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Separate wastewater from sewage, says ICE

Surface water run-off should be separated from sewage so water companies can become more energy efficient, the ICE has said.

The ICE’s 2010 State of the Nation report published last week said that reducing the volume of wastewater treatment will be essential to meeting government emission reductions targets.

“We must treat less wastewater, by using regulation to encourage separation of sewage and surface water drainage and using localised natural infiltration techniques in developments,” the report said.

Water industry energy use has nearly doubled since 1990 due to the increase in treatment required by recent water quality regulations, it said. “The industry cannot reduce its carbon footprint enough to meet government targets without large reductions in the volume of wastewater treated.”

Industry body Water UK’s Meeting Future Challenges report published earlier this month expressed similar views.

Readers' comments (8)

  • It's taken us so long to come up with this solution?
    Its also taken us too long not to come up with a similar solution for other related problems - lower grade water for toilet flushing as introduced in Hong Kong many years ago, and wastewater re-use, at least for non-potable water, as provided in the Middle East and other dry areas throughout the world for over 30 years.

    Again, no National Plan over many years. All the above needs separate and additional pipework systems - an expensive element of the works, but which could be relatively cheap if provided on all new-build housing and developments, particularly total new areas of housing and commercial developments.

    We could, by now, have had lower treated water flow and quality demands, and lower treated effluent flow demands - in all a major saving.

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  • Retrospective separation was carried out in parts of New Zealand, but after doing a few, the idea was dropped - high cost/minimal environmental benefit/disruption. There is some justification for partial separation to reduce spills and obviously for new projects to have separate systems, but retrospective separation is a really really expensive option.

    Consider basically constructing all new sewerage system (right down to separating roof drainage from household waste pipes) and pump stations and leaving combined pipes for stormwater - because sewage pipes are smaller therefore cheaper than stormwater pipes. Then all your combined pump stations will become stormwater pumps, but will require new outlets for discharge to receiving environments. How big a carbon footprint would that take on?

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  • Barry Walton


    I had been discussing the ICE sewerage proposal with a learned colleague. I put to him some concerns about the approach - a) we have, I presume, a vast combined sewerage system that is not going to be replaced, b) with infiltration there is going to continue to be a considerable amount of surface water/ground water getting into foul and combined sewers and draining out of them into the ground - more concentrated pollution from leaks in foul sewers? c) the so called surface water is not clean and may well benefit from going through a works - what will they do with it? d) will recirculation to neutralise peak sewage flows mean a lot of 'water' going round in circles in the works, e) is a whole new approach to capacity needed if savings are to be realised?

    The contributers above have raised similar issues but are perhaps not aware that new build normally has separated systems with, for our newish house. untreated road runoff disappearing to some water course. That will doubtless become a problem to be solved with treatment demanding more carbon use.

    What may be important for the State of the Nation report is that it avoids newsy sweeping changes that are not practical. It would be useful then for the ICE to spell out how what is proposed will work or withdraw it from the shopping list.

    B Walton (F)

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  • It is impractical, as well as prohibitively expensive, to now try and install the parallel pipework systems needed within existing urban areas. I don't suggest that. The tragedy is that for the new towns and major extensions to towns over the last 30 years or more such systems as suggested could quite easility have been employed and shown, even then, to be cost effective for the overall pipework/treatment systems involved.

    Hong Kong introduced seawater for all new works toilet flushing 40-50 years ago because of population increases and water shortages and managed this problem exceptionally well. This is the same problem that the UK has to accommodate!

    However, one of the biggest inefficiencies within wastewater treatment plants is the frequent need to hydraulically cope with peak storm flows, over and above normal diurnal peak flows. I know of a recent major new works in Europe and to a lesser extent others in the UK where peak storm flows as high as 5 times ADWF were required to be accommodated when even relatively small storm tanks would have significally reduced the capital works and even to some extent the O&M works costs and with minimal, if any, increased net area of site needed or amounts of energy required.

    With the eventual move to BNR plants, and with minimal costs of basic tertiary works, the quality of wastewater effluent would be suitable for many applications, particularly for irrigation in farming areas, and with even relatively little additional costs to provide general water quality, if not even potable water quality. As it is we are spending an inordinate amount of money on expensive wastewater treatment only to dump that water in the rivers or even into the sea. Water Treatment then has to start from scratch again. It isn't cost effective!

    I have also been involved with smaller WWT plants where buffer tanks are provided to level out even diurnal flows. This can be directly and even indirectly more efficient, if only because a "constant" flow plant has much simpler systems and is easier to control as well as providing more efficient use of equipment.

    We just need better lateral thinking and more efficient overall systems designs!

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  • Barry Walton

    And this is what the learned colleague offered.


    1. The vast sewerage system in the UK whether separate or combined is not going to be replaced.
    2. There will be exceptions where there is flooding of combined systems (sewage on the street) and it might be good engineering to add a separate surface water drain but I suspect few and far between.
    3. There will always be water flowing into and out of sewers of both types. Whether or not they will be replaced will depend on their category according to the WRc Sewer Rehab Manual. Only replacement for 'critical sewers' - ie where there is a danger of flooding hospitals, schools and the like. Others (> 80%) will be repaired on a breakdown as needed basis.
    4. The advocates of separate systems seem to ignore
    a) the fact that there will always be cross contamination. In the industrialising/developing world some 'separate systems' have as much as 50-60% of the sewage in the wrong pipe (no regulation/control of connections). In fact we have very expensive two pipe combined systems with no chance of future separation. Ideally, all of these flows need to be transmitted to STPs but reality is that they will not.
    b) in the UK the EA is concerned with DIY builders connecting to the wrong pipe (not a very big problem) but more so with gardeners etc putting excess chemicals down the surface water drains and hence straight to the watercourse without treatment.

    5. During high flows we do not send all the flow through the works but can by-pass some to storm tanks which can be emptied through the works when the flow subsides.

    There is no universal solution. We would be better with improved storm water facilities at treatment plants and more storage in the networks than trying to separate foul and 'clean' water - clean is not clean! And pipes are difficult!

    B Walton

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  • The above misses some of the points raised. The reduction in inflow rates for any given Wastewater Treatment Plant, generated by separation of storm flows from sewage flows, reduces the rise rates in the Final Settlement Tanks - a major source of "non-compliance from the risk of carry over and effluents failing the discharge consent. Separation of flows either increases the process engineering performance of any Works or increases the capacity of any such existing treatment works. Engineers must not be dictated to by process engineer considerations alone, i.e. one of the many engineering discipline considerations involved, and should consider the overall optimum engineering system for any particular site and system, i.e. collection/conveyance and treatment as an overall engineering system.

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  • P.S I'm not impressed by the NCE Magazine's editorial control - possibly from the typically younger generation of less educated people. The word is "separate" and not "seperate"!

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  • We also do stormwater treatment in New Zealand - again put in retrospectively for developed areas. Now we try and remove heavy metals, oils, etc from even the smallest of sediments. There are a whole raft of options to choose from, though fundamentally they are one or a combination of screening, oil and grease traps and settlement (tanks and pond systems).

    Before Europe gets into stormwater treatment in a big way, consider that if cars become electric and brakes become ceramic what metals and pollutants are you left to treat? Mostly just litter (relatively easy to remove).

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