Nutrient and Heavy Metals Release from Mixtures of Organic Residues and Food Wastes in Composting

Abstract

Composting has various benefits to achieve sustainability, such as substituting the use of fertilizers and preventing organic residues from being dumped in landfills. Thus, the objective was to evaluate nutrient and heavy metal release dynamics during composting with different mixtures of organic residues containing food wastes. The study was conducted in a community association in Mossoro, Rio Grande do Norte, Brazil, and the chemical analysis was carried out at the Universidade Federal Rural do Semi-Arido. Proportions between bovine manure (BM) and food wastes (FW) were Pile 1–0:3 (0% BM and 30% FW); Pile 2–1:2 (10% BM and 20% FW); Pile 3–1:1 (15% BM and 15% FW); Pile 4–2:1 (20% BM and 10% FW); Pile 5–3:0 (30% BM and 0% FW) (Pile considered as control), and the remaining 70% was filled with plant residues (tree prunings). Increment of BM proportion in compost piles with FW led to increase in C mineralization, but C mineralization decreased in the pile with only tree prunings and BM. Nitrogen immobilization occurred only in the pile with 15% BM and 15% FW; in the others, N was mineralized. Food wastes showed greater amounts of potentially mineralizable K fractions. For the micronutrients copper and zinc, in general, the initial contents decreased, whereas iron contents increased. The contents of all heavy metals diminished in the final product of the composting process, with no risk of contamination.