###### Abstract  
Biogas production from wastewater as a function to curb waste and provide energy security has gained worldwide attention. Ensuring the stability of anaerobic digestion (AD) of physiochemical and biological complexity necessitates optimization. In this study, a central composite design (CCD) from a response surface methodology (RSM) was employed to evaluate and optimize the effects of bio-stimulation of banana peels coupled with magnetite on the anaerobic digestion of wastewater to produce biogas. An experimental matrix of 14 runs using the CCD, with two factors (nanoparticle and biochar load) as a function of pH, biogas production, and COD removal by the AD process was operated at a constant mesophilic temperature (37 \({}^{\circ}\)C) for 28 days. The analysis of variance (ANOVA) showed that the quadratic models attained were significant (\(p\)-values \(<\) 0.05) with a high coefficient of determination (R\({}^{2}\)) values closer to 1. The optimized conditions, including nanoparticle (0.46 g) and biochar (0.66 mgVS/L), resulted in biogas production (19.26 mL/day), pH (7.07), and COD removal (75.17%). This suggests 100% desirability at a 95% confidence level. This finding depicts the trade-off between biogas productivity, biodegradability, and stability of the AD process established for future consideration of using nanoparticles as bio-stimulant. a pacs: 12.20.-q, 12.20.-r, 12.  
their ability to release metallic nutrients for anaerobic microorganisms, nano-sized irons, as well as their oxides and other composites, are the most widely used nano-additives for optimizing the performance of an anaerobic digester for wastewater with a low to medium biodegradability index [7; 10; 11; 12; 13]. Food waste accounts for a large component of municipal solid waste, with almost 1.3 billion tons of food waste created globally each year [13]. It is anticipated that this amount will rise much more in the coming years. As a result of its heavy consumption, fruit waste, such as peels and seeds, is generated. The disposal of these wastes has become an issue globally [14]. For example, banana peels are usually thrown instead of being consumed by livestock. This has led to their conversion into biochar for other useful purposes [15; 16]. Biochar, a precursor to activated carbon, is a solid carbonaceous material formed when biomass is thermochemically converted in an oxygen-depleted environment [17]. Numerous wastes, including agricultural wastes such as fruit and vegetable wastes [18], animal manure [19], wood [20], and sewage sludge [21], can be used as feedstocks for biogas production. Since the effects of iron nanoparticles (magnetic) and biochar have been documented independently, examining the synergetic effect of iron nanoparticles and biochar generated from a banana peel as an AD bio-stimulator comes in handy. The major mechanisms underlying biochar's efficacy are its favourable physicochemical properties, such as a high cations exchange capacity, large porosity, and surface area, which enable surface complexation for the interaction with nutrient cycles, mineral precipitation for immobilization or adsorption, and modified symbiotic relationships between microbial communities [22; 23]. Thus, biochar supplementation is an alternate strategy for enhancing the metabolic activity of anaerobic microbes involved in the AD process [24; 25]. Studies have shown that biochar could significantly reduce the lag phase, increase methane production, and relieve inhibitor stress during the AD process [26; 27; 28]. As a result, an attempt to optimize biochemical processes in maximizing efficiency eludes the principles of the third rule of thermodynamics. In the biotechnology sector, process optimization for industrial operations has shown a significant impact on maximizing finished products. In this case, an increase in biogas production and quality (methane content increment and CO2 reduction) involves complex biological and physiochemical reactions [29; 30].