## 2 Materials and Methods
### System Setup  
The experimental system for this study (Figures 1 and 2) comprised a raw wastewater reservoir, a wastewater mixing tank, a trap for the retention of larger solids, the vermifilter, the hydroponic deep-water culture (DWC) unit, and a final reservoir for treated water. The mixing tank was a cylindrical 160 liter barrel containing a total liquid volume of 100 L, stirred by a 120 W CAT R50 overhead stirrer with a four-flat-blade impeller (diameter 100 mm, blade width 50 mm) at 120 rpm, that served to dilute the raw wastewater in order to decrease its starting EC values, since less than 1 S/m has been found to cause total mortality in _Eisenia fetida_[37]. From there, diluted wastewater was pumped by a Heidolph Pumpdrive 5101 peristaltic pump at 11 L/day through a 4-mm plastic tube, trickling onto the top of the vermifilter unit. The vermifilter was constructed based on previously described models [21; 38]. An opaque plastic cylinder (total height 63 cm, internal diameter 16 cm) with 4-mm lateral perforations for aeration in the lower half, 6 cm apart, was filled bottom to top with 22.4 by 45 mm gravel (10 cm), 16 by 22.4 mm gravel (7.5 cm), 6.3 by 14 mm gravel (7.5 cm), 2.0 by 6.3 mm gravel (5 cm), coarse river sand (3 cm), fine river sand (10 cm), and a 15 cm layer of a 1:2 mixture (by apparent dry volume) of Earthworm humus (SiroTM) with pine wood chips from a local sawmill. This last layer was inoculated with live _Eisenia fetida_ earthworms ranging from 3 to 6 cm in length (10 to 12 g/dm3). The worms were initially supplied by a private breeder and were bred in a household pot filled with soil and topped with regularly renovated vegetable waste. Water flowed through the vermifilter by gravity, trickling into the hydroponic unit placed below. It was ensured that the flow through the vermifilter was free enough to be set by the peristaltic pump alone. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline TDS & 3100 mg/L \\ TSS & 1900 mg/L \\ EC & 0.9000 S/m \\ pH & 8.00 \\ COD & 1997 mgO\({}_{2}\)/L \\ BOD\({}_{5}\) & 149 mgO\({}_{2}\)/L 1  \\ NH\({}_{3}\)-N & 574 mg/L \\ NO\({}_{2}\)-N & 0.034 mg/L \\ NO\({}_{3}\)-N & 1.50 mg/L \\ TP & 159 mg/L \\ PO\({}_{4}\)-P & 34.0 mg/L \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical and chemical parameter values of the raw piggery wastewater collected from the selected lagoon [36]. TDS: total dissolved solids; TSS: total suspended solids; EC: electrical conductivity; COD: chemical oxygen demand; BOD\({}_{5}\): 5-day biochemical oxygen demand; NH\({}_{3}\)-N: ammonia nitrogen; NO\({}_{2}\)-N: nitrite nitrogen; NO\({}_{3}\)-N: nitrate nitrogen; TP: total phosphorus; PO\({}_{4}\)-P: free phosphate phosphorus. The DWC hydroponic unit consisted of a rectangular 120 cm long, 80 cm wide, 25 cm high black plastic tray. Aeration was ensured by a grid of perforated 4 mm plastic tubes  
Figure 1: Schematic representation of the built vermifiltration-hydroonic system. Arrows indicate the liquid and air flow directions. Figure 2: Vermifiltration-hydroonic system. Cp: air compressor; HP: hydroponic tray; MT: mixing tank; P: peristaltic pump; Tr: trap for solids; TWR: treated water reservoir; VF: vermifilter. disposed in 20-cm side squares, fed by a 60 W, 70 L/min Hailea ACO-328 air compressor. A standpipe of defined height placed on exit allowed for controlling the total volume and hydraulic residence time for a constant volumetric flow. Two polystyrene foam rafts were placed on top of the container, floating directly on water surface. The effective liquid volume in the completely assembled unit under aeration was measured to be 114 L. Therefore, the hydraulic residence time (HRT) was estimated to be 10.4 days on average. The hydroponic unit was illuminated by diffuse natural light from the laboratory windows. The vermifilter was pre-operated alone for 60 days to allow the earthworms to get acclimated to swine wastewater, before the plants were introduced in the hydroponic unit.