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A large amount of fruit waste is being a great environmental and social problem due to a lack of adequate storage. Among the most abundant waste is papaya, due to its high consumption in various varieties. These wastes can generate bioelectricity through organic waste, being an important parameter the pH. In this research, low-cost laboratory-scale microbial fuel cells were fabricated, using papaya waste as fuel at different pH (4, 5.73, 7, and 9) to obtain the optimum operating pH. It was possible to observe the maximum values ​​of electric current and voltage of 17.97 mA and 1.02 V on days 16 and 14, in the cell with pH 7; while the cell with pH was the one that showed the lowest values. The electrical conductivity values ​​increased from the first day, observing a maximum peak of 172.50 mS/cm for the cell with pH 7. However, the internal resistance values ​​were low, the maximum value being for the cell with pH 4 (234.61 ± 34 Ω) and the minimum for the cell with pH 7 (46.543 ± 3.6 Ω). In the same way, the maximum power density was for the cell with pH 7 of approximately 645.74 ± 33.64 mW/cm2 and a current density of 5.42 A/cm2.

The effluents generated by the tannery industry have a high content of chromium and other toxic elements, representing a potential threat to ecosystems. An eco-friendly alternative to treat these effluents is the use of microorganisms, such as fungi, with the capacity to biosorb heavy metals. The present work aims to determine the effect of the molasses concentration, pH variation, and time on the removal of total chromium using the filamentous fungus Trichoderma spp. An experimental design was adopted using pH (4 and 6), concentrations of molasses (0.5 and 1%), and time (8 and 12 days) as independent variables. The Trichoderma inoculum was constant in all the treatments. The different treatments were evaluated after 0, 8, and 12 days by taking 50 mL of sample from each bioreactor. The chromium concentration was subsequently determined in each sample. The results show that treatment 3 (1% molasses and pH 4) showed higher chromium removal after both 8 and 12 days. The concentrations of total chromium decreased from 665 mg/mL to values of 568 mg/mL by day 8 and 486 mg/mL by day 12. These values are, however, still above the maximum threshold imposed by Peruvian law regarding the discharge of non-domestic effluents into the sewage system. The results show that Trichoderma spp. can increasingly remove chromium from the effluent with longer incubation periods. However, future studies are necessary to determine the mechanisms of chromium biosorption by the fungus and the influence of other physicochemical parameters.

This research aimed to use kiwi waste as fuel to generate bioelectricity through microbial fuel cells. It was possible to generate an electrical current and voltage peaks of 3.807 ± 0.102 mA and 0.993 ± 0.061 V on day 11, showing an electrical conductivity of 189.82 ± 3.029 mS/cm and an optimum operating pH of 5.966 ± 0.121. The internal resistance of the cells was calculated using Ohm’s Law, resulting in a value of 14.957 ± 0.394 Ω, while the maximum power density was 212.68 ± 26.84 mW/m2 at a current density of 4.506 A/cm2. Through the analysis of the FTIR spectra carried out on the substrate, a decrease in the characteristic organic peaks was observed due to their decomposition during the electricity-generation process. In addition, it was possible to molecularly identify the bacteria Comamonas testosteroni, Sphingobacterium sp., and Stenotropho-monas maltophila adhered to the anodized biofilm. Finally, the capacity of this residue to generate bioelectricity was demonstrated by lighting an LED bulb with a voltage of 2.85 V.

The biosorption of arsenic (As) with macroalgae has aroused much interest as a clean and low-cost technology. To evaluate arsenic biosorption by Chondracanthus chamissoi and Cladophora sp., approximately 5 kg of algae was collected from Huanchaco’s beach and Sausacocha lake (Huamachuco), La Libertad. As biosorption was carried out in four column systems, with 2 g of algae pellets each, circulating As solutions of 0.25 and 1.25 ppm, respectively, at 300 mL/min cm2. As concentration was determined at 3 and 6 h of treatment by flame atomic absorption spectrophotometry. Data were analyzed using Student’s t-test with 95% confidence. At 6 h, Chondracanthus chamissoi presented an As biosorption of 95.76% in a 0.25 ppm mg/L solution and 85.33% in a 1.25 mg/L solution. Cladophora sp., at 6 h, presented an As biosorption of 95.76% in a 0.25 mg/L solution and 42.03% in a 1.25 mg/L solution. It was concluded that Chondracanthus chamissoi achieves higher percentages of biosorption than Cladophora sp. in solutions of 1.25 mg/L As (p < 0.05), and that there is no significant difference between the biosorption percentages of Chondracanthus chamissoi and Cladophora sp. in a 0.25 mg/L solution of As at 6 h of treatment (p > 0.05).