Study On Fenton Pre-oxidation&Biochemical Treatment Of Oilfield Wastewater Containing Hydrolyzed Polyacryamide

Followed by enhancing oil recovery, Polymer flooding also produced large amoutof oil wastewater containing partially hydrolyzed polyacrylamide （HPAM）. Theexisting wastewater treatment technology in oilfeild can not effectively deal with thiskind of oil wastewater. The biological treatment process, due to its lower-cost andmore thoroughly treatment has been used in the field of oil wastewater treatment.However, large amount of HPAM existing in this oil wastewater leads to its poorbiodegradability, which makes trouble in its biological processing. Fenton oxidationpretreatment is an effective way to improve the biodegradability of oil wastewatercontaining HPAM, with the advantage of simple operation, low cost and hightreatment efficiency. Therefore, Fenton pre-oxidation&biochemical treatment wasattempted to be used to deal with this kind of oil wastewater in this paper.6bacteria were isolated from oil wastewater containing HPAM, who canbiodegrade both HPAM and crude oil. The evaluation of the degradation effect of oilwastewater containing HPAM by the6strains was done, the nutrition and degradationconditions of the6complex strains were optimized, and the characteristics ofpolyacrylamide and crude oil biodegradation by the6complex strains wereinvestigated. In order to enhance the activity of activated sludge, the6complex strainswere added to the activated sludge system, and Fenton oxidation was applied toimprove the biodegradability of the wastewater. The Fenton oxidation combined withbiochemical treatment of the wastewater was carred out in small scale experimentsbased on the optimal treatment conditions. All the conclusions were as follows:1)6fuction degradation bacteria were screening from the wastewater containingHPAM. The6bacteria were Bacillus sp. PAM, Bacillus sp. PAM-2, Ochrobactrum sp.PAM-3, Acinetobacter sp. PAM-4, Bacillus sp. PAM-5and Bacillus sp. PAM-6. The6complex bacteria had a synergistic effect on the degradation of both HPAM andcrude oil. The biodegradation efficiencies of HPAM and crude oil were higher than asingle strain, which were up to46.1%and47.5%. The6complex bacteria werecultivatied well and had higher HPAM and crude oil removal efficiencies under theconditions of pH of5-9, temperature of30-45℃, salinity of5^-12.5g·L^-1. Smallamount of Fe³⁺and Mn²⁺(≤0.01g·L^-1) can promote microbial growth and metabolism in wastewater biodegradtion.2) The effect of coexistence of crude oil and HPAM on HPAM/crude oilbiodegradation was exploared. The results showed that the coexistence of crude oilcan promote the two substances biodegradation, respectively, in their lower contentrange (0⁵g·L^-1crude oil,0¹g·L^-1HPAM). The effect of coexistence of crude oiland HPAM on Fenton oxidation of HPAM or crude oil was also explored. The resultsshowed that the presence of crude oil reduced the oxidation removal efficiency ofHPAM, however, in the lower content range (0⁶00mg·L^-1), this effect was slight.While, the presence of HPAM in the lower content range (0⁵00mg·L^-1) couldpromote the oxidation removal of crude oil.3) The removal rate of chemical oxygen demand （COD）, HPAM and crude oil inoil wastewater containing HPAM by Fenton oxidation can be up to61.5%,74.0%and47.2%, under the Fenton oxidation conditions of H₂O₂of15mL·L^-1、FeSO₄·7H₂O of700mg·L^-1, pH of5.0, temperature of30℃and reaction time of1h. More than80%of suspended solids （SS） and98%sulfate-reducing bacteria （SRB） in thewastewater were also removed during this process. After Fenton oxidation treatment,the biodegradbality of the wastewater was improved obviously （the value of BOD₅/COD was up to0.4）. The residual H₂O₂after the Fenton oxidation treatment not onlydid not inhibit bacterial growth, but also promoted the biodegradation of the organicmatter in the wastewater. After Fenton pre-oxidation and biodegradation coupledtreatment, the removal efficiencies of COD, polyacrylamide and crude oil inwastewater were up to84.7%,92.1%and83.1%, respectively.4) A first-order reaction dynamic model could be used to describe thebodegradation characteristics of HPAM by the complex strains. The mechanism ofHPAM biodegradation under aerobic condition was preliminarily proposed based onthe results of HPAM infrared spectra and time-off-light mass （TOF-MS） spectrabefore and after bodegradation, the characteristics of HPAM bodegradation by thecomplex strains and others’ research results. The complex bacteria ultilzed the smallmolecules fragments as carbon sources, which obtained from HPAM biologicalcatalysis degradation （Fenton-like process）, the amino-group as nitrogen source,which obtained from HPAM hydrolysis by amidohydrolase. These obtained cabornand nitrogen sources maintained the microbe growth. The HPAM samples by differenttreatment were analysed by scanning electron microscope, IR spectrometry and TOF-MS spectrometry. It showed that HPAM was degraded more thoroughly by Fenton oxidation than that by biodegradation. After Fenton oxidation, HPAM transformed tosmall molecule products, which were lower biotoxicity lead to improve the utilizationeffiency by these microorganisms.The characteristics of crude oil biodegradtion by the complex strains wereexplored via GC-FID and GC-MS ananysis. The results showed that the complexbacteria prefered to utilized aromatics, other than alkanes. The utilization of differenthydrocarbons by the bacteria presented different characteristics. The GC-FID andGC-MS analysis results of crude oil samples by different treatments showed that theexistence of HPAM improved the crude oil removal efficiency in biodegradation,Fenton oxidation and Fenton preoxidation&biochemical processes.5) The actived sludge, which obtained was domesticated in oil wastewatercontaining HPAM from municipal sewage plant. The6complex strains were added tothe activated sludge to enhance the activity of activated sludge. After domestication,the COD removal efficiency of actived sludge adding the complex bacteria wasincreased by30%than that of the common activated sludge.In the continuous feed water conditions, the wastewater was treated by hydrolyticacidification-biological contact oxidation processes, and the water flow conditionswere optimized. The results showed that the removal rates of COD, HPAM and crudeoil in oil wastewater containing HPAM by hydrolytic acidification-biological contactoxidation processes can be up to67.6%,63.7%and58.7%, under the water flowconditions of pH of7.0, hydraulic retention time （HRT） of72h, and temperature30⁴0℃. The SS content maintained15³0mg·L^-1, SRB content dropped to102cell·L^-1during this process.6) The Fenton pre-oxidation combined with biochemical treatment of the oilwastewater sample containing HPAM sampling from Shengli Oilfeild was carred outin small scale experiments. It showed that the removal rate of COD, HPAM and crudeoil was up to94%,93%and95%, respectively. The removal rates of SS and SRBcould reach90%and99%. Flocculation treatment was also carried out to furtherreduce the content of pollutants. After flocculation treatment, COD mantained about20mg·L^-1, the HPAM content was less than5mg·L^-1, the content of crude oil was lessthan2.5mg·L^-1, and the SS content was less than5mg·L^-1, which could meet there-injection or efflux demand.The Fenton pre-oxidation&bio-treatment coupled with flocculation treatment ofthe oil wastewater sample containing HPAM sampling from Daqing Oilfeild was also carred out in small scale experiments. After treatment, the removal rate of COD andHPAM reached97%and98%, which met the secondary standards of DB37/676-2007.The crude oil removal rate of was up to98%, which met the A1-class of SY/T5329-94and the primary standards of DB37/676-2007. The SS removal efficiency of was up to97%, which meet the B class of SY/T5329-94. The SRB removal efficiency was up to99%, which can meet the minimum standards of SY/T5329-94.