Generation Of Persulfate In Electrolytic System And Treatment Of Oilfield Wastewater

In this study,oil recovery wastewater from the Liaohe oilfield was used as the target material,and the removal of COD and TOC as well as the automatic generation mechanism of persulfate in the anodic oxidation system with Na₂SO₄ as the electrolyte was examined.The anodic oxidation and the preparation of polymerized ferric sulfate are organically combined into one,which achieves the purpose of reducing the cost of water treatment and waste resource utilization.The details of the study are as follows:Initially,oilfield recovery wastewater was pretreated using a novel vortex coagulation method,and the effects of the coagulant dosage,p H level,agitation time,agitation speed,and type of filter cotton on the removal of COD and TOC from the oilfield wastewater were examined.The outcomes demonstrated that after 40 minutes of stirring with glass fiber filter cotton,the COD of oilfield wastewater decreased from 1100 mg/L to 264 mg/L and the TOC decreased from 500 mg/L to 220 mg/L under the ideal conditions of a coagulant dosage of 0.25g,p H=7.0,and stirring speed of 150 rpm.Based on pretreatment,the wastewater was further treated in a daylight/anodic oxidation system with Na₂SO₄as the electrolyte to reduce the cost of water treatment while meeting the discharge standard.The effects of electrolysis time,current strength,sodium sulfate dosage,p H on the production of persulfate,and the effect of COD and TOC removal from oilfield wastewater were investigated,and the results showed that at p H=7.0,the applied current strength was 1.2 A,[Na₂SO₄]=0.8 mol/L under the optimum conditions,the concentration of persulfate in the system reached 0.45 mmol/L after 50 min of electrolysis,at which time the TOC of oilfield wastewater was reduced from 220 mg/L to 131.3 mg/L and COD from 264mg/L to 144.5 mg/L.Following the completion of the electrolysis,0.1 g of ferrous sulfate was added to the system and stirred,resulting in the formation of flocs.The TOC of the tested supernatant was 58.7 mg/L after 30 minutes of resting,and the COD was 53.8 mg/L.Infrared spectroscopy and X-ray diffraction analysis revealed that the flocs formed in the system were polymerized iron sulfate linked by hydroxyl bridges.For waste resource utilization,an attempt to prepare ferrate using persulfate produced in the electrolytic system was carried out in the thesis.The pretreated wastewater was subjected to electrolysis in the anodic oxidation system as described in the previous paragraph,i.e.,at p H=7.0,[Na₂SO₄]=0.8 mol/L and current intensity=1.2 A for 50 min;after the electrolysis,sodium hydroxide,and iron sulfate were added to the system so that[Na OH]=10 g/L,[Fe₂（SO₄）₃]=10 g/L After 3 h of reaction,the TOC value of the supernatant was 25.1 mg/L and the COD value was<50 mg/L.At the same time,a purple-red substance was formed in the supernatant,and analysis of the UV-visible spectrum,FTIR,and X-ray diffraction revealed that the material was ferrate（VI）with a concentration of 0.98 mmol/L.