Nowadays organic waste is not considered to be waste any more. It is considered to be a resource. Legislature adjusted to this change in perception in 2012 by adapting the amended Closed Cycle Management Act, which includes a mandatory separate collection of organic waste from households from 2015 onwards. Estimates predict that this could lead to a doubling of the collected amount of organic waste. The German waste management system does not have enough treatment capacity for this growth, which is the reason why new plants have to be built. In order to decide which kind of plants should be built, the project examines the question "How can organic waste be treated most efficiently from an ecological and economical point of view?"
To answer this question, the entire process chain is examined, from collection through to deposition by means of LCA according to ISO 14040/44 and eco-efficiency assessment according to ISO 14045. In a literature review regarding the state of the art, the necessary data is identified. Additionally the state of scientific knowledge is researched and existing data gaps are identified.
The existing data gaps are closed through a collection of data about the entire German digestion plants which process organic waste from households (response rate of almost 70%) and through specific inquiries to data for plant construction, biogas use and other processes. As part of the data collection the plant types to be examined are differentiated by the parameters temperature (mesophilic/thermophilic), solid content (wet/dry) and mode of operation (continuous/batch) (e.g. TDC means Thermophilic, Dry, Continuous). As comparison closed and open composting plants as well as non-household organic waste digestion plants and green waste digestion plants for analyzing the input effect are adducted. Models of individual process chains based on the data are created to calculate the environmental impacts. The depiction of the humus reproducing effect of the carbon in the treatment products is a further emphasis to compare composting and anaerobic digestion. Here an allocation formula is designed to reflect the effect with practical relevance.
The evaluation of environmental impacts is carried out with seven midpoint impact categories, the three endpoint indicators and the aggregated overall indicator of the ReCiPe impact assessment method. According to the calculations the most environmentally benign choice is the TDB option.
In the cost comparison practice data is compiled from the survey and from literature sources. The MWC technology is identified as most economical option.
For the eco-efficiency assessment a dual normalization is developed to create eco-efficiency portfolios. The most eco-efficient system for the treatment of organic waste is the TDC option, which is only suitable for large waste streams for economic reasons (minimum throughput required). The next best options for smaller flows are the closed composting and then, as a second best digestion option, the TDB systems.
A comparison on the macroeconomic level between TDB (most environmentally benign), MWC (most economical) and TDC (most eco-efficient) shows that, apart from one category, the TDC system is only slightly worse concerning environmental effects than the TDB option. This is why in this work the TDC option, with the mentioned restrictions, is recommended as the best option for treatment of organic waste from households.