Evaluation of Co-Composting as an Alternative for the Use of Agricultural Waste of Spring Onions, Chicken Manure and Bio-Waste Produced in Moorland Ecosystems

Abstract

Composting is an adequate method for treating and valorizing agricultural waste such as those from spring onion (SO) cultivation and chicken breeding (chicken manure–CM). However, the low content of Total Organic Carbon in the waste from SO and the high concentration of total nitrogen in CM are limitations for the composting process. This research studied the co-composting of SO and CM in a moorland ecosystem, together with locally available co-substrates such as biowaste (BW) and woodchips (WC), focusing on the effect of co-composting in process development and end-product quality. A pilot-scale experiment was carried out using three treatments in triplicated composting piles: (i) Treatment A: 43% CM + 41% BW + 16% WC; (ii) Treatment B: 52% CM + 32% SO + 16% WC, and (iii) Treatment C: 70% SO + 30% WC. Treatments A and B reached thermophilic temperatures after two days of the process start and remained at that level for 17 days. However, treatment B reached environmental temperature during curing in a shorter time (43 days) than treatment A (53 days). Treatment C did not achieve thermophilic temperatures. Tests carried out at the end of the process showed end-product stability and non-phytotoxic characteristics (germination indexes 80%). The fertility index of the products showed that treatments A and B presented values of 4.3 (over 5.0) while treatment C obtained a value of 2.5. From the perspective of agricultural use, products from the three treatments had limitations due to deficiencies in essential nutrients like phosphorus. Still, they had potential as a soil amendment for restoration processes. In summary, we have demonstrated that this waste, in combination with other organic materials, could be a good amendment for the composting process and the end product.

Evaluation of Biochar as an Additive in the Co-Composting of Green Waste and Food Waste

“…The EC reflects the concentration of water-soluble inorganic ions in the processed material. The EC was higher (EC > 1000 µS/cm) at the start of the process in T 2 , T 3 , and T 4 with respect to T 1 (see Figure 3d), which is associated with the dominance of Sd, an additive with salts of sodium and calcium [15]. In these treatments, a generalized trend of a rise in EC was observed.…”

“…These wastes were manually shredded to achieve a particle size of between 30 and 50 mm [13]. Sd was added as a bulking material with 54.3% total organic carbon (TOC) and Pr with 28% P 2 O 5 to increase the phosphorus content in the substrates and contribute to the reduction of the nitrogen volatilization [6,15,32]. Pr was obtained from a commercial establishment that had TOC (1%), CaO (38%), Al 2 O 3 (0.5%), Fe 2 O 3 (0.4%), MgO (0.1%), and K 2 O (0.1%).…”

“…These strategies have increased lignocellulose degradation [6], reduced processing times by between 50% and 73% [6,7,12], and improved end-product quality, especially in terms of nitrogen and carbon availability [9,13]. Previous research on the co-composting of GW and FW together with sawdust (Sd) and phosphoric rock (Pr) improved the structure and nutritional content of the end-products and accelerated the transformation process of the substrates [14,15]. However, challenges remain regarding the reduction of nitrogen losses and the increase in the degradation rates [9].…”