An Eclectic View: Composting standards

BS EN 14995 and BS EN 13432 are the specifications in the UK/EU for compostability of plastics and packaging, respectively. Several test houses have published modifications to them to make them more accurate for a wider range of materials.

Composting is the controlled aerobic breakdown of material. Materials capable of disintegration are placed into a pile and an inoculum of thermophilic/mesophilic (heat-loving/room-temperature loving bacteria and fungi). With a constant feed of air (containing oxygen) into the pile the microorganisms begin to break the materials down. In their breakdown the pile generates heat, lots of heat. It is not unusual for a compost pile to reach 55-60°C with the heat generated. In industrial composting huge amounts of compost are manufactured and the heat is staggering - allowing easy sterilisation of the material that harbour pathogens. Industrial composting has efficient inclusion of air (and oxygen) and the piles of material are consistently turned with water being added. The industrial facility will also do rigorous testing and screening of the compost to ensure a high quality. Plastic fragments and sharps (glass and stones) are limited and removed to ensure the mix (often used by gardeners is consistent and safe for use.

Home composting, with generally smaller piles of material, seldom heat up and do not achieve the breakdowns and sterilisations that industrial facilities are able to achieve. Home composting temperatures are normally 20-30°C (with higher temperatures possible especially in Southern Africa). Home composts have less control when it comes to process quality but have the advantage of controlling the inputs closer than industrial (unless industrial has a very homogenous material source).

Figure 1

In an agreement between a supplier and a composting facility that will guarantee the processing of the supplier's material source - the first question will be about the nature of the materials going into the process. So, for example, let’s say a shoe factory in Pietermaritzburg is negotiating with a compost factory that they want to arrange a take-back scheme with SA customers and then they want the shoes deconstructed and composted. The shoe factory would be questioned about the materials in the shoe - are they compostable? A supplier may answer, “yes, of course”. Well, the composter could take the materials and try to compost them and find that the incoming shoes have spoiled (contaminated) the entire batch of compost - because the materials were not compostable.

To get around this the compost industry installed two tiers of compost certification that must be met to ensure that farmers and gardeners are protected from bad waste streams:

• Incoming materials for composting
• Outgoing composts

Materials for composting
To prevent that batch spoiling, mentioned above, the composting industry worked hard to pre-emptively work with manufacturers to identify materials that can safely enter the compost supply chain (pre-procurement systems). The creation of specific composting criteria that specified a material was safe for use in compost manufacture. Interestingly, organic natural materials are exempt from the biodegradability requirement, but not from the disintegration requirement. The reason for this is that some natural materials break down slowly. Compost facilities have a 3-month turn around and if a material entering the value chain takes 9-months to decompose then it will severely slow the composting process. Cotton and hair are notable examples of these types of materials.

Two notable compostability specifications were the first to appear on the market in the early 2000s. At the time the plastics industry was pushing oxo-degradable plastics - plastics that broke down under the influence of oxygen (which happen to degrade into plastic bits, like microplastics). These were quickly banned, and the plastics industry were looking for biodegradable plastics (and packaging) - but needed industry benchmarks to prevent supplier deception. The first to emerge was a specification called BS EN 13432 that guided the compostability of packaging (mostly plastics). This specification forms the core of scrutiny for labelling schemes like the “seedling” symbol managed by the BPI and EUBP (bioplastics regulators) scheme, see Figure 1. The second specification came out for plastics that were not packaging materials. A major source of discontent is that the compostable symbol is connected to the BS EN 13432 specification, even if it is not a packaging material. This will change as the regulations improve.

Figure 2. The “Seedling” eco-label managed by the BPI or EUBP organisations (see also the TUV OK Compost scheme)

• Characterisation
• Biodegradability (organic natural materials exempt)
• Disintegration
• Ecotoxicity
• Recognisability

Home composting also requires these requirements to be met, but the testing considered must be suitable for home biodegradation and disintegration systems. Characterisation looks for restricted substances that are entering the composting system with focus on metals and fluorine. A positive for fluorine will immediately trigger a potential perfluorinated substance warning and the chance of that material being rejected will be high.

Biodegradability tests whether the material can be broken down sufficiently into carbon dioxide, water, and biomass. Disintegration tests if the material can be broken down by more than 90% so that a compost pile can be reduced to produce more nutritious and dense soil improver. The ecotoxicity focusses on plant response to the presence of the compost - a phytotoxin will suppress plant growth. SATRA in their certification will go one step further by asking for a full soil ecotoxicity screen that test for known problem active substances. In the TUV OK Home compost certification they insist that earthworm toxicity is passed to meet the requirement of the Australian Standard (AS 5810) - home composting of plastics.

The fifth criterion is the recognisability of the final compost. This ensures that purple compost is not certified, especially if the compost is full of plastic fragments.

Outgoing compost
If materials pass those requirements, then the material is safe to enter the facility and will be composted. There is one more hoop to jump through before the compost product is marketable. It needs to pass a compost certification that guarantees it is a good compost. A popular scheme is the PAS 100 compost certification or the US STA Compost Certification Scheme. Here the compost is tested for weeds, levels of nutrients, ecotoxicity, pathogens, sharps, plastic fragments, and particle size. The consumers will ultimately decide whether these composts are good or not as their use will immediately result in purchase or the product will stay on the retail shelf.

In the next issue: Social management - what are brands and retailers looking for when they ask for responsible social sustainability. In addition to statutory and workers union obligations what do companies need to have in place to ensure they are conforming to global standards? Are there “must haves” and “nice to haves”?