Any one interested in re-opening discussion on this thread.

For those that participated, what were the major conclusion(s) you took away from this discussion?

I am interested in discussion everyone's experience with shallow sewer systems with grinder pumps

David
 
Dr. David A. Bates, P.E.
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I think that is a helpful explanation, Dean.

Although it is is possible to remove N in other ways - if there is a fast growing crop which is being harvested, for example. Or even maybe in the worms themselves.

I am not really convinced that a reported 80-90% reduction of N is really telling us very much. As well as the potential losses Dean mentions, presumably this could just be due to dilution.

As an advocate of Soil Science, I really do recommend people read up about the term "nutrient availability" (particularly N, P and K). I am sure there are good explanations on wikipedia.

Hi Wendy,

lets explore the science of nitrogen removal in simple terms for readers. Nitrogen is "removed" in two different ways:

Firstly, nitrogen can be removed as gas. Ammonification and denitrification are processes that remove nitrogen as gases (ammonia or nitrogen gas). Most sewage treatment plants use anaerobic processes to deliberately remove the nitrogen as gas, because the treated wastewater gets discharged into watercourses where nitrogen is a pollutant, leading to algal growth and eutrophication of the watercourse. Denitrification occurs in anoxic environments. Anoxic environments are not suitable for worms and my experience is that the substrate needs to be aerobic for worms to survive. I suppose it is possible that the bottom of your digester is anoxic, thus inducing denitrification, while the top layers are aerobic for the worms. My systems are entirely aerobic because I don't want to lose the nitrogen. I see nitrogen as a key element in the nutrient cycle, an essential plant nutrient that should be conserved. In my view an onsite sewage system that denitrifies goes against the principles of permaculture. 

The other method for removing nitrogen from your wastewater stream is using carbon to generate a high carbon to nitrogen ratio in the substrate. The nitrogen will be temporarily "locked up" as organic's oxidise the carbon. However, eventually the carbon gets used up and the nitrate is released (dissolved into the water). Please keep in mind that I use exclusively organic materials as substrates for vermifiltration. Woody materials with high carbon will remove nitrogen for a while. They also need topping up regularly because the carbon is oxidised. But what needs to be understood is that the nitrogen is not actually removed. Eventually the carbon to nitrogen ratio in the lower substrate will go in nitrogen's favour and nitrate will be discharged from the reactor. As you add more carbonaceous material to the top this will remove nitrogen, but eventually that material will work its way downwards and its carbon will reduce.

Please ensure your tests are long term and that your "composting" vermifilter has been operating continuously for say five years before you start testing for nitrogen, then test for another five years. I just don't understand why you see removal as good. And I can't accept that there are no nutrients coming out of your tank. Worm juice is rich in dissolved nutrients. You surely want to grow something in your impoverished soils?

I accept that you are achieving secondary treatment in your percolation trenches, but because they are trenches you have no control over percolation into your soils and water table. Seepage is the water table. I would accept that there is no "detectable" nutrient in your discharge if you explained nutrient levels with lab test results. But I would then ask what is happening to the nutrient? What can also occur is that by limiting one key nutrient (e.g. using woodchips to intercept nitrogen), plants will not grow even though the water is rich in P and K. So I prefer primary and secondary vermifiltration using a stable organic substrate such as pine bark, that remains porous without maintenance or topping up, followed by surface dripper feeding the plants directly with nutrient-rich treated water.

cheers
Dean

Please appreciate that percolation trenches are not secondary vermifiltration.

Mine are. They replicate the ecosystem contained in the primary processing unit. ie. organic (mainly woody) substrate which is colonised by the worms and their associated ecosystem.

Because the nitrogen is retained using vermifiltration (unlike some treatment systems), and the phosphorous and potassium (along with other plant nutrients) are also leached into the water as the worms digest the solids, the wastewater exiting your system will actually be very rich in nutrients. Indeed all vermifilter toilet systems that I have set up using surface irrigation generate excellent plant growth. You may find that your lemon tree has not responded because of excessive water resulting from high subsurface water table (i.e. soakage field). Citrus require free drainage.

