Partial Nitritation Process For Ammonium-rich Wastewater Treatment

Anammox process, which is based on autotrophic denitrification via nitrite without organic carbon dosen, is a more sustainable way for nitrogen removal from ammonium- rich wastewater. The influent for the Anammox process must be composed of NO₂^--N and NH₄⁺-N in a ratio of 1:1 to 1.3:1 and therefore Partial Nitritaiton process (P-N process), which converts only 50% to 57% of influent ammonium to nitrite without production of nitrate, is needed to be the pre- treatment process for Anammox. The controllable parameters for the P-N process can be temperature, sludge retention time (SRT), influent ammonium load, pH value, dissolved oxygen (DO) and influent HCO₃^-/NH₄⁺ ratio. DO is not suitable for nitrogen removal from ammonium- rich wastewater.Continuing stir tank reactors (CSTR) are used for the study of P-N process at different temperatures (35℃, 30℃, 25℃, 20℃), defferent influent ammonium concentrations, different influent HCO₃^-/NH₄⁺ ratios and different sludge retention times (SRT). The scopes of these operation parameters are obtained and the conclusions are as follows:1. Temperature is one of the most important parameters for the P-N process. The stability and the capacity of withstanding nitrogen load strike and free ammonia inhibition of P-N process are better at higher temperature. It is obtained that 35℃is the optimum temperature for the P-N process.2. For Constance, the P-N process needs lower SRT to achieve the washout of nitrite oxidation becteria. However, lower SRT leads to higher sludge load, which is not suitable for ammonium- rich wastewater treatment. Nitrogen removal from ammonium- rich wastewater needs higher SRT which can be adjusted by sludge rejection ratio in the real plant. The considerable SRT scopes for the P-N process at different temperatures are given. The considerable SRT scopes are narrowed at lower temperatures (at 35℃, 30℃, 25℃and 20℃are 1.8-6.0d, 1.9-5.5d, 1.9-3.5d and 2.3-4.5d, respectively), and the highest values rise after the first drop.3. The scope as well as the highest value of the tolerable influent ammonium load for the P-N process decrease when the temperature is lowered (the tolerable influent ammonium loads at 35℃, 30℃, 25℃and 20℃are 0.13-0.7 gN/(L ? d), 0.13-0.53 gN/(L ? d), 0.2-0.32 gN/(L ? d) and 0.17-0.26 gN/(L ? d), respectively). 4. The inlet HCO₃^-/NH₄⁺ ratio is mainly used to control the ammonium oxidation rate and to father affect the effluent NO₂^-/NH₄⁺ ratio for the Anammox process. The influence of the inlet HCO₃^-/NH₄⁺ ratio to the P-N process is studied and it is concluded that: the inlet HCO₃^-/NH₄⁺ ratio of 1:1 is needed to achieve an effluent NO₂^-/NH₄⁺ ratio of 1:1, and to achieve an effluent NO₂^-/NH₄⁺ ratio of 1.3, the inlet HCO₃^-/NH₄⁺ ratio should be 1.13 at 35℃, 30℃and 25℃, and 1.3 at 20℃.5. The feasible pH values for the P-N process are obtained and the limit pH value tends to increase at lower temperature (the feasible pH values at 35℃, 30℃, 25℃and 20℃are 6.5-8.0, 6.7-8.4, 6.5-8.3 and 6.9-8.1, respectively).6. The Haldane substrate inhibition model fits the P-N process for the nitrogen removal from ammonium- rich wastewater. The P-N process inhibition kenitics at different temperatures in the CSTRs are obtained.The Partial Nitritation process is a result of comprehensive interaction of several parameters and a single parameter leads to different result when combines with different parameters. To achieve a more stable and economical P-N process, these controllable parameters should be considered comprehensively.