###### Abstract  
The growing consumption of poultry meat has spurred the development of meat-processing plants and an associated rise in wastewater generation. Anaerobic digestion is one of the preferred processes for treating such waste. The current push towards biogas upgrading and out-of-plant use necessitates new, competitive ways of heating digesters. One such alternative is to use electromagnetic microwave radiation (EMR). The aim of the study was to assessment how EMR used as a heat source impacts the anaerobic processing of high-load poultry slaughterhouse wastewater (H-LPSW) and its performance. Microwave heating (MWH) was found to boost the CH\({}_{4}\) fraction in the biogas under mesophilic conditions (35 \({}^{\circ}\)C) as long as the organic load rate (OLR) was maintained within 1.0 kgCOD/dm\({}^{3}\) d to 4.0 kgCOD/dm\({}^{3}\)-d. The best performing variant--EMR heating (55 \({}^{\circ}\)C), OLR = 3.0 kgCOD/dm\({}^{3}\)-d, HIRT = 5 days--produced 70.4 \(\pm\) 2.7% CH\({}_{4}\). High COD and TOC removal, as well as the highest biogas yields, were achieved for loadings of 1.0 gCOD/dm\({}^{3}\)-d to 4.0 gCOD/dm\({}^{3}\)-d. Effluent from the EMR-heated reactors (1.0 gCOD/dm\({}^{3}\)-d) contained, on average, 0.30 \(\pm\) 0.07 gO\({}_{2}\)/dm\({}^{3}\) at 55 \({}^{\circ}\)C and 0.38 \(\pm\) 0.10 gO\({}_{2}\)/dm\({}^{3}\) at 35 \({}^{\circ}\)C. The corresponding COD removal rates were 97.8 \(\pm\) 0.6% and 98.1 \(\pm\) 0.4%, respectively. The 5.0 gCOD/dm\({}^{3}\)-d and 6.0 gCOD/dm\({}^{3}\)-d OLR variants showed incremental decreases in performance. Based on the polymerase chain reaction results of 16S rDNA analysis, diversity of bacterial communities were mostly determined by OLR, not way of heating. a 2023133553 20231353 20  
treatment is usually used [9]. The high temperature of the processes accelerates waste degradation, improves treatment efficiency, ensures partial sanitization of the effluent, and boosts methane production [10]. This does, however, require some energy input to keep the reactor temperature within the 50-55 \({}^{\circ}\)C range [11]. To that end, efficient, effective, and energy-saving solutions are needed to provide and maintain heat in the system [12]. CHP (combined heat and power plants), common in biogas production and processing, are often used for this purpose [13]. Such plants generate both electricity (fed into the power grid) and waste heat, the latter of which can be reused to heat digesters [14]. However, operators are increasingly turning to other, competitive methods of harnessing and utilizing biogas that eliminate free heat exposure. It has been noted that it is more economically and environmentally sound to instead condition/upgrade biogas and feed it into gas pipelines and/or use it as vehicle fuel [15]. This necessitates other, competitive methods for heating anaerobic digesters to ensure stable temperatures and maintain high rates of waste biodegradation during AD. Sought-after methods should also successfully eliminate processing complications, i.e., fouling and blockage occurring when using exchangers, water jackets, or vapor injectors [16]. One such alternative is to use electromagnetic microwave radiation (EMR). This technique has been shown to be effective in studies, but requires additional validation and experimental work before it can be implemented in practical settings [17]. Microwaves (MW) are part of the electromagnetic spectrum with a wavelength ranging from 1 mm to 1 m, which corresponds to a frequency range of 300 MHz to 300 GHz [18]. MW radiation is selective, meaning that it interacts exclusively with materials characterized by specific dielectric properties [19]. In conventional heating, heat energy radiates into the material through convection and heat transfer from the surface. By contrast, MW energy is delivered directly to the material through molecular interaction with the electromagnetic field.