Solid thickening and methane production of livestock wastewater using dissolved carbon dioxide flotation

Dilute manure is classified as wastewater due to the large quantity of water used in livestock production in Korea. Livestock wastewater treatment is required in order to reduce high moisture content and treat fluids discharged from the digestion process. In livestock wastewater treatment plants, large quantities of CO₂ gas are produced at combined heat and power facilities as well as in the anaerobic digestion (AD) process. This gas produced during livestock wastewater treatment can be used as a separator of solids from liquid in wastewater. In this study, a flotation system using recycled CO₂ gas was used for sludge thickening. An anaerobic toxicity assay (ATA) and a biochemical methane potential assay were used to assess the toxicity impact of recycling CO₂ on the methane production potential. ATA experiments confirmed that CO₂ toxicity did not impair the AD process. The tests indicated that the cumulative methane yield from influent livestock manure enriched with CO₂ was approximately 190 mL-CH₄/g-VS_added. The data demonstrated the potential of using dissolved CO₂ flotation in the AD of diluted livestock wastewater.