Low-carbon Nitrogen Removal For Low-strength Ammonium Wastewater Based On Adsorption And Biological Desorption

It is a big challenge to realize the low-carbon and economical nitrogen removal for low-strength ammonium wastewater with low C/N ratio.Compared with anammox,though nitritation-denitrification saves less energy and carbon source,this process is more stable and available for low-strength ammonium wastewater.However,there is still a big obstacle that how to achieve stable nitritation of low-strength ammonium wastewater right now.Based on the excellent ammonium adsorption performance and nitrifiers carrier of zeolite,this study intended to figure out whether nitritation of low-strength ammonium wastewater could be realized by adsorption and biological desorption by the zeolite biological fixed bed?ZBFB?,and carry out the further denitrification by an anoxic sequencing batch reactor?ASBR?.This study tried to support theoretical basis for the application of adsorption and biological desorption by ZBFB to nitritation-denitrification of low-strength ammonium wastewater.The best operational influent upflow rate for the adsorption low-strength ammonium wastewaiter?NH₄⁺-N=50mg/L?by ZBFB was 1.8m/h and the breakthrough point was 32h.It was found that adsorption capacity of ZBFB changed slightly after the cultivation of biofilm.In the biological desorption process,with 2g/L Na₂CO₃,operational time of 16h?aeration of 0.06Nm³/h and internal recycling upflow rate of 1.8m/h,the main product in biological desorption effluent was NO₂^--N.The key for successful nitritation in biological desorption was the inhibition of FA on NOB and the strict operational parameters.Then ZBFB-ASBR was applied for treatment of low-strength ammonium wastewater by cycle operation of adsorption,biological desorption and denitrification.It was found that the adsorption effluent NH₄⁺-N was always lower than 5.0mg/L.In earlieroperationalcycles,ZBFB-ASBRdefinitelyrealizedthe nitritation-denitrification for low-strength ammonium wastewater.However,because of decrease of FA and adaption of NOB in biological desorption process,nitritation was gradually destroyed after 35 cycles.The damage of nitritation in biological desorption resulted in the nitrogen removal pathway in ASBR from nitritation-denitrification to nitrification-denitrification,which increased carbon source consumption in ASBR.Sufficient relative abundance of Nitrosomonas and Nitrosococcus in ZBFB were the key for nitritation in biological desorption,while subsequently Nitrobacter became more and more,leading to the damage of nitritation.Dominant relative abundance of Paracoccus?8.44%?and Pseudomonas?2.30%?were the reasons for excellent denitrification in ASBR.It was tried to find the way for recovery of nitritation in biological desorption in ZBFB.Changing of aeration mode could not work,while the operation of gradual temperature increase to 36^oC could restore nitritation in the biological desorption of ZBFB.The main reasons for recovery of nitritation in biological desorption were the faster desorption rate of NH₄⁺-N,higher specific growth rate of ammonia oxidizing bacteria?AOB?and FA inhibition on NOB caused by temperature increase.Controllingthebiologicaldesorptiontemperatureat36^oC,stable nitritaion-denitrification of low-strength ammonium wastewater could be realized by the adsorption,biological desorption and denitrification of ZBFB-ASBR.High throughput analysis and QPCR results further demonstrated that significant relative abundance incease of Nitrosomonas happened in ZBFB with long-term biological desorption operation at 36^oC,while Nitrobacter and Nitrospira were both obviously inhibited.The increase of biological desorption temperature were the guarantee for stable nitritation in biological desorption by ZBFB for treatment of low-strength ammonium wastewater and the key for realizing nitritation-denitrification for low-strength ammonium wastewater by ZBFB-ASBR.