Sustainable Bio-Fertilizer Production From Anaerobically Digested Organic Wastes

Abstract

This study compared digestate from two anaerobic digesters of different feedstocks (food waste and dairy manure) and produced solid and liquid fertilizer products for inclusion in a farm-scale tomato plant growth experiment. Laboratory experiments were conducted to evaluate vibratory screening and membrane filtration and to characterize elemental flows during the processing of two digestates. Solid and liquid fertilizer products were produced in a developed pilot scale integrated vibratory screen, membrane filtration, and ambient drying system. Experimental results showed that the elemental compositions of the two digestates were different but shared some similarities. The food waste digestate had higher N and Na, similar P and K, and lower Mg contents than the dairy manure digestate. The coarse solids of both digestates were nutrient poor and the K and Na were present mostly in the liquid obtained following filtration with 0.45 m membrane. The dairy manure digestate had a higher amount of fine solids between 0.45-75 m than the food waste digestate but the majority of N was contained in these fine solids for both digestates. P and Mg were present in larger particle sizes for the food waste digestate than the dairy manure digestate. For the fertilizer products produced with pilot scale equipment, the TKN in the liquid product for the food waste and dairy manure digestate was 2.3 and 1.2 g/L, respectively, over 90% of which was contributed by NH₄-N. The dried solid products of approximately 60% moisture content contained TKN concentrations of 6.3% and 4.7% for the food waste and dairy manure digestates, respectively (dry basis).