Microalgal Biosorbents Production By Microalgae Cultivated From Cephalosporin Antibiotics Wastewater

Microalgae cultivation from wastewater is a very promising technology of wastewater treatment and bioresource utilization technology bioavailability.The growth inhibition of microalgae by toxic and harmful substances in wastewater,and reused technology of microalgae biomass are the two main hot points of this technology.To solve the above issues,this study utilized cephalosporin wastewater as a representative and high toxicity industrial wastewater to cultivate microalgae.Visible-light photocatalytic technology was proposed as the pretreatment of wastewater to reduce the growth inhibition of residual antibiotics on microalgae and increase its yield.The cultivated microalgal powder was prepared as pollutant adsorbent to realize the resource utilization of wastewater.In this research,the mechanisms of photocatalytic degradation of antibiotic residues and adsorption of different types of pollutants by microalgae adsorbents were analyzed in detail.This provides novel strategies and technical supports to solve the problems of microalgael biological inhibition cultivated in industrial wastewater and the reuse of microalgae biomass.The main contents and results are described as follows.The two microalgal strains could utilize nitrogen and phosphorus sources in wastewater for rapid microalgal cell growth.However,the presence of antibiotics in the wastewater could significantly inhibit the microalgal growth activity and yield,and also inhibit the performance of NH4+-N and COD removal.The growth inhibitory effects of different cephalosporin antibiotics on Chlorella sp.Cha-01 and Chlamydomonas sp.Tai-03 were analyzed by single factor experiments.Cefadine and ceftazidime obviously inhibited the growth of Chlorella sp.Cha-01;Cefradine,ceftazidime and cefoperazone also had strong inhibition on Chlamydomonas sp.Tai-03.In microalgae cultivation,it was found that the cephalosporins itself could be quickly removed.The single factor experiments on various environmental factors showed that the removal of cephalosporin antibiotics was a complex process,which consists of microalgae adsorption,hydrolysis,photolysis,and so on.All six cephalosporin antibiotics could be hydrolyzed rapidly in water,and their hydrolysis rates were further enhanced under light radiation.Some cephalosporins,such as cefradine and cefoperazone could have more growth inhibitory effects on microalgae than the original substance.To reduce the inhibition of antibiotics on the microalgae,the visible light photocatalysis was applied as the pretreatment of wastewater.The pollutants removal and the enhancement of microalgae growth in wastewater caused by photocatalysis were studied.A high photocatalytic active visible light catalyst Bi2WO6 which assembled from a small 2D layer was prepared by adding the surfactant CTAB to control the photocatalyst structure in the hydrothermal synthesis catalyst.The mechanism analysis shows that CTAB can not only improve the microstructure of Bi2WO6,but also enhance its optical absorption by doping Br in the process of synthesis.In the process of photocatalytic degradation,·OH and h+ are the main predominant reactive species produced by Bi2WO6.All degradation kinetics could fit the the first-order dynamics model.The degradation rates were decrease in the order of: 7-ACA>cefoperazone>ceftriaxone >cefazolin>cefadazine>ceftazidime.The degradation products and pathways of each cephalosporin were analyzed by the combination of quantum chemical calculation and mass spectrometry.It was found that the presence of Cl-、SO42-、NO3-、PO43-and NH4+ would inhibit the photocatalytic removal rate,when applying visible light photocatalysis in simulated wastewater pretreatment.Next we enhanced the photocatalysis performance by increasing the amount of Bi2WO6,adding H2O2 and adjusting the initial p H.Under photocatalysis with 2 hours,99.4% cephalosporin antibiotics in wastewater could be removed.Then the performances of microalgae cultivation in wastewater with different photocatalytic pretreatment time were studied.After 3 h photocatalytic pretreatment,the yields of microalgae Chlorella sp.Cha-01 and Chlamydomonas sp.Tai-03 can be enhanced by 1.29 times to 1.88 times of that in raw wastewater without pretreatment.Meanwhile,29.0%-40.1% and 21.2%-39.8% of COD and NH4+-N removal rate were increased respectively due to the increase of microalgae yields.Two kinds of adsorbents,microalgal residue and microalgal biochar,were prepared from the harvested microalgae cultivated with wastewater.Compared with raw microalgal powder,the physicochemical property changes of microalgae after homogenization fragmentation were relatively small,rich functional groups like-OH、-CH and C=N on the surface of microalgae were retained.The chemical composition and surface properties of the microalgal biochar prepared by high temperature pyrolysis were obviously changed.Carbonization could lead to great reducing in the content of functional groups such as-OH、-CH、C=N、-N-H、-NH3 on the surface of the microalgae.Therefore,microalgal residue adsorbent had extremely high efficiency on Cd2+ adsorption by heterogeneous monolithically chemical adsorption though large amounts of functional groups like raw microalgal powder nearly 87.5%-96.5% equilibrium adsorption could be achieved in 2 minutes which the adsorption capacity was much higher than microalgal biochar.However,the results of PNP adsorption on microalgal biosorbents were very different.Carbonized Chlorella sp.Cha-01 exhibited very strong adsorption capacity,and the equilibrium adsorption capacity was 2.47 times that of the original microalgae powder and 2 times of Chlamydomonas biochar.The mechanism analysis of its high adorption capacity was conducted,which indicated that Chlorella biochar was more polar and hydrophilic than Chlamydomonas biochar and activated carbon.Chlorella biochar could not only adsorb PNP through π-H and π-electron adsorption force due to a large number of polar groups,could also form π-π force with PNP to achieve high adsorption performance by its aromaticity like activated carbon.This study combined the visible-light photocatalytic pretreatment for cephalosporin antibiotics wastewater with microalgae cultivation for producing microalgal biomass and preparing bioadsorbents used for high-efficient pollutants removal.This study could not only realize the resource utilization of antibiotic wastewater,but also reduce the cost of microalgae cultivation,and would provide new schemes for the resource utilization technology of high toxic industrial wastewater and the high value utilization of microalgae biomass.