Fig. 2. Schematic of experimental tank system with varying root concentrations. Plant root concentrations were manipulated by changing the proportions of the tanks; tank volumes and hydraulic retention times were the same across treatments. One such experimental tank system was inserted into each of the two pond system tank trains. T2 and T5, aerated Tanks 2 and 5; SB, flow splitter box; L3 and L4, low root concentration treatment (2.5 g L^-1 septage); H3 and H4, high root concentration treatment (7.1 g L^-1 septage).