Home Biogas system- part four- the mulch pit

Since the toilet is up and running, we need to get the mulch pit finished. At the moment it is hard to concentrate on any project. The constant threat of fire and the despair that comes with knowing that so much of our ecosystem is destroyed keeps us in a constant state of depression. It is hard to concentrate on anything except watching the media releases about the fires all over Australia. However, it is important to keep working towards the future we want; how else will we reach it? In between the fire threats and increadibly hot days we made a plan that involved digging a pit to drain the effluent into then covering the lot with gravel, wood chip, soil and mulch.

The biogas system continues to impress me, the only down side I have discovered is the flammable nature of methane (which is kind of the point) and the fact that we can’t move the unit away from the house in the event of a bushfire threat (we are at a count of three direct threat situations so far in the last twelve months). We have countered this by releasing the methane into the atmosphere when there is any risk of fire. There is a handy tap that allows the gas to be vented easily. The refill time is getting less every day; currently the tank will fill in about ten hours and the effluent has proven fairly easy to bucket into the old toilet pit on a weekly basis.

Since the effluent is from human poop, it needs to be handled carefully. The effluent is passed through a chlorine chamber before it emerges from the unit. Treatment with chlorine is the accepted way to treat human effluent, it kills off a lot of nasties and oxygenation and exposure to sun takes care of the rest. After it emerges from the unit our effluent goes into a bucket, which is then emptied into the old toilet pit (which helps the waste in this pit continue to decompose). It is time to put in a hands free option for handling the effluent. In our situation we have several options; we could feed it into our septic system (except we don’t have one), we could build a dedicated transpiration pit or we could build a mulch basin. We went with a combination of the transpiration pit and the mulch pit ideas.

First we (and by ‘we’ I mean my hard working partner) dug a pit that was about 40cm deep.

I took this photo after we had begun to fill the bottom with gravel.

Then we put in a layer of gravel in the bottom. This layer is about 5cm deep. The plumbing part of the project was then completed before the pit could be filled up all the way.

Next step was adding a straw layer to slow down the migration of soil into the gravel.

After that there is a layer of wood chips (to soak up any nitrogen rich moisture that makes it that far) and a layer of soil to seal the pit off from the surface.

After that I planted the passionfruit vine I bought to (hopefully) take advantage of all that moisture and nutrient. I mulched around the vine, then realised that it is now a fire risk and would be raked away when the next fire threatens. To counter this a little, I buried the mulch under a deep layer of soil again. I hope this will protect the mulch from ember attack in the event of a fire.

So now we have a new garden bed that doubles as a transpiration pit. Hopefully the roots of the passionfruit won’t bung up the draining system and hopefully the buried mulch will be safe from ember attack (I am thinking that this method might be good for the new vegetable beds when we get to that). We, like most of Australia, are still in shock from the magnitude of the fires this year. We fear that next year will be more of the same, so everything we do from now on needs to be focused on fire safety and how to keep our family safe.

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