Performance And Mechanisms Of Salt-tolerant ANAMMOX Process

Nitrogen pollutants, with large discharge, wide distribution and serious damage, are in urgent need of effective management in China. Anaerobic ammonia oxidation (ANAMMOX) is a highly efficient and cost-effective biological process, which is promising to become an upgrading technology for nitrogen removal from wastewaters. However, ANAMMOX process is susceptible to the inorganic salts in wastewaters during its application. Therefore, the performance and mechanisms of salt-tolerant ANAMMOX process were studied in the present work. The major conclusions are as follows:1) The relationships between morphology, structure, component and settleability of ANAMMOX granular sludge were revealed.① A settling model of ANAMMOX granular sludge was established and validated to correlate the settling velocity with the density (ρp), mass calibration factor (Ψmass), shape calibration factor (characterized by sphericity (Φ)) and projected area equivalent sphere diameter (dp) of ANAMMOX granular sludge. The settling model could well describe the settling velocity of ANAMMOX granular sludge. The sensitivity of four parameters was in the order of ρp, Ψmass, dp and Φ.② A suitable size range of ANAMMOX granular sludge was put forward for good settlement. Based on the settling model, the diameter of ANAMMOX granular sludge had better be controlled above 1.75 mm. Based on the gas pocket volume model, the diameter of ANAMMOX granular sludge should be controlled at less than 2.20 mm.③ According to microscopic observation and theoretical calculation, a hypothetical mechanism for the granulation and floatation of ANAMMOX biomass was proposed.2) The relationships between morphology, structure, component and reactivity of ANAMMOX granular sludge were revealed.① The relationships between porosity, specific surface area (SSA) and dp of ANAMMOX granular sludge were estabilished. The porosity and the SSA of ANAMMOX granular sludge were 0.693～0.939 and 4.0612～5.2151 m2·(g-SS)-1, respectively. Both of the porosity and the SSA decreased with increasing diameter of ANAMMOX granular sludge.② The main component of ANAMMOX granular sludge was determined. The volatile suspended solids/total suspended solids (VSS/SS) value and the extracellular polymeric substances (EPSs) content of ANAMMOX granular sludge were 0.819～0.918 and 177.70～207.31 mg·(g-VSS)-1, respectively. The ANAMMOX granular sludge with diameter of 0.5～3.0 mm were commonest in ANAMMOX reactor, and it has the average VSS/SS value of (0.912±0.005) and the EPSs content of (202.74±5.63) mg·(g-VSS)-1.③ A suitable size range of ANAMMOX granular sludge was put forward for high activity. The dehydrogenase activity (DHA) and the specific ANAMMOX activity (SAA) of granular sludge were 1.978～2.462 mg-TF(g-VSS·h)-1 and 0.385～0.644 g-NO2--N·(g-VSS·d)-1, respectively. To get the high activity, the diameter of ANAMMOX granular sludge should be controlled at 1.0-2.0 mm.3) The short-term effect of inorganic salt on ANAMMOX granular sludge and its mechanism were revealed.① The short-term effect of inorganic salt on the settleability of ANAMMOX granular sludge was investigated. ANAMMOX granular sludge would lose water and adsorb salt in the salt solution, which led to the decrease of the dp for ANAMMOX granular sludge. The greater the salt concentration was, the more significantly the dp decreased. Along with the increase of salt concentration, the pp for ANAMMOX granular sludge increased, and the density difference (△ρ) between ANAMMOX granular sludge and salt solution first increased and then decreased, so did the settling velocity. The △ρ was the main factor affecting the settleability.② The short-term effect of inorganic salt on the DHA of ANAMMOX granular sludge was investigated. Inorganic salt had both the stimulatory effect and the inhibitory effect on the DHA depending on its concentration. The stimulatory effect of inorganic salt was in order of sodium phosphate salt> potassium chloride> sodium chloride> sodium sulfate> calcium chloride> sodium bromide> sodium fluoride; the inhibitory effect of inorganic salt was in order of sodium fluoride> calcium chloride> sodium bromide> sodium sulfate> sodium chloride> sodium phosphate salt> potassium chloride.③ The short-term effect of inorganic salt on the SAA of ANAMMOX granular sludge was investigated. Inorganic salt had both the stimulatory effect and the inhibitory effect on the SAA depending on its concentration. The stimulatory effect of inorganic salt was in order of potassium chloride> sodium phosphate salt> sodium sulfate> sodium chloride> sodium fluoride> calcium chloride= sodium bromide; the inhibitory effect of inorganic salt was in order of sodium fluoride> sodium bromide> calcium chloride> sodium phosphate salt> sodium sulfate> sodium chloride> potassium chloride.④ The mechanism of potassium chloride and sodium chloride effect SAA was proved. Na+-K+-2Cl- transporter and K+-Cl- transporter were assumed to be ammonium ion channels of AnAOB. Potassium chloride and sodium chloride inhibited ANAMMOX activity by competing ion channel with NH4+4) The long-term effect of inorganic salt on ANAMMOX and its mechanism were revealed.① The long-term effect of inorganic salt on the settleability of ANAMMOX granular sludge was investigated. The settling velocity of ANAMMOX granular sludge decreased after long-term exprosure to the inorganic solution. Low concentration solutions of sodium chloride, sodium sulfate, sodium fluoride or sodium bromide could decrease the granule size by influencing the EPSs synthesis or secretion by AnAOB, which slowed down the settling velocity of ANAMMOX granular sludge.② The inhibitory effect of inorganic salt on ANAMMOX system was evaluated. Using relative volumetric nitrogen removal rate (VNRR) as evaluation indexes, low concentration solutions of sodium chloride, sodium sulfate or sodium fluoride had "serious inhibition" to the ANAMMOX system, and low concentration solutions of calcium chloride or sodium bromide had "slight inhibition" to the ANAMMOX system, and low concentration solution of sodium phosphate salt had "no inhibition" to the ANAMMOX system.③ The long-term effect of inorganic salt on the nitrate production of ANAMMOX system was determined. Low concentration solutions of sodium chloride, sodium sulfate, sodium phosphate salt, calcium chloride or sodium bromide could strengthen the nitrate production of ANAMMOX system, and low concentration solution of sodium fluoride could reduce the nitrate production of ANAMMOX system.5) A salt acclimation model of ANAMMOX system was put forward, and a salt-tolerant ANAMMOX process was developed.① A salt acclimation pattern of ANAMMOX system was put forward. Betaine could not enhance salt-tolerance of AnAOB, but improve denitrification of ANAMMOX granular sludge. The "low loading rate & gradually raising salinity" pattern was suitable for the start-up and the operation of ANAMMOX system.② A salt-tolerant ANAMMOX process was successfully developed by using "first raising salinity, then shortening HRT" as operation pattern. The maximum volumetric nitrogen removal rate (VNRR) of (3.46±0.04) kg-N·m-3·d-1 was achieved at the salinity of 30 g·L-1.