## 4 Discussion
This is in line with our own findings, as we also observed diminishing treatment performance as the OLR increased from 1.0 to 6.0 gCOD/dm\({}^{3}\cdot\)d. [PERSON] et al. [53] further demonstrated biogas yields of approx. 5.0 dm\({}^{3}\)/day and methane yields of 0.38 dm\({}^{3}\)/gCOD\({}_{\rm introduced}\) at OLR = 10 gCOD/dm\({}^{3}\cdot\)d. Again, these results are close to those obtained in our study, where OLR \(\approx\) 4.0 gCOD/dm\({}^{3}\cdot\)d led to biogas yields of 4.56 \(\pm\) 0.57 dm\({}^{3}\)/day to 5.01 \(\pm\) 0.54 dm\({}^{3}\)/day, with CH\({}_{4}\) production of approx. 0.26 dm\({}^{3}\)/gCOD\({}_{\rm introduced}\). [PERSON] and [PERSON] [54] tested a packed UASB reactor, reaching 95% COD removal at OLR = 7 gCOD/dm\({}^{3}\cdot\)d and HRT 10 h. Similar TOC removal rates were achieved in the present study, but only at lower OLRs (1.0 gCOD/dm\({}^{3}\cdot\)d to 4.0 gCOD/dm\({}^{3}\cdot\)d). Increasing OLR to 5-6 gCOD/dm\({}^{3}\cdot\)d significantly diminished TOC biodegradation. [PERSON] et al. [55] set out to optimize PSW treatment in a UASB reactor. The highest pollutant removal performance was achieved at 35 \({}^{\circ}\)C, HRT 15 h, OLR 3.5 gCOD/dm\({}^{3}\cdot\)d, and pH 7. The biogas output was 0.46 dm\({}^{3}\)/gCOD with a COD removal rate of 80%. Similar parameters were achieved with ACSTR in the present study at loadings of 1-4 gCOD/dm\({}^{3}\cdot\)d.  
These examples clearly show that studies on poultry slaughterhouse wastewater treatment focus primarily on UASB reactors. However, it is important to note that such reactors require that the wastewater be efficiently pretreated via filtration, flotation, and/or coagulation to remove lipids, suspended solids, and protein [56]. The waste fed into the reactor is thus clear of suspended solids, with most of the COD being dissolved [57]. This conditioning enables high OLRs and short HRTs while maintaining high treatment performance [58]. The drawback, however, is that the pretreatment process generates additional investment and operating costs, while also limiting the volume of organic feedstock used for biogas production [59]. This is why we chose to use the ACSTR design instead for our study. Anaerobic treatment of slaughterhouse waste carries a number of technological challenges, such as the high nitrogen content. Degradation of nitrogen during hydrolysis and subsequent acidogenesis can release free (un-ionized) NH\({}_{3}\)-N and ionized ammonia N (NH\({}_{4}\)-N). Inhibition of AD is related to the levels of these nitrogen species [60]. High levels of total ammonia (NH\({}_{3}\) and NH\({}_{4}\)+), toxic and inhibitory to bacteria, are observed during anaerobic digestion of slaughterhouse wastewater [61, 62]. Another problem is the production of sulfides and odors (H\({}_{2}\)S) during biodegradation of proteins [63]. Furthermore, the presence of sulfur allows sulfate-reducing bacteria to divert electron equivalents from CH\({}_{4}\)-forming pathways to H\({}_{2}\)S-forming pathways. Approx. 0.7 dm\({}^{3}\) CH\({}_{4}\) of methane is consumed for each gram of H\({}_{2}\)S produced [64]. The present study aimed to investigate the effect of electromagnetic microwave radiation on the performance of anaerobic treatment and digestion of H-LPSW. It was based on and inspired by studies demonstrating that MW improve wastewater treatment in aerobic [65] and anaerobic biofilters [66], and can also boost biogas yields [17]. However, the benefits of microwaves have mostly been touted in the context of pretreatment and hydrothermal depolymerization of various organic matter prior to waste-to-energy processing [67; 68]. MW disintegration has been shown to improve anaerobic digestion of plant biomass [69], microalgae [70], sludge [71], and organic fraction of municipal waste [72]. On the other hand, there is a dearth of research on MW as a way to heat anaerobic continuous stirred-tank reactors (ACSTRs) [21; 73].