| Coking wastewater is with complex component and hard to be treated. Ammonia andrefractory organic compounds which included in coking wastewater may cause greatenvironment pollution. High concentration of free ammonia can directly affect fish and otheraquatic organisms even to die. In addition, nitrite and nitrate produced by ammonia oxidationhave carcinogenic effects. Refractory organic pollutants in coking wastewater containphenolic compounds, polycyclic aromatic hydrocarbons and nitrogen-, oxygen-, sulfur-heterocyclic organic compound. Within these pollutants, alkyl phenol, phthalic acid (ester),pyridine etc. are considered to be environmental endocrine disruptors, and polycyclicaromatic hydrocarbons are also identified as priority pollutants by the United States EPA.Generation and accumulation of these kinds of refractory organic pollutants in wastewater,may cause the conventional processing methods is difficult to reduce the risk.Bio-electrochemical method which applied to wastewater treatment has high electriccurrent efficiency and desired treatment effect. However, the technique, at present, isimmature and there are some key problems to be solved, for example, the difficult biofilmgrowing, and the low efficiency electron transference. So, bio-electrochemical method appliedto coking wastewater treatment is worth studying.This study aimed at treating of simulated coking wastewater containing highconcentration of ammonia and refractory organic compounds. Based on the AO biologicalfluidized bed reactor, strengthening methods, as organic degraders enrichment andelectrochemically inducing, are applied to improve nitrogen and organic pollutants removalefficiency in wastewater. By fluidized sludge and the electrolyte adding, thebio-electrochemical fluidized bed system can easily transfer electrons through electrode,microbial and the pollutants without bioflim growing.Based on the operation data of coking waste water treatment plant, the compersition ineffluent from biological fluidized bed A/O1/H/O2integrated process were COD145.5mg/l,phenolic compounds0.10mg/L, and ammonia0.53mg/l. By results of GC-MS, degradableorganic matter such as phenol, pyridine, quinoline, could be efficiently removed, whereasrefractory or toxic organic pollutants such as long-chain alkane, polycyclic aromatichydrocarbons, and benzene still remained in the effluent after treatment.Biological fluidized bed treatment system was constructed, and the optimal conditionswere: CO32--C/N=2:1, CH2-C/N=1.5:1. The removal rate of ammonia was up than95%wheninfluent ammonia concentration was under300mg/l; and the nitrate removal efficiency can also reach up to95%when influent ammonia concentration was less than200mg/l. Nitrateand organics can not thoroughly removed under low temperature. The nitrate removal rate isonly2.87mg/l/h under22℃, and80%of the nitrate remained in the effluent.As to treating the refractory organic pollutants in wastewater, polycyclic aromatichydrocarbons was studied as typical pollutants. By enrichment and domestication method,microbial grown with pyrene as sole carbon source were isolated from sludge of cokingwastewater treatment station and named Pyr2, Pyr41and Pyr42. By16S rDNA identification,Pyr2, Pyr41and Pyr42may belong to Castellaniella spp, Pseudomonas spp. andBurkholderia spp., respectively. Results showed that, optimal growth environment of Pyr2ispH6.5, temperature32℃and shaking speed is70rpm, and100.39mg/l pyrene can bedegraded by97.2%within12d under optimal conditions. Pyr2pyrene degradation processwas simultaneously accompanied with nitrification and denitrification, thus their biologicalmetabolism process of C/N is about1.776. Optimal growth environment of Pyr4(composedof two strains Pyr41and Pyr42) is pH7, temperature35℃and shaking speed is100rpm, and50mg/l pyrene can be degraded by65.02%within48h under optimal conditions. Pyr2pyrene biodegradation process is consistent with a first-order kinetic reaction. According tothe dynamics calculation, speed of Pyr4pyrene metabolism is about10times fastor than thereferrance.Pyr4pyrene biodegradation can be stimulated when glucose or anthraquinone added, andthe specific degradation rate increases from0.0337h-1to0.0689h-1or0.0721h-1. By theanalytical results of GC-MS, intermediate involved in Pyr2biodegradation process was notdetected, while1-naphthol was detected as one of the inermediates in the Pyr4biodegradation process.In the bio-electrochemical fluidized bed treatment process, there is a synergistic effectbetween electric and biological, but biological electrochemical reaction can not be obviousaccelerated when current supplied more than10mA. In the condition of the influent ammonia200mg/l, COD650mg/l, temperature22℃, reflux ratio1:1.5, HRT15h,10mA biologicalelectrochemical system could make nitrate removal rate reach up to10.92mg/l/h, which was3times higher than traditional bio-system. Adding of Cu2+could accelerate thisbio-electrochemical process. by contrast of phenol, quinoline and pyrene removal bytraditional bio-system was only63.1%,50.4%and56.2%, these removal bybio-electrochemical system could reach up to95%. By the PCR-DGGE analysis, in theanaerobic reactor after electrochemical inducing,2strains, Pseudomonas sp. and Rhodobacter sp. were obviously increased; in the aerobic reactor, microbial polymorphism had adecreasing trend, and there were3strains gradually disappeared, which were Bacillus sp.,Rhodococcus sp. and Sphingomonas sp..Nitrogen and refractory organic compounds are commonly exist in coking wastewater, sosimultaneous degradation of organic matter and nitrogen is the main problem of cokingwastewater treatment. Pyrene degradation process of Castellaniella Pyr2obtained from theactivated sludge was coupled with nitrification and denitrification. Thus, the specific strain ofCastellaniella Pyr2is worth scientific research and can be applied in industrial wastewatertreatment.The bio-electrochemical fluidized bed treating approach is the first time for fluidized bedreactor applied in bio-electrochemical reaction. Electron transfer and the limits of electrodemicrobial biofilm were effectively solved by the application of this approach. By using thebio-electrochemical fluidized bed approach to treat coking wastewater, the biologicalhydraulic remain time can be shortened for3times, and environment risk can also be deducedfor the efficient removal of refractory organic pollutants. |
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