With the greatest of respect for your experience and expertise, you do NOT know the details of my installation. I deliberately designed the soakage area to show up any nutrient release from the tank. There is no detectable amount. And neither would I expect any based on the lab results from Anna Edey's vermicomposting systems which show between 71-96% of nitrates removed by the ecosystem in the primary processing unit (see below).

I live on a terraced mountainside. There is no subsurface water table anywhere close. There is sloping bedrock around 1m below the surface, which conveniently channels any water reaching it forwards to appear half way up the wall of the terrace below. Thus I can monitor any seepage and its effect on the vegetation at the foot of the terrace wall. The vegetation there has not changed in 7 years. It's typical of an impoverished soil. When I say there's no detectable nutrient coming out of that tank, then I mean no detectable nutrient is coming out of that tank.

I don't know whether the systems you've worked with are based on largely inorganic substrates? Most of the published papers which I studied prior to designing this system were. This system is not. It uses organic material as a substrate and this is what makes the difference. That's why I refer to it as vermicomposting, not vermifiltration, because what is going on in that tank is far more than mere filtration. There is an entire ecosystem in there - essentially it's a replication of a large part of the soil microbiome - which has a major role in the bioremediation of wastes.

Further, the secondary metabolites of that microbiome have notable antifungal/antibiotic activity, meaning that faecal pathogens are also being dealt with.

I'm looking forward to working with my local municipality and the university department they select to monitor and evaluate the system. When we have some test results, I'll come back and post them here.

Hi Wendy,
It doesn't matter how many holes there are and their size, once silt builds up inside the soakage lines, the system will fail, even with earthworms present. For longevity, perforated soakage lines require free flow of water to the holes, along with coarse media surrounding the line, with geotextile on top of the media and this covered with soil.

Please appreciate that percolation trenches are not secondary vermifiltration. Secondary treatment is a process to remove the suspended sediment, reduce BOD and pathogens, suitable for surface application. The thing about surface irrigation is that it can be moved to where you want it, to plants where nutrient-rich water is required. Because the nitrogen is retained using vermifiltration (unlike some treatment systems), and the phosphorous and potassium (along with other plant nutrients) are also leached into the water as the worms digest the solids, the wastewater exiting your system will actually be very rich in nutrients. Indeed all vermifilter toilet systems that I have set up using surface irrigation generate excellent plant growth. You may find that your lemon tree has not responded because of excessive water resulting from high subsurface water table (i.e. soakage field). Citrus require free drainage.

The vermifilter toilet "wheel" seems to get reinvented at regular intervals, but it is always good having different people looking at ways to improve it and open source their ideas. I started this thread because of frustration that people seem to be attempting to be claiming this simple, low cost technology as their own, clearly for pecuniary gain. For example "Walter Gibson, MA PhD, talks about his invention call "Tiger Toilet" The inventor of "Tiger Toilet" project, Walter Gibson, a microbiologist by Profession ..."  thewaternetwork.com/article-FfV/tiger-to...NfE2HCzVOMVSRVimsr3g

cheers
Dean

Furthermore there is quite a difference between a constructed soakaway and an openly draining pipe. Again, I am not an engineer and I don't really like either solution - however there must be a difference between installing a reasonably large engineering unit and telling unskilled and uneducated users that a pipe outflow is safe.

There is a difference when claims are being made about effective pathogen destruction which cannot be proved without rigorous microbial testing. And from our existing knowledge cannot possibly be true.

Systems exist. Yes. That doesn't mean they are safe.

I remain perplexed about how engineering solutions are prioritised over and above basic microbiology. Unless you kill the pathogens (with heat, acid, alkalinity, etc) if there is no testing of the output then there is an unknown risk of spreading them.

It surely isn't good enough to just assert things that a) are not tested and b) seem highly unlikely to be true.

