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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    Hello, please can I ask for views on small sewage treatment plants. I'm planning a replacement for the present septic tank, as it discharges to a watercourse. It's to be rated for 7 persons, and is in a field about 40 metres from the house. The field doesn't belong to me, is grazing land with a tractor passing very occasionally (likely not to go on the tank, but it has to take account of the possibility).

    The soil is shallow and stony. Solid rock, slatey and cleaving vertically, is just 200mm below the surface. It's generally hard enough to be used for stone walls, and appears to be typical in limited exploration just next to the existing septic tank. The existing tank (about 1.4m square and 1.3m deep, concrete block and brick, with a concrete cover) is smaller than any replacement, and I assume is in a hole excavated from solid rock.

    What questions should I be asking, and please does anyone have experience of small sewage treatment plants?

    Present check list is something like:
    rated for number of persons, BS EN 12566-3 and CE marked
    dimensions and shape (for excavation)
    weight (as a proxy for robustness)
    construction material of tank (robustness). grp, hdpe, mdpe, smc - any experience of these?
    shape (for robustness). I assume a horizontal axis cylinder will be a good shape if well buried. Vertical axis cylinder with hatch the full diameter not good. Conical with sloping shoulders I'm not sure about.
    electricity use. Would be wonderful to have an unpowered one but they need a good ventilation stack and the tank is too far from my boundary.
    noise from compressor. Would prefer a remote compressor in my garden (for maintenance), and would like it inaudible even in quiet conditions.

    I've looked at quite a number of manufacturers, and spoken to several. I've made a short list (not sure whether I'm supposed to state makers' names here, and it would be unfair without proper grounds).

    Are there other (obvious or less obvious) questions I should be asking? Any experience, good or bad, or particular makes, or hints about choosing installers (I don't want to diy).

    Most people who have these installed probably do it once only, so a record of tips would be helpful, especially as others will be doing this in the next year or two because of new regulations. Thanks for any comments.
    • CommentAuthorowlman
    • CommentTimeJul 19th 2018 edited
     
    Some time ago I came across this article. Apologies if you've seen it already. If not it may be food for thought.

    https://www.treehugger.com/green-architecture/omega-center-sustainable-living-eco-machine-living-building-water-treatment.html
    •  
      CommentAuthordjh
    • CommentTimeJul 19th 2018 edited
     
    It may also be worth talking to the people at Hockerton.

    PS that system does look impressive. I think a common factor is that both sites have plenty of area for treatment.
  2.  
    An interesting article from owlman, although I somehow don't think it would down size to a single dwelling.

    carrotandturnip - From the brief description of your site it does not sound like a reed bed would be possible. You say you don't own the field but do you have any rights to install new or modify the existing tank in that field?
    Have you had a look at the Biorock system, it runs without electricity unless you need a pump to discharge the outflow and can use an existing tank as the initial settlement chamber.
  3.  
    The references from owlman and djh are certainly impressive.

    Peter_in_Hungary - yes, I have to work with the site as it is, so using an outlet to the watercourse. The non-electric Biorock looks interesting, as does the Filterpod, but I can't provide adequate ventilation as the tank is well away from my boundary. There is some caution about performance of non-electric systems in
    https://www.wte-ltd.co.uk/non_electric_wastewater_systems.html
    though I have no experience of them.

    Using the existing tank would be tempting but it probably wouldn't be clean enough to meet the standard needed for liquid to enter the second tank.

    Have I omitted anything from my list that might be clear to someone who has done this before but is not obvious to the first-timer?
    • CommentAuthorskyewright
    • CommentTimeJul 20th 2018 edited
     
    You may have already considered this, but...

    Turning the problem on its head to an extent you could greatly decrease the amount of treatment need if you adopt a composting loo rather a flush one. N.B. This doesn't need to involve a 'little house' out back, e.g. (a couple of links from a web search...)

    https://www.toiletrevolution.com
    http://www.littlehouse.co

    Just a thought...

    Edited to change format to get clickable links
    • CommentAuthorSteveZ
    • CommentTimeJul 20th 2018
     
    I hope you have better luck with the composting toilet idea than I did with my other half. There will still be the grey water to treat, so it was not such a great problem

    If you search through the site there are a few entries on this topic. My system is still working well after 8 years, but it would not suit your situation as it is an in-tank system for an onion tank.

    I would be looking at the Vortex if I was in the market for another domestic sewage system. It has a compressor but splits the air stream to do different tasks. The pump is mounted on the tank, but you might be able to site it remotely and run an air pipe to the installation. Mine just pumps air into the liquor and runs the airlift to expel the finished water higher than the tank, but so far it works fine.
  4.  
    Posted By: carrotandturnipPeter_in_Hungary - yes, I have to work with the site as it is, so using an outlet to the watercourse. The non-electric Biorock looks interesting, as does the Filterpod, but I can't provide adequate ventilation as the tank is well away from my boundary. There is some caution about performance of non-electric systems in
    https://www.wte-ltd.co.uk/non_electric_wastewater_systems.html
    though I have no experience of them.

    The inference I take from the WTE article is that the non electrical systems are marginal in their ability to function to the required standard but work OK if under utilised. (quote "No wonder that the Test Results are good as it was under-loaded.") so an over sized unit should be OK. (Manufactures will push the limits on sizing as a marketing point. Think about cars and declared MPG.)
    The article points out the maintenance cost of the non electric units but says nothing about the running cost and maintenance of an air pump!
    Posted By: carrotandturnipUsing the existing tank would be tempting but it probably wouldn't be clean enough to meet the standard needed for liquid to enter the second tank.

    The first tank does not have to be clean, it is a settlement tank. Everything goes into this tank first and then the liquid passes to further treatment. Settlement tanks need periodic de-sludging. But if the existing tank is not on your land then perhaps you are limited to using it as a pass through to the discharge point without it being part of the new system. The Biorock system uses your existing tank as the settlement tank and you then have to put the Biorock unit after this. If you don't have an existing cesspit/septic tank available then for the Biorock system you need to put in a settlement tank.

    The air-vents can be taken some distance from the units underground and then have a stack pipe to create a chimney effect.

    For my curiosity, why do you need a new system as usually if it exists then it can stay in use.
    • CommentAuthordickster
    • CommentTimeJul 20th 2018
     
    Hi, I've got a bio rock, all good, but no slope away so have to pump back up into the drainage field, so uses a tad of electricity every now and then.

    If you are on a slope then no need for power.

    There's just two of us, but the occasional weekend friends camping with 20+ people seems to cause no problems.

    Just a thought... why not site it on your own land?
  5.  
    Posted By: Peter_in_HungaryThe air-vents can be taken some distance from the units underground and then have a stack pipe to create a chimney effect.


    About 40 metres in this case, and crossing drains in hard ground with shallow bedrock. Would like to do this but sadly I doubt that it's practical, and can't really risk such a major operation that might not work.

    Posted By: dicksterJust a thought... why not site it on your own land?


    Not space close to the house, so no advantage in this case.

    A rep called today, and I'm hoping an installer will contact me next week, so will report if anything useful transpires. Thanks both for comments.
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