Life Cycle Assessment Study on the Treatment of Bio-waste

23/07/2012 - To date, life cycle assessments have allowed only a very limited evaluation of the ecological benefits of applying compost to agricultural land. A new study by the German ifeu-Institute and ahu AG Aachen aimed at analysing for life cycle assessments previously unquantifiable effects of compost application in agriculture, and integrating these findings into life cycle assessments.

The following three areas were covered by the study:
1. a soil impact assessment
2. the modification and development of life cycle assessment methods
3. a re-evaluation of treatment systems for biodegradable household waste

The project partner ahu AG Aachen compiled all direct chemical, physical and biological effects of adding compost to soil, established the causal links, and described the resulting impact. According to the findings, regular addition of compost considerably improves the condition of the soil. For example, soil water retention is improved, meaning that less irrigation is required. For many minerals (kalium, magnesium, phosphate), compost is fully equivalent to mineral fertilizers. Furthermore, the soil’s filter function against contaminants is improved, and the danger of erosion reduced. A sub-report describing the findings in detail will be published separately as a companion volume to this report.

Based on the study’s findings, environmental impact categories/ assessment criteria such as greenhouse effect, acidification of the soil, etc., could be adapted and specificied. As far as direct and resulting impacts were quantifiable, the findings of the soil study were integrated into the existing life cycle assessment structure. Certain significant modifications were made: for instance, nitrogen from compost was found to be equivalent to the one added to the soil through mineral fertiliser. Newly introduced was the assessment of the effect of humus (humus reproduction and humus enrichment), as well as criteria based on water retention capacity (reduced irrigation requirement) and the addition of mineral mass (reduction in erosion).

To conclude, the study addressed whether the treatment of bio-waste needed to be re-evaluated from an ecological perspective. The use of compost was found to be significantly more beneficial than previously assumed, and the findings support the separate collection and treatment of biodegradable waste in principle. However, the treatment process must be designed to ensure the greatest possible use of bio-waste properties whilst complying with strict emissions reduction standards. In order to meet this objective, the study recommends compost production at fermentation plants which meet stringent emissions and efficiency standards.

Detailed examples of home and collective composting schemes implemented in Europe, such as the Promotion of Decentralised Composting in Brussels, are listed in the Pre-waste good practices report.