Performance of aerobic nitrite granules treating an anaerobic pre-treated wastewater originating from the potato industry

- The nitrite-route was successfully obtained after 80 days.
- Full granulation was achieved after 64 days.
- Anaerobic feeding stimulated slow growing organisms, especially PAO.
- Nitrogen and phosphorus removal efficiencies of respectively 95.3% and 65.7%.
- Nitrous oxide was an important denitrification product.

In this study nitrogen removal via nitrite >80% was achieved after approximately 80 days in a sequencing batch reactor (SBR) treating pre-treated industrial wastewater originating from the potato industry. Thereafter, SBR performance was investigated during the formation of aerobic nitrite granules (ANG). The first granules appeared after 26 days leading to full granulation after 64 days. ANG showed excellent settling properties, as the Sludge Volume Index (SVI) went down to 16 mL/g and a SVI10/SVI30 = 1 was obtained. qPCR analysis showed that slow growing organisms, especially polyphosphate accumulating organisms (PAO) were stimulated by an anaerobic feeding strategy. The average nitrogen removal was 95.3% over the entire operational period, and it mainly followed the “nitrite-route”. Moreover, with ANG also phosphorus removal efficiencies up to 65.7% could be achieved. However, it has to be mentioned that nitrous oxide was an important denitrification product, which implies some environmental concerns.