. And to add it to a reservoir — for example pumping it from the coast to a dam that’s inland and uphill. It will also take a lot of energy to build new infrastructure for the recycled water schemes.

However, other strategies for increasing water supply — such as desalination, which involves treating seawater by reverse osmosis to make it suitable for drinking — can use even more and could therefore be more costly.

That said, Australia needs a number of strategies working together to overcome water shortages — for example, water conservation measures, evaporation control, rainwater tanks, groundwater recharge and efficient appliances.

In southeast Queensland, desalination and recycled water are expected to eventually contribute over half the total water supply. But, of course, for inland centres desalination of seawater isn’t a viable solution.

 

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