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Quality of the water coming out of a constructed treatment wetland  RSS feed

 
gardener
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I made another post asking about converting an existing septic system to use a subsurface constructed treatment wetland but my follow up question on a related but different topic is what is the quality of the water coming out of a subsurface constructed treatment wetland? Would it still be classified as grey water?

I'm currently considering having the water from the wetland flow into what will be a surface wetland which would overflow into a swale which will be lined by trees and finally that swale would overflow during high flow into a seasonal stream that flows through my property.

The seasonal stream is not recorded on any legal records and I'm planning on building a series of ponds in the stream channel. I have already checked with local regulators and no issues there.

What do you all think? Would this system effectively deal with any negative elements of the water coming out of the treatment wetland?
 
pollinator
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The key to effective bioremediation wetlands is growing the right combination of plants and getting them in the right order.  There has been a lot of research done on this over the past 40 years or so, particularly for surface run-off from parking lots, streets, industrial sites, etc.  Different plants are good at capturing different chemicals, heavy metals, acids, etc. 

I have a friend who used to do this for a living (he's now retired).  He did it for golf courses, who are frequently approached by city engineers asking if they'll be open to creating rain surge ponds as a part of their golf course.  The city would pay for the instillation of the pond and for the necessary bio-engineering.  The golf course would get a water feature and the good press that would come along with it by helping the city capture and infiltrate rain water after a big storm.  My friend was part of the team that would come out and help set up the wetland necessary to purify that water before it would wash down into the pond/water-feature.

Usually, it's nothing more than 4 or 5 zones, with a specific aquatic plant growing in each zone as the water progressively flows down through it.  When it comes out the other end, all the salts, metals and hydrocarbons have been captured, leaving (mostly) clean water.  The worst stuff had been taken out.
 
Daron Williams
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Interesting - I will have to look into it more... I would love to get a system setup that could handle all the waste water from my house. The soil here is all clay making traditional drain fields not practical so I have been trying to figure out an alternative.
 
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Daron, have you had the soil tested? Do you know if any of the clay soil amendment tricks will work to open up the soil structure and increase infiltration?

The last time I had to deal with heavy clay soil, it was in a finished housing development where they had scraped away all the topsoil, smoothed the largely clay subsoil out into an impermeable barrier, spread some of the now-dead topsoil back in a layer of about an inch or so, and dropped sod atop it. It was a muddy mess.

After most of the grass died, first because it drowned, then because it baked, I tested the soil, which showed a calcium deficiency, and a lack of organic material.

So I made a bunch of garden beds in one backyard. I got a truckload of ramial wood chips dropped off by a local arbourist I know, took some buckets of gypsum powder and grit that used to be untreated drywall until it fell off a truck, scraped back the topsoil and spread the amendments all out where I wanted them, and forked two-thirds of the wood chips and all of the gypsum into the top foot of the clay, reserving the rest for mulch.

I cannot adequately express the change that took place. The grass, as it turns out, wasn't as dead as I had thought, because along the perimeter of the new beds, it all came back lush and green. The next major rain event showed that, while on the unamended former lawn, ponding still occurred, the improved soil soaked it up, and the area of effect extended to just outside of the greened perimeter areas of the beds.

Not that I am suggesting that you improve your soil to allow a traditional drain field, of course, but I think there are a number of ways to use improved soil around the perimeter of the ponds you're considering to enhance the cleaning effect, and mitigate the risk of travelling pathogens, simply by increasing the vitality of the soil, and it's ability to out-compete pathogens, and eat them.

There's also the idea, whatever the length of the run of the entire system, that by introducing micro-booms, basically biodegradable fabric socks containing wood chips, designed and inoculated like Paul Stamets' mycobooms, it is possible to encourage the water to zig-zag the whole length of the run, increasing surface area, habitat for fungi and bacteria to do their decompositional duty, as well as spots where reed bed populations can be planted, acting as physical filters in the water to grab and slow particulates and solids for processing.

One concern I don't always see addressed is that of untreated water leaching out of the treatment ponds and channels into the surrounding earth. I like the idea of planting up the perimeters of these constructs with water-loving poo-eaters like willow, building up an artificial riparian treatment barrier, just in case there are leaks.

But let us know how it goes, and good luck.

-CK
 
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Hi Chris,

Fascinating insight into your experiences with remediating heavy clay soil. Do think the improvement in grass growth may have been due to the additional storage space for water in the new upper soil horizon - in the woodchips and gypsum - rather than due to any opening up of the drainage capacity of the clay subsoil itself? You'd have half of many Irish counties queuing up for your recipe if you can open the clay subsoil enough to permit percolation. I'm intrigued.

:-)

Féidhlim
 
Feidhlim Harty
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Daron Williams wrote:I made another post asking about converting an existing septic system to use a subsurface constructed treatment wetland but my follow up question on a related but different topic is what is the quality of the water coming out of a subsurface constructed treatment wetland? Would it still be classified as grey water?

