Banana is the most cultivated fruit plant in the world. It is produced in Latin America, Asia and Africa. India and China are the world’s largest banana producers, with almost 41% of the world’s production. This fruit reaches a total world production of 158.3 million tons per year. However, during their production cycle, the banana agroindustry produces large volumes of solid waste derived from overripe fruit. It contributes between 8–20 percent of the waste (around 100 kg of banana waste for every ton of banana produced). Therefore, the use of overripe banana waste represents a huge opportunity for bioenergy production. This work demonstrates that banana waste can be further used for power generation using a microbial fuel cell (MFC) coupled with anaerobic digestion (AD). First, the maximum methane production (MMP), methane production rate (MPR) and biochemical methane potential (BMP) were measured using an anaerobic batch bioreactor for 64 days of monitoring. Finally, the digestate generated from AD was used in the MFC to determine the polarization curve, maximum voltage, maximum power density (MPD), resistance and current. As a result, the AD generated an MMP of 320.3 mL, BMP of 373.3 mLCH₄/gVS and MPR of 18.6 mLCH₄/Lb⋅day. The MFC generated 286 mV (maximum voltage), 41.3 mW/m² (MPD), 580.99 Ω (resistance) and 0.0002867 A (current). Both processes together produced a total bioenergy of 13.38 kJ/gVS. This coupled system showed a suitable and promising use of banana waste for ecofriendly bioenergy generation. Therefore, this feedstock could be taken advantage of for generating sustainable processes and developing a circular economy in the banana agroindustry.

Cheese whey wastewater (CWW) is the major by-product of the dairy industry. CWW is produced in large quantities, has varied characteristics and is usually disposed of. The disposal of CWW causes a negative impact on the environment of different agroindustrial areas due to the physic-chemical composition that significantly increases its high organic load and nutrients. For this reason, the aim of this work was to carry out an evaluation of the anaerobic treatability of an Expanded Granular Sludge Bed (EGSB) bioreactor as a new sustainable alternative for treatment of these effluents with bioenergy production. In this study, the bioreactor was operated under stable conditions (i.e., buffer index of 0.23 ± 0.1, pH 7.22 ± 0.4 and temperature 26.6 ± 1.4 °C) for 201 days. During evaluation the hydraulic retention time (HRT) was 6 and 8 days, and it was buffered with NaHCO₃. At these conditions, the COD removal rate and biochemical methane potential (BMP) were 90, 92%; and 334, 328 mLCH₄/gCOD, respectively. The evidence found in this study highlighted that the CWW is a viable substrate to be treated in the EGSB bioreactor as long as it keeps buffered. Furthermore, the process to treat the CWW in an EGSB bioreactor can be a sustainable alternative to simultaneously solve the environmental pollution that this agro-industry confronts and produce renewable and environmentally-friendly bioenergy.

Untreated agro-industrial wastewaters are undesirable in the aquatic environment due to the presence of high organic matter contents. However, they may constitute a large potential for biogas production. The present investigation is focused on three laboratory-scale anaerobic expanded granular sludge bed (EGSB) bioreactors, continuously operated for 60 d under mesophilic condition with the aim of exploring the feasibility of treating three most significant agro-industrial wastewaters in Chiapas, Mexico (i.e., cheese whey, vinasse, and coffee-processing wastewater). The EGSB bioreactors were operated with a hydraulic retention time (HRT) of 6 d under stable conditions (i.e., buffer index (BI) of 0.31, 0.34, and 0.03), generating a maximum chemical oxygen demand (COD) removal efficiency of 91, 74, and 96% with an average methane production of 340, 245, and 300 mL/g COD∙d for cheese whey, vinasse, and coffee-processing wastewater, respectively. According to the obtained results, the EGSB bioreactors could be a sustainable alternative to simultaneously solve the environmental problems and to produce bioenergy.

The coffee processing agro-industry generates large quantities of wastewater requiring systematic treatment prior to disposal. For this reason, the aim of this study was to evaluate the hydraulic retention times (HRT) in treatment of coffee processing wastewater (CPWW) using a laboratory scale Expanded Granular Sludge Bed (EGSB) bioreactor at different HRT (3 to 9 days). The EGSB was evaluated in mesophilic condition (26 ± 2 °C) with an average pH of 7.5 ± 0.2 to determine the chemical oxygen demand (COD) removal efficiency. According to the results, the COD removal efficiency increases from 94 to 98% when the HRT increase from 3 to 9 days; the α factor remained stable (0.98) throughout the evolution of the bioreactor. The HRT´s between 7–9 days generated effluents capable to be dischargeable into water bodies with a permitted COD concentration according to World Health Organization (WHO) and Official Mexican Environmental Regulations permissible limits. Results evidenced that the HRT of 9 days was the one that greater COD removal generated, so the EGSB bioreactor can be a sustainable alternative to solve the environmental problems, compared to other conventional methods to CPWW treatment.