Bio-Refractory Organic Compounds Removal In Fixed-bed Column By Highly Effective Iron-carbon-bentonite-alginate Beads(Fe~0/C-BABs)Activated Persulfate System

Due to the disadvantages,such as complex process equipment,large energy consumption and serious loss of catalyst of refractory organic wastewater treatment by advanced oxidation process.Fe⁰ carbon gel beads?Fe⁰/C-BABs?were prepared and fill in the filter column to active persulfate?PS?.The benzalkonium chloride?BAC?and acetaminophen?APAP?as two kinds of bio-refractory organic compounds were selected as target contaminants.The degradation efficiency of those target pollutants,best operating conditions and the possible degradation path were analyzed.Two-stage process of Fe⁰/C-BABs and oyster shell-filled column was developed to control pH levels and iron releasing problems in effluent.This research could suggest optimal operation strategy on refractory organics treatment in PS continuous process.Fe⁰/C-BABs was prepared by using sodium alginate gel method with iron power and particle carbon,and was characterized by SEM,EDS,TGA.The size of the bead was 4.66+0.02 mm and the iron and activated carbon powders uniformly loaded on the inner surface of a bead.The regeneration experiments of beads were carried out and after 5 times recycle the treatment efficiency of APAP was nearly 76.20%.With target pollutant of BAC,the operating conditions for Fe⁰/C-BABs activated persulfate process with filter column were set to pH=7,the flow rate was225 mL/h,the concentration of PS was 100 mmol/L,and the loading of 40 g Fe⁰/C-BABs.After 6 h of operation,the treatment efficiency reached 92.87%.As determined by GC-MS analysis,the C-N bond of the BAC was first attacked to produce N,N-dimethyl?phenyl?methanamine and dodecane.Through economic accounting,the cost of removing per ton of BAC wastewater from Fe⁰/C-BABs activated PS process was only costs$3.04.With target pollutant of APAP,86.29%efficiency can be achieved with the operation condition of pH=7.0,[APAP]=50 mg/L and bead weight 40 g at PS and APAP flow rates of 25 and 225 mL/h.Compared with the impact of Cl^-,HCO₃^-significantly inhibited the efficiency of the persulfate system.Under different condition of lower concentration of dissolved oxygen,the degradation of APAP was increased firstly and then declined slightly.The degradation products of APAP were initialed with the broken of C-N bind and hydroquinone and acetamide or4-aminophenol were generated as the major byproducts,which could finally further degradation into small molecules?e.g.,acetaldehyde and butyric acid?.Due to the effluent of combined process of continuous Fe⁰/C-BABs filter column has pH 3.05 and total iron concentration of 106.25 mg/L,oyster shell filter column was carried out in sequentially.After treatment with oyster shell filter column,the pH of the effluent increased from 3.05 to 6.32,and the total iron decreased from 106.25 mg/L to 21.43 mg/L,and the total iron removal rate reached80%.Meanwhile,the combined process effluent COD_crr decreased from 411.84 mg/L in the initial water inlet to 170.28 mg/L,and BOD₅ increased from 34.87 mg/L to83.33 mg/L,while the BOD₅ value increased from 34.87 to 83.33 mg/L.With the BOD₅/COD_crr ratio of the effluent greatly increased from the initial 0.085 to 0.49,the biodegradability was also improved.