Biogas production in an anaerobic sequencing batch reactor by using tequila vinasses: effect of pH and temperature

Abstract

In recent years, anaerobic digestion has been recognized as a suitable alternative for tequila vinasses treatment due to its high energy recovery and chemical oxygen demand (COD) removal efficiency. However, key factors such as the lack of suitable monitoring schemes and the presence of load disturbances, which may induce unstable operating conditions in continuous systems, have limited its application at full scale. Therefore, the aim of this work was to evaluate the anaerobic sequencing batch reactor (AnSBR) configuration in order to provide a low cost and easy operation alternative for the treatment of these complex effluents. In particular, the AnSBR was evaluated under different pH-temperature combinations: 7 and 32 °C; 7 and 38 °C; 8 and 32 °C and 8 and 38 °C. Results showed that the AnSBR configuration was able to achieve high COD removal efficiencies (around 85%) for all the tested conditions, while the highest methane yield was obtained at pH 7 and 38 °C (0.29 L/g COD added). Furthermore, high robustness was found in all the AnSBR experiments. Therefore, the full-scale application of the AnSBR technology for the treatment of tequila vinasses is quite encouraging, in particular for small and medium size tequila industries that operate under seasonal conditions.

Effect of the organic loading rate on the performance and microbial populations during the anaerobic treatment of tequila vinasses in a pilot‐scale packed bed reactor

“…The PBR was fed with tequila vinasses stored in three 5000 L tanks at room temperature. The initial COD of tequila vinasses was 50 g L ‐1 but decreased gradually during storage due to natural fermentation of organic compounds, agreeing with previous studies . The natural fermentation observed during vinasses storage and the variability of organic compounds that were fed to the PBR simulates the changes in substrate composition to which full‐scale reactors are subjected, since the vinasses are commonly cooled and stored in large ponds.…”

“…This factor correlates the partial and intermediate alkalinities that are related to bicarbonate and VFAs buffer capacities and has been suggested as a parameter to evaluate the stability of anaerobic digestion processes . Even though it has been reported that successful anaerobic digestion occurs at α values below 0.3, it is clear that during the present study, the stability of the process was maintained at slightly higher values. The probable reason for this difference may be related to the titration processes, since unlike previous work where titration was performed manually, during the present work it was performed by an automated device (AnaSense ® ).…”

“…Nonetheless, such increase has also impacted the generation of the main residues produced by this industry: bagasse and vinasses. Due to the physicochemical characteristics and high production rate of tequila vinasses, approximately 10–12 L per litre of tequila, much attention has been paid to investigate suitable technologies for the treatment and valorization of this residue . According to López‐López et al, only 20% of the vinasses generated by the tequila industry are adequately treated.…”

“…Several works have evaluated the potential of methane production from different types of vinasses, such as those generated during the mezcal, winery and tequila production . Nonetheless, in the case of tequila vinasses, most studies have been carried out in lab‐scale reactors, from 0.5 to 5 L working volume . Thus, it is clear that implementation of pilot‐scale studies are needed in order to evaluate the reproducibility of lab‐scale reactors' performance and to improve the understanding and transfer of this technology.…”

“…Some of the reactor configurations that have been evaluated during the anaerobic digestion of tequila vinasses are the CSTR, AnSBR, UASB and PBR . According to Jáuregui‐Jáuregui et al ., the PBR is a promising configuration because it has demonstrated great COD removal efficiency (> 90%), even when high OLRs and starvation periods of up to 6 months are applied.…”