Thermal treatment technologies for low moisture and dehydrated manure feedstock

Abstract

The research carried out throughout this project has helped to further advance the area of producing biochar from animal manure feedstocks, as well as producing biochar from virgin wood for its application in manure management systems. On-farm auto-thermal updraft gasification of poultry litter (PL) was carried out to yield a low calorific value product gas (3.39 MJ m-3N LHV), along with a tar and char residue. The ash melting point of 639 °C of PL made low temperature operation necessary, resulting in a low cold gas efficiency (GCE = 0.26). The same PL feedstock, dehydrated cow manure, and pre-digested swine manure were subject to slow pyrolysis to produce nutrient rich biochars and to recycle them back to agricultural land. All biochars exceeded the set thresholds of Zn and Cu (400 g t-1 and 100 g t-1 respectively) for European biochar certification. Recoveries in biochars were high (~90 wt.%) for all nutrients except for N and S (28-62 wt.%) and some heavy metals, e.g. Pb and Ni (21-31 wt.%). Biochars produced at 400 °C resulted in a significantly higher nutrient uptake to lettuce (Lactuca sativa) than biochars produced at 600 °C, and slow pyrolysis biochars significantly increased N uptake as opposed to the gasification char. Sitka spruce biochar was produced using a uniquely designed Kon-Tiki kiln. The biochar along with sulfuric acid were used as cow slurry additives to evaluate their impact on NH3, CH4 and H2S emissions. Biochar alone had no significant effect on NH3 and H2S, but biochar might be able to reduce CH4 emissions. Sulfuric acid reduced cumulative NH3 by about 50 % and cumulative CH4 by about 80 %, but increased H2S emissions. Pre-acidification of biochar might be promising and needs further investigation. The same Sitka spruce biochar was amended with cow slurry to see the effect on nitrate leaching, nitrogen uptake to grass (Lolium perenne) and changes in nitrification and denitrification capabilities in soil by determining the abundances of bacterial and archaeal amoA and nosZ genes. Biochar alone had no significant effect on either of the investigated parameters; however, in combination with slurry biochar decreased the abundance of archaeal amoA at the slurry application zone and increased the abundance at lower soil depth. This might be attributed to adsorption of dissolved organic carbon to biochar, and an increase in ammonium leaching. The results of this study reveal that biochar affects soil-N dynamics differently when in combination with slurry than in its un-amended state