Removal of amino acids, biodegradable organic carbon and chlorine demand by biological filtration in cold water

This paper presents the removal profiles of total amino acids (TAAs), total dissolved amino acids (TDAAs), biodegradable organic carbon (BDOC) and chlorine demand in a biological filter operating in cold water (< 2 degrees C). Biological filtration achieved a removal of 46% for TDAAs (0.08 +/- 0.04 mg C l(-1)) and a removal of 24% for BDOC (0.2 +/- 0.1 mg C l(-1)). Since the filter studied was functioning in biological mode, these results suggest that TDAAs have a higher biodegradability than that shown by the global BDOC pool. The use of the CHABROL model, which predicts BDOC removal in biological filters, permitted comparison of the TDAA removal profile with removal profiles associated with the three classes of BDOC distinguished by the model. The theoretical chlorine demand associated with TAAs, calculated with individual amino acid chlorine demands, varied from 5.6 to 6.4 mg Cl-2 per mg TAA. The removal of the chlorine demand associated with TAA removal (0.5 +/- 0.15 mg Cl-2) accounted for 34% of the 240 hour water chlorine demand removal, corrected to take into account the chlorine demand of ammonia. This percentage is higher than that associated with the participation of TAA removal in the removal of TOC (16%). These results reflect the high chlorine reactivity of amino acids with chlorine. Removal by biological filtration of a significant fraction of TAA partially explains the increased biological and free chlorine stability of water produced by this treatment process.