## 2 Microplastics and Microfibres in WWTPs
### Analytical Methods Used to Analyse MPs from Wastewater and Sludge Samples  
Different factors, such as the sampling method, pretreatment process and detection techniques, can affect the analysis and quantification of MPs and microfibres from wastewater and sludge samples. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Dry Sludge Generated**} & \multicolumn{2}{c}{**Dry Sludge**} & \multicolumn{2}{c}{**Number of MPFs per**} & \multicolumn{1}{c}{**References**} \\  & **per Day (kg)** & **(MPs/g)** & **\% MFFs** & **(MPFs/g)** & **Day Retained in Sludge** & **References** \\ \hline \multirow{3}{*}{Germany} & 1.2 \(\times\) 10\({}^{3}\) & 12.5 & - & - & - & [86] \\ \cline{2-7}  & 2.9 \(\times\) 10\({}^{11}\) & 495 & 46 & 227.7 & 6.7 \(\times\) 10\({}^{13}\) & [156] \\ \cline{2-7}  & 3.5 \(\times\) 10\({}^{7}\)b & 0.20 b & 19.9 & 0.04 b & 7 \(\times\) 10\({}^{6}\) & [157] \\ \hline \multirow{3}{*}{Iran} & - & W1: 6.57 & W1: 55.1 & W1: 3.62 & \multirow{3}{*}{-} & [92] \\  & & W2: 5.57 & W2: 44.2 & W2: 2.46 & & [92] \\ \cline{2-7}  & 1.4 \(\times\) 10\({}^{4}\) & 129 & 87.5 & 112.9 & 1.6 \(\times\) 10\({}^{9}\) & [158] \\ \hline \multirow{2}{*}{Ireland} & - & 8.51 a (4.20–15.39) & 75.8 & 6.45 & - & [58] \\ \cline{2-7}  & 3.7 \(\times\) 10\({}^{4}\) & 112.8 & 47.25 & 53.3 & 1.6 \(\times\) 10\({}^{9}\) & [95] \\ \cline{2-7}  & 3.4 \(\times\) 10\({}^{3}\) & 4.74 & 20 & 0.95 & 3.3 \(\times\) 10\({}^{6}\) & [96] \\ \hline \multirow{3}{*}{Korea} & W1: 2.0 \(\times\) 10\({}^{4}\) & W1: 14.90 & W1: 24.2 & W1: 3.61 & W1: 7.3 \(\times\) 10\({}^{7}\) & \\  & W2: 6.1 \(\times\) 10\({}^{4}\) & W2: 9.66 & W2: 47.2 & W2: 4.56 & W2: 2.8 \(\times\) 10\({}^{8}\) & [97] \\ \cline{2-7}  & W3: 5.6 \(\times\) 10\({}^{4}\) & W3: 13.20 & W3: 45.8 & W3: 6.04 & W3: 3.4 \(\times\) 10\({}^{8}\) & \\ \hline \multirow{3}{*}{Netherlands} & - & W1: 0.66 & \multirow{3}{*}{-} & \multirow{3}{*}{-} & \multirow{3}{*}{-} & \multirow{3}{*}{[99]} \\  & - & W2: 0.51 & & & & \\  & W7: 0.76 & & & & & \\ \hline \multirow{2}{*}{Norway} & 3.47 \(\times\) 10\({}^{4}\) & 6.08 a (3.5 \(\times\) 10\({}^{3}\)–1.05 \(\times\) 10\({}^{5}\)) & (1.70-19.84) & 28.9 & 1.76 & 6.1 \(\times\) 10\({}^{7}\) & [124] \\ \hline \multirow{2}{*}{Poland} & - & 31.3 a (6.7–62.6) & 85 & 26.59 & - & [100] \\ \hline \multirow{2}{*}{Scotland} & - & 2 & - & - & - & [52] \\ \cline{2-7}  & - & 112 & 94 & 105.6 & - & [105] \\ \cline{2-7}  & 1.9 \(\times\) 10\({}^{4}\) & 165 & 84 & 138.6 & 2.6 \(\times\) 10\({}^{9}\) & [107] \\ \cline{2-7}  & - & 50.1 & 15 & 7.52 & - & [159] \\ \hline \multirow{2}{*}{Sweden} & 8.0 \(\times\) 10\({}^{3}\) & 1401 & - & - & - & [111] \\ \cline{2-7}  & - & 16.7 & 72.5 & 12.1 & - & [112] \\ \hline Thailand & - & 103.4 & 32.2 & 33.3 & - & [113] \\ \hline \multirow{2}{*}{UK} & 3.06 \(\times\) 10\({}^{6}\) & 3408 a (30–10,380) & - & - & - & [116] \\ \hline \multirow{2}{*}{USA} & 1.09 \(\times\) 10\({}^{6}\) & 1 & - & - & - & [122] \\ \hline \end{tabular}  
* Data obtained from the average values of different WWTPs (W \(\geq\) 6) analysed in the study (MPs/g) and (MPFs/g) are shown as the mean value, whereas in parentheses the minimum and maximum values found are reported. b Values are expressed in L\({}^{-1}\). Parts A and B correspond to two parallel treatment systems within the same WWTP.  
\end{table} 
Table 2: _Cont._The most common way of sampling wastewater is by storing the sample in a container and filtering it through sieves of different mesh sizes. This method of sampling is represented in 51% of the studies reported in Table 1[48; 51; 52; 57; 61; 64; 65; 70; 71; 76; 78; 80; 81; 89; 90; 93; 95; 97; 98; 99; 100]. Additionally, other methods used imply the direct filtration of samples during sampling (12%) [66; 67; 73; 74; 75; 118; 121; 122], automatic collection of single or composite samples during a time interval (15%) [49; 68; 83; 84; 91; 94; 96; 114; 117] or use of a device for pumping and filtration of the samples (22%) [62; 63; 69; 72; 79; 82; 83; 84; 85; 86; 87; 88; 89; 111; 116; 117].