Maintainability of denitrifying granular sludge in soft to marginally hardwaters in an upflow sludge-blanket reactor

The maintainability of denitrifying granular sludge in a bench scale reacto r treating soft groundwater with low nitrate (21 mg N l(-1)) was investigat ed. With influent alkalinity at 180 mg CaCO3 l(-1), a calcium addition to a relatively low total hardness of 120 mg CaCO3 l(-1) and an influent pH of 8.5, generation of mineral precipitation needed for production of a heavy g ranular sludge with good settling characteristics was achieved. Bed biomass concentration increased with increasing granule mineral content due to imp roved retention. With reduced mineral precipitation at a lower influent pH of 7.9, an increase in volumetric loading rate was also shown to be effecti ve in cultivating biomass in a manageable granular sludge.