EFFECTIVE MICROORGANISMS (EM) AS BIOFEEDERS FOR ANAEROBIC DIGESTION

Resumo

Soil micro-organisms called Effective Microorganisms (EM) were first cultivated and used in the 1970s. Researches about these cultures have since then demonstrated their effectiveness in improving soil characteristics and as an alternative for accelerating organic matter decomposition in waste treatment systems. The objective of this study was to test whether the addition of EM to substrates incubated in anaerobic digesters would increase the efficiency of waste treatment and biogas production. EM cultures were obtained from bacterial colonies captured within the A-horizon of a Brazilian forest soil. They were left to grow during 15 days on cooked rice contact with the soil; afterwards, the established colonies were separated according to their colors, discarding all shades of black, gray and white, according to recommendations from related literature. Remaining colonies were further grown in sugarcane broth medium for 18 days, being this the final EM culture. Twelve bench digesters were used, each with a total capacity for three liters. The experiment was composed by four treatments consisting of different concentrations of EM inoculum [15% (T1), 10% (T2), 1% (T3) and 0% (T4)] applied to dairy cattle manure, with three replications per treatment. Anaerobic digestion was carried out under controlled temperature (35oC) over 99 days. Data collected included concentrations of total, fixed and volatile solids (TS, FS and VS), pH and Chemical Oxygen Demand (COD). The pH of the EM inoculum was 3.34 and COD was 24.25 mg L-1. The best reduction efficiencies for COD and TS removal were 79.44% and 42.50%, respectively, in T4. Among the treatments with EM addition, 1% (T3) resulted in better COD reduction. The maximum accumulated biogas production was 20.60 L biogas L substrate-1, also for T3. In conclusion, EM as an inoculum in low concentrations may be advantageous to anaerobic digestion.