Starting up anammox system with high efficiency nitrogen removal at low temperatures: Performance optimization, sludge characterization and microbial community analysis

Anaerobic ammonia oxidation (anammox) has potential advantages for nitrogen removal when operating at medium temperatures, but the increased operation costs of heating limit its application. It would be advantageous to start and operate anammox at low temperatures, the feasibility of which was studied here on a lab scale. Two identical expanded granular sludge bed (EGSB) reactors were inoculated at 35 +/- 1 degrees C (A(med)) and 15 +/- 3 degrees C (A(low)). Results showed that anammox was successful after 138 d for A(low), only 7 d longer than A(med). Stable operation to 194 d in A(low), the nitrogen loading rate (NLR) increased to 1.01 kg m(-3).d(-1), giving a high nitrogen removal efficiency (NRE) of 85%, which was only slightly lower than that of Amed (90%). More extracellular polymeric substance (EPS) was produced by the microbes of A(low) compared to A(med), which prevented anaerobic ammonia oxidizing bacteria (AnAOB) against low temperature stress. Microbial community revealed presence of Candidatus Jettenia in A(med) with relative abundance 7.4%, while the cold-tolerant Candidatus Kuenenia with 4% was the dominant anammox bacteria in A(low). The anammox granules adapted well to low temperatures and demonstrated high efficiency in anammox process without heating. Therefore, constructing an energy-saving and cost-effective anammox system in high latitudes or high altitudes can be considered.

Automated summary

This study investigates the feasibility of starting and operating anammox at low temperatures and finds that it is possible to achieve high nitrogen removal efficiency without the need for heating, making it a potentially energy-saving and cost-effective method.