Cultivo de Chlorella sorokiniana LBA#39 em digestato da suinocultura com simultânea remoção de nutrientes e incremento no potencial energético de biogás

Abstract

The global demand for mitigating the effect of climate change and minimizing excessive dependence on fossil fuels highlights the microalgae use to remedy swine digestate and produce value-added biomass, making a circular economy scenario applied to the anaerobic digestion process attractive. However, there are still challenges in the digestate use as a culture medium, which includes varying its composition and controlling toxicity by free ammonia (NH3) in the microalgae cell, triggered by the high total ammoniacal nitrogen (NAT) concentration in the digestate. In this context, the objective was (i) to investigate the swine digestate use as a culture medium for microalgae, as well as the simultaneous nutrients removal from the liquid fraction and (ii) to evaluate the biogas production potential of microalgae biomass integrated with pig farming in the circular economy context. For this, the strain of microalgae C. sorokiniana | LBA # 39 was used as an inoculum in the experiments execution and the digestate samples were collected in the treatment a commercial piglet production farm system. The NAT concentration effects and pH effects on the biomass productivity responses and nutrient removal different evaluated through statistical planning using a central rotational composite design (CRCD) 22. The best cultivation condition replicated and the resulting biomass characterized and used to evaluate the Biogas Biochemical Potential (BBP). Finally, scenarios simulated in order to evaluate the biogas production potential of swine farming by integrating microalgae into the process. The results showed the swine digestate use for the production of microalgae biomass and simultaneous polishing becomes a promising alternative. In the data statistical analysis, the independent variable NAT concentration had a significant positive effect, while the pH variable had a significant negative effect for the responses of biomass productivity and phosphate removal. This means that the higher the NAT concentration and the lower the pH, the greater the responses. Thus, C. sorokiniana | LBA # 39 was able to tolerate high NAT concentrations (≤ 1300 mg · L-1) at neutral pH (pH 7.0-7.5), obtaining high biomass productivity (198.0 mg · L-1 · d-1) and satisfactory phosphate removal (≤ 90%) and nitrogen (≤ 70%). The biomass harvested after digestion phytoremediation showed a high content of volatile solids (95.4%) and proteins (59.5%). The biochemical biogas potential from microalgae monodigestion was 392 ± 14 mLN · gSVad-1 (CH4 = 65%) and the scenarios of the integration of microalgae cultivation with anaerobic digestion resulted in a potential to increase up to 31.2% in the biogas production from a swine production farm. This is an attractive approach for integrating raw materials into existing agro-industrial facilities, introducing the circular economy concept, as well as mitigating GHG emissions and improving biogas production and the economic viability of the power generation system in the agribusiness current scenario.