Waste to diesel

One of the worst things I have ever smelled in my life was a rotting pumpkin. We'd spent the summer travelling around Aotearoa in my van and it had accompanied us the entire journey. Coming back through Taupo someone picked it up by the stalk intending to use it in a soup, but the little handle pulled off with a wet slurp to reveal the decomposing putrescence inside. The only good thing about that day was that no-one managed to spill the contents of the curcubita all over the upholstery.

I was taken back to that unpleasant event last week at the presentation of a new report into household organic waste. It's been known for some time that one of New Zealand's big waste / resource recovery issues is the kitchen waste going into landfills. This and other organic waste is the main source of methane emissions going into the atmosphere from landfills (3 percent of NZ's greenhouse gas emissions) and a major source of toxic sludge out the bottom.

The stupid thing about it is that, like most of the stuff going into landfills, kitchen and green waste is a valuable resource if properly processed. By simply composting food and garden scraps, for example, it is transformed by an amazing natural alchemy into rich, fertile soil. Applied to agricultural and horticultural land it adds nutrients, builds topsoil, increases earthworm counts and healthy microbial activity, increases the water holding capacity of soils and boosts yields. Since New Zealand loses a significant amount of topsoil each year it seems amazing that we don't already do it.

Unfortunately New Zealand's waste stream is mostly locked up by multinational corporations who make money by trucking rubbish to landfills and burying it. Foreseeing the rise in environmental awareness, and an increase in reuse and recycling, they have been preparing for the future by locking councils into long term contracts that guarantee waste volumes for their tips. They often use their monopolistic position to bully smaller councils into signing contracts that more or less prevent the introduction of comprehensive recycling services.

Luckily there are a number of New Zealand operators who take a more responsible approach. Many people are already aware of the stunningly successful efforts of the various enterprises making up the Community Recycling Network and the huge environmental, social and economic benefits they bring to their local communities. They and other New Zealand businesses are demonstrating that taking environmental and social responsibilities seriously makes for better business practises.

So I was eager to go along to the report launch and hear what other options there are when it comes to kitchen waste. The report was written by Eunomia Research for Greenfingers Garden Bags / Earthcare Environmental Ltd and Envirofert Ltd and develops a cost / benefit analysis for household organic waste. It looks at what best practise councils do around New Zealand, what different authorities do overseas and models a variety of options for New Zealand to see where the greatest benefits are likely to be found.

In the end what seems to give the best outcome is a weekly kitchen waste collection and a fortnightly other rubbish collection. Food scraps makes up the bulk of most people's residual rubbish (after recycling) and if that is collected separately then the residual rubbish is halved. Smell is probably the biggest problem with a fortnightly pick up, but if the food scraps are gone this shouldn't be a problem. The presenters demonstrated a neat sample kitchen caddy for the bench, with a locking lid to keep out pests and with watertight, breathable compostable bags for a liner.

The costs to implement such a scheme are minimal, given the other savings to be gained from reducing frequency of residual rubbish collection and savings in landfill charges. The research suggests that a substantial consumer surplus can be gained from composting the waste in this way instead of landfilling it. When organic waste is composted it is broken done by aerobic (air loving) bacteria. This means it either has to be turned regularly or to have air forced into it. The main by-products are carbon dioxide, heat and plant food.

Even better than composting, according to the report, is putting the waste into am anaerobic methane digester. Anaerobic digestion is when anaerobic (air hating) bacteria break the waste down. The byproducts of that are methane (a powerful greenhouse gas), heat and plant food. This is what happens in a landfill, and even with methane capture most of the methane goes into the atmosphere. In a digester all the methane is captured and can be used as a natural gas for burning, or can be turned into diesel to run vehicles. This is being successfully done overseas.

So we can turn the country's kitchen waste into diesel and run all the rubbish trucks on it, instead of letting it rot in the landfill and pollute the ground and the atmosphere? That's worth getting on to your council about!