## 3 Case Studies of Pilot and Full-Scale STRBs
### Water Works Sludge (England)
#### 3.4.2 Sedimentation and Capillary Suction Time  
The dewaterability of WW sludge can be evaluated via a simple and easy sludge sedimentation test. The low fat and oil content in the sludge from Hanningfield WW resulted in a relatively rapid sedimentation of the suspended solids, and a settled sludge layer (8-10 cm) was formed after 30 min [53]. The liquid phase (i.e., above the settled sludge) is transparent without any colouring. The sludge sedimentation properties should be regularly tested during the experimental period to detect any changes at the WW.  
The capillary suction time (CST) provides another good indication of the sludge dewatering properties, measuring how fast the sludge wets a filter paper. A CST between 10 and 100 s indicates a good dewaterability. The CST measured for WW sludge is usually higher compared to that for WWTP sludge, indicating that this sludge presents more difficulties in dewatering. Nevertheless,  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Feed Sludge**} & \multicolumn{2}{c}{**Whitacre WW**} & \multicolumn{2}{c}{**Hanningfield**} \\  & \multicolumn{2}{c}{**(P)**} & \multicolumn{2}{c}{**WW (P + F)**} \\ \hline
**Monitoring Period:** & & **Autumn 2015** & **2008–2013** & \\ \hline
**Parameter** & **Unit** & **Aver. (_n = 2_)** & **Aver. (_n > 25_)** & \\ \hline Dry solids & \% & 0.3 & 0.2 & 0.1–0.5 \\ Suspended solids & mg/L & 2630 & 1262 & 100–8000 \\ Loss on ignition & \% & 40 & 23 & 10–40 \\ pH & - & 7.3 & 7.4 & 6.8–87 \\ Fat and oil & g/kg ds & & 0.60 & 0.010–2.4 \\ Total iron as Fe & g/kg ds & 259 & 233 & 100–400 \\ Total aluminium & g/kg ds & 0.43 & 0.41 & 0.1–3 \\ Total nitrogen (TN) & g/kg ds & & 2.3 & 1–14 \\ Total phosphorous (TP) & g/kg ds & & 6.96 & 1.5–11 \\ Phosphate (as P) & g/kg ds & 7.24 & & 2000–8000 \\ Chloride & g/kg ds & 16,30 & 41.6 & 15–45 \\ Total calcium & g/kg ds & 33.6 & 98.1 & 32–290 \\ \hline \hline \end{tabular}
\end{table}
Table 4: STRB feed sludge characteristics at the Whitacre and Hanningfield WW (England). Both facilities utilize ferric sulphate as a coagulant (P = pilot, F = full-scale, WW = Water Works) [53; 58; 60].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Drained Water**} & \multicolumn{2}{c}{**Whitacre WW**} & \multicolumn{2}{c}{**Hanningfield**} \\  & \multicolumn{2}{c}{**(P)**} & \multicolumn{2}{c}{**WW (P + F)**} \\ \hline
**Monitoring Period:** & & **Autumn 2015** & **2008–2013** & \\ \hline
**Parameter** & **Unit** & **Aver. (_n = 3_)** & **Aver. (_n > 25_)** & \\ \hline Dry solids & \% & 0.06 & 0.05 & 0.001–0.06 \\ Suspended solids & mg/L & 93 & 0.01 & 0.001–0.05 \\ pH & - & 7.9 & 7.7 & 7.0–8.0 \\ BOD5 & mg/L & 5 & 2.4 & 1–36 \\ COD & mg/L & 44 & 33 & 3–380 \\ Total iron as Fe & mg/L & 29 & 4.5 & 0–120 \\ Total phosphorous as P & mg/L & 0.1 & 0.2 & 0–4.6 \\ Total nitrogen as N & mg/L & - & 3.3 & 0–10 \\ Chloride & mg/L & 52 & 74 & 50–100 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Drained water characteristics in STRB at the Whitacre and Hanningfield WW (England) (P = pilot, F = full-scale, WW = Water Works, BOD5 = Biochemical Oxygen Demand, COD = Chemical Oxygen Demand) [53; 58; 60].  
the dewatering process was not affected by the higher CST values of the WW sludge and the cracks on the sludge layer surface [53]. The CSTs at the Hanningfield and Whitacre WW were both around 2-4 times (30-110 s) higher than the CST of the surplus activated sludge (10-40 s) (Figure 10). On the other hand, the digested WWTP sludge can have CST values higher than 2000 s. These sludge types typically possess higher fat and oil contents.