Die Bodenkultur - Journal for Land Management, Food and Environment


About the utilization of raw glycerin as slurry additive


For more than three months the effects of a raw glycerin admixture to cattle slurry were tested for their chemical, physical and biological characteristics by means of a storage experiment. The influence of the raw glycerin admixture to slurry on the yield in permanent grassland was determined in a pot lysimeter test. A main problem of the utilization of raw glycerin, which is a couple product of the rape oil-methylester production, is the relatively high percentage of methyl alcohol (about 15 weight %). Even after 100 days of storage, up to 70% of the originally existing methyl alcohol in the 10 %-varieties could still be measured, which means that only a part of it was transformed or decomposed. As far as the 2 %-varieties are concerned, the thinning, which is necessary for the gaschromatographic analysis of methyl alcohol, may above all be responsible for the fact that no methanol could be detected when stored out. The admixture of raw glycerin caused a distinct rise of the potassium content of the slurries which, from a plant researcher's point of view, led to an unfavourable expansion of the nitrogen: potassium oxygen relation. Compared to the untreated slurry, the pH value of raw glycerin slurries declined distinctly. This fall may probably be connected with a higher biological activity resulting in partly very strong mould sediments on the surface of the glycerin slurries. The rest soap in the raw glycerin led to an increase in the volume of raw glycerine varieties. This has also been recently reported by farmers. Also the regular homogenization led to a renewed development of a foamy, pulpy substance, connected with a rise of the volume. The 2 % admixtures of raw glycerin caused a decrease of up to 30% of the yield on permanent grassland compared to untreated slurry. With an additive of 10% of raw glycerin, the yield reduction was up to 40% compared to untreated slurry. With regard to the methyl alcohol, an analysis of the infiltration water with the pot lysimeter test showed that an admixture of 10% of raw glycerin to slurry has to be expected a leaching of methanol, which may result in the pollution of the ground water. Key-words: rape oil-methylester, raw glycerin, methanol, slurry additive, leaching.