Aplicação de pré-tratamentos ácidos e alcalinos para produção de bio-hidrogênio e bioetanol a partir das cascas da mandioca (manihot esculenta)

Abstract

World economic growth and rapid urbanization require efforts to produce sufficient energy to meet the growing demand for energy of nations. In this scenario, the exploitation of clean and renewable energy alternatives is shown as a key socio-economic solution. In order to produce hydrogen, ethanol and methane by anaerobic digestion process, the present study used cassava peels (Manihot esculenta) as substrate to assess the effects of pretreatments with acid (HCl) and alkaline (NaOH) solutions in different concentrations at saccharification of this biomass and, consequently, in the production of biofuels. The experimental procedure was carried out in batch operated reactors maintained at the mesophilic temperature (35 ± 1 ° C) using a rotating shaker incubator at 120 rpm. Reactors were inoculated with sludge from Sewage Treatment Station and pH was initially set to 7. Results evidence that concentration of carbohydrate in the substrate and the efficiency of biofuel production of reactors were greater where there was application of chemical pretreatments in biomass. The best hydrogen production was obtained using pre-treatment with 0.5% (v/v) dilute acid HCl. In this condition, the production rate was 0.95 mL of H2 per hour, presenting a cumulative production 195% higher than the reactor without chemical pretreatment. The specific production of the reactor with untreated biomass was 0.52 mL H2/gSSVh, whilst, the reactor with 0.5% (v/v) acid pre-treatment of HCl was 1.19 mLH2/ gSSVh. The alkali pre-treatment with 0.5% (v/v) NaOH concentration generated the highest final concentration of ethanol among the studied conditions, 24.78 mmol of ethanol/L versus 7.69 mmol of ethanol/L when it was not used any chemical pre-treatment. Chemical pre-treatment with 1.0% (v/v) acidic solution of HCl generated 57.19 mL of methane per gram of cassava peel, a rate 26.19% higher than the production in the reactor where there was no chemical pretreatment. The highest studied concentrations of NaOH / HCl (4 and 8% (v/v)) caused a decrease in H2, CH4 and ethanol production.