Effect of Sodium Bicarbonate Recarbonation on the Biodegradable Dissolved Organic Carbon Measured by Fixed Biomass

Abstract

It was observed that biodegradable dissolved organic carbon (BDOC), measured by a fixed biomass method, in samples recarbonated with sodium bicarbonate, were always lower than those obtained in similar non recarbonated samples. Biomass used for all measurement was developed and sustained with non-recarbonated water (base water). The increase of alkalinity, pH and sodium concentration resulting from recarbonation seems 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, when sodium concentration was increased to 109 mg l⁻¹ (recarbonated water; 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-chemical 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 used (Mille-Iles river) the minimal adaptation period seems to be between 45 and 80 days.

Keywords:

• Biodegradable organic carbon
• BDOC measurement
• recarbonation
• dissolved organic carbon
• fixed biomass