Digestão anaeróbia do resíduo da industrialização da mandioca em processo com separação física de fases

Abstract

The effluent deriving from the pressing stage of a manioc processing plant (manipueira) was treated by anaerobic digestion process. Which one has presented acid and methane phases separation. The effluent was collected at INDEMIL, a manioc starch and flour mill, which is located in Formosa, Districit of Paranavaí, Northwest of Paraná. It has presented a variable composition that probably was on account on the period collects done during the experiments. Its main characteristics were: 56,252 mg/L average COD, 3,828 mg/L of CH3COOH volatile acid; 1,853 mg/L of CaCO3 alkalinity; 312,6 mg/L free cyanide and pH4,7. The separated phases system was composed by a complete stirred 5-liter acrylic tank reactor, and by a hybrid (UASB + fixed bed) PVC reactor, where the acid and the methane stage took place, respectively. The acidogenic reactor was kept on ambient temperature and operated with a 1-day hidraulic retention time. This reactor was fed with "manipueira" diluted to COD concentration of 7500 mg/L, 9000 mg/L, 11000 mg/L and 14000 mg/L and pH between 5,0 and 6,0. The methanogenic reactor operated with a 4-day hydraulic retention time, using rigid dried 2X2cm bamboo, which has been sterilized at 150°C, as packing oft he fixed bed portion. 40% of the reactor volume was filled with that packing. The reactor operated under ambient temperature and pH varing from 6,8 to 8,0. The affluent of this reactor was the effluent deriving from the acid reactor, which has passed through a neutralization tank for the pH correction. The results show a good biogas production, with na 80% average methane theor. The average reductions of COD and free cyanide by the hole process was about 96% and 94%, respectively. The separation of the phases was responsable for the selection of the bacterial groups which influenced on the proces. First, in the acid phase, was observed the predominance of the propionic, n-butyric and n-valeric acids, with biomass mainly composed by fermentative bacilli, which was responsable for 90% reduction of free cyanide concentration. In the methane phase, on the other hand, there was a predominance of a wide microbial population of methanogenic bacteria of the genus Methanotrix, Methanosarcina, Cocos and Bacilli, which was responsable for the high indexes of organic matter removal and methane production.