In noticing a few websites and blogs who have linked back to 'Bag it (Part 1)' (including Plastic Free July), it has provided the motivation to write the overdue companion piece discussing compostable bags.
Perhaps a bit of context first: At community events such as the recent Dog Lovers Show, a few environmentally conscientious dog owners told us that they compost their dog waste in their backyard. Duncan says that Poo Power! is a solution, not the solution to sustainable dog waste management and we all have the power to make our own decision based on the information that we are presented.
Composting is an aerobic process, that is, it occurs in the presence of oxygen through the use of microorganisms, mainly a wide range of bacteria and fungi, which break down organic matter - in this case, dog poo. However composting dog waste can be tricky as like anaerobic digestion to generate biogas, there are a number of variables that can dictate its success (or failure), specifically temperature and retention time.
As dog waste is pathogenic, it is widely agreed following a review of scientific testing that backyard composting is not a safe option for disposal and/or treatment of dog waste due to poor management of the composting process. Backyard composters rarely maintain "hot piles" that reach temperatures high enough (approximately 65-70 C) and for a long enough duration to kill the pathogens. For example, in one trial from Oregon (USA), backyard compost containing dog waste that was composted for a year and matured for another year and a half, resulted in decreased, but positive, levels of fecal coliform, Salmonella, and viable Helminth Ova. On the flip side, the Ithaca project in New York shows what happens when it's done right but you need a lot of poo and someone who knows what they are doing. Watch the YouTube clip above to discover more about Ithaca, but if you'd like to give it a go, we recommend this resource but do not to use the finished compost on plants grown for human consumption: Composting Dog Waste (USDA)
But back on topic, when it comes to picking up your dog's poo out at the dog park, should you use a "compostable" bag instead of a "biodegradable" one? Remember that all compostable bags are biodegradable, but not all biodegradable bags are compostable. (Feel free to read that last sentence again.)
Compostable bags are made from polymer resin, mainly consisting of cornstarch, and they are engineered to provide similar characteristics to that of regular plastics bag made from non-renewable resources (i.e. petroleum). It's important to note that most compostable bags are made with 'third grade' corn, which is not suitable for human or animal consumption. Because bioplastics are made with organic plant materials, they break down between 45-90 days in a compost environment which includes moisture, microbes and soil.
After understanding the difference between compostability and biodegradability, there are standards by which plastics and bioplastics need to be measured against. The European Standard (EN 13432-2006) is the most widely recognised of all the standards, with the American Standard (ASTM D6400) and Australian Standards (AS 4736-2006) based on it. The Australian Standard adds on the additional requirement of a set of eco-toxicity tests (worm test and plant growth test), which are not included in the European or American Standards. In order to comply with the AS 4736‐2006, they need to meet the following requirements which are verified by a third-party:
This ensures that when a compostable material breaks down within a composting environment (for example), it does not negatively affect the worms that consume it or the health of plants that are subsequently grown in it.
Next, look carefully at the labelling on your bags. Fortunately the Australian Bioplastics Association (ABA) has launched the seedling logo to identity clearly certified compostable plastics. Also the ABA co-operates with European Bioplastics, and BPI (USA) to meet their certification requirements too.
Both compostable and biodegradable dog waste bags have their positive and negative points, but it's up to you how they will be used to determine which type is the best choice for you, your dog and the environment. Remembering to pick up your dog's poo is an excellent place to start.
Poo Power! is a community solution to the growing problem of dog waste in Australia.
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