Characterization of nutrients and pilot biofertilizer production from food waste and dairy manure digestates

Food waste and dairy manure digestates from commercial digesters were characterized in the lab for particle and nutrient distributions before pilot-scale processing (vibratory screen, ultrafiltration, sun drying) to produce solid and liquid biofertilizer products. Experimental results showed that the elemental compositions of the two digestates were different but shared similarities. The coarse solids of both digestates had lower concentrations of nutrients than the liquid fractions, which contained most of the K and Na. The dairy manure digestate had a higher amount of fine solids between 0.4 and 75 μm than the food waste digestate, but the majority of TKN was contained in the fine solids of both digestates. An optimization analysis concluded that optimal combinations of digestate fractions included over 70% coarse solids to obtain desired nutrient and salt ratios. The solid and liquid fertilizer products derived from the pilot-scale processing were similar to those expected from the lab-scale investigation.