Purificação de biogás de aterro sanitário por tratamento químico e metabolismo de microalgas

Abstract

The metabolized biogas in landfills has the potential for energetic usedue to its high Inferior Calorific Power (ICP), which is directly related to its methane (CH4) content. Hence, aiming to maximize the content of CH4 in landfill gas, purification processes are applied, in order to remove the non energetic fraction of biogas, which is notedly composed of carbon dioxide (CO2) and trace gases, increasing its calorific power. Landfill gas is composed mostly by CH4, from 35 to 65%, CO2, ranging between 15 and 50%, and other compounds found in lower concentrations, such as hydrogen sulfide (H2S), nitrogen (N2), water steam, oxygen (O2) and ammonia (NH3). In that context, the present research evaluated the biogas purification of a deactivated landfill in Curitiba - Paraná, through chemical, biological and combined treatments, by using sodium hydroxide (NaOH) in the concentrations of 3% and 30%, lead acetate in 2% concentration, activated carbon, silica gel and a microalgae cultivation of Chlorella sp. in two types of photobiorreactors, one kitassato with one liter of capacity and the other a tubular reactor with two liters of capacity, individually and sequentially. The purification system was placed in field; the biogas was collected and the analysis of its composition were made in the laboratory. The CH4, CO2, H2S and NH3 contents were measured, with a commercial kit, especially developed for biogas analysis. In the same time, during the experiment, a work of follow up of microalgae’s growth with landfill injection was developed, through spectrophotometric and gravimetric analysis, for the quantification of the produced biomass. Chemical treatment processes resulted in maximum efficiency of 23.08%, highlighting the good performance of NaOH in the CO2 removal. Microalgae-based purification process in the kitassato photobiorreactor reached a maximum efficiency of 23.08% when applied individually. When the biological process was applied with NaOH 30%, silica gel and activated carbon resulted in the efficiency of 82.05%. At the same time, the purification system with the tubular photobiorreactor reactor was able to remove 74.36% of the CO2. During a 35 day period of permanence in the landfill, the microalgae cultivation showed a liquid biomass gain of 4.0 g.L-1. The results demonstrate the viability of using Chlorella sp. for the CO2 fixation in landfill gas purification processes, proving the possibility of obtaining a biogas richer in CH4 and producing microalgae’s biomass, which can be applied for oil, carbohydrates, and another economically valued nutrients extraction.