Study on Biodegradation-Active Coke Adsorption Treatment of Heavy Oil Wastewater

Author:Zuo Kun

Supervisor:zhang yi he


Degree Year:2012





Heavy oil wastewater is enriched with dissolved recalcitrant organic compounds such as polymers,surfactants,and heavy oil with high density larger than 0.94g/cm-3.Characterizes of this wastewater is high stable,poor nutrients of nitrogen and phosphorus,low BOD5/COD ratios and high toxicity.It is difficult to meet the discharge standards with single method treatment.Chemical method is commonly used on heavy oil wastewater demulsification for remarkable advantage of direct use without adjusts the existing equipments.A reverse emulsion breaker(REB)is combined with cationic polymer Epichlorohydrin-Dimethylamine(EPI-DMA),cationic polyacrylamine(CPAM)and calcium chloride(CaCl2)to treat super heavy oil wastewater in this paper.The optimal ratio of the three demulsifiers is determined to be 20:1.2:600(m/m).The optimal mineral oil and COD removal rates are 98.04 and 94.48%respectively,higher than those of EPI-DMA only and EPI-DMA combined with concentrated sulfuric acid,but this process is more economical and less dangerous.Gas chromatography-mass spectrometry(GC-MS)indicates that this demulsifier can removal more organic compounds than other demulsifiers and most of the residues are oilfield chemicals such as corrosion inhibitors,scale inhibitors,biocides,and demulsifiers.Almost all the mineral oils are removed by REB and this efficient,safe and economical technique is suitable for demulsification of super heavy oil wastewater.Biological methods are cost-effective and environmental friendly technologies for heavy oil wastewater treatment.In this paper,a conventional activated sludge process(CAS)coupled with immobilized biological aerated filter(I-BAF)was constructed to treat moderate biodegradable heavy oil wastewater with stable concentration.After treatment,COD of the wastewater was removed around 64%when the hydraulic retention time(HRT)was 18 h.The average effluent COD reached approximately 75 mg/L,which met the criterion specified by the Chinese discharge standard for water pollutants.GC-MS indicated that the CAS process could completely remove phenolic,alkenes,aldehydes and organic acid groups from the wastewater and the alkane components were removed by the I-BAF.Environment scanning electron microscopy disclosed that bacteria flourished in both reactors during the operating period and most of them resemble rods and filamentous.The bacterial community structure analysis based on Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis(PCR-DGGE)technology revealed that the predominant bacteria in the CAS reactor belonged to the Pseudomonas and Planococcus groups and the Agrococcus and Acinetobacter groups that were major degraders in the I-BAF reactor.Some high molecular weight n-alkanes(C15-C23)were found to be refractory in this biotreatment system.Another process has been constructed with an upflow anaerobic sludge blanket(UASB)and I-BAF to treat heavy oil wastewater with large amounts of dissolved recalcitrant organic compounds,low nutrient of nitrogen,phosphorus and lower biodegradability with unstable concentrations.By operating the system for 252 days(including the start-up of 128 days),BOD/COD ratio of the wastewater increased from 0.176 to 0.252.COD,oil,TN,and NH3-N removal rates are 77.33,99.23,84.57 and 84.54%respectively when HRT of UASB and I-BAF is 12h respectively.ESEM showed that large quantity of rods and filamentous microorganisms are flourished in reactors.The predominant bacteria are Bcillus spp.and Rhodobacterales。Activated coke(AC)was studied to adsorb organic pollutants from heavy oil wastewater after biotreatment.This study focused on the absorption kinetics and equilibrium isotherms of AC for the removal of COD from heavy oil wastewater.UV-vis spectra and GC-MS were used to detect the changes of super heavy oil wastewater quality.The surface morphology of AC before and after adsorption was observed using scanning electron microscope(SEM).The results showed that when the dose of AC was 0.5 g/L,COD in effluent less than 50 mg/L at 30℃.The kinetics of adsorption of COD from heavy oil wastewater onto AC is fit to the pseudo-second order model.The adsorption of COD onto AC was enhanced with an increase of temperature,indicating that the adsorption process would be a chemical adsorption rather than a physical one.Freundlich gave a better fit to all adsorption isotherms than Langmuir,Temkin,Dubinin-Radushkevich.