Ditch plastic dog poo bags, go compostable



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Don’t do these doggie-doo don’ts.
Shutterstock

M. Leigh Ackland, Deakin University

We humans have a habit of avoiding our waste. We find organic waste particularly unpleasant. We bag it and dispose of it as soon as possible.

Even the most environmentally conscious person would rather not handle something like decomposing food or dog poo with their bare hands. Plastic bags are often the first step we take to disconnect ourselves from our waste – until we can get rid of it somewhere else.

Traditional plastic bags are made from ethylene, derived from petroleum or natural gas. Ethylene does not degrade easily. So these types of bags are major contributors to plastic pollution.

More than three-quarters of plastic ends up in landfill, while up to 5% finds its way to the ocean. Only 9% of plastics are recycled.




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Many environmentally conscious pet owners are turning to biodegradable bags as the solution to their doggy-doo woes, but many brands won’t break down in landfill, compounding the problem. Alternatives are at hand, though, with compostable bags and community sharing programs that can help non-composters.

A ‘biodegradable’ statement on a bag isn’t enough: it needs a logo

“Biodegradable” means something that can potentially be broken down naturally in the environment, particularly by microorganisms but also by other factors such as heat, light and oxygen. We usually think of biodegradable materials as derived from natural sources such as plants, but synthetic materials can also be biodegradable.

But there are issues with the term “biodegradable bag”. Bags can be labelled biodegradable, but after being used and discarded they might only partly decompose because the conditions are not right for full decomposition. Or else the decomposition might take a long time.

Full decomposition means complete conversion of the bag into simple substances such as carbon dioxide and water that can be re-used by microorganisms like bacteria and fungi.

Food becomes poop, which becomes…?
Carol Von Canon/Flickr, CC BY-NC-SA

The biodegradability of plastic can be measured in a laboratory using methods such as carbon tracking. There are international standards for testing biodegradability of plastics. The International Organization for Standardization (ISO) has developed these standards.

Unfortunately, ocean and landfill environments are not conducive for degradation of biodegradable plastic. Marine environments often don’t contain the right types of microorganisms needed to break down plastics, or there aren’t enough to be effective in a reasonable time frame. Landfill conditions often lack oxygen, which limits the types of microorganisms that can exist there.

Compost, however, provides an ideal environment for biodegradation. Compost contains a diverse range of organic materials that support the growth of many different varieties of organisms.

DNA sequencing has revealed the huge diversity of microorganisms that exist in compost. These include bacteria, fungi and invertebrates that can digest a wide range of organic materials. In particular, fungi are found to possess enzymes that are capable of breaking down many different organic substances.

Compost to the rescue

You can now buy compostable bags. These are a type of biodegradable bag that is suitable for disposal in compost only (not in the ocean or landfill!).

How can you tell if a compostable bag can actually be fully broken down in compost? Standards Australia produces standards for the biodegradability of plastic bags. Code AS 4736-2006 specifies a biodegradable plastic that is suitable for overall composting (which includes industrial processes) and other microbial treatment, while AS 5810-2010 specifies home composting.

Standards Australia provide a brief overview of the testing carried out for AS 5810-2010. Other countries have similar standards – for example, the US has ASTM code D6400, which certifies that the material meets the degradation standard under controlled composting conditions.

The Australian Bioplastics Association administers a voluntary verification scheme. This enables manufacturers or importers to have their plastic materials tested and certified.

There is a double arrow logo you can watch out for on bags that have been certified as home compostable and there is a seedling logo for certified compostable. If you cannot locate a certified compostable bag in your area, you can source them online. Make sure they have have the certified compostable logo of the country from which they come.

It is interesting to observe the biodegradability of a plastic bag in your compost heap, as I did with a compostable bag full of dog poo. After two weeks buried in the compost, the only evidence of the bag was some small black fragments. These looked like leaf mould except they had the print from the bag label on them. In comparison, a normal plastic bag buried at the same time was completely unaltered. Of course, this experiment is not proof of total bag degradation – proper laboratory testing would be required for this.




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What if you can’t compost?

If you cannot compost, you will probably be relying on your local council to dispose of your waste. If the council uses landfill for waste disposal then there may be no point in using compostable bags for your waste, as landfill does not have the right conditions for composting to occur.

