|Abstract or Summary
- Liquid manure lagoons are known to be sources of odor and environmentally damaging gas emissions. Land application of the manure slurry after storage can lead to detrimental nutrient runoff and leaching. Floating lagoon covers (biocovers) are one option for reducing emissions, but to date they have only been used to address odors and emissions but not to address the problem of nutrient loss. This study evaluated the potential of floating biochar covers to reduce odor and gas emissions while simultaneously capturing nutrients from liquid dairy manure. The unique physical and chemical properties of biochars make them promising materials for odor, gas, and nutrient sorption. This new approach has the potential to mitigate multiple environmental problems.
Two biochars were used to test this approach: one made from Douglas-fir chips under a low oxygen combustion environment at 650°C (FC650), and the other made from Douglas-fir hog fuel pyrolyzed at 600°C (HF600). The HF600 biocover reduced mean headspace ammonia (NH₃) concentration by 7.5 to 13.6 μL/L. No significant reduction was found with the FC650 biocover. These biochars were able to sorb and hold nutrients while floating on the surface. Nutrient uptake by the two biochars ranged from 0.21 to 4.88 mg nitrogen g biochar⁻¹ and 0.64 to 2.70 mg phosphorus g biochar⁻¹. Potassium ranged from a loss of 4.52 to a gain of 2.65 mg g biochar⁻¹. The biochars also sorbed calcium, magnesium, sodium, iron, aluminum, manganese, and silicon. In a separate experiment, a panel of judges evaluated the odor offensiveness (-10 to 10 scale) and odor threshold (1 to 10 scale) of five cover treatments including four biochars. Mean odor offensiveness ranged from -0.4 to -1.4 vs. -2.1 for the control. Mean odor threshold ranged from 1.6 to 2.1 vs. 2.6 for the control. These results show that biochar covers hold promise as an effective means for reducing odor and gas emissions while sorbing nutrients from liquid dairy manure. More research is needed to determine optimal biochar feedstock, production temperature, pH, and particle size distribution for use as a biocover material.