Countries with a Separate Sewer System

[Erina]

The British sewage network is one of the oldest still in service today, it designed for less heavy usage than today, but ultimately succumbing to the amount of rainwater washed into the system.

Although this rainwater helps to naturally clean the system, there would be no possibility of discharge into natural water supplies, were the network designed to separate the two.

Which countries have taken this route ?

[CharonY]

I think it is a less a national, but more a municipal decision. There are many cities where storm drains are separate from household lines and therefore do not get to the wastewater treatment plants and are released into local waterbodies.

You often see are bylaws that e.g. forbid to wash your car because the detergents can get into the storm drains, for example.

[studiot]

1 hour ago, Erina said:

The British sewage network is one of the oldest still in service today, it designed for less heavy usage than today, but ultimately succumbing to the amount of rainwater washed into the system.

Although this rainwater helps to naturally clean the system, there would be no possibility of discharge into natural water supplies, were the network designed to separate the two.

Which countries have taken this route ?

A point.

Sewerage is the network or pipes etc, sewage is the effluent the flows through it.

Further terms with particular meanings are drain and drainage.

 

I think the British system is not as old as you think and definitely much more complicated than you portray.

I also agree with Charon Y that even within countries, arrangements vary from place to place.

 

What is your interest in the subject of wastewater engineering ?

[Erina]

I would like to know where the separation of storm drains are from household lines, to find out how well this works. Are there any such examples with in the UK ?

An important matter of trust is needed to make such a system effective, if the storm drainage is not treated e.g. full of detergents from car washes.

I would like to know how well a segregated system works and the practicality of retrofitting developed areas with such a system would therefore be.

Thames Water (London) have decided to continue with their combined system with a significant investment called Tideway Tunnel, so I was wondering if a segregated system really was better ?

Edited April 10, 2023 by Erina

[studiot]

16 minutes ago, Erina said:

I would like to know where the separation of storm drains are from household lines, to find out how well this works. Are there any such examples with in the UK ?

An important matter of trust is needed to make such a system effective, if the storm drainage is not treated e.g. full of detergents from car washes.

I would like to know how well a segregated system works and the practicality of retrofitting developed areas with such a system would therefore be.

Thames Water (London) have decided to continue with their combined system with a significant investment called Tideway Tunnel, so I was wondering if a segregated system really was better ?

I'm not sure what you mean by 'storm drains', espcially in London or the Thames Valley more generally.

A good deal of rainwater finds its way to the highway drainage network, which is the responsibility of the Highway Authority.
I'm not sure what car  washes you mean individual prive drives or commercial car washing stations which will have interceptors and commercial disposal arrangements.

As regards cars the main problem with them is the danger of inflammable petroleum products finding its way into the existing system and causing fires and/or explosions.Petrol Interceptors started to be introduced in the mid 1980s when a BS on the subject was published.
I remember designing new highway drainage on new schemes in the 1990s + to include these.

[exchemist]

39 minutes ago, Erina said:

I would like to know where the separation of storm drains are from household lines, to find out how well this works. Are there any such examples with in the UK ?

An important matter of trust is needed to make such a system effective, if the storm drainage is not treated e.g. full of detergents from car washes.

I would like to know how well a segregated system works and the practicality of retrofitting developed areas with such a system would therefore be.

Thames Water (London) have decided to continue with their combined system with a significant investment called Tideway Tunnel, so I was wondering if a segregated system really was better ?

There's an explanation of the process for separating rainwater from sewage here: https://www.wavin.com/en-en/News-Cases/News/Pros-and-Cons-of-separating-rainwater-from-sewers-to-prevent-sewer-overflow-in-urban-areas

From the description it does not look as if any country has really embraced this idea fully, though there seem to be some pilots at municipality level, Vancouver perhaps being one. It is evidently a very costly and disruptive exercise to retrofit a twin-pipe system, though I suppose it could be put in place on new housing developments if planning regulations were changed to require it.

[Erina]

It seems then that there is no real advantage to a segregated system as they would both need to be treated.

[TheVat]

Out here in the western US, storm drains go to creeks or rivers, untreated.  All sewerage is separate from this, obv. , and consists of enclosed pipes.  

The municipal ordinance here is regarding dumping used motor oil down storm drains.  Soap is apparently not a concern.  Probably written back when a lot of people changed their own oil at home.  Hardly anyone does that these days, so there's less concern about scofflaws illegally dumping.  

[Erina]

My main focus was on developed land. I suppose anybody could dump anything really. Better, if they did, that it be treated I suppose. That way surrounding water (Britain is an island after all) will likely end up with cleaner waterways.

I don't particularly trust anybody, so filtering the water is a safer bet.

Oh good, the cheaper option is better.

[Ken Fabian]

Much like where TheVat lives, separate sewage and stormwater is the norm in Australia - stormwater dumps into natural waterways without treatment, but sometimes with some form of separator that catches plastics and other rubbish. Sewage has it's own dedicated pipework and goes to treatment facilities before release. In some cases eg parts of Sydney it is partial treatment and pumping it out into the ocean via "deep ocean outfalls". These systems don't cope well with flooding but work okay most of the time.

[CharonY]

Storm drains are also not unusual in the UK, but they are often upgraded, newer systems. Here is a wiki article for Brighton, for example https://en.wikipedia.org/wiki/Brighton_sewers, mentioning a storm water collection system. However, they are apparently not entirely separated as overflow from sewer system can get into the storm system. In North America, many sewage and storm system are simply separate pipes as shown in exchemist's link.

[Erina]

Ultimately though, the storm overflow could be contaminated.

My original goal was to prevent that, believing storm water to be somehow untainted, but that just cannot be guaranteed.

I think therefore that the combined system, as demanding as it is, is still the most reliable, were the system to have the capacity to deal at peak demand.

[CharonY]

1 hour ago, Erina said:

Ultimately though, the storm overflow could be contaminated.

My original goal was to prevent that, believing storm water to be somehow untainted, but that just cannot be guaranteed.

I think therefore that the combined system, as demanding as it is, is still the most reliable, were the system to have the capacity to deal at peak demand.

Well, the issue that separate system have been in use specifically to avoid overflow, where contaminated sewage can overflow. In areas where weather patterns are shifting, this might become an increasing issue. Essentially what is the best solution really depends on the specific region.