Environmental Engineering Reference
In-Depth Information
• BS EN ISO 17556 specifies a method for determining biodegradability of
plastic materials in soil (see also ASTM D5988).
• BS ISO 15985 specifies a method for the evaluation of the ultimate anaerobic
biodegradability of plastics based on organic compounds under high-solids
anaerobic-digestion conditions (see also ASTM D5511).
Standard tests for biodegradability have also been developed for other sectors
including biolubricants (ASTM D6731 (biodegradability in soils) and ASTM
D5864 (aquatic biodegradability)).
Definitions and standards help to differentiate between materials, as the
associated standards are designed to provide assurance and guarantee effective
performance and compatibility of the materials in question to the process being
considered.
8.6.3
Composting Standards
The process of composting is an important parameter in the biopolymer sector, as
this ranks as recycling rather than disposal and is therefore credited as being
higher on the waste hierarchy that promotes reduction and reuse options over
disposal.
Compostability is particularly important for materials used for packaging
operations that commonly appear in the waste stream. In these cases it is important
to ensure that these materials will not interfere with biological waste treatment
options, such as composting and anaerobic digestion systems.
Composting standards for materials are designed to protect the status of high-
quality material outputs from composting and anaerobic digestion. Commonly
quoted standards for compostable plastics are ASTM D6400-04 and EN 13432
that relate to the performance of plastics in a commercially managed compost
environment. Both standards were developed for hydro-biodegradable polymers
(e.g. aliphatic polyesters plus modified starch) where the mechanism inducing bio-
degradation is based on reaction with water. In order for a product to be composta-
ble according to these standards, the following key criteria need to be met: (1) the
polymer must be able to fragment into non-distinguishable pieces after screening
and safely support bio-assimilation and microbial growth; and (2) they must be
biodegradable, whereby 60% and 90% respiration of carbon to CO
2
is achieved
over a period of 180 days for ASTM D6400 and EN 13432, respectively.
Break-down products should not pose any toxicological or environmental
threat. In the case of composting, the time taken to degrade is the key parameter
defining suitability for commercial composting operations, to which most of the
composting standards relate. Composting and anaerobic digestion (AD) plant
operators working to quality standards for compost and digestate (e.g. BSI PAS
100 Compost specification) can only accept materials that comply with compost-
ing standards agreed within each composting or digestate standard.
