| With the effective control of organic matter and ammonia nitrogen in water and wastewater in recent years,nitrate nitrogen has gradually become one of the key indicators that water quality is difficult to achieve.Excessive nitrate in water may cause eutrophication which may endanger the survival and environmental ecological balance of fish and other organisms.And taking excessive nitrate can lead to methemoglobinemia and cancer.Therefore,an efficient and effective technique is needed urgently to remove nitrate.Anion exchange resin which suggested by EPA is a feasible adsorbent for nitrate removal because of its high efficiency and cost-effectiveness,but brine regeneration complicates subsequent wastewater procedures and may cause secondary pollution.Theoretically,bio-regeneration,as an alternative to brine regeneration,degrades the nitrate from the nitrate-laden resin into N2.It will not produce regeneration solution and avoid the secondary pollution for its reuse of bio-regeneration system.In this paper,based on the study of the adsorption properties of resins,styrene resin(IRA-900)and crylic-acid resin(IRA-958)were used to investigate the feasibility of bio-regeneration to remove nitrate.Combined with its batch adsorption-bio-regeneration,the mechanism of resin contamination was studied in depth.The main contents and conclusions are as follows.(1)Both resins reach the equilibrium in 45 min.And adsorption capacity of IRA-900 and IRA-958 resin is 50.15 mg·g-1 and 47.23 mg·g-1 respectively.Bio-regeneration includes two processes:chemical desorption and denitrification of nitrate.The two processes are carried out at the same time,but speed limiting step is denitrification.The amount of inoculation determines the kinetic process of biological regeneration.The inoculation amount can significantly improve the biological regeneration efficiency.When the concentration of VSS is higher than 0.6 g.L-1,the two kinds of resin can be completely regenerated in 24 h when the solid-liquid ratio of 0.2 g:200 mL.(2)In this bio-regeneration suspension,sodium lactate and sodium acetate can be used as sole carbon source of resin bio-regeneration,while glucose as carbon source,the regeneration rate was slower.NaCl is beneficial to the chemical desorption of nitrate,but when its concentration is more than 20 g·L-1,it had an adverse effect on the regeneration rate of nitrate.When sodium acetate is used as carbon source,,it did not affect nitrate desorption with the increase of sodium acetate concentration,but it promotes the process of microbial denitrification,thus speeding up the bio-regeneration rate.The increase of resin saturation and solid-liquid ratio would extend linearly the time of bio-regeneration.As IRA-958 is more hydrophilic than IRA-900,the desorption rate of IRA-958(81%)in bio-regeneration system is higher than that of IRA-900(75%),which leads to the difference of biological regeneration behavior:Under the lower inoculation(VSS=1.8 g·L-1),saturation of IRA-958 had little effect on the bio-regeneration rate,while the high degree of saturation of IRA-900 was beneficial to biological regeneration.However,with the increase of inoculation amount(VSS=2.8 g·L-1),high inoculation may compensate for this deficiency.The denitrification process may cause the increase of pH,which affected reuse of the bio-regeneration system.Adding K2HPO4 as a buffer could keep the stability of resin adsorption capacity between 41 mg·g-1-46 mg·g-1 during the batch adsorption-bio-regeneration process.(3)In the batch adsorption-bio-regeneration experiment,resins can be used to repeat the reusing of bio-regenerative suspension.But adsorption of nitrate in the first 4 batches of IRA-900 and IRA-958 decreased by 8%and 14%respectively,and then maintained at 41?46 mg·g-1 and 35?41 mg·g-1 respectively.Compared with the adsorption kinetics of fresh resin,the adsorption equilibrium time of the regenerated resin was prolonged from 45min of fresh resin to 120 min.The adsorption kinetic constant k1,k2 of it was significantly reduced in the first 4 times and then remained stable,indicating that the resin was rapidly polluted during the early use of bio-regeneration,but the pollution did not increase significantly during the subsequent batch use.(4)Based on the characterization of regenerated resin and the change of solution environment,the cause of resin pollution was analyzed.It was found that biomass was covered on the surface of the bio-regeneration resin,but it had no obvious correlation with the microorganism and extracellular polymeric substances(EPS).According to the 3D-EEM,resin pollution of bio-regeneration(the reduce of adsorption capacity and the reduce of adsorption)was mainly caused by the protein-like substance in the SMP.And resin will reach the equilibrium capacity of the protein-like substance and it maintain a stability of adsorption capacity with the increase of regeneration times.In this paper,the effects of the resin and biological suspension on the bio-regeneration were investigated,and the operating conditions of the resin bio-regeneration were optimized The bio-regeneration mode of the resin for the application of the biological regenerative liquid was proposed.On this basis,it reveals the pollution mechanism of resin in bio-regeneration process,and evaluates its batches running stability.The experimental results provides important theoretical and technological support for bio-regeneration to remove aqueous nitrate. |
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