ULV toilets water conservation problematic 3

[falcofalco]

I have heard that the current municipal water conservation fad of requiring ULV (~6 litre) toilet installation and retrofitting is ill-thought through and problematic because it represents the solve-one-problem-at-a-time, linear-thinking for which engineers are frequently criticized. The greater the number of ULV toilets installed, the claim goes, the lower will become the needed hydrostatic head required by existing (& aging) sewer main infrastructures designed for, and requiring the water volumes generated by thousands of conventional 18 litre flush toilets.

So the poop stops moving or requires ad hoc 'solutions' like increased use of pumps to maintain the hydrostatic pressure.

I have heard that this has become such a problem in some jurisdictions that have been so 'successful' in having ULV toilets adopted in large numbers that they have had to issue public advisories to flush the ULV toilets two and three times thus negating any water conservation!

Can anyone direct me to documentation of any jurisdictions where this scenario has occurred and how the problem was handled?

Thank you.

 

[BobPE]

Its not the engineers that are linear thinking, its the people responsible for implementing their ideas that are linear thinking, put blame where blame is due.

I am not sure how you got on hydrostatic head, that sure doesn't change with reduced flows from ULV's. That said, both pressure and gravity systems are impacted by ULV's in very straight forward predictible ways, its not a big secret to the waste water engineers of the world. With reduced flow comes increased retention times in force mains and decreased velocities in gravity mains. This leads to creating septic waste conditions and nasty solids plugging, and odd wastewater strength profiles depending on diurnal hydraulic conditions.

Short of restoring flows in the piping systems, how to address the problem is simple...rip up all the infractructure and replace it with the correct diameter pipe. That is an expensive proposition, that is why on the surface it appears that people are thinking in linear ways about addressing the problem.

BobPE
BobPE

 

[LHA]

This is a very interesting. I never even gave it a thought. But it seems like it would create the problems you've cited.

That being said, do we replace all the sewer in the world, OR put more potable water into the existing sewer to make it work. Bob is right, we have to do one or the other.

I vote for slowing population growth so we have enough potable water to put in the large sewers. This will in turn eliminate the need for large mains and wetwells, so low flush toilet can be phased in concurrently with upgraded, smaller conveyance facilities.

By slowing population growth, this problem, and almost all environmental problems become less of an issue. But most people appear to disagree, so I must be off-base.

 

[dicksewerrat]

I have seensewer systems that have been heavily rehabilitated by lining the old pipes. This seals the groundwater out of the old pipe and the same problems start to crop up in the sub systems. Low flows and solids dropping out. the sealing takes out much more water than using high volume toilets will add. The primary reason most of these new technologies are applied is because the waste treatment plants are having major overflows with storm events. Raw sewage in the rivers and lakes is a NO NO. And some systems are under EPA compliance orders to stop the overflows. Yes it would be nice to dig and replace all the pipes with the new proper size but the guy that foots the bill can't afford ity. That guy is the user of the systems. All of us. Look at what it would cost to replace the 4-5 million miles of pipe in the US. The numbers are staggering. At only $100.00 perfoot it would be $5.28 E+11 for each million miles. And that is a low estimate. Not all the pipes are 10 inch and to be replaced with an 8 inch. Those 12 foot pipes cast a lot more.

 

[waterworker]

The ultimate solution: