I respectfully disagree with ...

I respectfully disagree with some of the respondents below.  Manganese can be precipitated at pH 7 without chemicals in an aerobic wetland environment.  Iron must be virtually absent.  The reaction is facilitated by cyanobacteria/algae which utilize the Mn to create hold-fasts that allow them to anchor themselves to rocks, etc.  See the attached 1999 paper by E. Robbins et al. that identified 11 different biota, including Leptothrix discophora and Ulothrix algae that were precipitating MnO2 in a constructed wetland in the USA.  The reaction is basically powered by sunshine/photosynthesis.  We used this process to design a passive treatment system to lower Mn concentrations from over 3 mg/L to less than 50 ppb (again, without chemicals) at a peak flow rate of 4,542 L/min at the Empire Mine State Historic Park in California, USA.  That system has been operational since 2011.  A paper documenting the design process (Gusek et al., 2011) is attached.  Use this as a guide to bench and pilot scale testing.  The manganese removal portion of the passive treatment system at the Empire Mine covered about 4,520 square meters of surface area.  Over time, manganese oxide deposits accumulate into "manganocrete", which can also be observed in the geologic record.   Mother Nature has been using this process for eons...