Study On Low-temperature Low-strength Ammonium Wastewater Treatment By Zeolite Adsorption And Its Bio-regeneration

In winter period of Northern China,because of the great inhibition of nitrifier's activity at low temperature,ammonium cannot be effectively removed based on traditional nitrogen removal process for many wastewater treatment plants,failing to reach the discharge standard.Adsorption is hardly influenced by temperature that can guarantee the effluent ammonium meeting discharge standard with easy opearation and no secondery pollution.For the adsorption effluent could discharge meeting the standard,it only needs to treatment adsorbed ammonium in adsorbent thus desearcing the wastewater treating volumn.Zeolite is cheap and abandunt so it is the often applied adsorbent.For the limited adsorption capacity,zeolite needs to be regenenrated for recycling use.Among all the regenetion methods,bio-regenertion was economic and clean,of which zeolite bio-regenertation solution could directly discharge after denitrification.Thus,this research applied zeolite biological fixed bed?ZBFB?to treat the low-temperature?6¹0^oC?low-strength ammonium wastewater by zeolite adsorption–zeolite bio-regeneration-denitrification of zeolite regeneration solution.To solve the problem of low zeolite bio-regeneration efficiency,two-stage reactors operation in series was proposed and the optimum operation conditions were explored.The ammonium nitrogen removal mechanism of this process was also investigated,which provided the technique guidance and theoretical fundament for practical low temperature ammonium wastewater treatment.After the successful establishment of ZBFB,the study of adsorption characteristics of ammonium onto bio-zeolite?zeolite covered by bio-film?was investigated.It was found that the bio-film had little effect on ammonium adsorption capacity of zeolite.In the researches of ammonium-saturated zeolite bio-regeneration,the lower regeneration rate was obtained with lower influent temperature,longer adsorption period and larger particle size.At zeolite regeneration stage,that ZBFB and ceramsite biological aerobic filter?CBAF?run in connected series prompted the zeolite bio-regeneration rate whose efficiency was 2 to 5 times that of it in single-stage ZBFB.With the optimized experimental conditions of adsorption stage,zeolite bio-regeneration rate reached over 90%in 24 h.Alkalinity played two important roles as ion exchanger and substrate for nitrification in zeolite bio-regeneration process,which exerted a profound impact on improving zeolite bio-regeneration efficiency.With NaHCO₃ supplied as alkalinity,the higher zeolite bio-regeneration rate was obtained with more dosage.Compared to several times addition mode of alkalinity,one dose mode achieved highest bio-regeneration rate.And the zeolite bio-regeneration process was found to meet the pseudo-first order kinetics.The mechanism of ZBFB-CBAF enhancing zeolite bio-regeneration could be concluded as follows:with the addition of alkalinity,firstly Na⁺exchanged the NH₄⁺-N from zeolite;then the desorbed ammonium was converted into NO₂^--N and NO₃^--N by nitrifying bacteria.The circulation of regeneration solution not only helped to form the ammonium concentration gradient between regeneration solution and inner zeolite,thus enhancing the further desorption of ammonium,but also made ZBFB inoculated by nitrifying microorganisms of high activity from CBAF and prompted ammonium conversion.The repeats of ammonium desorption and biological conversion improved the quick zeolite bio-regeneration.With optimized alkalinity conditions,30 cycles consistent operation of ZBFB-CBAF was conducted treating synthetic ammonium wastewater of 30³7 mg/L with 8^oC.It was shown that the effluent ammonium concentration was 0.9¹.5 mg/L and zeolite bio-regeneration rate was about 76.0%⁸6.1%.The dynamic ammonium adsorption experiment was then carried out.The treated wastewater volume was 81 times of filling's which indicated that zeolite still kept relatively high ammonium adsorption capacity after numerical cycles'operation.Finally,the regeneration solution was treated by denitrification,with CH₃COONa as external carbon.The total nitrogen removal rate exceeded 98.7%,effluent TN<3 mg/L and effluent COD was about 16.4³9.7 mg/L.The results suggested that ZBFB adsorption–ZBFB-CBAF zeolite bio-regeneration–regeneration solution denitrification in DNSBR was feasible for efficient low-temperature low-strength ammonium wastewater treatment.