Digestato de reator anaeróbio oriundo de resíduos alimentares como fonte de nutrientes

Abstract

The improper disposal of food waste contributes to greenhouse gas emissions and the contamination of soil and water. One alternative to this issue is the treatment of such waste through anaerobic digestion, a process that generates biogas and a nutrient-rich by-product known as digestate, which has potential use as an organic fertilizer in agriculture. This project aims to evaluate the potential of digestate as a fertilizer for maize plants, seeking to reduce dependence on mineral fertilizers and improve soil properties. The hypothesis is that digestate derived from food waste can provide results comparable to mineral fertilization in maize cultivation. To test this hypothesis, a greenhouse experiment will be conducted at the Federal University of Ceará, using soil samples and digestate produced from food waste. The experimental design will be completely randomized, with six treatments and four replicates:T1: Control (no fertilizer), T2: 100% mineral fertilizer, T3: 75% mineral fertilizer + 25% liquid digestate, T4: 50% mineral fertilizer + 50% liquid digestate, T5: 25% mineral fertilizer + 75% liquid digestate, T6: 100% liquid digestate. Fertilizer dosages were defined based on the chemical analysis of the digestate, taking into account the availability of nitrogen, phosphorus, and potassium, and following agronomic recommendations for maize. The mineral fertilizers used were urea, triple superphosphate, and potassium chloride. Plant biometric parameters were evaluated, including height, number of leaves, and stem diameter. Dry and fresh shoot biomass were analyzed, as well as the chemical composition of macro- and micronutrients in the plants. Soil analyses included: pH, electrical conductivity (EC), phosphorus, calcium, magnesium, potassium, sodium, copper, iron, manganese, zinc, sum of bases, cation exchange capacity (CEC), exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR), and potential acidity. Data were analyzed using multivariate techniques, including principal component analysis and ANOVA. Treatment means were compared using mean comparison tests, with analyses performed in SAS (Statistical Analysis System, 1995), considering a significance level of 5%. The results showed that treatments T2, T3, T4, and T5 promoted higher means for plant biometric variables, nutrient accumulation in plant biomass, and soil fertility. Treatment T4 (50% mineral fertilizer + 50% digestate) stood out by significantly increasing plant height (128.5 cm), representing an 83.57% increase compared to the control; it also promoted the largest stem diameter (21.72 mm), with a 125.78% increase compared to the control, and the highest number of leaves, with a 33.33% increase over the control. The combination of digestate with mineral fertilizers enhanced the availability of macro- and micronutrients, increasing their concentration in the soil without causing harmful sodium accumulation. Although treatment T6 (100% digestate) presented lower results compared to those with mineral fertilizer blends, it performed better than the control, suggesting its potential as a standalone fertilizer, albeit with reduced productivity. Partial replacement of mineral fertilizers with liquid digestate—especially in the 50% mineral fertilizer + 50% digestate ratio—proved effective for maize fertilization, providing agronomic results equivalent to or superior to conventional fertilization and offering environmental benefits by utilizing food waste.