Clean Technology 2010

Using liquors from the wet oxidation of biomass for denitrification and methane generation

P.J. Strong, D. Gapes, B. McDonald
Scion, NZ

Keywords: bardenpho, solids removal, nitrate, anaerobic digestion, waste utilisation

Abstract:

Laboratory-scale thermal deconstruction tests on municipal biosolids achieved solids destruction rates of 90% under single stage wet oxidation conditions and high concentrations of small molecule carbon compounds (particularly acetic acid) were present in the process liquors. The process liquor was assessed as a carbon source for denitrification as well as its potential to generate biogas. The study confirmed that carbon supplementation was essential to maintaining the rate of nitrate removal in the Bardenpho system. When acclimated inocula were used in a batch assay study, ethanol, acetate and deconstruction liquors yielded the highest nitrate removal efficiencies. The wet oxidation liquor yielded results as good as those obtained with acetate supplementation, which was due to acetate being the dominant VFA formed during wet oxidation. An anaerobic digestion study compared of the effects on methane generation potential from RDC municipal biosolids using thermal hydrolysis or wet oxidation. The optimal pre-treatment of biosolids for methane production was thermal hydrolysis at 140 or 165°C, but the gain of in methane generation was only 11% more compared to the unprocessed biosolids. Wet oxidation at 220°C produced half the biogas relative to the unprocessed material, but the methane was derived solely from the liquid fraction of the cook. The wet oxidation liquor was an excellent carbon source for denitrification, while the solids remaining after deconstruction have no biological methane potential - indicating that if separated and disposed of they would not generate any harmful emissions associated with the breakdown of organic matter.
 
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