MEASUREMENT OF DISSOLVED FREE AND COMBINED AMINO-ACIDS IN UNCONCENTRATED WASTEWATERS USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Dissolved free amino acids (DFAA) and dissolved combined amino acids ( DCAA, e.g., discrete dissolved polypeptides and proteins as well as am ino acids, peptides, and proteins adsorbed to humic material) were mea sured in unconcentrated domestic wastewater at a detection limit of 10 to 100 nM (coefficient of variation less-than-or-equal-to 0.10 at 100 nM) using precolumn ortho-phthaldialdehyde derivatization, reverse-ph ase high performance liquid chromatography separation, and fluorometri c detection. Wastewaters were sampled at three types of wastewater tre atment plants: trickling filter, conventional activated sludge, and pu re-oxygen activated sludge. Raw wastewaters contained the largest conc entrations (58 muM) of dissolved total amino acids (DTAA) with 7% as D FAA. The DTAA were between 28 and 40 muM in primary clarifier effluent s with 7% to 29% as DFAA. Removal percentages during biological treatm ent were > 70% for DFAA and 23% to 79% for DCAA. Molecular weight sepa rations indicated that most dissolved organic carbon (DOC) (> 68%) in the trickling filter influent had small molecular weights (< 1 000 ato mic mass unit [AMU]), whereas the majority of DTAA had large molecular weights (> 10 000 AMU). The DTAA were a small fraction (8% to 13%) of DOC in both influent and effluent samples.