EFFECT OF SODIUM-BICARBONATE RECARBONATION ON THE BIODEGRADABLE DISSOLVED ORGANIC-CARBON MEASURED BY FIXED BIOMASS

It was observed that biodegradable dissolved organic carbon (BDOC), me asured by a fixed biomass method, in samples recarbonated with sodium bicarbonate, were always lower than those obtained in similar non reca rbonated samples. Biomass used for all measurement was developed and s ustained with non-recarbonated water (base water). The increase of alk alinity, pH and sodium concentration resulting from recarbonation seem s to affect BDOC values. Results have shown little variation of BDOC ( 0.1 to 0.2 mg l(-1) C) when the sodium concentration is raised from 3 mg l(-1) (base water; alkalinity = 25 mg l(-1) as CaCO3) to 40 mg l(-1 ) (recarbonated water; alkalinity = 100 mg l(-1) as CaCO3). However, w hen sodium concentration was increased to 109 mg l(-1) (recarbonated w ater; alkalinity = 250 mg l(-1) as CaCO3) important underestimation of BDOC (0.4 mg l(-1) C to 0.6 mg l(-1) C) occurred. In order to obtain better results, it was decided to adapt the biomass to the physico-che mical characteristics of each water for 45 days, 80 days and 120 days. BDOC results obtained with biomass adapted for 80 or 120 days reached those obtained without changing pH or alkalinity. So, for the water u sed (Mille-Iles river) the minimal adaptation period seems to be betwe en 45 and 80 days.