Avaliação de fontes de nitrogênio suplementares da digestão anaeróbia de resíduos alimentares com vistas a produção de biometano

Abstract

The progress of studies on anaerobic digestion (AD) of organic waste is mainly due to the demand for clean energy sources, growth of waste generation and its impacts, demand for biofertilizers and depletion of natural resources. However, the methods and microbiological interactions involved still need to move forward. Inserted in this context, the carbon nitrogen (C: N) ratio plays a crucial role in process performance and efficiency. For this reason, the present research sought to investigate the equilibrium of the C: N ratio in the AD (carbon rich) food waste using different nitrogen rich waste alternatives (septic tank sludge, human urine and urea). Aspects of dosage, biogas generation, methane content, pathogenicity and ammonia inhibition were explored and studied. The codigested residues performed relatively similarly when the C: N 17 ratio was used. All allowed significant reduction of total solids (ST) and volatile solids (SV), generated biogas and showed no pathogenicity in the digested materials. However, a low calorific power composition in biogas and a relatively limited performance were observed, especially for human urine (UH) mixing. In order to investigate a possible toxicity suffered by ammonia excess, the variation of C: N ratio (17, 23, 29 and 35) for the RA + UH mixtures was tested. The lower ratio (17) confirmed the composition of biogas with high CO2 content and lower CH4 content. The best performance was identified for ratio 23, with higher values of ml CH4 / gSV (288.18 ± 13). When the highest ratios (29 and 35) were evaluated, there was a yield decay, indicating a possible leakage of the optimal nitrogen dosage. Therefore, despite the nitrogen intake, pH and moisture balance provided by the co-digestion, it is essential to adopt optimal dosages to obtain higher quality in biogas and digestate. Finally, the economic feasibility study of the design of a biodigester for the treatment of organic waste supplemented with UH was carried out, which presented VPL> 1 and investment period of six years and eleven months.