# Efficiency of Chemical Toilet Sewage (CTS) Co-Fermentation with Typical Energy Crops
## 3 Results
### Toxicity and Bacterial Community  
CTS contains biocides, toxic substances, bioinhibitory chemicals, and hard-to-degrade substances [33]. For these reason, it can negatively affect the structure and activity of anaerobic bacteria communities [34]. The toxicity of the tested feedstock composition rose proportionally to the CTS% in the dilution fluid. V1 (maize silage only) was found to be non-toxic. However, the CTS doses in V1 (10%) and V2 (20%) gave rise to some toxicity, which was statistically comparable at 2.4 \(\pm\) 0.3% and 3.3 \(\pm\) 1.6%, respectively. Significantly (\(p\) = 0.05) higher rates of 17.1 \(\pm\) 3.2% were found for V4 (30% CTS), followed by another statistically significant increase for V5 (40% CTS) at 32.4 \(\pm\) 7.1. V6 (50% CTS) and V7 (60% CTS) fared even worse, with toxicity rising to almost 50%. AD significantly reduced the toxicity rates, with complete detoxification in variants V1 to V4 (no toxicity in the digestate). In V5, it was markedly reduced to 4.9 \(\pm\) 0.8%. V6 and V7 digestates remained relatively toxic, with rates of 20.7 \(\pm\) 2.7% and 28.2 \(\pm\) 3.3%, respectively. A very strong positive correlation was noted between the CTS dose and the toxicity of the feedstock (R\({}^{2}\) = 0.9303), but not the digestate (R\({}^{2}\) = 0.7335) (Figure 2a). There was also a clear direct linear relationship between the toxicity of the AD feedstock and the output of gas metabolites. A particularly pronounced negative correlation was found for CH\({}_{4}\) (R\({}^{2}\) = 0.9423), with a slightly weaker one for biogas (R\({}^{2}\) = 0.8497) (Figure 2b). According to [PERSON] et al. (2022) [35], the toxic shock caused by the transfer of biocide-contaminated fecal sludge (FS) from chemical toilets to conventional wastewater treatment plants (WWTP) can pose a serious problem for activated sludge processing. The researchers argue that new environmental approaches need to be developed to mitigate biocide toxicity so as to prevent biocides from impairing WWTP performance [35]. [PERSON] et al. (2021) [29; 34] found that the deactivation of toxic biocidal agents (BA) in fecal sludge (FS) from chemical toilets resulted in a considerable improvement of AD performance, with several-fold increases in biogas yields [29; 34]. Figure 1: Biogas and methane production vs. CTS% in the feedstock. The contribution of basic taxonomic groups in the anaerobic bacterial community is shown in Table 5. The microbial communities consisted primarily of bacteria (EUB338), with proportions thereof falling within the narrow range of 68 \(\pm\) 5% in V5 (40% CTS) to 71 \(\pm\) 3% in V3 (20% CTS) (Table 5). No relationship was found between the CTS dose in the feedstock mixture and the share of bacteria in the anaerobic microbe community. A strong negative correlation (R\({}^{2}\) = 0.8991) was found between the CTS dose and the share of Archaea (ARC915) in the anaerobic microbe community (Figure 3a). In variants V1 (0% CTS) to V3 (20% CTS), this share ranged from 24 \(\pm\) 2% to 27 \(\pm\) 2% (Table 5). Significantly lower rates were recorded for V3 and V4 at 19 \(\pm\) 1% and 17 \(\pm\) 2%, respectively. Archaea (ARC915) were statistically the least numerous in V6--12 \(\pm\) 3% and V7--13 \(\pm\) 3% (Table 5). Similar trends in bacterial community structure were found for _Methanosarcinaceae_ (MSMX860) and _Methanoseta_ (MX825). As the CTS input increased, the contribution of methanogenic bacteria in the community consistently decreased. For _Methanosarcinaceae_ (MSMX860), it was between 12 \(\pm\) 1% and 13 \(\pm\) 3% in V1-V3, falling to between 10 \(\pm\) 1% and 11 \(\pm\) 2% in V4-V5, and finally to 9 \(\pm\) 2% in V6-V7 (Table 5). The coefficient of determination