In a previous article on reducing our household waste, I described how I implemented a worm farm to reduce our food organics waste. I got a kitchen caddy from my local council to put kitchen scraps into, before moving them to the worm farm. In order to help to keep the kitchen caddy clean and free from smells and stains, I lined it with compostable bags, which could then be placed in the worm farm after a few reuses.

Despite providing a multitude of benefits like,

some local councils do not allow these compostable bag to go in the green bin as part of that council’s food organics collection.

Council Food Organics Collection

Glen Eira Council (my local council) implemented its food organics and garden organics (FOGO) collection in May 2018. While this is a great step forward by the council in reducing the amount of waste going to landfill, there are a few shortcomings which make this option less attractive:

Contrasting this with Byron Shire Council’s food organics collection service, where I was on holiday at the start of the year - they have a weekly green bin collection (and fortnightly red and yellow bin collections) and they do allow council-approved compostable bags in the green bin. This makes it much easier for households to recycle their food organics because:

This got me thinking - just how compostable are the various biodegradable bags on the market?

The Experiment

I decided to take 5 biodegradable/compostable bags from different manufacturers and test them under the same conditions, first subjecting them to use - lining my kitchen caddy and filling them with food scraps - followed by putting them in my worm farm and assessing how quickly they degrade. I was keen to find out:

In order not to confuse the experiment (or myself!), a maximum of 2 bags were added to the worm farm at a time, one at each end. Food organics were then added as per normal use of the worm farm, but no further bags were added.


Bag 1 - epi Degradable Plastic Bag

The epi degradable plastic bag The epi degradable plastic bag

Rather than making plastic products themselves, epi-global manufactures chemical additives called Totally Degradable Plastic Additives (TDPA™), which plastic manufacturers can add to their products to help them bio-degrade. The degradation process should take 24-36 months, according to their website.

The chemicals help the plastic undergo an oxidation process, triggered by heat, UV light and stress.

According to the Australasian Bioplastics Association, these oxo-degradable plastics do not really break down but instead fragment into many tiny pieces, which remain in the environment. Because of this, it is unlikely that this type of bag would ever be suitable for use in a council food organics collection.


Bag 2 - Compost-A-Pak

The Compost-A-Pak bag The Compost-A-Pak bag

Compost-A-Pak are Australian-made bags which are manufactured from corn and are certified as compostable for home and council use.

The bags conform to the Australian Home Composting Standard (AS 5810-ABAP 20001) 1 and claim to degrade by 99% in only 45 days in a commercial composting facility, exceeding the requirements of AS 4736.

Compost-A-Pak utilise GMO-free corn, classed as third-grade - corn that would otherwise be thrown out - adding to the company’s green credentials.


Bag 3 - Ecovend Kitchen Organics

Ecovend Kitchen Organics bag Ecovend Kitchen Organics bag

The Ecovend bags are specifically designed for kitchen food organics caddies. The company works with local councils which are implementing FOGO (Food Organics and Garden Organics) collection programs to supply their compostable bags from vending machines in the council area. Ecovend bags are industrial composting certified.


Bag 4 - maze

Maze bag Maze bag

Maze make a number of products for composting, including compost bins, water tanks and biodegradable bags.

Like Compost-A-Pak and Ecovend, Maze bags are also AS 4736-ABAP 10059 (industrial composting) certified as well as being suitable for home composting. They are manufactured from a starch-based polymer and made in Australia.


Bag 5 - Multix Greener

The Multix Greener bag The Multix Greener bag

Multix Greener bags are probably the most widely available compostable bags, being carried by most major supermarket chains in Australia.

The bags are certified for industrial composting (AS 4736-ABAP 10060) and home composting (AS 5810-ABAP 20006) and are made of corn starch and will biodegrade in 180 days.

The Results

First up were the epi degradable plastic bag and the Compost-A-Pak bag. Both bags went in to the worm farm at the start of winter, once the initial problems I had with the worm farm were resolved.

I checked in progress every month and by the third month, only small traces of the Compost-A-Pak bag remained. The epi bag, on the other hand was not eaten by the worms at all, nor did it appear to degrade naturally. Even after 9 months the bag was still in a complete, albeit dirty, state in the worm farm. I ended up just taking it out as it was clear the worms had no interest in it and it wasn’t decomposing naturally at any perceptible rate.

Next came the Maze and Ecovend bags, which went into the second stackable bin. The Maze bag bag larger and was made of considerably thicker material than the Ecovend one, given the latter is intended as a kitchen caddy liner and this had a definite impact on how quickly each bag broke down. After 3 months the Ecovend bag had been almost completely broken down, with only a few small pieces remaining, whereas the Maze bag took a further 3 months to reach that same state.

Finally, the Multix Greener bag went in by itself. The bag had started to degrade in the caddy (I’m guessing, because of moist food organics places in the caddy) before even getting to the worm farm. That said, the bag was reused a few times before it went in the worm farm. Once in the worm farm, it continued to degrade at about the same rate as the Ecovend bag, so only some small traces were left after 3 months.

Conclusion

Bar the epi bag, all the compostable bags degraded in my worm farm, showing that they can be used in a home worm farm. Certainly they would also break down in an industrial composting facility where local council FOGO waste is sent.

The difficulty of allowing compostable bags for FOGO waste, without the council actually supplying those bags to households, is that some households may abuse the system by putting bags similar to the epi one (or worse) into the green bin, resulting in contamination and potentially damaging the ecosystem of the industrial composting facility.

I will continue to use compostable bags to line my kitchen caddy as a way to minimise dirt and smells in the caddy.

  1. Yes, there is a standard on biodegradable plastics suitable for home composting (AS 5810), and also one for industrial composting (AS 4736)! [return]