Large‐Scale Biological Nitrate and Ammonia Removal

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Abstract
In order to treat water containing nitrogen in excess of the European Drinking Water guideline, an innovative large‐scale biological, nitrogen‐removal process has been used. After extensive pilot‐scale testing and a first full‐scale (80 m3/h) demonstration at Eragny (France), a 400 m3/h installation, serving about 50000 people, was built at Guernes‐Dennemont, near Paris. The raw water source is a combination of percolation from agricultural plains and river bank infiltration, and contains both nitrates and ammonia.The plant consists of two fixed‐bed biological reactors in series. An anoxic filter, using ethanol as a carbon source for heterotrophic bacteria, removes nitrates at filtration rates up to 10 m/h. The denitrified water is then polished on an aerated two‐layer filter, packed with activated carbon and sand. Excess carbon from the first stage, together with reduced nitrogen (ammonia and nitrates), is oxidized at this stage before ozonation of the water.Design data and operational performance are given for total nitrogen (NO3 and NH,), total organic carbon (TOC) and chlorinated hydrocarbons. A specific dosing method for biodegradable carbon was developed to monitor the efficiency of the post‐treatment. Special attention was paid to (a) nitrate control through improved backwash, and (b) reducing the potential for bacterial contamination and aftergrowth in the distribution network.