Avaliação da capacidade de produção de metano em sistemas UASB tratando vinhoto sob diferentes condições operacionais.

Abstract

Vinasse is the waste water from ethanol distilleries with a high concentration of soluble organic material. If this waste water is submitted to anaerobic treatment, the main objective will be to generate methane at a high rate, which then can be used for electrical energy production. The methane production rate depends on the feasibility to maintain a large sludge mass with a high methanogenic activity in the reactor. In this paper an experimental investigation was carried out to evaluate if the methane production rate can be increased by optimizing two operational parameters: (1) temperature and (2) the COD loading rate. To evaluate the effect of temperature identical reactors were operated at the optimal mesophilic and thermophilic temperatures: 37 and 54 oC respectively. Systematic overloading of reactors was applied to stimulate the accumulation of Methanosarcina and eventually substitute Methanosaeta. It was expected that by maintaining a high concentration due to overloading a more active sludge would develop, because Methanosarcia have a much higher specific methane generation capacity. An experimental investigation of 180 days at pilot scale showed that Methanosarcina were unable to establish themselves as the dominant population under the conditions of an upflow reactor system. This is probably due to their reduced propensity to incorporate into sludge granules. It was also observed that in the thermophilic reactors a phenomenon of thermal coagulation of proteins restricted the mass transfer. Yet, overall it was indeed possible to digest vinasse at very high rate in UASB mesophilic reactors: conversion rates in the range of 40 to 50 kgCOD/m3.d were achieved. This very digestion rate and cponsequential high methane production rate opens the possibility of achieving an electrical energy production of more than 2 kW/m3 of reactor, with excellente economic perspectives.