Methane potential of industrial oil-clay by-product
Valtavaara, Minna (2014)
2014
Ympäristö- ja energiatekniikan koulutusohjelma
Luonnontieteiden tiedekunta - Faculty of Natural Sciences
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Hyväksymispäivämäärä
2014-11-05
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201410221513
https://urn.fi/URN:NBN:fi:tty-201410221513
Tiivistelmä
In this thesis suitability of industrial by-product oil-clay to produce biogas in anaerobic digestion was studied. Oil-clay (spent bleaching earth) contains high amounts of fats and clay (sand).
The methane production potential was studied by methane production batch assay with two mesophilic and one thermophilic inoculum. Methane production potential of oil-clay was high in all assays ranging from 532 to 664 l CH4/kg substrate VS added and from 728 to 922 l CH4/kg substrate VS removed. The yield was close to the theoretical maximum of fats. No inhibition caused by high lipid content of the substrate was ob-served, only some differences in the lag phase before the methane production initiated. Pretreatment with alkali increased the soluble COD but it did not have an effect on the methane production potential of oil-clay in batch assay. Thermal pretreatment had no effect on soluble COD levels. The behavior of oil-clay in the anaerobic digestion vessel was observed to be problematic, because of its tendency to float and after wetting sink quickly to the bottom. The spent oil-clay is acidic (pH 3.5) causing the need to adjust the pH before feeding it to the digester.
As a conclusion it can be postulated that oil-clay substrate used is a potent feedstock for methane production by anaerobic digestion. Its methane production potential is high and the volatile solids of the substrate are efficiently used for methanogenesis. However the acidic nature, high lipid content and behavior in the vessel need to be taken into account when planning full scale application. More studies with actual reactors and careful planning of the input amounts and processes are needed to evaluate this issue further.
The methane production potential was studied by methane production batch assay with two mesophilic and one thermophilic inoculum. Methane production potential of oil-clay was high in all assays ranging from 532 to 664 l CH4/kg substrate VS added and from 728 to 922 l CH4/kg substrate VS removed. The yield was close to the theoretical maximum of fats. No inhibition caused by high lipid content of the substrate was ob-served, only some differences in the lag phase before the methane production initiated. Pretreatment with alkali increased the soluble COD but it did not have an effect on the methane production potential of oil-clay in batch assay. Thermal pretreatment had no effect on soluble COD levels. The behavior of oil-clay in the anaerobic digestion vessel was observed to be problematic, because of its tendency to float and after wetting sink quickly to the bottom. The spent oil-clay is acidic (pH 3.5) causing the need to adjust the pH before feeding it to the digester.
As a conclusion it can be postulated that oil-clay substrate used is a potent feedstock for methane production by anaerobic digestion. Its methane production potential is high and the volatile solids of the substrate are efficiently used for methanogenesis. However the acidic nature, high lipid content and behavior in the vessel need to be taken into account when planning full scale application. More studies with actual reactors and careful planning of the input amounts and processes are needed to evaluate this issue further.