Advanced Treatment Of Coking Wastewater By Peroxymonosulfate Oxidation Process

Coking wastewater is a typical refractory organic wastewater containing phenolic compounds,heterocyclic compounds,polycyclic aromatic hydrocarbons,ammonia nitrogen,sulfide,and cyanide,and its biodegradability is poor.At present,anoxic/oxic（A/O）and anaerobic/anoxic/oxic（A2/O）processes are the dominant biological treatment process in for coking wastewater treatment.However,color and chemical oxygen demand（COD）of effluents of bio-treated coking wastewater are difficult to meet the“Emission Standard of Pollutants for Coking Chemical Industry”（GBl6171-2012）.There are still a large number of toxic and non-biodegradable organic pollutants in bio-treated coking wastewater,which will directly be reused or discharged to cause adverse effects on the environment and pose a great threat to human health.Therefore,it is necessary to seek economical and effective advanced treatment technology of coking wastewater.In this paper,UV activated peroxymonosulfate oxidation（UV/PMS）,Fe₃O₄activated peroxymonosulfate oxidation（Fe₃O₄/PMS）and base activated peroxymonosulfate oxidation coupled sequencing biofilm batch reactor（base/PMS+SBBR）were used to treat bio-treated coking wastewater.The effects of different factors under each technology were investigated,and the changes of organic components before and after treatment of bio-treated coking wastewater were analyzed by using three-dimensional fluorescence spectrum and GC/MS.In addition,Fe₃O₄ materials before and after use were characterized and their reuse effects were explored in Fe₃O₄/PMS system.The specific research contents and results were as follows:（1）Advanced treatment of coking wastewater by UV/PMS system was studied.The effects of p H,PMS concentration,UV light intensity and temperature on bio-treated coking wastewater were examined.The best experimental conditions for advanced treatment of coking wastewater by UV/PMS technology are:PMS concentration of 11 mmol/L,UV light intensity of9.94 mw/cm2,initial p H value of 3,temperature of 25℃,reaction time of 60 min.Under the above conditions,the removal rates of TOC,color and UV₂₅₄ were65.7%,99.5%and 93.9%,respectively.The three oxidation systems of UV/H₂O₂,UV/PS and UV/PMS can all treat bio-treated coking wastewater,and the treatment effect was ranked as:UV/PMS>UV/PS>UV/H₂O₂.Three-dimensional fluorescence analysis of bio-treated coking wastewater showed that after treatment by UV/PMS system,humic acid-like substances and fulvic acid-like substances were completely removed,and aromatic protein-like substances were partially removed.（2）Advanced treatment of coking wastewater by Fe₃O₄/PMS system was studied.The effects of PMS concentration,Fe₃O₄ dosage,p H and temperature on bio-treated coking wastewater were examined.The best experimental conditions for advanced treatment of coking wastewater with Fe₃O₄/PMS system are:Fe₃O₄dosage of 3 g/L,PMS concentration of 7 mmol/L,initial p H value of 3,temperature of 30℃,reaction time of 120 min.Under the above conditions,the removal rates of color,UV₂₅₄ and COD were 97.4%,81.9%and 64.6%,respectively.The oxidation capacity of Fe₃O₄/H₂O₂ and Fe₃O₄/PS systems was significantly lower than that of Fe₃O₄/PMS system.With the increase of Fe₃O₄ reuse times,the COD removal rate gradually decreased,and the COD removal rate only reached 31.7%after Fe₃O₄ was used for 5 times.The mechanism of Fe₃O₄ activation was that Fe2+on the surface can activate PMS to produce SO₄^·-and?OH,and Fe2+was converted to Fe3+after the reaction.Three-dimensional fluorescence spectroscopy and GC/MS analysis showed that Fe₃O₄/PMS system can effectively remove organic matter in wastewater,and was particularly effective for the removal of humic acid-like and fulvic acid-like substances.Most of the long-chain organics were broken or opened.（3）Advanced treatment of coking wastewater by base activated peroxymonosulfate oxidation was studied.The effects of PMS concentration,p H,base type and temperature on bio-treated coking wastewater were examined.The best experimental conditions for advanced treatment of coking wastewater with base/PMS system are:PMS concentration of 7 mmol/L,p H value of 10,temperature of 30℃,Na OH as activator,reaction time of 4 h.Under the above conditions,the removal rates of color,UV₂₅₄ and COD were 96.1%,71.4%and45.9%,respectively.The treatment effect of the base/PMS system was significantly better than that of base/H₂O₂ and base/PS systems.In addition,the biodegradability of wastewater after treatment by base/PMS system was improved.The treatment effect of SBBR process on the effluent from base/PMS system was analyzed.The results showed that:SBBR used instantaneous inflow and instantaneous drainage.Under the conditions of temperature of 20℃～25℃,filling ratio of polyurethane filler of 44%,operating period of 8 h,aeration time of 4 h,precipitation time 1 h,idle time of 3 h,and water exchange ratio of 1:3,average removal rates of COD,BOD₅ and NH₃-N in the effluent of base/PMS system were44.2%,50.0%and 52.2%,respectively.The results of base/PMS coupled SBBR process for advanced treatment of coking wastewater showed that the average removal rates of color,UV₂₅₄ and NH₃-N were 96.1%,81.5%and 58.6%,respectively.The average removal rate of COD was 66.7%,and COD decreased from 165 mg/L of raw water to 55 mg/L of SBBR effluent.The three-dimensional fluorescence spectrum and GC/MS analysis showed that base/PMS system can remove most of aromatic protein substances,humic acid-like substances and fulvic acid-like substances.Most long-chain macromolecules were degraded.After the effluent treated by base/PMS system was processed by SBBR process,the humic acid-like substances remaining in base/PMS system effluent were completely removed,and aromatic protein-like substances were partially removed.