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  • Jo Wills

Are compostable bags as good as we think?

I've been doing a bit of research for Straws Suck lately about single use plastic bags...this is a local movement to help raise the awareness of single use plastics and the alternatives. Check out the Facebook page and make a pledge to reduce! There’s a lot of talk at the moment about banning plastic bags, this is a good thing right? Our nation drawing a line in the sand and stopping this nonsense of a single use plastic bag for everything from a loaf of bread (conveniently already in its own plastic bag) to a weekly shop.

However the question we’re now asking is, what are we swapping to? And, are the alternatives currently being touted actually any better for our environment than the plastic bag. We’ve spoken to three experts in the waste minimisation sector for their views and kept our focus to Tauranga. This is because it’s important we make informed decisions based on the facilities available to us.

'What do you recommend as the environmentally best form of shopping bag given the myriad of options now being made available by the major players (supermarkets and chain stores) and why?'

Let’s start with Kim Renshaw, Founder of Beyond the Bin.

In terms of what I recommend as the best form of shopping bag…nothing! Get a resuable bag and keep using it. Jute is a good option or cotton if you’ll keep it. I prefer cotton as you can wash it and mend it when it needs replacing. I also think it’s worth getting cotton bags for storing veggies that you can also wash.”

Next up, Lisa Eve, a Waste Management Consultant. “The waste hierarchy should always be applied. So refusing the bag is the best. The preferable alternative is a reusable bag made from natural material that you can reuse. To be a better environmental choice than the thin plastic bags, studies show that a paper bag would need to be reused 4 times, a ‘reusable’ plastic bag 5 times, a reusable bag (the plastic-lined ones sold in most supermarkets) 14 times, and a cotton bag – a whopping 173 times.”

The number of times refers to the comparable whole of life environmental impact of the alternatives – to a plastic bag. While one hundred and seventy three times sounds like a lot, that’s only just over one weekly shop for three years, and cotton lasts that long, so as a longer term decision, it checks out.

The third person we asked is Rebecca Maiden, Manager Resource Recovery & Waste, Tauranga City Council.

“Tauranga City Council encourage the community to opt for reusable bags made from quality, environmentally friendly materials such as cotton or hemp. Bags made from these materials last longer and can be reused over and over again,avoiding the need for single use bags.

Tauranga City Council does not support the use of compostable bags as an alternative to plastic bags. This is mainly due to the inconsistency of how ‘compostable’ products breakdown and also the lack of collection service and drop off facilities located in or near Tauranga.

If LoveNZ introduce their Soft Plastic Recycling Scheme in Tauranga, Tauranga City Council would recommend plastic bags over compostable bags, as the Soft Plastic Recycling Scheme would provide a drop off point to enable plastic bags to be recycled. There is no such option for compostable bags."

A strong common theme emerged from these responses. The use of a reusable natural fibre bag that gets used over and over is preferable to using a compostable bag.

For Tauranga right now, there are no collection services for compostable bags, nor are there any facilities for processing them (close by). This would leave our backyard composts to deal with them and these home systems are not adequate to process the material efficiently. And really, we have to ask the question, does it make sense to perpetuate the behaviour of a single use, disposable product over something that can be used multiple times?

It’s important we understand this problem as part of a bigger system and the role we can play within that. Which leads me to the next issue raised by reducing plastic bag use. Bin liners.

A plastic supermarket bag reused as a bin liner is as kiwi as gumboots. So what happens when we lose our supply by switching to a natural reusable bag? We naturally want to use a bin liner because our rubbish can be wet and smelly due to all of our food scraps. Lisa Eve shared more insight on that issue. “Biodegradable waste, of any kind, should be kept out of landfill if at all possible. Nearly 5% of our greenhouse gas emissions are from waste, and the vast majority of this is methane that comes out of landfills, due to biodegradable waste breaking down anaerobically.” says Lisa.

Food scraps in our bins, that we then send to landfill is not a good environmental option. Composting it at home is better, and the more we do this, the more we will reduce the need for a bin liner.

However if we still have a need for a liner, Lisa suggests using one of the soft plastics bags we get as part of our weekly shop such as a bread bag, although no liner is the ideal option. Either option requires a behaviour change. Thinking twice about the amount we throw out because our bin capacity may have shrunk somewhat (if using a bread bag), or rinsing the bin out a few more times (if using no bag).

The sustainable choice is not necessarily always the easy one, it can take some thought and almost always a bit of behaviour change. It’s easy to get sucked in by the latest big marketing push or product on the shelf, in this instance, compostable bags are definitely making their presence known. But, they are not the answer for Tauranga, at least for now.

The conclusion is the waste minimisation hierarchy remains the same. The first response, wherever possible is to refuse. If you can’t refuse, reduce. Then comes reuse (reuse, reuse!), and only after all other options have been exhausted, recycle.


There is currently work being undertaken to come up with labelling, definitions and standards for New Zealand for terms such as compostable, biodegrable and degradable.

Straws Suck will share these as soon as they are available, in the meantime, we thought Foodstuffs did a pretty good attempt with their layman descriptions from this article.

Degradable – basically, a standard plastic with a chemical added that disintegrates the bag into tiny pieces of plastic.

VERDICT: Environmentally damaging as tiny pieces of plastic will remain in the environment for a very long time and will be impossible to clean up.

Biodegradable – unregulated and not guaranteed to break down or do so without any residue.

VERDICT: Potentially environmentally damaging.

Compostable – there are two standards here, home compostable and commercially compostable. The majority of rigid bio plastics are only compostable in a municipal composting environment where they require moisture and temperatures of 70 degrees centigrade minimum to breakdown.

VERDICT: If all bio plastics were guaranteed to be correctly disposed of to appropriate composting environments, this would be arguably better than standard single use plastics. However, they are not, and there are major flaws in the end of life disposal of these items meaning only a tiny percentage would ever be composted. The reality is the majority will go to landfill where they are unlikely to breakdown.

At present:

  1. They are not accepted in commercial composting operation from kerbside collections for fear of the general public not distinguishing the compostable from standard plastic and causing contamination.

  2. Rigid plastics are usually not home compostable.

  3. In the standard plastics kerbside recycling system, compostable plastics are considered a contaminant.

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