Preliminary performance and biofilm characteristics of ANAMMOX process in an improved FBR with mixture of honeycomb-like and non-woven carriers

Honeycomb-like polypropylene carriers and ring non-woven carriers were filled in a fixed bed reactor (FBR) and mixed at the ratio of 1: 1 to enrich ANAMMOX bacteria from the conventional activated sludge and start up ANAMMOX process. The DO concentration in the influent was below 0.05 mg/L and the temperature was maintained at 35 degrees C inside the FBR. The reactor was operated for 87 d and the whole process was divided into start-up period and nitrogen loading enhancing period. In start-up period, influent NH4+-N and NO2--N concentrations were both 70 mg/L at HRT of 48 h. ANAMMOX activity first occurred on day 21. The removal efficiency of ammonium, nitrite and total nitrogen (TN) reached 90.24%, 100%, 88.8% respectively on day 53, indicating that ANAMMOX was successfully started up. In nitrogen loading enhancing period, influent NH4+-N and NO2--N concentrations both increased from 100 mg/L to 230 mg/L and subsequently HRT was shortened from 48 h to 36 h. The maximum TN loading rate and removal rate reached 0.31 kg N.m(-3).d(-1) and 0.25 kg N.m(-3).d(-1) with the average TN removal efficiency of 77.27%. Quantitative PCR indicated that ANAMMOX bacteria responsible for ANAMMOX reaction predominated in the mature biofilms from both the carriers. The scanning electron microscope (SEM) photograph showed that the mature biofilm scratched from the honeycomb-like carriers exhibited a morphology of self-aggregates while the mature biofilm attached on the non-woven carriers was bound or enwrapped by fine non-woven fibers. The mature biofilm in both carriers had the typical cauliflower appearance of ANAMMOX consortium. The FBR improved with mixture of two kinds of carriers can enhance ANAMMOX performance.