Construction Of An Adsorption-biodegradation Coupling System For The Enhancement Of Cyanide And Phenol Removal

Biodegradation is an effective method for completely eliminating environmental pollutants.However,there are some restrictions and limitations for the treatment of toxic wastewater with the conventional biological process,such as easy of inactivation of microorganisms,system failures and inadequate degradation of target pollutants.As a result,the discharges of such wasterwater are always difficult to meet the accepted standards.Therefore,developing a robust and efficient biological enhanced system is one strategy for the treatment of industrial wastewater.Cyanide and phenol are both listed as priority pollutants by environmental monitors worldwide.Many industrial wastewaters often contain these two pollutants.In the coking industry in China,the total amount of cyanide-phenol wastewater that is discharged is nearly 300 million tons per year.Given the strong toxic effects of cyanide and phenol on microorganisms,the degradation of cyanide and phenol is particularly important.In this paper,a bioaugmentation system was developed for the treatment of coking wastewater based on immobilized high-efficient-degrading microbial strains.Research work included five contents as follows:（1）Screening and isolation of cyanide-phenol degrading strains.Industrial coking wastewater was selected as a simulated object.Models for screening of simple inorganic cyanide（including free cyanide and thiocyanate ions）and phenol were established.Seven strains screened from the polluted soil could tolerate alkaline condition（pH 10.0）and could simultaneously degrade both free cyanide and thiocyanate ions.All these strains showed a common characteristic for preferentially degrading free cyanide ion with more than 80%of degradation efficiency,and four strains could degrade more than 60%of the thiocyanate ion.One strain,Alcaligenes sp.DN25 simultaneously degraded cyanide,thiocyanate and phenol at initial concentration of 100 mg·L^-1 by 98.4%,72.8%and 81.6%respectively.（2）Characteristics of the typical cyanide-phenol degrading strain DN25.In accordance with the known degradation mechanism of cyanide and phenol,the cyanide-phenol degrading enzyme system of strain Alcaligenes sp.DN25 was discussed.The genes of cyanide-degrading enzyme and phenol hydxoxylase were successfully cloned.It was found that iron ion played an important role in the synthesis of cyanide-phenol degrading enzymes.Phenol was degraded via an orhto-pathway,and the products included catechol,cis,cis-muconic acid and succinic acid.The strain DN25 was inhibited when phenol concentration exceeded 100 mg·L^-1 and completely failed to degrade at a concentration of 600mg·L^-1.In a binary system containing cyanide and phenol,both pollutants were degraded simultaneously.Moreover,the degradation of phenol by the strain DN25 was accelerated in the presence of cyanide,and phenol at 600 mg·L^-1 was completely degraded within 7 days,thereby demonstrating a good potential use in the biological treatment of multi-pollutant wastewaters.The strain DN25could use cyanide and its degradation product ammonium as the sole source of nitrogen,and phenol as the sole source of carbon for growth.Cell growth and proliferation were considered the main reasons for accelerating phenol degradation.（3）Research on the simultaneous adsorption and biodegradation（SAB）system.Analyzing the mass transfer in the process of biodegradation,polyurethane foam（PUF）was selected for cells immobilization.The removal mechanism of the SAB system was studied using the single substrate cyanide as a model.The results indicated that the PUF physically adsorbed free cyanide ion and the experimental value of maximum adsorption was 5.78 g[CN^-]·g（PUF）^-1at 30℃,pH 8.0 and 120 rpm.Biodegradation played a leading role in the SAB system and the level of gene expression of cyanide-degrading enzyme was up-regulated by approximately 40%after strain immobilization.At a cyanide concentration of 200 mg·L^-1,92.6%could be removed within 3 hours by the SAB system,which was significantly higher than the removal obtained by PUF adsorption or biodegradation alone,and was higher than that obtained with both combined.The synergistic effect of the SAB system could be attributed to the interfacial adsorption by the PUF,which led to（i）better contact between the strain and cyanide,（ii）activation of cyanide-degrading enzyme activity,and（iii）the improved production and expression of cyanide-degrading enzyme.（4）Research on phenol and cyanide-phenol removal by the PUF-immobilized cell SAB system.For phenol as the single substrate at 600mg·L^-1,the degradation efficiency of the freely suspended cell system only reached 42.5%during 6 days in a case of doubling the biomass,while the SAB system completely degraded in 120 hours.In the binary system of cyanide and phenol,only 58 hours was required for the removal of phenol by the SAB system.There were three synergistic effects on the removal of cyanide and phenol by the PUF-immobilized cell SAB system:（i）synergistic adsorption of cyanide and phenol,（ii）synergy of adsorption and degradation,and（iii）enhanced degradation of phenol by cyanide.（5）Research on the scale-up of the PUF-immobilized cell SAB system.A packed bed bioreactor with a working volume of 850 mL was designed and operated for the treatment of simulated cyanide wastewater.When the inlet cyanide concentration was greater than 200 mg[CN^-]·L^-1 and the pH was gradually increased from 8.0 to 9.0,the running of the freely suspended cell reactor completely failed on the 23rd day,while the PUF-immobilized cell reactor steadily run for 31 days with the average removal rate of 91.5%and still maintained degradation activity.In addition,the PUF-immobilized cells were also employed for the bioremediation of the cyanide-contaminated soil.In a case of doubling the biomass,44.6%of remediation efficiency was obtained in 8days for the freely suspended cell system at the average total cyanide concentration of 60.8 mg[CN^-]·kg（soil）^-1.By contrast,the remediation efficiency of the immobilized cell SAB system could reach 74.8%during 6 days,indicating a good stability and great potential for practical applications.