| Phenol and its related compounds are common contaminants in wastewater especially from petroleum,papermaking,pharmaceutical and chemical industries.As the simplest phenolic organic substance,it is hazardous and bioaccumulation.With the rapid development of industry,the discharge of phenol-containing wastewater are still increasing,which posed a serious threat to the ecological environment.Therefore,an urgent approach is needed to treat phenol-containing wastewater effectively.Because the immobilized technology has attracted widespread attention of the researchers for its advantages of high treatment efficiency,low loss of microorganisms,easy separation of solid-liquid in the process of biological treatment of phenolic wastewater.In this paper,an efficient phenol-degrading bacteria ZS01 isolated from activated sludge was employed as the research object.Firstly,the effects of metal ions on the growth and phenol removal efficiency of ZS01 were investigated.It showed that the proper amount of metal ions could promote the growth and metabolism of microorganisms.The growth and phenol degradation of strain ZS01 have a certain promotion effect when the concentrations of Al3+,Mg2+,Fe3+ and Ca2+ were 25 mg/L,90 mg/L,80 mg/L and 100 mg/L.Among them,the promotion effect of Fe3+is the greatest.The inhibition effect on ZS01 appeared with the further increase of metal ion concentration.Next,four different materials(agar,carrageenan,gelatin and Polyvinyl alcohol)were used as immobilized carriers of ZS01 and their effects on phenol degradation rates were studied.The surface structure,the mechanical stability,the storage stability and the reusability of the immobilized bacteria were characterized.The results showed that the performance of the immobilized beads formed by embedding bacteria with 3%agar was the best.And the degradation rate of 1500 mg/L phenol could reach 100%within 60 hours.After 20 cycles,the agar-immobilized pellets remained intact and the viability of the bacteria in the pellets remained above 130%.After stored at 4? for 30 days,the microorganisms still maintained a relatively stable degradation capacity,and the degradation rate of phenol by agar immobilized bacteria was 90%.Then,the agar with stronger bioaffinity and the carrageenan with stronger stability coupling were selected to construct the composite strengthened phenol-degradation microspheres.According to the spherical shape,rheological properties and phenol-degradation properties of the mixed microspheres,the optimal mixing ratio of the two materials was optimized.2%agar+2%carrageenan showed the best sphere forming performance and the superior gel performance,and the highest strong phenol-degradation properties after embedding the bacteria.The advantages of composite-immobilized cells were further verified by comparing the kinetic parameters of phenol degradation about the immobilized cells and free cells.In order to improve the phenol-degradation performance of immobilized bacteria in composite materials,nano-Fe3O4 was co-cultrued with the bacteria and then added to the composite support material.The results showed that when the concentration range of Fe3O4 was from 0 to 150 mg/L,the phenol degrading performance of Fe3O4-immobilized cells was higher than that suspended cells and non-Fe3O4-immobilized cells.When the concentration of Fe3O4 was 50 mg/L,the immobilized bacteria had the best phenol-degradation performance.All 1500 mg/L of phenol was degraded within 50 hours.The improvement of phenol-degradation performance was attributed to the promotion of substrate mass transfer efficiency and cell metabolic degradation rate by Fe3O4.After 40 cycles,the immobilized pellets of the bacteria embedded in the magnetic composite carrier still maintained a complete morphological state without fragmentation.It indicated that the magnetic composite carrier has strong mechanical strength.Although the viability of the immobilized cells slightly decreased,it still remains above 120%.The strong mechanical strength of the magnetic composite carrier may be due to the electrostatic interactions between the positive charge of nanoparticles and the negative sulfate-ester groups of the carrageenan biopolymer matrix.Finally,the effects of nano-Fe3O4 coupled microspheres on the treatment of simulated phenol-containing wastewater by activated sludge were investigated.It was found that both immobilized bacteria and free bacteria can significantly promote the treatment of phenol-containing wastewater by activated sludge especially for the immobilized bacteria.The removal rate of phenol after 28 hours was 93%,and that of COD after 48 hours was 93%.Four kinds of metal ions(Al3+,Mg2+,Fe3+,Ca2+)added to the activated sludge containing immobilized bacteria could promote the treatment efficiency of activated sludge,of which 80 mg/L Fe3+ has the most obvious promotion effect on activated sludge.The removal rate of phenol by activated sludge reached 100%within 28 hours,and the removal rate of COD within 48 hours reached 99.3%.Due to the high efficiency of high-performance magnetic immobilized materials in the simulated phenol-containing wastewater treatment,it provides a theoretical basis and reference for the application in actual industrial wastewater. |
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