## 3 Results and Discussion
### AD Performance and Wastewater Treatment Efficiency
In the presented study, a specific reactor construction made it possible to achieve the same methane yield at OLRs ranging from 4 kg COD/m\({}^{3}\)-d to 6 kg COD/m\({}^{3}\)-d. In turn, [PERSON] and co-workers [47] obtained a slightly higher methane yield of 0.264 L/g COD and 91% of COD removal, but in lower OLRs from 1.3 kg COD/m\({}^{3}\)-d to 4.3 kg COD/m\({}^{3}\)-d in a hybrid reactor combining a continuous stirred tank reactor (CSTR) with an anaerobic baffled reactor (ABR) treating dairy effluent. [PERSON] and [PERSON] [48] obtained a higher methane yield and COD removal efficiency up to 0.9 L/kg COD removed and 84.4% in a two-stage system of CSTRs with a separate methanogenic stage at an OLR of 3.58-7.15 kg COD/m\({}^{3}\)-d enhanced. However, in experiments, cheese whey was co-digested with ensiled sorghum and liquid cow manure, which, according to the literature, improves the treatment process [48]. Figure 2: The efficiency of anaerobic dairy treatment in stage 1: (**a**) organic compound removal as COD with a standard deviation in experimental variants V1–V5; (**b**) COD concentration in the effluent during the experimental time (variants V1–V5). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**COD**} & \multicolumn{3}{c}{**Biogas Production**} & \multicolumn{3}{c}{**CH\({}_{4}\) Production**} \\ \cline{3-10}
**Variant** & **OLR** & \multicolumn{1}{c}{**Removal (\%)**} & \multicolumn{1}{c}{**Load Removal**} & \multicolumn{1}{c}{**(L/d)**} & \multicolumn{1}{c}{**(L/g COD\({}_{\text{high}}\))**} & \multicolumn{1}{c}{**(L/g COD\({}_{\text{memoved}}\))**} & \multicolumn{1}{c}{**(L/d)**} & \multicolumn{1}{c}{**(L/g COD\({}_{\text{label}}\))**} & \multicolumn{1}{c}{**(L/g COD\({}_{\text{memoved}}\))**} & \multicolumn{1}{c}{**VMPR**} \\  & **(G CCD/L-d)** & **Removal (\%)** & **(L/d)** & **(L/g COD\({}_{\text{high}}\))** & **(L/g COD\({}_{\text{memoved}}\))** & **(L/d)** & **(L/g COD\({}_{\text{label}}\))** & **(L/g COD\({}_{\text{memoved}}\))** & **(L/L-d)** \\ \hline
1 & 4.0 & 94.1 \(\pm\) 1.3 & 3.76 \(\pm\) 0.1 & 71.8 \(\pm\) 2.7 & 0.28 \(\pm\) 0.09 & 0.31 \(\pm\) 0.03 & 53.0 \(\pm\) 0.6 & 0.17 \(\pm\) 0.05 & 0.23 \(\pm\) 0.02 & 0.7 \(\pm\) 0.01 \\
2 & 6.0 & 93.8 \(\pm\) 0.8 & 5.63 \(\pm\) 0.1 & 112.3 \(\pm\) 1.9 & 0.24 \(\pm\) 0.05 & 0.32 \(\pm\) 0.02 & 79.6 \(\pm\) 0.8 & 0.17 \(\pm\) 0.01 & 0.23 \(\pm\) 0.01 & 1.02 \(\pm\) 0.01 \\
3 & 8.0 & 87.5 \(\pm\) 2.8 & 7.00 \(\pm\) 0.2 & 112.3 \(\pm\) 1.4 & 0.18 \(\pm\) 0.07 & 0.27 \(\pm\) 0.02 & 93.6 \(\pm\) 1.0 & 0.13 \(\pm\) 0.03 & 0.18 \(\pm\) 0.01 & 1.2 \(\pm\) 0.02 \\
4 & 10.0 & 78.9 \(\pm\) 1.4 & 7.89 \(\pm\) 0.1 & 117.0 \(\pm\) 1.3 & 0.15 \(\pm\) 0.03 & 0.24 \(\pm\) 0.02 & 101.4 \(\pm\) 1.9 & 0.11 \(\pm\) 0.09 & 0.16 \(\pm\) 0.01 & 1.3 \(\pm\) 0.03 \\
5 & 12.0 & 74.1 \(\pm\) 1.3 & 8.89 \(\pm\) 0.2 & 121.7 \(\pm\) 2.9 & 0.13 \(\pm\) 0.08 & 0.23 \(\pm\) 0.01 & 93.6 \(\pm\) 0.9 & 0.09 \(\pm\) 0.06 & 0.13 \(\pm\) 0.01 & 1.2 \(\pm\) 0.02 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Removal of organic compounds and production of biogas and CH\({}_{4}\) in stage 1. Figure 4: The efficiency of anaerobic dairy treatment in stage 1: (**a**) CH\({}_{4}\) concentration in biogas with a standard deviation in experimental variants V1–V5; (**b**) biogas and methane yield per gram of COD inlet during the experimental time (variants V1–V5). Figure 3: The efficiency of anaerobic dairy treatment in stage 1: (**a**) FOS/TAC ratio in the methanogenesis tank during the experimental time (variants V1–V5); (**b**) pH in the methanogenesis tank during the experimental time (variants V1–V5); (**c**) nutrient removal (nitrogen and phosphorus) with a standard deviation in experimental variants V1–V5. Taking into account the influence of the OLR on the course of the AL-FB, the anaerobic digestion of dairy wastewater was the most effective at OLRs ranging from 4.0 g COD/L-d to 8.0 g COD/L-d.