###### Abstract
Therefore, low VFA concentrations in the effluent results in excellent sludge retention, and consistent reactor performance, and the up-flow anaerobic sludge blanket (UASB) reactor is destined to be superior to traditional procedures [15]. As the name implies, effluent enters the UASB reactor from the bottom of the tank and travels upward through a layer of sludge blanket before being released from the top of the tank. The setup is intended to improve the interaction between the wastewater and the mixed culture sludge by lowering the up-flow velocity. Similarly, solid retention is improved because the relatively heavier solid part settles to the bottom, far from the effluent outflow at the top. This, in turn, adds to the easier granular solid formation, which is frequently associated with improved treatment efficiency. As a result, the UASB system is preferred because it promotes good settleability, can handle large biomass concentrations, provides excellent solids/liquid separation, and can operate at high loading rates [14]. To improve AD performance and enhance biogas production, many researchers suggest the introduction of trace elements in the form of nanoparticles to the AD feedstock. In anaerobic digesters, nanoparticles (NPs) enhance direct interspecies electron transfer, serving as excellent immobilization matrices and preventing the selection of resistant bacteria and genes, as well as dominating metabolic pathways of microbial communities [16]. Amongst many metallic NPs, iron NPs are excellent additives to the AD process due to their ability to lose or gain electrons, creating oxides/hydroxides on the metal surface [17; 18; 19]. The iron oxide NPs with unique properties slowly dissolve to supply the living microorganisms with the required iron ions without causing toxicity to the bacteria. The authors of [20; 21] found that the use of Fe\({}_{3}\)O\({}_{4}\) results in a 180% increase in biogas production and a 234% increase in methane production if applied in optimum anaerobic conditions. However, excess iron generates toxic free radicals for the effect of Fe\({}^{2+}\) ions on the AD of organic matter, which affects the stability and growth of the microbial community, thus, affecting methane production after the first four days. Several operating variables influence the performance of the anaerobic digestion process. These include substrate-to-inoculum ratio, carbon-to-nitrogen ratio (C:N), temperature, pH, HRT, volatile fatty acids (VFA), organic loading rate, toxicity accommodation, nutrients, volatile solids (VS), total solids (TS), and alkalinity. These operating variables are very significant in assessing the performance of the AD process and give a warning of system disturbances that may arise so that preventive measures can be performed appropriately early in the system [14]. The operating variables affecting the anaerobic process have to be properly controlled and well-designed in order to optimize the efficiency of the process, improve stability, enhance the treatment of biological wastewater, and avoid process inhibition. Hence, the one-factor-at-a-time (OFAT) method is a good choice for investigating the effect of operating variables on the AD process. Most AD studies focused on the optimization of pH, VFA, and temperature, with fewer studies on HRT and organic loading rate. Currently, the inefficiency of AD technology for the production of biogas from South Africa's wastewater is associated with varying physicochemical properties and lack of process optimization. Furthermore, the presence of biodegradable biomaterials affects performance and the quality of biogas produced from the digester. Therefore, this study investigated the biodegradation of local industrial wastewater into bioenergy using an up-flow anaerobic sludge blanket reactor operated batch-wise. The aim was to study the effect of HRT, magnetite load, and organic loading rate (OLR) on biogas production and chemical oxygen demand (COD) degradation using the OFAT method.