Uso de aditivos para a retenção de nitrogênio em compostagem de resíduos gerados da produção animal

Abstract

Agribusiness is one of the main Brazilian activities, generating tons of waste daily. Composting comes as an environmentally friendly alternative for these residues, recycling nutrients and generating quality organic fertilizer. However, high N losses occur, so the use of additives, such as biochar and crude glycerin, which have shown benefits for this purpose, can be used to improve the quality of the final product. Thus, the objective of this work was to evaluate the effect of biochar and crude glycerin in reducing nitrogen losses during the composting of fish and slaughterhouse waste from cattle and pigs that were associated with bulking agent (straw) in the proportion of 3: 1 (mass: mass). A completely randomized design was adopted, with five treatments (without addition, 5 and 10% biochar and 5 and 10% crude glycerin) and 20 repetitions. The experimental repetitions were formed by TNT bags with the capacity to contain an average of 1 kg of substrate, and the mixtures were packed inside the bags only after being prepared and homogenized, and then incubated inside the field windrows (average capacity of 200 kg) between the formation of layers of waste and bulking agent. For windmills containing cattle and pig slaughterhouse residues, forced aeration with PVC pipes was used. Aeration was performed daily for 15 minutes with a flow of 0.6 L.min 1. In the first 20 days, N losses were evaluated every four days, and temperatures were measured daily. At 50 and 70 days, rotations were performed and at 90 days the experiment ended. At each turn and at the end of the process, samples were collected to determine the levels of total solids (TS) and volatiles (VS), N, hemicellulose, cellulose and lignin. At the end of the composting of fish residues, the TS reductions did not differ with an average of 44.26% except for biochar in the largest addition (42.45%). For slaughterhouse waste, the biggest reduction was for 5% of biochar (64.07%). Regarding the VS contents in fish residues, the greatest reduction occurred with the use of glycerin at 5% (57.74%) and for slaughterhouse residues, the greatest decreases occurred with both additives at 5% (average 67,66%). The additives were effective in retaining N. The control treatment lost more N in the first 20 days (47.01 and 45.60%) for slaughterhouse and fish residues, respectively. At the end of the 90 days, the control of both residues ended with more N losses, with 52.43 and 54.70%, for fish and slaughter. The lowest final loss in slaughterhouse was for glycerin at 10% (27.32%) and in fish was for biochar and glycerin at 10% (32.66 and 29.72%). The levels of hemicellulose in both residues were greatly reduced with averages starting at 25 and 22.84% and at the end 11.84 and 13.62% (fish and slaughterhouse). The addition of biochar in both residues increased the initial levels of cellulose and lignin, mainly to 10%. In slaughterhouse (14.31 and 12.08%) and fish (9.63 and 8.73%), initial and final values of cellulose, however at the end it was the condition that most reduced the content. So also, in lignin, the biochar with 10% of fish started with 10.52 and ended with 7.60%. In slaughterhouse, he started with 10.53 and finished with 8.90%. It is concluded that the additives used in both residues were efficient in retaining nitrogen, however the most suitable is the 10% biochar and still with a high reduction of solids. The greater addition of glycerin makes it difficult to reduce solids. The tested methodology can be used because it results in values similar to those in the literature in a conventional way.