Abstract:
Grey water (all waste water not including sewage) can normally be disposed of along with sewage. However, this is quite wasteful, and unnecessary for most waste water. Folke Gunther, a sustainability advocate, developed a design for s structure called a Folkewall. A Folkewall has greywater added/pumped in at the top, where it flows through the structure in a zig-zag pattern through a porous material such as gravel, where organic material is removed by bacteria living in the porous section. This is should theoretically remove many of the disease-causing particles in the water, making it at the very least safe to use for more widespread irrigation, if not domestic consumption. My hope is to apply these concepts to my grey water disposal system to either increase its efficiency, or possibly even push my design to take in greywater and produce clean, drinkable water at the end. Even if that level of clean isn’t possible, the addition of a biofilter to the design would be beneficial in a multitude of other ways.
Background
For most households, greywater and sewage are disposed of the same way: down the drain, to the sewage plant. There, the water is treated and returned to the ecosystem, wherein it re-enters the water cycle. However, these treatment plants take large amounts of area, maintenance, and infrastructure in the form of piping to function. To combat this, Folke Günther of Sweden developed his design for home treatment of greywater combined with home gardening.
Gunther based his design on the irrigation walls of another Swede, Dr Gösta Nilsson. At his nursery in Botswana, Dr. Nilsson tested multiple different methods of dry climate farming, but the nursery itself used a system of stacked cinder blocks filled with sand, seen below.
These planters were fed with regular well water for irrigation. Gunther’s design, however, was developed with greywater in mind. His design (see below) consisted of two walls of overlapping bricks that converge at the top, with the dead space between filled with a porous material such as gravel, perlite or pebbles. As the structure gets wider, sheets of plastic are added between layers to force water to take the longest, ziggiest, and even zaggiest path possible. This ensures the water has the maximum amount of time in contact with the biofilm, allowing the bacteria to remove as much biological material from the water as possible. Finally, the water is collected in a tank at the bottom of the wall, where it can either be used domestically or re-added to the top of the wall.
Beyond the standard brick design, Gunther also designed two other versions: One built out of a poured concrete slab, and another built out of worn-out tires and shopping bags.
Analysis & Findings
I found Gunther’s work after doing some research on greywater to potable water treatment, and found a lot of info about using ‘biofilters’. Normally these are things like cattails, reeds and artificial wetlands, so the idea of using bacteria seemed kind of strange until I realized that this is the exact same thing that actually happens to water in the ground. In that case, the bacteria just live in the dirt instead of the gravel. This makes the idea of using biofilters much more accessible, since a biofilm is magnitudes easier to keep alive than a plant.
This does, however, bring up the question of bacteria in the water. There is bacteria on and in everything, yes, but if large amounts of even safe bacteria enter the body, it could possible make those with weak immune systems sick. A bacteria sample from the water ran through the system a few times would be interesting to look at, but I also think that most of those concerns could be solved with a UV source somewhere between the bottom of the wall and the access point.
The design using just concrete bricks, plastic sheets and gravel as it’s building materials is really interesting, because it makes the structure non-permanent by default. Gunther states that the design is supposed to be mortar-less, specifically so it can be torn down and moved. However, if move-ability is an important factor in the design, something such as treated wood might have been a better choice. On the other hand, the current materials and their densities do ensure that the structure will be stable as heck, which allows the lack of mortar in the first place.
Gunther describes the wall as having a few other features, including cooling. He describes building these walls on the sunny sides of houses to block the sun. In addition, I believe that the water running down the wall and evaporating from the plants leaves would also create a swamp-cooler type effect, thereby further cooling the home.
One of the more obvious things about this project is just how little is actually documented. While the different concepts themselves are well known, the lack of rigor in his write up, and no mention of contaminant levels makes me a bit nervous.
Gunther doesn’t mention the minimum or maximum water capacity of his design, which might be important. If there is too much water, it could drown the plants and grow mold inside. If there isn’t enough water, the biofilm might dry out and die, thereby starting you basically from scratch in terms of potency.
Relevance to my work
While my original idea was for a grey water evaporator, reading about biofilters has got me thinking about pivoting the idea into a grey water purifier. An evaporator is great for getting rid of excess waste water, but you still have to bring that water out in the first place. If you are able to re-use all the non-sewage water, then you can greatly decrease the total amount you need to bring in the first place.
It seems that the most important part of this design is to have the water in contact with the filter as long as possible, which means this wouldn’t be applicable if speed becomes a concern to me. But disregarding speed, adding a long path for the water could be as easy as a screw shape inside of a pipe, like an Archimedes screw. By adjusting the angle of the thread, I could adjust exactly how much time it takes water to pass through, and dial in a design that maximises water filtered in the shortest time. Even if I decide to stick with the evaporator design, having a length of pipe with a biofilter inside before the evaporator itself will remove most of the organic material that would normally build up in the basin of an evaporator.
One thing that was not explained was: does the biofilm come from the plants, or from natural bacteria from the gravel/air/water/etc? If it comes from the plants, can it survive without them? If it comes from the environment, then portability of the project doesn’t change much. If the plants ARE necessary, then I will have to find which plant species has the best bacteria for the job, while also being hardy enough to stand up to packing, moving, set up, tear down, and the ride back home.
I believe I could find a way to implement a biofilter into my design, so rather than just disposing of greywater, I can instead (1) get rid of a waste (2) create a resource and (3) scare people by drinking dishwater. My only concern is, like I mentioned in the Analysis section, that this isn’t going to get the water clean enough, no matter how long the water is in contact with the gravel.
Resources
https://www.holon.se/folke/projects/openliw/openlev_en.shtml
http://www.holon.se/folke/projects/Sanitas/index.shtml
http://www.hydroponicsequipment.co/vertical-gardening/