The PRVRB effectively degraded phenol in a laboratory flow-through study. Figure 10a illustrates two sampling points: 1) Pre-PRVRB representing the phenol concentration prior to entering the PRVRB, and 2) Post-PRVRB representing the phenol concentration after passing through the PRVRB. One PV is around 56 h at flow rate of 30 cm/day. All the breakthrough curves gradually increase from time zero and reach a steady state after 56 h (Figure 10b). By comparing the breakthrough curve prior to entering and after passing through the PRVRB at the steady state, the 40-cm PRVRN achieved 28% and 38% removal of phenol and COD, respectively, at a 32-h retention time. With this finding, we estimated that the 1st order phenol and COD removal rate constants were 0.010 and 0.012 h-1, respectively. The phenol and COD removal rates by the PRVRB were greater than that of vetiver on a floating platform at the initial state (Phase I at 78 h), but similar to that of Phase II (kphenol = 0.0097 h-1), as the presence of soil presumably stimulates rhizomicrobial growth at a faster rate than in wastewater, thereby moving the system to Phase II faster. This hypothesis needs further verification.