Generation of bio-based products from omsw by using a solid-liquid separation technique and an anaerobic treatment

Abstract

The present paper provides an overview of the investigations (involving different liquids) regarding a new technology that is able to generate valuable bio-based products by using the liquid phase from organic municipal waste as raw material. The liquids used in this study were tested and treated in different ways to find out which substrates are most suitable for the process. For the purpose of generating bio-based products from organic waste, a solid-liquid separation process was performed first. Thereafter, in order to increase the amount of non-polar fatty acids (FAs) in the liquid substrate, an anaerobic digestion process was used. However, after the digestion, most of the FAs found in the liquid substrate were polar FAs. To increase the amount of non-polar FAs further, another treatment step, “ethanol maturation”, was carried out as the third step. Subsequently, the refining process was started with the extraction of the FAs from the liquid substrate by using a non-polar extraction solvent, such as Oleic acid methyl ester (OME). At this point, “extractive digestion” takes place. The FAs can be extracted over a longer period of time and during the digestion. As a result, the amount of longer-chain fatty acids in the OME increases. After re-extracting the FAs from the solvent, a transesterification process was used to produce fatty acid ethyl esters, which can be sold as cleaners or solvents to the metal industry for surface treatment. The production of other bio-based products, such as lubricants, fuels and polymers, is also possible. The following five substrates were mainly used for the investigations: (1) a liquid phase from organic municipal waste, produced by a percolation process; (2) fresh percolate from German kitchen waste; (3) percolates of different stages from a digestion plant in Germany; (4) old leachate from German landfills; and (5) young landfill leachate or leachate from pressed municipal solid waste, which was used to imitate African waste. These substrates were treated using the method described above. The results show that young landfill leachate has the highest potential. The highest availability of FAs occurs after biological pre-treatment of percolates. For this reason, very fresh percolates hardly contain any fatty acid. They must first be generated by the biological degradation of the organic ingredients.