Carbon sequestration and biogas

Thu, 02/28/2013 - 07:12 — Compost Stu

The rain has set in and the orchard gully is flowing merrily through unmown Kikuyu, which sieves and filters the road runoff until its clean and clear. The wet season is well and truly upon us, along with some of the compromises many of us choose to bring us closer to nature. My toilet paper is slightly damp, making things quite tricky toward the end……one must apply just the right amount of pressure!! I normally incinerate my used TP and add the ash to the loo below, but today all I can manage is a smoldering wad of paper. The wet season is definitely the price we pay for living in paradise the other 9 mths of the year.
I’ve just been listening to Auntie rave on about carbon farming and how farmers can get paid for sequestering carbon. It would seem to me that I’ve been sequestering my own carbon for years. In fact anyone that owns a composting toilet is doing just that. The concept that, as individuals, we are taking responsibility for our own by-products by composting them, is not only sustainable in the short term, but combats climate change in the long term. In fact we are making a contribution to reducing climate change every time we poo. People that have a septic system, on the other hand, are actively contributing to climate change. Septic tanks break down our carbon by-products anaerobically and produce methane, a potent climate change gas. The gas may leach out slowly though the soil so you don’t smell it, but it’s still there, and being much lighter than air, it will rise into the atmosphere. If you’re going to produce methane, you’d be much better off producing bio-gas. If you’ve ever lit a fart, you’ll know how flammable methane is. Millions of people in China and India use bio gas every day to generate heat and light. Biogas for cooking is produced using a reactor vessel into which the by-products of the whole family PLUS a dozen or so pigs, chooks, goats etc. It will not work unless it has a large enough volume of by-product to digest. The slurry breaks down anaerobically and produces methane. Often a crust forms on the surface impeding the release of gas. The bio-gas produced is often quite dirty, containing significant proportions of sulphur dioxide. This is highly corrosive, so the system needs to be entirely plastic or masonry. One way to remove the SO2 is to bubble the gas up through a scrubber, such as Sodium Hydroxide (NaOH). This will remove some of the impurities and result in a cooking gas that won’t stink the house out if you leave the tap on. Unfortunately this leaves you with a highly corrosive waste product good only for stripping paint. Whilst traveling in Vietnam, I saw quite a few bio-digesters. One I remember well used a large clear plastic sausage bag about three metres long to store the bio-gas in. It was tied off to pressurize it with bits of what might have been pigs intestine. It was suspended directly above a row of gas cookers in the kitchen, a brave place to put it in the event of a kitchen fire.
On a lighter note, I’d like to encourage readers to send in their favourite toilet graffiti (keep it a bit clean…), just for a laugh. We’ll print the best ones at the end of my article each month and draw a winner at the end of the year. The prize is $300 worth of consultancy by yours truly, to assist you with re-using all your by-products as wisely as possible. Who remembers this one:
“Here I sit all broken hearted, paid ten cents and only farted” ”. From a bygone era when we paid to use some public toilets.


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