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Topic Title: Water harvesting and conservation
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Created On: 30 August 2013 01:14 AM
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 30 August 2013 01:14 AM
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justyburns

Posts: 8
Joined: 30 August 2013

OK, it might not affect the UK and Ireland (I'm Irish) as much, but this is an interesting approach to water conservation.

"Saving water is a good thing, right? But what if I told you it could also cause problems.

A recent study from Victoria University indicates water-conservation can have unintended consequences for residents and water managers - a problem that is only set to get worse.

Our research found that reducing and replacing potable water lead to smellier sewers and more rapid corrosion of the sewer pipes beneath our homes."

Taken from the Australian site theconversation.com/whats-that-smell-water-savings-unintended-consequences-11649

As engineers, we need to remedy this, the article goes on to say that the life span of sewage networks could be halved. This is a potential societal problem in the long term i.e. we will end up paying more taxes for things that we could have solved.

It's certainly not my area of expertise, but I know there are people on here that have answers.

Edited: 03 September 2013 at 05:41 PM by IET Moderator
 30 August 2013 08:06 PM
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kengreen

Posts: 400
Joined: 15 April 2013

I understand that many of the sewers beneath (say) London are brick lined and built in Victorian times. They may indeed be in need of repair but modern sewers are formed by pipes which one would imagine had been manufactured to cope with the corrosive effects of our effluents. I think this particular matter is starting a dead hare.
 01 September 2013 12:50 AM
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justyburns

Posts: 8
Joined: 30 August 2013

I would hope the same, but a dead hare can make a good meal. I'd be grateful if someone would kill this for me.

To quote the article from Victoria University:

"A recent study from Victoria University indicates water-conservation can have unintended consequences for residents and water managers - a problem that is only set to get worse.

Our research found that reducing and replacing potable water lead to smellier sewers and more rapid corrosion of the sewer pipes beneath our homes.

While our level of water use varies, our level of waste going into the sewer does not. So by reducing water and replacing potable water with rainwater, treated greywater and wastewater, we are simply creating more concentrated wastewater. It's this concentrated wastewater that leads to a higher percentage of odour-producing gases and a greater rate of pipe corrosion.

Beneath Melbourne's northern suburbs, sewer conditions were modelled under a current water conservation scenario and four water conservation scenarios for the residents: simple reduced water usage, greywater reuse systems, rainwater harvesting and wastewater recycling through sewer mining technology. For each scenario we also measured levels of hydrogen sulphide gas, the chemical largely responsible for pungent "rotten egg" sewage odours and corrosion of sewer pipes.

Current water conservation practice in the study area shows 30% of households installed a rainwater tank and 3% installed a greywater reuse system. From data collected in the study area, the average amount of hydrogen sulphide was found to be 18 ppm. This could threaten public health if this gas is accidentally released to the above ground environment and inhaled. The sewer pipe lifespan was estimated to be 147 years.

However, when four water conservation scenarios were modelled, all of them increased the hydrogen sulphide to various levels of concentration that could endanger public health.

The reduced usage scenario assumed residents were using about 22 litres a day less water per person. The impact of this scenario was calculated to reduce the average local sewer network's lifespan through corrosion by 40 years, from 147 to 107 years, and raise the hydrogen sulphide levels by 12 ppm.

Greywater reuse systems
When calculating what might happen if all residents installed greywater reuse systems - using bathroom and laundry wastewater for toilet flushing and garden irrigation to reduce potable water consumption by 25% - results were more alarming. Hydrogen sulphide levels would increase by 46 ppm which could cause bad headaches, nausea as well as eye and respiratory injuries. Nobody likes smelly sewers in their suburb, but this really would be something intolerable.

The average lifespan of sewer pipes under those conditions would be reduced from 147 years to just 70 years, causing major issues for water authorities charged with maintaining and replacing the network."

That's a reduction based on a new installation. However I'd guess that much like Ireland, there are significant portions of the existing network in the UK already close to its sell by date.

I hope that I don't sound like I'm anti water saving, I am very much about water conservation and protection. I just want to be sure if we embrace and do something, we do it correctly.
 04 September 2013 04:51 PM
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kengreen

Posts: 400
Joined: 15 April 2013

Oh Justin,

I don't know if you realise but you have touched on a very big subject here. At school I had drummed into me the mantra that you interfere with natural systems at your peril. Over the years I have learned that no matter your scholarship there is always an unknown waiting to bring you down. There are innumerable cases such as the Titanic and bridges and buildings which collapse and aircraft which fall from th.e sky seemingly against all the odds.

And here we have a dirty trick being played by one of the most ubiquitous facilities on earth - Namely water which flows anywhere and everywhere, obligingly comes at the turn of a tap, less obligingly but mercifully falls on our heads - well some of us anyway!

Here on the north coast of Cornwall we have seen several tragedies where the "unexpected" big wave has swept the beach or cliff. I'm sure that you too have seen the terrifying speed at which fire can progress. I have long since declared that no one should be allowed to design even a toffee apple until they have spent at least two years on the repair and maintenance bench. Regrettably today's world is plagued by too many designers who know not what they do.

Ken Green

But
 19 September 2013 02:41 AM
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justyburns

Posts: 8
Joined: 30 August 2013

LOL, Ken, you read the words I quote, not state. These are not my words, my repetition of others that are learned.

If you can kill the hare, I'll make the meal and add my own spices. I am not of the chicken little ilk. I simply want the truth.
 02 November 2013 05:13 PM
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HarryJMacdonald

Posts: 254
Joined: 15 May 2002

I may have missed something but I fail to see how using rainwater to flush the loo changes the concentration of sewage,

Clearly only flushing the loo when really needed would. "If its yellow let it mellow, if its brown flush it down".
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