BACKGROUND
The aim of the present research was to provide a strategy for the start‐up of upflow anaerobic sludge blanket (UASB) reactors treating sugar cane vinasse, with emphasis on the relevant sulfur compounds along the reactor height. To this end, a laboratory‐scale UASB reactor was started up and its performance under the applied conditions was studied.

RESULTS
Biomass was able to assimilate organic loading rates from 3 to 10 kg chemical oxygen demand (COD) mR−3 d−1, reducing VFAs accumulation, while increasing biogas production rate (BPR) from 0.92 to 4.12 m3 mR−3 d−1. The COD and sulfate (SO42−) were mainly removed in the reactor bed, showing homogenous distribution in the blanket and settler zones. However, from bottom to top of the reactor, a slight decrease of total and free sulfide concentrations was observed, indicating that the sludge bed in the UASB reactor was exposed to H2S concentrations higher than those measured in the reactor effluent.

CONCLUSIONS
During 54 days, the development of macroscopic granules, the COD removal efficiency, the BPR and the CH4 content proved good indicators to monitor the start‐up period. Further research will be needed for strategy validation in pilot and full‐scale UASB reactors treating vinasse.@en

BACKGROUND: Microbial community dynamics during the anaerobic digestion of vinasse has been little studied. However, having knowledge about it is essential for early detection of reactor operational difficulties to apply preventive actions. This research studies the microbial community dynamics in the anaerobic digestion of vinasse, linking to experimental observations about product yields and organic matter degradation. RESULTS: Methane and sulfide yields decreased with increasing SO₄ ^2-/COD ratio, while the fraction of organic matter degraded by sulfate reducing bacteria increased from 4.5 ± 0.3% to 27.1 ± 0.6%. The archaeal community showed that acetoclastic Methanosaetaceae were little affected by the increase of the SO₄ ^2-/COD ratio, in contrast to the Methanomicrobiales and Methanobacteriales population, which decreased during the experiment. The total bacterial diversity was influenced mainly by substrate composition, showing that the increase of the SO₄ ^2-/COD ratio above 0.10 shifted the bacterial community to a lower richness. CONCLUSION: These results provide knowledge on the dynamics of the microbial communities, which can be useful to control the anaerobic digestion of sulfate-rich vinasses, showing that reactor stability equates to the higher ratios between total methanogens and total bacteria gene copy numbers, whereas operational difficulties can be associated to lower bacterial richness and higher community organization.

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The treatment of vinasse in lagoons causes methane emissions during the anaerobic decomposition of the organic matter. The recovery of this methane, to produce renewable energy in anaerobic digestion power plants (ADPPs) replacing fossil fuels and reducing greenhouse gas emission, could bring environmental benefits. The aims of this work were: (1) to compare alternatives of ADPPs available for the treatment of vinasse; and (2) to evaluate the impacts of ADPPs as alternative for lagooning Cuban vinasse; both by means of Life Cycle Assessment (LCA) and exergy analysis (EA). The LCA and EA showed that the ADPPs improve the environmental profile with respect to the lagooning of vinasse, reducing up to 77% the total score and recovering up to 46% of the exergy extracted from the natural environment during the process, respectively. The highest environmental benefits for the ADPPs were observed when the subprocesses biogas production from raw vinasse, sulfide removal by biooxidation with air oxygen addition and energy generation in spark ignition engines were used. In that case, the treatment of 1072 ton of vinasse (exergy content of 740.6 GJ_ex) can produce 175 GJ_ex as "electricity and heat", 191 GJ_ex as "wastewater for fertirrigation", 21.7 GJ_ex as "digestate", and 0.41 GJ_ex as "sulfur in the filter cake". This way, the produced 1.3 million cubic meters of vinasse (1.34·10⁶ ton/year) reported by the Cuban Ministry of the Cane Sugar Industry can replace 485263 GJ_ex per year as energy and bio-fertilizers, reducing the negative environmental impacts for the studied categories.

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