Biogas potential of biowastes
In line with the requirements of the Recycling Management Act, many corporations to which the disposal obligation has been transferred are currently examining the possibilities for extending and/or setting up separate collection of biowastes. Recovery of the biowastes in a biogas plant with downstream composting is frequently advantageous under ecological and economical aspects.
However, not only reliable estimates of the quantity produced are important for the planning, but above all, reliable information about the quality of the biowastes arising in the catchment area is essential:
The biowaste quality determines decisively the quantities of biogas and in particular methane that can be obtained.
Different factors affect the quality of the biowastes
The initial decision as to which wastes are to be collected as biowastes in the catchment area has a decisive influence on the biogas generation potential of the wastes. High gas yields can be achieved above all by co-collection of the food wastes that are produced in households. Here it is necessary to take into account that the collection system itself also has a large effect on how much of the gas generation potential available in the fresh biowaste is still available at the time of delivery to the recovery plant.
While food can be protected against microbial degradation by cooling or preservation, biowastes are initially stored for several days at room temperatures in the households and then often for up to two weeks in the biowaste containers. It is not rare for the collected biowastes to be temporarily stored again at transfer sites.
As a result, microbially partially degraded biowastes with significantly reduced biogas generation potential get into the recovery plants. How strongly the different influencing variables affect the biogas generation potential in the respective collection area can ultimately only be evaluated through appropriate analyses of the real biowastes produced.
Recommendation: Waste-characterising random samples over a longer period
Due to the marked annual load, especially for the green and garden wastes arising, it is advisable to examine the gas generation potential of the biowastes produced in the catchment area over a lengthy period of time by taking waste-characterising random samples. The random sampling and preparation of the samples to be examined for the different analyses requires particular care. To this end, bifa uses methods successfully established in various R&D projects and therefore has a good database for evaluation of the results.