GROUNDWATER DENITRIFICATION USING AN UPFLOW SLUDGE BLANKET REACTOR

Results of groundwater denitrification experiments using a USB reactor , with ethanol as the carbon source, indicate that it can efficiently treat affected water. However, this type of reactor was found to be st rongly affected by the hardness of the water as a result of changes in the mineral fraction of the granules. During a period when water cont aining between 150 and 380 mg/l (average of 244 mg/l) of hardness (as CaCO3) was used, floating sludge and biomass washout occurred as a res ult of a low granule mineral content, 10-15% of TSS, and a gradual inc rease in granule size, accompanied by poor settling characteristics. W hen water of higher hardness was used, 380-450 mg/l as CaCO3, high bio mass concentrations of 30-40 g/(1 sludge blanket) were maintained in t he reactor. This high concentration resulted from the development of g ranules having good settling characteristics and containing about 25% minerals (CaCO3) with very low SVI values (between 15 and 30). Under t hese conditions the USB reactors exhibited stable operation with volum etric loading rates of up to 4 kgN/m(3)day, corresponding to a retent ion time of 8 min.