## 3 Results
### Toxicity of the PAM and its Possible Degradation under Anaerobic Conditions
#### 3.1.2 PAM Biodegradability  
PAM biodegradability was tested by adding different concentrations of the PAM to digested sludge (inoculum) with subsequent anaerobic incubation of the mixtures (series B). The results are presented in Figure 1b and Table 2.  
Increasing the PAMt amount resulted in a decreased specific methane yield per flocculant VS (Figure 1b). This was an indication that the PAM organic matter was not degraded directly to methane. However, signs of partial degradation of PAM were found. Formation of VFA, primarily acetate, was observed in all samples. The acids were mainly produced in the course of degradation of organic matter of the digested sludge used as the inoculum. A certain amount of the organic acids resulted from PAM degradation, as was indicated by increased amounts of acetate produced in the samples with higher PAM concentrations. Higher concentrations of ammonium nitrogen were observed in the flocculant-containing samples by the end of the experiment. Ammonium nitrogen could be released during the  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{
\begin{tabular}{c} **Day of** \\ **Incubation** \\ \end{tabular} } & \multicolumn{4}{c}{**Volatile Fatty Acids Concentration**} & \multicolumn{2}{c}{**Ammonium**} & \multicolumn{2}{c}{**Methane**} \\ \cline{3-8}  & & **Acetate,** & **Promionate,** & **Butyrate,** & **Total VFA,** & **Concentration,** & **Content in** & **Chiot in** & **Yield, mL** \\ \hline \multirow{4}{*}{Control} & 0 & 0.121 & 0.009 & 0.008 & 0.01 & 35.2 & 0 & 0 \\  & 6 & 0.175 & 0.011 & 0.032 & 0.01 & 72.1 & 67.54 & 8.53 \\  & 22 & 0.203 & 0.240 & 0.012 & 0.03 & – & 68.77 & 17.25 \\  & 42 & 0.176 & 0.042 & 0.015 & 0.01 & 95.8 & 37.33 & 20.54 \\ \hline \multirow{4}{*}{B-5} & 0 & 0.121 & 0.009 & 0.008 & 0.01 & 35.2 & 0 & 0 \\  & 6 & 0.169 & 0.021 & 0.032 & 0.01 & 92.3 & 66.10 & 8.58 \\  & 22 & 0.351 & 0.062 & 0.054 & 0.03 & – & 69.79 & 16.57 \\  & 42 & 0.224 & 0.009 & 0.013 & 0.01 & 104.5 & 37.67 & 19.95 \\ \hline \multirow{4}{*}{B-40} & 0 & 0.121 & 0.009 & 0.008 & 0.01 & 35.2 & 0 & 0 \\  & 6 & 0.142 & 0.047 & 0.014 & 0.01 & 55.1 & 64.14 & 7.01 \\  & 22 & 0.429 & 0.015 & 0.042 & 0.03 & – & 68.05 & 14.57 \\  & 42 & 0.154 & 0.011 & 0.008 & 0.01 & 106.1 & 38.12 & 17.67 \\ \hline \multirow{4}{*}{B-80} & 0 & 0.121 & 0.009 & 0.008 & 0.01 & 35.2 & 0 & 0 \\  & 6 & 0.179 & 0.116 & 0.019 & 0.02 & 83.2 & 66.09 & 7.6 \\  & 22 & 0.556 & 0.018 & 0.037 & 0.04 & – & 68.98 & 14.87 \\  & 42 & 0.171 & 0.020 & 0.007 & 0.01 & 109.4 & 35.84 & 17.81 \\ \hline \multirow{4}{*}{B-200} & 0 & 0.121 & 0.009 & 0.008 & 0.01 & 35.2 & 0 & 0 \\  & 6 & 0.803 & 0.327 & 0.078 & 0.08 & 112.1 & 67.96 & 8.74 \\  & 22 & 0.158 & 0.020 & 0.047 & 0.01 & – & 66.45 & 17.97 \\  & 42 & 0.128 & 0.011 & 0.013 & 0.01 & 127.1 & 38.05 & 21.24 \\ \hline \multirow{4}{*}{B-400} & 0 & 0.121 & 0.009 & 0.008 & 0.01 & 35.2 & 0 & 0 \\  & 6 & 1.221 & 0.313 & 0.071 & 0.09 & 125.3 & 50.99 & 5.15 \\ \cline{1-1}  & 22 & 0.689 & 0.362 & 0.029 & 0.07 & – & 74.84 & 15.65 \\ \cline{1-1}  & 42 & 0.141 & 0.078 & 0.009 & 0.01 & 137.4 & 23.71 & 19.67 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Characteristics of the process in the course of batch incubation of the mixture of digested sludge with different concentrations of the polyacrylamide flocculant as a substrate.  
cleavage of nitrogen-containing groups of PAM molecules. H2 concentration in the gas phase did not exceed 0.044%.  
A correlation was observed between the size of the floccules formed in the presence of PAM and the flocculant concentration: larger floccules were formed at higher flocculant concentrations. Gradual floccules decomposition was observed in the course of the experiment, which led to an acceleration of the processes of microbial decomposition of VS during the experiment.