Thermal treatment and densification of manure and biomass blends to produce stabilized soil amendments.

Abstract

Land application of dairy manure is the most common practice for disposal of this waste. Agricultural fields surrounding concentrated animal feeding operations (CAFOs) often have high levels of N and P because of manure over-application. However, its low bulk density limits the amount of manure that can be profitably transported for use as fuel or fertilizer. As an alternative, selective carbonization can be used to create densified-stabilized N-containing products that can be delivered to regions with low soil N and P contents. This research reports developing a biomass (Douglas fir)/manure thermally treated product containing a maximum fraction of N integrated into the biochar structure. Response Surface Methodology (RSM) was used to identify processing conditions resulting in high C and N conversion efficiencies. Experimental results show maximum N conversion efficiencies were achieved at Douglas fir contents higher than 50 wt % and temperatures close to 260 °C. H₃PO₄ levels at 2 wt % seems to be sufficient to catalyze the desired reactions. The KOH treatment did not significantly affect product yield and the efficiency of C and N conversion. The structural strength of densified char was evaluated using dynamic rheometric (amplitude sweep test).