# Food Waste as Feedstock for Anaerobic Mono-Digestion Process
## 3 Performance Profile of Single-Stage Anaerobic Mono-Digestion Process
### Food Waste to Inoculum Ratio  
The results presented in Table 2 clearly demonstrate that the experiments reported in the literature were conducted under a wide range of FW/I ratios. [PERSON] et al. [116] pointed out that this parameter plays a vital role in the batch high-solids AD process and in the assessment of the anaerobic biodegradability of solid wastes. Furthermore, it affects its biochemical pathways and kinetics. [PERSON] et al. [111] indicated that the optimization of this parameter should be based mainly on the composition of the fermentation substrate. In turn, according to [PERSON] et al. [17], the FW/I ratio is especially important in the large-scale batch reactors used for biogas production. Hence, it can be clearly indicated that investigating the most suitable value of this parameter is necessary to provide the highest methane yield obtained during the AD process of FW. From Table 2, it can be seen that the impact of the FW/I ratio on the performance of FW mono-digestion has been considered in several studies [17; 87; 127; 128; 149] (Table 2).  
For instance, [PERSON] et al. [128] demonstrated the impact of the FW/I ratio on the performance and kinetics of the lab-scale batch AD of food waste. The process was under mesophilic conditions (35 \(\pm\) 0.5 \({}^{\circ}\)C) for 57 days. The applied FW/I ratio was equal to 0.5:1;2; 3; 4; 5; and 6 based on the VS compositions. The above-mentioned authors showed that among the applied FW/I values, the ratio equal to 1 ensured the highest average biogas yield (674.40 \(\pm\) 29.10 L/g VS). In turn, the lowest process performance (24.61 L/g VS/d) was reported for the FW/I ratio of 6. This findings confirmed the fact that the FW/I ratio is one of the key factors affecting the AD process yield. In a subsequent paper [17], it has been documented that the methane production performance for the mono-digestion process of kitchen waste (KW) conducted under mesophilic temperature (37 \({}^{\circ}\)C) and an FW/I ratio of 3.0 was 74% lower than that obtained for an FW/I ratio equal to 1.5. It has been indicated that higher values of FW/I result in more serious acidification processes and consequently, biogas production is noticed. Similar values of this parameter (1 and 3) have been applied in a following paper [127], wherein AD experiments were performed under a temperature of 37 \({}^{\circ}\)C. An interesting finding presented in the above-mentioned study demonstrated that for the processes conducted under an FW/I of 3, the methane production was suppressed by itself. With regard to thermophilic conditions, the effect of FW/I on the biogas yield for the AD process of FW was presented in [149]. The investigations were conducted under various values of the FW/I: 1.6; 3.1; 4.0; and 5.0. In the above-mentioned paper, the highest values of the biogas yield (0.784 L/g VS) and methane yield (0.518 L/g VS) have been reported for the studies performed under an FW/I of 4. Increasing the FW/I to 5 resulted in a significant decrease in the process performance. The above-mentioned authors have pointed out that this finding can be attributed to the inhibition of methanogenic bacteria that occurred under an FW/I of 5.  
To sum up, the results discussed above may be useful for selecting the most suitable FW/I ratio for the single-stage anaerobic mono-digestion process of FW.