It goes without saying that the bag chosen should be compostable to standard. Bags that meet AS4736 or the European Standard EN13432 on which AS4736 was based will compost in industrial composting conditions. This is not just theoretical as countless millions of compliant bags have been composted in facilities all round the world from N America, through Europe and Australia. Where there have been reports of difficulties this is a reflection of the method employed.
Where there are differences is in strength and breathability. Quite a number of bags use older technology, which means that they are compostable but are more susceptible to tearing and failure. More modern materials are very strong even down to a low gauge. Quite a number of materials are based on genetically modified corn. Wholly petroleum based materials will have a very low WVTR (water vapor transmission rate). The higher the WVTR, the more breathable the material and the less smell. Also thinner materials will generally have a higher WVTR.
It is worth noting that compostable shopping bags will have a lower WVTR than bags designed specifically for composting. This is because they will be thicker and probably made of a tougher grade of material designed to be stronger. This strength is usually achieved at the expense of breathability. The outcome is that while compostable shopping bags will breakdown in industrial composting they will take longer than composting bags and there will be more smell even if used in ventilated bins because the breathability will be significantly lower.
Education
It is a vitally important element in establishing an effective system. There are some excellent examples from South Australia and City to Soil.
BioBag helps out in Brisbane
BioBag shipped compostable bags to Brisbane at the request of volunteers ho wanted to minimize adverse impacts from using plastic bags in the clean up.
