Biodiesel waste products as soil amendments : evaluation of microbial, biological, and plant toxicity.
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2011-10-22
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Edition:Final report; 7/1/2010-9/30/2011.
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Abstract:During biodiesel production, about 200 lbs of glycerol, commonly called glycerin, is produced for every 1 ton of biodiesel. As the
biodiesel industry grows, so does the need to dispose of this waste product. While potential uses for glycerin exist, such as in food,
industrial chemicals and pharmaceuticals, surplus glycerin from large recent increases in production is disposed of by incineration.
Application of glycerin to soil for dust control or as a beneficial soil amendment is an alternative that has advantages. This approach
could be more carbon neutral than burning as some of the carbon may be sequestered in the soil, and also can enhance soil quality by
increasing soil organic matter. Potential issues regarding application of glycerin to soils include its effects on soil microbial activity,
biological systems, and plants.
The objectives of this research project were to evaluate the toxicity and growth effects of methanol-stripped glycerol from biodiesel
waste on microbial, biological, and plant systems in soils. Three tests were used: 1. Activated sludge respiration inhibition test; 2.
Earthworm toxicity; and 3. Plant toxicity.
Results of the respirometry studies suggest that there is no microbial inhibition due to the glycerol. Microbial activity was observed in a
wide range of glycerol amounts applied to soils. In plant studies, there was inhibition of growth and germination with glycerol
quantities above 1% by weight. Lower levels of glycerol did not appear to inhibit plant germination or growth and in fact appeared to be
beneficial to growth. In worm assays, glycerol concentrations above 1% were fatal on contact with earthworms due the glycerol
absorbing water and desiccating the worms. Worms survived when exposed to glycerol in lower concentrations.
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