Waste-organics supported treatment of nitrogen-rich digester supernatant

Abstract The goal of the study was to treat nitrogen-rich digester supernatant for water reuse in a three-stage system with an aerobic granular sludge batch reactor (GSBR), a post-denitrification (P-D) reactor and a membrane module. In the study, the effects on treatment efficiency of organic loading and aeration mode in the GSBR, the type of waste organics in P-D and the parameters of filtration were investigated. Denitrification efficiency was highest in the GSBR operated with 2 anoxic phases in the cycle and at 1.8 g COD/(L·d), but in this reactor, the N-NO2−/N-NO3− ratio was the highest (2.43). Shortening the anoxic period in the cycle and increasing organic loading to 2.1 g COD/(L·d) decreased nitrite accumulation in the effluent (the N-NO2−/N-NO3− ratio of 0.23). The effluents with different N-NO2−/N-NO3− ratios were subjected to P-D with glycerin fraction (GL), distillery residue (DR) and volatile fatty acids (VFAs) as waste organic sources. P-D of nitrate-rich GSBR effluent with VFA resulted in denitrification efficiency up to 97.9 %, and followed by microfiltration produced a final stream that could be directly discharged to the environment or used for irrigation. The use of P-D with GL and DR was most efficient for the treatment of GSBR effluent in which nitrite predominated. Denitrification efficiencies reached 26.7 % with GL and 22.0 % with DR. After polishing by ultrafiltration, the final stream had low COD and color, no turbidity, high concentrations of NOx, and could be used for algae growth for bioproduct recovery.