KaiMikkel, Wendy's system is no different from a septic tank feeding a soakage field. Except that humus is produced rather than sludge, which is a significant improvement. Now, we all know that soakage fields work when well constructed, but can fail miserably when poorly designed. Please keep the debate in context, it is fine for you to criticise soakage fields in general but there will be those who disagree and note that well designed soakage fields can be a component of good practice, safe onsite sanitation.

"A pathogen which can produce a fatal outcome in one context can be benign in another."

OK, so how's this for context? Water from your so-called sanitation system which is contaminated with Shigella bacillus, Vibrio cholerae serogroup O1 and e.Coli O157:H7 percolates into a community's drinking water supply. Children and elderly people then drink the contaminated water which results in everyone involved contracting either dysentery and/or cholera and/or experiencing severe abdominal distress with most people infected thereafter dying a few hours or days later owing to a lack of resources, poor availability of healthcare and/or owing to already compromised immune systems, etc.

Humus is stable carbon and does not decompose further in human time frames, it is the stable soil fraction that originates from plant carbon, as a result of photosynthesis. There are other factors that influence the time it takes for humus to build up... e.g. Washers or wipers? Worms digest toilet paper much more slowly than poo and more humus is produced per person. Also, suspended solids may be high in wastewater exiting the primary vermidigester. Claiming that the solids never build up only suggests to me that your soakage fields will have a limited life due to siltation.

For sure the contents of the tank will convert to humus over a period of time, but for as long as the losses to the system (CO₂ + wash out of the finer fraction of vermicompost) are close to the final accumulation rate, then build-up will be extremely slow. Possibly why Anna Edey claims her system never needed emptying in 20 years?

There is no detectable siltation in the soakage field because you also have the same vermicomposting ecosystem in that which ensures adequate movement and aeration of layers. There can be build-up of silt in perforated distribution pipes if the diameters of both pipes and perforations are too small.

Wendy's system clearly works but is it optimised?

No! That's the whole point of the open source community that exists around it. Currently I'm experimenting with a vertical perforated pipe for improved drainage/aeration.

The whole point in developing the system was to have a low-cost DIY open source solution for ecological waste management that's rooted in a real-world situation and is a bit more user-friendly than dry composting systems. Many people are not prepared to give up their flush toilets. Many people couldn't even dream of affording any of the proprietary systems I've seen. Most cost tens of thousands. And with ever-growing wealth inequality in our societies, I think it's important to have an accessible solution.

In rural Portugal, many people rely on ancient septic tanks. Most are DIY installations. Most don't work properly and in this mountainous region, there's no possibility of effective leach fields as the slopes are too steep and the soils are too thin. Consequently all the surface waters carry a background level of coliform pollution. My aim was to devise a system which would be an improvement on these septic tanks and which local people could afford to install.

The trade-off with low cost DIY is that you exchange your time for the up-front cost of a maintenance-free proprietary system. You acknowledge that the system is still experimental, and you join and contribute to the community working on optimising it.

Lots of novel ideas abound, but in my view to really take advantage of the nutrient rich water discharged form the primary vermidigester, a secondary vermifilter should be installed so that surface irrigation can be used. This means you can take the water directly to the plants you want to feed using drippers, with suspended solids removed, a low BOD and low pathogen levels.

That's exactly what Anna Edey's system (and hence mine also) features. However, in my experience, the water exiting the primary system is not particularly nutrient rich. Certainly not in its early years of operation. It may change once the entire tank contains humus but after 7 years, I'm not there yet. I deliberately planted a lemon tree as an indicator species as they are demanding feeders. The lemon does not thrive on the water leaving the tank. There's not enough nutrient in it. I have to supplement with compost additions.

The advantage with the 1 cubic metre vault is that the volume accommodates seasonal variations in decomposition efficiency (e.g. winter). However, required vault size is directly related to

1. number of users, and
2. required length of time before the contents need emptying.

A larger vault is required for more users, or if you don't want to empty it for a long time.