If you have a kerbside green waste collection that is composted, this service most likely will not accept food waste at the moment – which means dog poo is very unlikely to be included. Nor may compostable bags be allowed in green waste collections. Some councils, however, are working towards food organics/green organics waste collections for the future, and these may include compostable bags.

Moyne Shire in western Victoria, for instance, provides compostable bags for dog poo and accepts it along with green waste in its fortnightly “FOGO” collection.

If you have material for composting but do not have a compost heap, you can join Sharewaste. Sharewaste links people who want to recycle their organic waste with their neighbours who can use the waste for composting, worm farms or chickens. So this is a way to avoid sending your organic waste to landfill.

Composting your organic waste is like harvesting rain into your water tank or tapping into sunlight for your energy needs. These things are meaningful beyond their utility; they connect you to nature and give insights into the natural cycles of life on planet Earth.The Conversation

M. Leigh Ackland, Professor in Molecular Biosciences, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Here’s how many times you actually need to reuse your shopping bags



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Jeremy Piehler/Flickr, CC BY-NC

Trevor Thornton, Deakin University

The plastic bag ban by the major supermarkets (and Coles’ pivot away from its ban after backlash, then pivot back to the ban after a backlash to the backlash) has left plenty of people scratching their heads.




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What are the best replacements for single-use plastic bags? Given that reusable bags are much sturdier, how many times must we use them to compensate for their larger environmental impact?

The simple answer is that there is no simple answer. However, a kind of research called “life cycle assessment” can help us work out the impact of common types of reusable bags.

Life cycle assessments

I am not aware of any Australian studies of plastic-bag substitutes. Research conducted overseas can offer a basic guide.

Life cycle assessments consider a wide range of factors, including raw materials, manufacturing, transport, and eventual disposal.

Looking at all of these elements, researchers calculate greenhouse gas emissions, waste disposal, water and energy consumption and a variety of other impacts.

To complicate the decision further, if you choose a plastic bag, is it made from virgin resin or from recycled plastic? Even if the bag is recycled, transport is an issue – where was it made? Printing on the bag also adds to the environmental burden.

Finally, what happens to the bags when they can no longer meet their purpose? Are they recycled, reused as bin liners, or thrown away immediately?




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How many times must a bag be reused?

Once all of this information has been distilled, scientists can usually offer a fairly straightforward guide: the number of times a given bag should be reused when compared to the standard supermarket plastic bag.

A 2018 Danish study, looking at the number of times a bag should be reused before being used as a bin liner and then discarded, found that:

  • polypropylene bags (most of the green reusable bags found at supermarkets) should be used 37 times
  • paper bags should be used 43 times
  • cotton bags should be used 7,100 times.

Another UK study, which only considered the climate change impact, found that to have lower global warming potential than single-use plastic bags:

  • paper bags should be used three times
  • low-density polyethylene bags (the thicker plastic bags commonly used in supermarkets) should be used four times
  • non-woven polypropylene bags should be used 11 times
  • cotton bags should be used 131 times.

Note, however, that if a plastic bag is reused (even as a bin liner) the number of times an alternative needs to be used increases.

It’s worth noting that, according to the 2018 Danish study, using organic cotton has a greater environmental impact than non-organic due to higher production costs. Our assumptions about what is environmentally friendly don’t always stand up to scrutiny.

A 2014 study in the United States found that reusable LDPE and polypropylene bags do have a lower environmental impact than the usual plastic bags found in supermarkets – but only if they are reused enough times. This study found that about 40% of shoppers forgot to bring their reusable bags and therefore end up using the plastic bags. This then adds to the environmental burden of shopping.

One final consideration is how many bags you need. The Danish researchers equalised the volume of the bags so that evaluations were made on the same volume of space (this meant that for some assessments it was necessary to consider the impact of two bags).

As with all matters environmental, it’s essential that we have the right knowledge to make informed decisions. After looking at all this data, here are the things I’d like you to remember:

  1. whatever bag type you use, use it as many times as possible

  2. choose bags made from recyclable materials

  3. avoid bags that have printing or decorations – these alone can add significantly to the environmental burden of the bag

  4. never allow a bag to become litter – recycle, reuse and repurpose your bags.


The Conversation


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Trevor Thornton, Lecturer, School of Life and Environmental Sciences, Deakin University

This article was originally published on The Conversation. Read the original article.