I am currently designing a water filtration system for my allotment garden group. My location is Leiden, the Netherlands. 1.8 meters under sea level. USDA zone 8, a rather wet temperate climate.
The problem we face is that the garden estate I have a garden at, used rather toxic soil to heighten its groundlevel. It was mainly the composted muck that was scooped out of the canals of Leiden back when it the industrial revolution was booming. This muck was dumped near what is now the allotment gardens and what the heck, lets use it to establish a place to grow veggies!
Imagine that our soils are polluted to such a degree you'd need a permit to move them, only one grading away from toxic waste on the dutch scale... Think high levels of cadmium, lead, copper, zinc and a few of the polyetheen, PCBs, and suchlike modern chemicals as well. ICK!
And thats where the problem turns into a sollution. I was listening to the mp3 series from www.permacultureplants.net and Bill Mollison describes a rather beautiful way to filter out pollutants in water. Especially his way of decreasing the PH of the water by letting it flow through a pit of shell-grit captured my fancy, as the water looses its capabilities to carry the heavy metals.
I have suggested a similar system for our gardens and the commission has approved and is willing to provide funds, materials and people-power for it to be build. We will include other elements as well, a composting toilet, water playgroundish thingy and outdoor meeting space to add a little community and auto-didactic learning to the design.
My main design right now comes down to two IBCs (those big, white, 1000L beverage containers) that will be placed off the ground by a meter or so. These will contain two compartments underneath where the biomass of the rest of the system will compost to provide heat in the winter (to prevent the chambers from freezing). Two channels with the appropriate plants inside follow (scirpus and junkus). After that the water will flow through some flowforms for added oxygen and around a living willow dome that will be used as an outdoor meeting space and come into a shallow pond. Hopefully we will see some of the wildlife come back there (the water is quite dead right now). I will make sure to introduce sweet water mussels into this pond and perhaps water hyacinth as well, even though it will die off in winter.
We are hoping to use wind power to provide for the pumping of the water, either a wind driven pump, or by using an electrical generator and storing the energy in a battery. My problem is that I've been asked what kind of pump we will need and how many liters per minute it should be able to pump. This is where I draw a blank. I could start to make things up but want the system to work properly and definitively cannot end up with the same stagnant, water-weeded, oxygen deprived mush we have right now. It needs to bloody work! I have been trying to find similar studies in the scientific literature but I really cant seem to find anything like this (hey, isn't that a common problem in Permaculture related stuff... ).
Is there anyone around here that has a decent idea of this kind of system? I have enoughexperience in the department of designing and implementation but lack the knowledge on this specific section. I also remember Bill talking about the place that he designed it for, the place was called 'Panella' as far as I can make out from the audio but cant seem to find much about it. He does talk about the inlet being three-quarter-inch pipe, which comes down to about 19cm?
I do not have experience in this, but we were discussing bioremediation over at this thread in permies.com. Some additional things related to your issue include phytoremediation and mycoremediation. I think poplar trees would be a good addition with the willows in cleaning up the soil and water.