## 3 Results  
### Removal of Soluble Mn from Partly Processed Mine Water Using the MnOBs  
The effectiveness of the MnOBs in removing soluble manganese from partly processed synthetic mine water is shown in Figure 2. In phase C1, during which the influent liquor was that draining the sulfidogenic bioreactor with no pH adjustment (Table 1) and the HRT was maintained at \(\sim\)11 h, removal of soluble Mn decreased from 80 to 10% within the first 30 days of operating the packed bed bioreactor. This was followed by an increase of up to 55% (by day 40), though there was considerable variation in the performance of this MnOB, which lasted for a total of 126 days. Water draining this MnOB was more acidic than the influent liquor, varying between pH 4.1 and 5.6 (Figure 3). Figure 2: Variations in the percentage of manganese removed during the time course of the experiment. Key: phase C1 (green): 1-column system pH 5.0, HRT 12 h; C2a (yellow): 1-column system pH 6.5, HRT 12 h; C2b (red) 1-column system pH 6.5, HRT 24 h and C3 (blue): 2-column system pH 6.5, HRT 45 h. The arrow indicates where yeast extract (final concentration 100 mg L\({}^{-1}\)) was added to the influent liquor. To test whether the reduction in the efficiency of the MnOB used in C1 was due to the pH of the influent water being too low to sustain effective Mn removal, a new MnOB was commissioned and the pH of the influent liquor was increased to 6.5, and the HRT was initially maintained as that in phase C1. However, this did not result in an improved performance, with only \(\sim\)20% soluble manganese being removed from the influent liquor during the 28-day test period. The pH of the effluent liquor varied between 4.5 and 5.1 in phase C2a (Figure 3). The same MnOB was used in phase C2b, and the HRT was increased to \(\sim\)24 h. This resulted in a significant improvement of Mn removal (30-53%; Figure 2), though concentrations of soluble Mn in the effluent liquor (70-140 uM) were still considered to be too high for discharge into the environment. To address this issue, two coupled packed bed bioreactors were tested in phase C3, and the net HRT increased to \(\sim\)45 h. This resulted in 95 \(\pm\) 5% Mn removal from the partly processed mine water during the first 44 days of phase C3, though this subsequently declined (and stabilized) to \(\sim\)60%. The addition of 100 mg L\({}^{-1}\) yeast extract to the influent liquor at day 66 in phase C3 resulted in a rapid improvement in Mn removal (to >99%), though this was not sustained (Figure 2). pH values of the effluents obtained in phase C3 were similar to those found in the earlier phases (Figure 3). The column bioreactor in phase C2 and the first column bioreactor in phase C3 had a thin layer of pale-colored inert gravel placed between two layers of colonized pebbles. This layer was added in order to obtain a visual impression of whether, and how fast, the inert gravel would become colonized by Mn-oxidizing biofilms. Initially, most Mn removal occurred in the second (newly commissioned) MnOB in the coupled system, though this quickly changed with the first MnOB assuming a more significant role, particularly when yeast extract was added to the influent liquor (Figure 4). In addition to removing soluble manganese, the MnOBs were projected to have a potential role in the integrated bioremediation system, further ameliorating the processed water by lowering both the concentrations of dissolved organic components and numbers of bacteria prior to discharge. In the vast majority of tests, electron donors and/or carbon sources for the microorganisms within the MnOBs were only those present in the liquor that drained the sulfidogenic bioreactor (mostly small amounts of glycerol and acetate; [10]). Measurements, taken at the end of phase C3, showed that \(\sim\)96% of the DOC (glycerol and yeast extract) used to fuel the integrated system was used in the sulfidogenic bioreactor and that \(\sim\)74% of that which remained was catabolized in the MnOB (Table 2).