| In order to achieve efficient and stable autotrophic nitrogen removal,this research adopts the sequencing batch and continuously stirred tank bioreactor respectively to study the nitrification efficiency of different biofilm carriers in aerobic phase of the novel one-stage reactor with the internal reflux under the same conditions.As a result,the porous polyurethane carrier is determined as the suitable aerobic filler to achieve efficient and stable nitrogen transformation in order to satisfy the inffluent demand of subsequent anaerobic ammonia oxidation(Anammox).In order to maintain the system's acid and alkali environment to fit every target strain and to ensure efficient and stable autotrophic denitrification,this research at the same time uses CSTR to study the optimized bicarbonate dosage in both aerobic zone and anaerobic zone.On the basis of the results above the novel one-stage reactor with the internal reflux is adopted to determined the bicarbonate amount to improve nitrogen removal efficiency further.The main results are presented as follow:(1)The nitrite accumulation rate of porous polyurethane carrier as the suitable aerobic filler can reach to 0.84 kg/(m3·d)and polyethylene carrier's is just 0.56 kg/(m3 d).However,as the reaction proceeds,increasing friction results in loss of biofilm,so that polyethylene carrier conversion efficiency of nitrogen is reduced.Polyurethane carriers under the same condition still have high nitrite accumulation rate for 1.4kg/(m3 · d)and the experimental nitrite to ammonium effluent molar ratio maintains above 1.Nitrogen transformation efficiency remains the same after increase of hydraulic shock load,so it is determined as the suitable biofilm carrier for reactor in aerobic zone.(2)The nitrification performance decreases with the decline of bicarbonate to total nitrogen ratio.The nitrogen conversion rate that is 0.8 kg/(m3 · d)by controlling HCO3--C/TN=1.05 gets better while the influent's pH is above 8.25 ± 0.05.When the reactor's pH is controlled to maintain 8 by using a continuous whole mixed flow reactor using the dissolved carbon in the water and CO2 in air can meet the demand for carbon source the in the nitrification process.This indicates that HCO3-in the process of nitrification is mainly used to maintain the pH of the function.(3)Under the condition of constant volume loading and different HCO3-C/TN,the nitrogen removal efficiency of the anammox reaction will decrease as the influent HCO3-concentration decreases.The higher the mass ratio of HCO3-C/TN,the greater the removal rate of nitrogen.The nitrogen removal rate can reach 0.82kgN/(m3· d)While HCO3-C/TN is 0.37±0.01 for optimal dosing ratio and the influent's pH can be maintained around 7.2.Under the condition of constant HCO3-C/TN and different volume loading,the increasing of volume loaing impacts on the nitrogen removal efficiency.The nitrogen removal rate dropped to 40%or less in the anammox reaction by controlling the mass ratio of IC/TN is 0.37 and the volume load is 2.7kgN/(m3 · d)causing the reversible inhibition.(4)Changing of the HCO3-concentration in the combined reaction affect on the aerobic zone greater than on the anaerobic zone.When the amount of bicarbonate concentration is sufficient or not,it has the non-linear relationship between the mass ratio of HCO3--C/TN and the nitrogen removal performance.The best influent's mass ratio of HCO3--C/TN is 0.76 in the combined process while the influent's pH is around 7.7 and the nitrogen removal efficiency is 0.92 kgN/(m3·d).However,increasing the volume of the load impact on nitrogen removal efficiency.When the volume load is 5.2kgN/(m3 ·d),the effluent's pH is much greater than the influent's,the nitrogen removal performance of the joint reaction is affected to decrease to 1.2kgN/(m3 · d). |
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