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Plant-microbial fuel cells (PMFCs) are an interesting renewable energy technology that has the potential to generate clean electricity without competing with agriculture for land space. In this study, the electricity generation potential of mung beans (Vigna radiata) in a PMFC set-up with different electrode materials was explored. Three types of set-ups were prepared with five replicates each: PMFCs with stainless steel electrodes, PMFCs with graphite electrodes, and control pots without electrodes. This experimental set-up allowed for the evaluation of the better electrode material, and whether the PMFC environment harms or benefits the plants. The voltage gathered suggests that the potential difference generated in the PMFCs with differing types of electrodes were statistically the same (α = 0.05). The same can be said for power and power density, although the system with stainless steel electrodes generated more power towards the end of the experiment. It was also evident that PMFCs with stainless steel electrodes experienced prolonged time lags due to the reduced biocompatibility of stainless steel. Polarization studies showed that a single PMFC is capable of generating power densities of 0.35 mW/m2 and 0.12 mW/m2 for stainless steel and graphite systems, respectively. The increased power density of PMFCs with stainless steel indicate the lowering of internal resistance brought by the stainless steel. Plants in the PMFCs set-ups were seen to grow faster, taller, and have higher pod output than those in the control set-up. These results indicate that the PMFC technology can be implemented in agricultural land for the continuous generation of passive electricity while growing food crops, eliminating the competition between energy generation and agriculture.

Microbial fuel cells (MFCs) are a promising technology in bioelectricity production. Water systems may be utilized in producing electricity by bio-electrochemical catalytic activity of its inherent microbial culture while simultaneously treating wastewater. Current studies are focusing on design and material optimization for future up-scaling application. For large-scale application, optimization studies such as compartmentalization and stacking become important. In this study, a membrane-less microbial fuel cell is designed and optimized in terms of optimum electrode distances and optimum surface area ratios. It was found that the specific design yielded a maximum of 25.81 mV at the optimum distance wherein dissolved oxygen is sufficiently low enough in this level. Through the optimization of electrode distance was also found that the MFC designed is anode-limited with a 1:4 ratio of anode to cathode is required to produce its maximum power density output. Multiple electrodes study proves the MFC setup is stackable even without membrane separation. This paper reports the first known attempt to quantify an optimum surface area to volume ratio at 2.34 m2/m3.

Black soldier fly larvae (BSFL) are known to convert organic wastes into useful biomass, of which the composition depends on the substrate. It is of interest whether feed protein can be sustainably obtained from waste materials by feeding them to BSFL. This study aimed to convert rice straw and duck manure into BSFL biomass for conversion of waste into animal feed. The growth parameters of BSFL fed with pure fermented rice straw, pure duck manure, and an equal parts mixture of the two as well as its nutritional composition was determined. The larvae’s efficiency to consume and convert the different substrates was also evaluated. Results showed that BSFL fed with duck manure had significantly higher average individual weight of 0.0619±0.004 g, followed by mixture of duck manure and rice straw (0.0614±0.001 g), while those fed solely with rice straw did not accumulate the same biomass (0.0415±0.002 g). Correlations were also made for mass-length, mass-width, and length-width. Mass-length connection was the most reliable correlation (r = 0.732). The harvested BSFL protein was the highest for those fed with rice straw at 34.62%. Feed conversion ratio ranging from 3.71 to 11.3 was achieved for the substrates used. The availability of the waste substrate in large quantities coupled with efficient biomass conversion makes BSFL a sustainable organic matter converter primarily useful as additive to animal feed.