Destabilization Mechanism And Control Strategies Of The Anammox Attached Film Expanded Bed Reactor

Anaerobic ammonia oxidation?anammox?process has the advantages of high nitrogen removal efficiency,no additional external carbon sources,low energyconsumption and so on,and it has a wide application potential in the treatment of high ammonia nitrogen wastewater.However,there are still vital problems in anammoxreactor,such as low nitrogen loading rate,poor operation stability and sludgeretention capacity.The novel anammox attached film expanded bed?AAFEB?reactor has potential for realizing high nitrogen loading rate and forming granular sludge with high physical strength and settling velocity.However,the AAFEB reactor still faces the problem of reactor instability in the treatment of high ammonium nitrogenwastewaters.In this study,firstly,the nitrogen removal performance of the AAFEB reactor for high-strength wastewaters treatment under different influent substrate concentrations and loading rate was investigated.The kinetics of substrate degradation andstoichiometric variation was analysed.The spatial distribution of substrateconcentrations and granular sludge characteristics were combined to analyze thedestabilization mechanism of AAFEB reactor.Secondly,a series of control strategies,including effluent circulation,influent substrate ratio and p H real-time regulation,were analysed to avoid substrate self-inhibition as well as realize the long-term stable operation of reactor;in addition,the characteristics of anammox granular sludge was discussed and the mechanism of accelerating sludge granulation was analysed.Finally,a two-stage partial nitritation-anammox process was built to treat high ammonium wastewater,the control strategies for partial nitritation and theperformance of AAFEB reactor in two-stage process were investigate.The main research contents and results are as follows:?1?The removal and distribution characteristics of substrate nitrogen in the instability phase of the AAFEB reactor were investigated,it was found that thesimultaneous inhibition of FA and FNA caused reactor instability.In the initial stage of suppression,the high influent concentration and high p H induced FA suppression of bottom sludge;when the suppression occurred,the substrate removal efficiency dropped significantly?99%?80%?,resulting in a large amount of effluent NO₂^--N remaining?185.5 mg N/L?and a decrease in p H?8.5?7.8?,which in turn triggers FNA inhibition.?2?The characteristics of the granular sludge of the AAFEB reactor at different influent phosphorus concentrations were investigated.Severe granular sludge floating will occur at low influent phosphorus concentrations,resulting in the loss of the main sludge of the reactor and blocking the return pipe,which then initiates the reactor to destabilize.Increasing the phosphorus concentration in the influent?46 mg P/L?can effectively promote the formation of hydroxyapatite,thereby significantly improving the sedimentation rate of granular sludge?>200 m/h?and avoiding the occurrence of floating sludge.?3?The effects of effluent recirculation,influent matrix ratio(NO₂^--N_inf/NH₄⁺-N_inf)and p H real-time adjustment of influent on the reactor stability were studied.The effluent recirculation diluted the high-concentration influent?1667 mg N/L?so thatthe matrix concentration of the inlet of the reactor low than 112±8 mg N/L.Moreover,the influent substrate ratio and p H of the influent are adjusted in real time,whichfurther reduces the occurrence of FA and FNA inhibition on sludge.Three control strategies are used in combination to achieve long-term stable operation of theAAFEB reactor with a volume load of 16.7 kg N/m³/d.?4?The characteristics of granular sludge in the AAFEB reactor were investigated and the effect of enhanced hydroxyapatite formation on sludge granulation wasanalysed.The results showed that the formation of hydroxyapatite in the enhanced AAFEB reactor resulted in a high bio-enrichment?61.4 g VSS/L?,a reasonableparticle size distribution?1.42±0.60 mm?and a high sedimentation velocity?287 m/h?The granular sludge accelerates the process of sludge granulation.?5?A two-stage partial nitritation anammox process was established for high-strength wastewater treatment.The partial nitritation can be achieved by inhibiting the NOB with high free ammonia concentration and multiple factors.Finally,the loading rate of the partial nitrification process reached 2.4 kg N/m³/d,and the total nitrogen removal rate of the two-stage system reached 92.3±1.6%.