Uso de biomassa de microalgas e cianobactérias cultivadas em águas residuais de avicultura como potencial energético na produção de biodiesel e amônia como transportadora de hidrogênio

Abstract

Ammonia is used worldwide as a fertilizer, but its application as a hydrogen carrier has recently grown. It has the capacity to store hydrogen at 17.7% by weight (corresponding to 120 g/L), superior to methanol (12.5%). Certain microbial biomasses have the capacity to produce ammonia from gasification. The advantage is that these microorganisms can grow in wastewater, performing a dual role in the treatment of agro-industrial effluents and biomass generation. Thus, the objective of this work is to evaluate the cultivation of the microalga Desmodesmus sp. and the cyanobacterium Brasilonema sp. in poultry wastewater for the dual purpose of removing nutrients, nitrogen and phosphorus, as one of the industrial steps in effluent treatment and biomass reuse with potential generation of ammonia and biodiesel. The microorganisms were propagated in 3-liter borosilicate cylindrical photobioreactors. The growth of the microalga and cyanobacterium was monitored by chlorophyll (a) extraction using the solvent suspension method (SSM). Bacterial growth was monitored by the microdroplet plating technique. Wastewater characterization was performed to determine nitrogen by ion chromatography, phosphorus and chemical oxygen demand by spectrophotometer reading, and metals by ICP OES. The biomass was collected and characterized for carbon, nitrogen, oxygen, hydrogen, and sulfur composition through elemental analysis for simulation in Aspen Plus, in addition to lipid extraction and transesterification to evaluate biodiesel generation by fatty acid profile. Through modeling using the Aspen Plus program, the highest biomass generation was obtained from the microalga Desmodesmus sp. cultivated in poultry wastewater (PW) with a production of 1000 kg/h. The lowest production was obtained from the cyanobacterium Brasilonema sp. cultivated in BBM culture medium (CM), with 196.37 kg/h. The highest production of liquid ammonia was obtained from the biomass of the cyanobacterium Brasilonema sp. (PW) with 107.81 kg/h, followed by the microalga Desmodesmus sp. (CM) with 106.92 kg/h. Desmodesmus sp. (PW) showed a higher lipid content (23%) and protein content (42%) with greater CO2 biofixation (0.342 gCO2/L.d), reducing greenhouse gas emissions. Furthermore, it presented ideal proportions of the fatty acids palmitate (53.73% - C16:0) and oleate (8.75% - C18:1), improving the quality of biodiesel with a high cetane index and high oxidative stability. It was observed that for hydrogen generation, the best biomass was from the microalga Desmodesmus sp. cultivated in poultry wastewater, however, for ammonia production, the best species was Brasilonema sp. cultivated in wastewater, providing greater sustainability to the process. The discounted cash flow model indicated that the use of wastewater for ammonia and biodiesel generation reduces operational costs by approximately US$ 632,041.30 with a payback period of 4 years for return on investment. Thus, this study confirms and expands the evidence on the potential of microalgae and cyanobacteria as multifunctional biotechnological platforms, integrating waste treatment with the generation of clean and sustainable energy.