The inspiration for this system design came from Anna Edey, who first constructed a vermicomposting flush toilet in 1995 after decades of experimentation with compost toilets and biofilters.
Here, in her own words, is the story …
“Over the years I came to realize that very few people will adopt compostoilets any time soon, no matter how convenient, economical and clean they can be. This realization made me quite pessimistic about the potential for stopping the vast amounts of water pollution currently caused by standard septic systems. So I decided to design a method of combining flush toilets with composting. I am happy to report that I have discovered ways to keep the flush toilet AND to keep drinking water and aquatic ecosystems clean.
“In September 1995, with capable carpenter and plumber, the upstairs compostoilet in my home was removed, and a regular 1.6-gallon flush toilet was installed. The toilet drainpipe empties into an enclosed Compostfilter, a box, 3 feet tall and 4 feet wide, built of wood against the outside wall of the house. The top and the front of the box can open for servicing and inspection. It is lined with plastic to prevent rotting of the wood and the house shingles, and it is insulated with 2-inch rigid foamboard to prevent freezing.
“The Solviva flushtoilet composting system has been transforming human waste and toiletpaper into marvellous compost, healthy plants and clean effluent, since 1995.
“The box is watertight with a drain on the bottom and is divided into two connected compartments. Each compartment is half-filled with Biocarbon mix, consisting of the right type and proportions of partially composted leaves and wood chips. I also installed 3,000 earthworms which I ordered by mail from a worm farm in Georgia, for $19.
“I call this box the Brownfilter. The toilet waste pipe has an elbow at the end that empties into the box. This elbow can be flipped to empty into one or the other of the two compartments. The solids, including the toilet paper, are retained in the compost box, while the liquid quickly seeps through the Biocarbon mix, exits through the drain and into a sloped pipe that leads to a series of ground-level Greenfilters.
“I started flushing into the first compartment as soon as the installation was complete, September 20, 1995. Throughout the first cold winter, even through subzero conditions, the temperatures in the box stayed above 55 degrees F, without any heating source other than the low-temperature (mesophilic) composting process itself. My plan was to flip the toilet waste pipe over to the second compartment when the first one was filled. However, to my utter surprise, it never did fill up, because the process of decomposition has reduced the volume faster than it has increased by the additions of the daily flushings. Seven family members were at my home for a week over that first Christmas, all using this toilet because I wanted to provide a real stress test. The system continued composting and draining reliably.
“After my family left, I flipped the elbow of the toilet waste pipe to drain into the second compartment, in order to get an accurate reading of how long it would take for the solids to fully decompose. To my amazement, I found that within one week there was nothing recognizable left in the first compartment, nothing but rich black earthworm castings and healthy earthworms, which by this time had multiplied to hundreds of thousands of all sizes. When warmer weather returned I found that full decomposition was achieved in less than four days.
“The truly astonishing fact is that the more I put into the box, the less there is in the box. As I write this, in October 1997, 25 months have passed since the installation, with usage ranging from one to seven people. This box has by now received approximately 2,500 flushes, 140 rolls of toilet paper, and 35 cubic feet of leaves and woodchips (the original 12 cubic feet plus periodic additions). The action of the earthworms and other bioorganisms has reduced it all to about 9 cubic feet of magnificent earthworm castings. Even with all my previous experience I never would have expected this could be possible.
“When in its normal closed state, this compost chamber is absolutely odor-free. When you open it, it has a slight fragrance of a well-kept stable. It has never generated any flies, and no earthworms have ever ventured outside, probably because this box is clearly Earthworm Heaven.
“The liquid seeps quickly through this Brownfilter and runs via drain and sloped pipe to a series of Greenfilters. The first is a shallow growing bed filled with the same Biocarbon mix plus sandy topsoil and healthy plants, lined with a waterproof membrane, with a drainpipe that leads downhill to a second Greenfilter, same as the first. From there the liquid drains into a 20-gallon pump chamber equipped with a float switch-controlled sump pump that periodically pumps 15 gallons of effluent into a perforated pipe installed in the third Greenfilter. This is a flower bed, and the pipe is installed in a layer of wood chips 6 inches below the surface. From there the water perks through the subsoil, where any remaining pathogens are destroyed.
