Characteristics And Control Strategies Of ANAMMOX Process

Anaerobic ammonium oxidation (ANAMMOX) process is a novel biological nitrogen removal technology achieving high nitrogen removal rates over the conventional nitrification-denitrification process. The development and application of ANAMMOX process for the treatment of ammonium-rich wastewater have attracted increasing attention. In order to advance theories on ANAMMOX process, to promote technological innovation, and to accelerate the full-scale application of ANAMMOX process, the start-up, operational performance, process disturbances and the corresponding control strategies of ANAMMOX process were studied in the present investigation. The major conclusions are as follows:1) The start-up of ANAMMOX process using different inocula was investigated and the characteristics and control strategies during start-up were explored.It was found that the start-up course of ANAMMOX process consisted of 4 phases namely:cell lysis phase, lag phase, activity elevation phase and stationary phase. Cell lysis dominated during cell lysis phase without any ANAMMOX reaction in the reactor, resulting in increase of ammonium concentration in the effluent. Consequently, decreasing influent ammonium concentration was proposed. During lag phase, the reactor displayed very poor ANAMMOX performance. Thus, maintaining low influent substrate concentrations was suggested to prevent the substrates inhibitions. In spite of the significant increase in ANAMMOX performance during activity elevation phase, the number of AAOB (anaerobic ammonium-oxidizing bacteria) was still in accumulation. Thus, the nitrogen loading rate of the reactor should be steadily elevated in order to fulfil the substrate requirement and avoid the high pH and substrate inhibition. For stationary phase, the ANAMMOX capacity of the reactor was saturated. Keeping nitrogen loading rate at 70% of the maximum could contribute to the stability of the ANAMMOX reactor during start-up.2) The characteristics of normal-loaded ANAMMOX process were depicted; and the ’low substrate-high flux’ mode was proposed for stably operating ANAMMOX process.Results showed that self-inhibition of ANAMMOX process was caused by ammonium and nitrite. The unionized form ammonium i.e., FA could inhibit the ANAMMOX process. The nitrogen removal performance of ANAMMOX reactor deteriorated when NO2--N concentration and NO2--N/NH4+-N were high. The performance of ANAMMOX reactor heavily suffered from nitrite self-inhibition could recover with the recovery degree of 93%. Using the ’low concentration-high flux’ mode, the nitrogen removal rate of ANAMMOX reactor reached as high as 25.04 kg/(m3·d) by shortening HRT (hydraulic retention time) to 0.41 h with constant influent NO2--N concentration of 240 mg/L.3) The high-loaded ANAMMOX process was developed in this research; and the characteristics and control strategies of high-loaded ANAMMOX process were described.It was demonstrated that the HRTs of ANAMMOX UASB reactors could be shortened to 0.06-0.11 h and nitrogen loading rate increased to 150-220 kg/(m3·d), resulting in nitrogen removal rate of 100-130 kg/(m3·d). The values were 4-5 times of the highest values as reported in literature [26 kg/(m3·d), Tsushima et al.,2007]. The high-activity ANAMMOX granules cultivated under extremely high loading conditions possessed uniquely carmine color. The settling property of the high-activity ANAMMOX granules was much better than that of the normal-loaded ones. The packing pattern of ANAMMOX granules in high-loaded ANAMMOX reactors was simple cubic packing pattern. It was suggested that increasing sludge concentration was prone to enhance the volumetric nitrogen removal rate when sludge concentration of ANAMMOX reactor was less than 37.8 g VSS/L, but increasing nitrogen loading rate through shortening HRT was more effective to improve the volumetric nitrogen removal rate when the sludge concentration in ANAMMOX reactor was higher than 37.8 g VSS/L. 4) The disturbances to ANAMMOX process caused by organic matter and toxic substances were investigated. An innovative ANAMMOX process with sequential biocatalyst addition (SBA-ANAMMOX process) was proposed and developed in this research.It was demonstrated that organic matter and toxic substance could disturb ANAMMOX process. The ANAMMOX performance disappeared after a long-term operation under relatively high organic concentration (COD/NO2--N of 1.86). The enhancement of denitrification and sulfate reduction could contribute to the substrate competition and living space competition over AAOB. The pharmaceutical wastewater taken from antibiotics manufacturing factory possessed strong biotoxicity. More seriously, the cumulative toxicity was observed in the ANAMMOX sludge after long-term exposure to the pharmaceutical wastewater. Therefore, the ANAMMOX sludge finally autolyzed and the ANAMMOX activity of the reactor eventually disappeared.The SBA-ANAMMOX process was demonstrated to be effective in treatment of organic and biotoxic ammonium-rich wastewater. With the sequential addition of high-activity ANAMMOX granules, the ANAMMOX performance of the target reactor treating organic ammonium-rich wastewater was significantly enhanced. For the treatment of antibiotics manufacturing wastewater, nitrogen removal rate as high as 7.24-9.41 kg/(m3·d) was recorded at HRT of 1.0 h and biocatalyst addition of 0.025 g VSS/(L wastewater·d). The effluent NH4+-N concentration was below 50 mg/L, which met the Discharge Standard of Water Pollutants for Pharmaceutical Industry in China (Fermentation products Category) (GB 21903-2008).