| Along with the increasingly concerning to energy shortage,there is a wider application of anaerobic digestion process for energy recovery from wastewater,but treatment of a typical digestion liquid with high ammonia concentration and low C/N ratio is always difficult and energy intensive.Nitrogen removal via nitrite in a single MABR is a potential cost saving technology.However,how to sustain a stable nitritation performance and by what means to final remove nitrogen remains further studied.In this study,three continuous-flow MABRs equipped with inexpensive polypropylene hollow fiber membranes were constructed to explore nitrogen removal performance under different but limited air supply strategies: continuous air supply,intermittent air supply,and no extra air supply.Subsequently,the effect of MABRs under different influent conditions and operating conditions was studied.Finally,under proper operation conditions,nitrogen removal via nitrite in a single-stage MABR system were achieved by the denitrification or anaerobic ammonia oxidation process for high ammonia wastewater.Along with the increase of influent ammonia concentration,different but limited air supply strategies all get desirable nitrite accumulation rate: the one with lumn air pressure kept at 0 k Pa firstly accumulated more than 80% of the transformed ammonia on the tenth day under an influent ammonia loading rate(ALR)of 3.68 g-N m-2 d-1,subsequently reach up to 90% after another two weeks when ALR is 6.13 g-N m-2 d-1;intermittent aeration or continuous aeration shows a similar pattern of nitrite accumulation,getting high nitritation effect when ALR higher than 4.9 g-N m-2 d-1,with a highest nitrite accumulation rate upper than 98%,The differences in gas supply strategies influence the growth of biofilms and the removal of ammonia rather than the success of nitritation.Adequate air supply helppled to form thicker biofilms and degrade more ammonia;The success of nitritation results from the inhibition of free ammonia(>2 mg/L)in the liquid phase and the combined effect of dissolved oxygen(<0.5 mg/L)concentration in wastewater due to the consumption of organic matter and ammonia.Microbial community structure analysis revealed that the dominant microorganism of ammonia oxidizer in MABRs was Nitrosomonas,and no significant proportion of NOB genus was found,an excellent proof of the feasibility of using MABRs for nitritation.Anything else,the presence of multiple types of denitrifying microorganisms reveals the potential for single-stage nitrogen removal in MABRs.The nitrite accumulation rate in MABR dropped to a minimum of 20% when the influent alkalinity was insufficient and the ammonia nitrogen concentration was lower(?210 mg/L in this study).When the influent ammonia nitrogen concentration increased to 280 mg/L with an alkalinity of 4 times,the nitrite accumulation rate can still maintain over 90% even 50% ammonia was consumed.The influent ammonia loading rate has the greatest influence on the performance of MABR;the change of cross-flow velocity has no significant effect on the performance of MABR in a short period;the gas supply pressure has a certain influence on the operating effect,but the effectiveness of the gas supply will be influenced when the membrane fouled.When combined nitritation with denitrification in a single MABR,more than 80% nitrogen removal can be acquired,and more than 90% once combine with anammox.Effluent from MABR for denitrification contains more ammonia,which is hard to further degrade even reduced the ALR or higher the air pressure.The quantity of ammonia that the ammonia oxidizing bacteria can consume is nearly saturated,and it will be hard for AOB to capture ammonia since there is a small ammonia gradient caused by low bulk ammonia concentration,ultimately shows a poor nitrogen removal rate.Different with the former,nitrogen removal by anammox is less limited by ammonia consumption and achieves higher nitrogen removal efficiency than the former at the same influent ammonia loading rate. |
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