Methane production in a UASB reactor from sugarcane vinasse: shutdown or exchanging substrate for molasses during the off-season?

Operational strategies to maintain the potential for organic matter removal and methane production were applied to a pilot scale UASB reactor fed by vinasse. The beginning of the research took place after interrupting the system feeding for 5 weeks. Three consecutive phases were carried out. In Phase I, the UASB's restart with vinasse was studied; in Phase II, sugarcane molasses was used to replace vinasse; and in Phase III, resuming the vinasse operation was evaluated. In the whole experiment, the reactor maintained values close to 80% of COD removal efficiency. Phase I presented productivity and methane yield reaching 10.24 L CH4·L−1·day−1 and 0.40 L CH4·g−1 CODr, indicating the system's recovery capacity after shutdown. Exchanging vinasse for molasses (Phase II) caused a reduction of 69.7% in methane production, which was 3.10 L CH4·L−1·day−1. After resuming vinasse feeding (Phase III), the methane production was 1.19 L CH4·L−1·day−1. The results led us to conclude that after a period of feeding interruption, the reactor start-up procedure was more adequate than the strategy of replacing vinasse with molasses to maintain methane production.