The cold hard fact is that there WILL be an accumulation of carbonaeceous material, called humus. Anyone who has composted anything knows that the bulk reduces significantly but does not disappear. To explain, lets use the concept of half-life. A unit of carbon reduces by half over a unit of time. Over another unit of time it reduces by half again. Then over another unit of time it reduces by half again. It never disappears. Then, because each day you are adding more carbon, that carbon does the same. It is fantasy so imagine that the carbon all ends up oxidising to CO2, even under fully aerobic conditions. Even if you diligently turned a pile of turds regularly for rapid decomposition, whatever oxidising organisms you use, whether worms or micro-organisms, you end up with humus. Humus is stable carbon and does not decompose further in human time frames, it is the stable soil fraction that originates from plant carbon, as a result of photosynthesis. There are other factors that influence the time it takes for humus to build up... e.g. Washers or wipers? Worms digest toilet paper much more slowly than poo and more humus is produced per person. Also, suspended solids may be high in wastewater exiting the primary vermidigester. Claiming that the solids never build up only suggests to me that your soakage fields will have a limited life due to siltation.

Of course, vermifiltration does a remarkable job of decomposing the solids if the system is set up correctly. Compare this with pits, an extraordinarily primitive method for disposing of fecal matter, where solids usually do not reduce until removed from the pit. Quite ridiculous, yet still practiced in the 21st century! Primary vermifilters (e.g. vermifilter toilets) are also a big improvement on septic tanks (humus instead of sludge) and should be promoted more widely. What people often don't realise is that, like septic tanks, you can also put greywater and blackwater though them, provided the soakage fields are appropriate.

Next, the key to setting up the system correctly is that you need a flush toilet feeding into it. It might even be micro-flush, but this is essential to dilute the urine. A  250 gallon IBC tank "composting toilet" at events would likely not be a flush system, because for flush you also need soakage fields, which tend to only be set up for a permanent system.

Wendy's system clearly works but is it optimised? The idea with the one cubic meter IBC tank is great for temporary setups where cost must be low... but those cheap tanks tend to become brittle after a while. Why it works is not because of the 1m³ capacity, but the 1m² surface area. In times where biological activity is low (e.g. winter), solids will build up on the surface. The digester must have sufficient surface area for those contents to spread out unimpeded... a 1 m² surface area is sufficient for most households. Where I have some reservations in terms of overall efficiency is that ventilation of the substrate is limited in a tank with ventilation only at the top - and not at the bottom of the substrate where oxygen is needed the most. A well designed system allows for ventilation around and underneath the substrate, which I have shown how to achieve in other posts. However, I accept that a deep substrate and lots of coarse material may provide sufficient ventilation through the top layer of media for a domestic system. But I will say that a GOOD system requires NO monitoring, care or maintenance beyond removing the humus every x years.

I will also be clear that a well designed system must provide twin digesters, because eventually a single digester will fill up, which might take five years, ten years or even twenty years depending on capacity and average number of users. The fresh stuff will be on top and nobody likes cleaning that out from a hatch. In contrast, removing humus from the rested side is a pleasure. There must also be a means for the worms to migrate from one digester to the other.

Next, the "greenfield" or "leachate distribution system" is essential for a vermifilter toilet because it flushes... and therefore generates a quantity of primary-treated wastewater. This is not different from wastewater effluent from a septic tank. The simple rule of thumb is to design and construct soakage fields so that the water is dispersed (rather than concentrated) so it does not enter water tables. Lots of novel ideas abound, but in my view to really take advantage of the nutrient rich water discharged form the primary vermidigester, a secondary vermifilter should be installed so that surface irrigation can be used. This means you can take the water directly to the plants you want to feed using drippers, with suspended solids removed, a low BOD and low pathogen levels.

Wendy, I wrote a book about composting toilets.
That's my point: They are hard to empty. And some folks are saying that's not an issue. Then I find out it is an issue.
Those cubes are also used by people creating composting toilets. Two years later, you find they have abandoned that design because they are hard to empty without cutting them up and risking leakage after that.


Many (not all!) septic tanks go years before they are pumped out.
So much depends on the temperature, volume, throughput, design (the 2-chamber and 3-chamber designs work better), and leachate system.
Septage is sludgey but with enough moisture, a pump truck can remove it.