Waste-to-Energy: produção de biogás a partir dos resíduos da suinocultura

Abstract

The constant growth of the swine production chain requires waste destination and treatment planning. Parallel to this, the circular economy concept has been receiving increasing attention in the bio-economy era. Anaerobic digestion is critical in swine manure treatment systems, especially when considering environmental contamination caused by inadequate disposal of dead animal carcasses and manure risks. This doctoral dissertation sought to develop technological arrangements for biogas production from swine manure, with the goals of producing biogas, ensuring process stability, and producing fertilizer. The development of activities was divided into two stages. The first stage (Article I) investigates the effect of solid-liquid separation (SLS) on biogas production and process performance using different lab-scale and full-scale reactors fed with swine manure. The second stage (Articles II, III and IV) investigated carcasses from non-slaughtered animals used in co-digestion with swine manure to increase biogas generation. The characteristics of the residues were analyzed to identify strategies for increasing biogas production and process stability, considering energy potential, pre-treatments, and sanitary aspects, with the goal of using digestate as fertilizer. In a subsequent study, the potential for increased biogas production and its impact on the performance of the anaerobic digestion process with carcass addition was investigated using lab-scale reactors already fed with swine manure, covered lagoon biodigesters (CLB) and CSTR (continuous stirred tank reactor). It concluded with a case study incorporating SLS from swine manure and swine carcass co-digestion. The results of the laboratory scale can be used to forecast the methane recoverability of the full-scale system. The biogas productivity for the full-scale CSTR averaged 0.65 ± 0.23 NLbiogas L−1reactor d−1, while the BLC was 0.18 ± 0.05 NLbiogas L−1reactor d−1. In terms of swine manure and swine carcass co-digestion results, biogas production was efficient in both biodigester models. However, when comparing Phase I (0 kg carcass m-³manure) and Phase IV (68 kg carcass m-³manure), the CSTR biogas productivity increased from 0.41 ± 0.03 to 1.63 ± 0.14 NLbiogas L−1reactor d−1 and biogas yield from 0.33 ± 0.03 to 0.87 ± 0.10 LNbiogas kgVSadd-1which represents 397% and 263% in relation to manure monodigestion, respectively. While for the BLC, phase I (0 kg carcass m-³manure) and phase V (15 kg carcass m-³manure), the biogas productivity increased from 0.19 ± 0.02 to 0.61 ± 0.05 NLbiogas L−1reactor d−1 and the biogas yield from 1.12 ± 0.19 to 1.27 ± 0.24 LNbiogas kgVSadd-1 which represents 321% and 113% in relation of manure monodigestion, respectively. On the other hand, the ideal ratio of the solid fraction of swine manure and carcass was higher, reaching 98 kg carcass m-³manure. Analyzing Phase I (0 kgcarcassm-³manure) and Phase VII (98 kg carcass m³manure) the biogas productivity increased from 0.57 ± 0.04 to 2.77 ± 0.21 NLbiogas L−1reactor d−1 and biogas yield from 0.46 ± 0.05 to 0.90 ± 0.17 LNbiogas kgVSadd-1 which represents an increasing of 485% and 195% respectively. Although there is no evidence of inhibition of anaerobic digestion inhibition up to ideal optimal ratios for three reactors at the ratios of 100 kgcarcassm-3slurry (CSTR) and 134 kgcarcassm-3manure (CSTR), the reactors started to produce foaming, showing a decrease in biogas production and methane concentration. The technological arrangements presented throughout the work contemplate the possibility of treating swine residues, reducing costs and environmental impacts, improving the sustainability and profitability of the production chain, and could be one of the best strategies for the future of bioenergy production and economy circulates in animal waste treatment plants. The main advantages of using SLS followed by different reactors are cost savings in the construction and operation of biogas plants, consistent biogas generation, and a digestate treatment system. The co-digestion of carcass and manure or solid fractions proved to be an ideal technological arrangement for increasing biogas production in swine manure treatment systems, while adhering to the maximum allowed ratios for each biodigester model.