“Thus, all the wastes flushed down the toilet are transformed into excellent earthworm casting compost and irrigation water that benefit the landscaping. The nitrogen is absorbed by the Biocarbon filter materials and the plants and does not leach down to contaminate the groundwater.
“I have also conducted other experiments with different versions of my Biocarbon filter, one for treating effluent from a standard septic tank, the other for treating septage and sludge pumped from numerous different septic tanks, including restaurants, businesses and homes. In the case of the septic tank effluent, lab tests showed a 90 percent reduction of the total Kjeldahl nitrogen, from 86 ppm to 8.1 ppm, and a 96 percent reduction of the ammonia-nitrogen, from 77 ppm down to 2.5 ppm. In the case of the Biocarbon septage treatment filter, total nitrogen was reduced 88.2 percent, from 152.34 ppm down to 17.81, while BOD was reduced from 607 ppm to 59 ppm, and COD from 640 ppm to 85 ppm. In both cases the flow-through took less than 10 minutes, and the foul odor was totally removed.
“These results are nothing short of astonishing, to sanitation professionals and lay people alike. The Solviva Biocarbon filter systems demonstrate that we can manage our wastewater in ways that cause 90 percent less pollution than systems currently required by the state, and, in many cases, at far less cost.”
This is the original text I came across in 2013 when I was looking to trial a different compost toilet system to Joe Jenkins’ bucket-and-sawdust method I was already using successfully. It was sufficient for me to be able to figure out a system design which I reckoned would work. The site of the toilet within my off-grid property was such that the risk of potential pollution of waterways and neighbouring properties was non-existent and I decided to take the chance and experiment.
After studying papers on the performance of various vermifiltration/vermicomposting systems, I felt sure a 2-chamber bin was unnecessary and I simplified the design to work within a single 1m3 plastic IBC tank. Correspondence with Anna and with people who visited her nearly 20 years after she wrote her account above revealed that in all that time she has never had to empty her worm bin.
I also simplified the greenfilter element of Anna’s system. My system deals with black water only, so I reduced it to a single unlined biofilter bed and monitored it closely for a period of 2 years to assess the amount of nutrient both reaching the greenfilter and potentially escaping from it. The greenfilter bed is ideally situated for this purpose right at a terrace edge. Immediately downhill of it there’s a 4m-high dry stone wall. The lower third of its height is cut from steeply-sloping bedrock. Any water leaching down from the greenfilter bed would follow the slope of the bedrock to the foot of the bedrock section of wall where the surrounding vegetation would evidence both moisture and nutrient if it were present.
The foot of the terrace wall below the greenfilter bed has remained consistently dry throughout the summer months when the toilet gets heaviest use. There is no evidence in either summer or winter of the presence of any greater level of nutrient in the vegetation there. The soil remains poor and the vegetation reflects this.
I also planted a lemon tree in the greenfilter bed. Lemon trees are heavy feeders so it would act as an indicator of the amount of nitrogen and water entering the bed and being taken up by the tree.
I’ve had to water the lemon tree at times during the summer months and even add animal manure as the leaves were showing signs of chlorosis – a general and even yellowing of the foliage, starting with the older leaves, with little mottling or additional yellowing in between the leaf veins – indicating nitrogen deficiency. This would suggest the vermicomposting ecosystem is doing such a good job that the greenfilter itself is almost superfluous.
My experience of this system was so positive that when a problem developed locally with raw sewage discharging into the environment of a natural park from a village septic tank, I approached my local council (together with a Portuguese architect specialising in eco-construction techniques) with proposals for a vermicomposting solution. After investigating vermicomposting for themselves, they decided to commit to it. In addition, they’re now installing my version of Anna Edey’s system as a replacement option for household-scale septic tanks. It’s now possible to have a vermicomposting flush toilet system permitted and approved in this region (Arganil, Portugal).
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.