Start-up of a biological sequencing batch reactor to treat supernatant from anaerobic sludge digester.

Treating the supernatant (reject water) from an anaerobic sludge digestion (800-1200 mg NH4(+)-N l(-1)) may be a good solution for meeting local requirements. As reject water represents 0.6% of the total wastewater influent flow and contains 10-30% of the total N it is recirculated to the head plant. In this study, a lab-scale start-up of biological nitrification/denitrification process to treat reject water was developed in a sequencing batch reactor. Sludge acclimation to the denitrification process was quite fast (6-7 days) for both NO2(-)-N and NO3(-)-N, whereas in nitrification it was slower (20 days). The use of a sequencing batch reactor to treat reject water produced a complete biological reduction of the NH4(+)-N via nitrite, working with sludge age of 15 days, hydraulic retention time of 1.3 days, temperature of 28 degrees C, pH between 7-8.5 and biomass concentration around 3500 mg VSS l(-1). Specific efficiencies were 14 mg NH4(+)-N (g VSS h(-1)) and 30 mg NO2(-)-N (g VSS h)(-1).