I'm currently considering having the water from the wetland flow into what will be a surface wetland which would overflow into a swale which will be lined by trees and finally that swale would overflow during high flow into a seasonal stream that flows through my property.

The seasonal stream is not recorded on any legal records and I'm planning on building a series of ponds in the stream channel. I have already checked with local regulators and no issues there.

What do you all think? Would this system effectively deal with any negative elements of the water coming out of the treatment wetland?



Hi Daron,

Here are some wastewater classifications that may answer your question:
Grey water - water from showers, sinks, washing machines etc. but specifically excluding black water from the toilet.
Black water - water from the toilet. I think that Art Ludwig may also refer to grey water that has sat for too long and gone septic as black water, but in general terms the classification here is the one used. His distinction is important, but
Brown water - flush water from urine diverting toilets that contains only faeces, paper and water, but no urine.
Yellow water - the urine along with small volumes of flush water from urine diverting toilets.
Sewage - grey water plus black water, usually en route to the septic tank.
Septic tank effluent - settled sewage, or what is termed primary/preliminary treated effluent.
Secondary treated effluent - sewage that has been aerated in a mechanical treatment system or reed bed or constructed wetland. This reduces the BOD (Biochemical Oxygen Demand) and suspended solids down from about 300 and 200 mg/l respectively to about 20/30 respectively.
Tertiary treated effluent - secondary treated effluent that has undergone additional treatment in a reed bed or constructed wetland, percolation area, or other form of polishing filter. BOD and SS are usually down to about 10/10 or 5/5 mg per litre. (note that a natural river or stream will be about 1 mg/l of each, so we're still not at background levels).

There is also storm water - rainfall run off from roof, yard or road surfaces. Except in unusual circumstances this should be kept separate from any of the above. Note that sometimes municipal treatment systems use constructed wetlands to filter stormwater and secondary treated effluent together prior to discharge to water courses. Municipal stormwater can have a pollution load as high as 15% of that of raw sewage!

So, based on the above, you won't achieve grey water by filtering black water - what you get is secondary or tertiary treated effluent instead. It's not just a matter of terminology, it's also a matter of health and safety. Grey water is generally free of pathogens and can often be used safely in the garden as a source of irrigation. Treated sewage effluent, by contrast, usually has a high pathogen load. This isn't something that you can safely use as surface irrigation. However you can still use it to irrigate trees in a subsurface distribution system if you wish.

From your description of your proposed multi-stage filter system, and the fact that you've said you have heavy clayey soil which prevents conventional percolation, I think that the proposal you've outlined has a lot of merit. I'd propose fencing it though until you get to the stream anyway, so that you won't have people or livestock splashing about in a potentially contaminated swale or drain. Also, if you put in micro-booms like Chris has suggested across the flow of your swale it means that the water will have to pass through coarse sand, composted woodchip, or dense straw-bale dams to migrate downstream. These will all help to reduce BOD and suspended solids, and will also help to filter out bacteria if the conditions are right. After about 10 days there is a very high die-off of gut bacteria in sewage treatment systems, so if you can estimate the storage volumes in your system vs the volumes of effluent you produce, it should be possible to get a 10d retention time between the toilet and the stream.

Fire off any questions you may have, or any drawings of the site. it's an interesting set-up. I look forward to hearing how it goes.





 
Daron Williams
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Thanks for the responses! I'm still in the brainstorming stage at the moment and the comments are really helpful. I'm going to go tour a site on the 24th that as far as I know is the only private site in Washington State to have a permitted subsurface treatment wetland. I'm hoping they can help me figure out what will work. A while back I found a document from a city council in Australia that outlines the requirements for using reed beds as treatment. Since my area does not have any official documentations I have been using it as a guideline. I'm curious if you have seen this document and what your thoughts are on it.

I'm interested in using the swale in my system as an absorption trench (see below). My thought is that I would dig the swale and install the trench in the base of it using standard practices and then cover it all with a thick mulch layer. Potentially even using it as a walking path. I would still have an overflow area but I would make the swale large enough that this would rarely be needed.



Filename: Use_of_Reed_Beds_for_the_Treatment_opf_Sewage_and_Wastewater_from_Domestic_Households.pdf
Description: Document on reed beds from Australia
File size: 1 megabytes
 
Feidhlim Harty
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Hi Daron, I don't know the Australian code you mention. The Irish EPA have a good and brief description of reed beds and constructed wetlands in the Code of Practice on Domestic Wastewater Treatment Systems. Follow the link to the EPA Code of Practice on http://www.wetlandsystems.ie/permaculturereedbeds.html if you're interested in seeing it. To cut through the padding, just search "wetland" and you'll find the info you need pretty quickly.

What I understand of your proposal sounds good. Keep the base of the swale/trench as shallow as possible to ensure that tree roots can get down into it and to maximise the soil microorganisms that can deal with any contaminants or nutrients available.

All the best with it

Féidhlim
 
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