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Tapioca is a starch extracted from cassava and is one of the most important products of the secondary food industry in developing countries such as Indonesia. However, the processing of cassava to extract tapioca generates nutrient-rich wastewater. In this paper, the bioelectricity and biomass production from microalgae Spirulina platensis within a hybrid Microalgae-Microbial fuel cell to reduce the chemical oxygen demand in wastewater from home-made tapioca industry is investigated. Native microbes in tapioca wastewater are used as inoculum in the anode chamber to generate electrons, while Spirulina culture in cathode chamber produces oxygen for the Oxygen Reduction Reaction. Cheap graphite rods, singlet or doubled, are used as electrodes and the influence of dark/light period is also studied. The experimental results show that the device generates electricity up to 14.47 ± 0.7 mW·m−2 when doubled graphite rods are adopted, the membrane surface area is 2.85 cm2, and dark/light cycle is 0:24. The chemical oxygen demand removal is 67% in this configuration, while the average productivity of Spirulina is approximately 55.38 ± 6.39 mg·L−1·day−1, with average growth rate constant of 0.172 ± 0.015 day−1. The proposed systems for tapioca wastewater treatment provides an encouraging way to reduce treatment costs, to generate renewable bioelectricity and to produce useful microalgae biomass. [ABSTRACT FROM AUTHOR]

In this work, microalgae–microbial fuel cell (MMFC) was used as an alternative method to treat cafeteria waste in Indonesia to produce electricity and microalgal biomass simultaneously. The organic contents from cafeteria waste were used as substrates by Saccharomyces cerevisiae. Spirulina platensis acted as an oxygen producer for oxygen reduction reaction on the cathode side. A salt bridge was used as a separator and ion exchanger. Yeast (Saccharomyces cerevisiae) was used as an anode biocatalyst because of its availability, resistance to extreme weather, and ease of culture and incubation. A voltage of 0.17 V and current density of 400 mA m−2 were obtained using the MMFC system. Meanwhile, the power density and maximum power density (MPD) reached 73 and 98 mW m−2, respectively. The MMFC systems can easily reduce the chemical oxygen demand to 60% and the total dissolved solid to 82.83%. Meanwhile, the microalgae growing on the cathode side reached 0.74 g L−1 by utilizing CO 2 from the anode side. The MPD of the MMFC system was 2.38 folds higher than that of the MFC system (without microalgae) and 1.58 times higher than that of the MMFC system that used a commercial membrane. These advantages make the MMFC system for cafeteria waste highly suitable for use in countries with large populations or developing countries. ● Cafeteria wastewater was used as substrate for electricity generation ● The highest maximum power output was 98 mW m2. ● The dry weight of Spirulina platensis achieved 0.74 g L−1. ● MMFC system had ability to remove COD from cafeteria wastewater up to 60% [ABSTRACT FROM AUTHOR]

A Plant Microbial Fuel Cell (Plant-MFCs) has been studied both in the lab and in a field. So far, field studies were limited to a more conventional Plant-MFC design, which submerges the anode in the soil and places the cathode above the soil surface. However, for a large scale application a tubular Plant-MFC is considered more practical since it needs no topsoil excavation. In this study, 1 m length tubular design Plant-MFC was installed in triplicate in a paddy field located in West Kalimantan, Indonesia. The Plant-MFC reactors were operated for four growing seasons. The rice paddy was grown in a standard cultivation process without any additional treatment due to the reactor instalation. An online data acquisition using LoRa technology was developed to investigate the performance of the tubular Plant-MFC over the final whole rice paddy growing season. Overall, the four crop seasons, the Plant-MFC installation did not show a complete detrimental negative effect on rice paddy growth. Based on continuous data analysis during the fourth crop season, a continuous electricity generation was achieved during a wet period in the crop season. Electricity generation dynamics were observed before, during and after the wet periods that were explained by paddy field management. A maximum daily average density from the triplicate Plant-MFCs reached 9.6 mW/m 2 plant growth area. In one crop season, 9.5-15 Wh/m 2 electricity can be continuously generated at an average of 0.4 ± 0.1 mW per meter tube. The Plant-MFC also shows a potential to be used as a bio sensor, e.g., rain event indicator, during a dry period between the crop seasons.