The production of biogas from food waste is a good approach to the minimization of food waste and increase in the production of renewable energy. However, the use of food waste as a feedstock for biogas production currently poses a difficulty due to an ineffective hydrolysis process, which is a pretreatment procedure and the initial step of the biogas conversion process. This restriction results from the food waste polymers’ solubilization and breakdown. This has an impact on the volume of biogas produced during the methanogenesis stage. It is essential to increase the biodegradation of organic compounds (OC) during the hydrolysis process to increase biogas generation. This study focuses on the enhancement of biogas production by the anaerobic digestion (AD) of food waste (FW). FW was hydrolyzed by the immobilized biofilm and digested anaerobically in a semi-continuous digester. Four different digesters including the control were prepared. The control digester composed of no hydrolyzed food waste had no immobilized biofilm while the other three digesters had immobilized biofilm-hydrolyzed food waste with inoculum concentrations of 10%, 30%, and 50%. The results showed that the 50% digester had the highest biogas yield of about 2000 mL/500 mL. The 10%, 30%, and control digesters had a biogas yield of 1523 mL, 753 mL, and 502 mL respectively. Thus, the analysis of total volatile solid (TVS) reduction in the digesters with 10%, 30%, and 50% inoculum and the control have increased to 43.4% for the digesters with 30% and 10%, 60% for the digester with 50% inoculum, and only 29% for the control. Total chemical demand (TCOD) removal increased to 29%, 33%, 43%, and 56% for the control, and 10%, 30%, and 50%, respectively for the inoculum-to-feed ratio. From these results, the 50% inoculum-to-feed ratio has shown the highest biogas production and highest degradation based on TVS reduction and TCOD reduction. Based on this study, the biofilm pretreatment method can be considered a promising method for the enhancement of biogas volume and biodegradation. Biogas production was high (2000 mL) for hydraulic retention time (HRT = 20) days but the HRT = 15 days was also able to produce a significant amount (1400 mL) of biogas and the 50% inoculum-to-feed ratio has shown the highest volume of biogas production.

The present study shows the opportunity of using biofilm in the hydrolysis step of food waste (FW) to increase biogas production. Therefore, screened biofilm-producing microorganisms were adopted to facilitate the biodegradation of organic compounds (OCs) and enhance the volume of biogas production. The biofilm-producing microorganisms were first immobilized on a granular activated carbon (GAC) surface, and the optimum values of immobilization time, mass of the GAC surface, and size of the microbial inoculums were found using the statistical methods of one-factor-at-a-time (OFAT) and the response surface methodology (RSM) using a face-centered central composite design (FCCCD). Based on the results, 48 h of incubation, 8 g of GAC, and 1 mL of inoculum were the optimum conditions when shaken at 37 °C and 150 rpm. Different biofilm amounts (328 mg, 492 mg, 656 mg, 820 mg, and 984 mg) were used in hydrolysis flasks operated in batch mode to increase the degradation of the OCs. The optimal level of the hydrolysis degradation was on day 3 and at 328 mg of biofilm; the total solid (TS) content was decreased from 115 gL⁻¹ to 79 gL⁻¹ (31%), and the TCOD was decreased from 85.33 gL⁻¹ to 54.50 gL⁻¹ (36%).

Stevia (Rebaudiana bertoni) leave, is an ancient perennial shrub mostly found in South America in countries like Paraguay and Brazil. It contains a low-calorie sweetener, which is about 300 times sweeter than sucrose. Diabetes mellitus is among the common metabolic disorders affecting about 2.8% of the world’s population and is reported to reach 5.4% by the year 2025. In this work, insulin was successfully extracted from Rebaudiana bertoni to serve as an alternative to bovine insulin extracted from animals which is devoid of the risk of transferring infectious diseases from the animals to the diabetic patient as is the case with convectional animal-based insulin. Gas Chromatography-Mass Spectroscopy (GC-MS) and Fourier Transform InfraRed (FTIR) analysis were used to analyze and determine the functional groups available in the isolated compound and the results shows that it has retention time of 14.11 min; abundance/peak area (% PA) of 86.613 %; mass number (m/z) of 413 g/mol; molecular peak ion of 149; fragmentation patterns of 7; and C₂₀H₂₉BrO₄ as molecular formula and phthalic acid, 8-bromoctyl butyl ester as IUPAC name. The insulin was tested on three groups of rats (Rattus norvegicus) whereby the glucose level was monitored, and the result shows that the extracted insulin was found to be effective in addition to having antidiabetic effect.