Influence of Hydraulic Retention Time in the Treatment of Cane Alcohol Vinasse by UASB Reactor

The influence of the hydraulic retention time (HRT) on the removal efficiency of the organic matter in a UASB reactor was evaluated. Several tests were carried out in a continuous flow, maintaining the organic load rate (OLR) at a constant value of 6 gCOD/L.d and applying several HRTs of 24, 12, 5, 3 and 1 day. The average results show that the removal of organic matter from the applied HRT is in a range of 51 to 63% in CODsoluble. The average biogas and methane production for the HRTs of 24, 12, 5, 3 and 1 day were 3.265, 5.283e, 4.196, 3.350 and 2.450 L/d and 2.905, 3.815, 3.370, 3.275 and 2.200 L/d, respectively. The yield of methane (YCH4) presented average values of 0.306 to 0.459 L/g CODremoved in the HRTs applied. The reduction of the HRT or dilution of the vinasse influenced the reduction of sulphate toxicity and increased the efficiency of its removal. These changes impede the activity of hydrolytic bacteria, reducing the total volume of biogas and indirectly the risk of an overload from an uncontrolled additional input of organic matter. Under these conditions, the OLR could still be increased, since demonstrated the ability to process more organic matter.