Grey Water Clean-up - Mulch Filter
Revision of Current Experiment
In my other Hubs, concerning the use of Azolla filiculoides for the final "polishing" of grey water effluent, the process of initial filtration was described. (Further information about Azolla sp. may be obtained from the website of "The Azolla Foundation.")
This involves passing the raw grey water vertically downward, first through a layer of mulch, then through a deeper bed of gravel.
Within the mulch there is a diverse biological population of earth worms (predominantly Eisenia foetida), plus innumerable microscopic organisms. This population works its way through the mulch and any organic solids arriving within the raw grey water. It is able to deal with food waste, fats and grease (NOT those derived from fossil fuels), skin and hair particles, bacterial pathogens.
The gravel used below the mulch must be sufficiently aerobic. The particles must be large enough and irregular in shape, so that air pockets exist between the particles. If sand is used, this can exclude air to a large extent and water can ultimately not pass through easily. The result is anaerobic conditions, which we do not want. Blockages and offensive odours will result.
What happens in these two filter layers?
The organisms working away within the mulch are simply doing what they do in the natural environment. If the mulch is obtained from the local forest floor, or under a hedge, or from a hay field, the micro-organisms present in those natural habitats will be quite happy in the mulch filter. Thus this technology can be adapted for any locality in the world.
(I put this to anyone who is interested, please experiment in your area. If what I have said turns out not to be true, please write and tell us. Such information will be invaluable.)
The materials used as mulch will gradually be broken down by the diverse biota into humus. "Humus" is considered, as I understand it, to be basically the dead bodies of billions of bacteria, which in their lives took in nutrients broken down from the food waste, etc. which arrived with the grey water. Those dead bodies conglomerate into a Gel. This Gel is the Humus. It has the beautiful property of being a natural slow-release fertilizer.
(18 Nov 2013 - I have a new theory regarding this decomposition of the organic material. I suggest that some of the nutrients/elements become soluble in water and pass on to the Azolla pond, providing better nutrition for the Azolla. I have no way of establishing this, but welcome any feed back from the scientific community. )
Ultimately, (I have found over 9-12 months), the mulch is almost entirely broken down into humus, and does not allow fast-enough passage of water through. Passage is so slow that I get a back-up of grey water onto the surface of the mulch. Overflow can occur.
(One might be fearful of the worms being drowned by such a situation. However, I have found the worms multiplying enormously in that environment, provided the water does ultimately drain through.)
Therefore one needs to remove a quantity of the composted material to leave room for addition of new mulch. I have just done this after having the filter in operation for approximately one year. A small quantity of the old compost was left in the drum, complete with the attendant worms. The worms will rapidly colonize the new mulch.
This part of the filter is constructed so as to be aerobic, in other words, the water pulls air through the gravel as it falls. A tiny layer of water clings to each gravel particle and in this layer there forms another population of bacteria and microbes, which continue to remove pathogens from the water.
The mulch above is effectively an ecosystem. The gravel is another ecosystem. Each area of the complete filter performs a natural process, without any other assistance from us, other than providing the ideal conditions.
I have no expertise in microbiology, and remain open to others wishing to contribute here. It is my guess that potential pathogens will be destroyed within these two filter layers. Further research would be most valuable, to determine what depth of filtration, how slowly the water must traverse and the mortality rate of pathogens in such an environment.
Please check back to my other two Hubs regarding the use of Azolla. I have included a lab report, which shows E.coli are still present in the final effluent. Therefore the final effluent must be regarded as potentially unsafe (if the grey water is derived from the bathroom, laundry or shower) and should be either sanitized (with UV light or some other means) OR discharged into the topsoil, according to local recommendations. As a purely kitchen waste water disposal, i.e., simply as a grease trap, such sophistication would not be necessary, in my opinion.
What Materials Do You Have Available?
For the Mulch Filter
Which food crops are grown in your area?
Rice? Do you have a big stack of rice straw, close to your house, for feeding your goats? And around the rice stack, there is straw that gets trodden into the ground, it gets very dirty, the goats will not eat it? This has begun to partly decompose on the ground...... you could collect it up and use it as your Mulch Filter. Over time it will become good compost for your garden.
Bananas? Those dried, dead leaves on the ground below the banana plants could be broken up small, mixed with any other weeds or leaves you can find. It needs to be brown and dry when you first use it. Collect up enough to provide you with the Mulch Filter.
Pine trees? Collect up the pine needles from under the tree. This will make a good filter medium.
Sweet Corn (Maize) Sorghum or Millet? Find out which part of the plant is usually discarded as waste, and try using that as mulch.
In the desert? Maybe in Rajasthan? No Trees!!! No Leaves!! I suspect you already have an efficient way of dealing with your washing water, because it is very precious and you are very careful with it. If you still need a way to deal with dirty water, please look around you and find a solution.... I would most interested in hearing how you get on.
For the Gravel
The size of the particles is important. Too small and it will block up. Too big and the water will rush through too fast and not give the bacteria time to do their work. 7mm average size of particle is ideal.
It is desirable that as the raw grey water reaches the surface of the mulch filter, it is spread all over the surface instead of pooling in one spot.
Simplicity is the key
I imagine that in a family, or small community situation, where the women folk will simply pour their bowl of dirty water onto the top of the mulch filter, they can just spread the water over the filter by hand. No fancy technology is involved. They will soon get the hang of it.
You could obtain a domed plate of some kind, place it on the surface of the mulch so that water coming from the pipe splashes outwards and is quite simply distributed. Please see photograph.
Hoping for Feed Back
It would be much more informative to have some laboratory tests done on my filter system.
1. After the grey water has passed through the mulch, then down through the gravel, I would like to know the bacterial/viral load, the dissolved oxygen, suspended solids, nitrogen level, etc. at this point.
2. Presuming that a slime layer builds up on each particle of gravel, I would like to know if this is true. Does that slime layer really reduce pathogen levels?
3. The water then passes upwards through a 300mm layer of crushed glass. This is designed to be anaerobic for de-nitrification to take place. Does it? Is the water passing through this area slowly enough?
4. What are the dissolved nutrient levels in the final effluent? Is this water valuable for watering plants?
5. Is the final effluent safe? What about viral die-back? Are there any viruses that could get past the relatively short path through this system.
6. Research is also going on in other parts of the world, in the use of Azolla filiculoides. (Please see my other Hub, http://jonnycomelately.hubpages.com/hub/Azolla-filiculoides-in-Tasmania for details.) How effective is this plant in "cleaning up" the water?
If anyone reading through my Hub is able to give useful feedback, I would be most grateful.
© 2013 Alan