Development and Scale-up Production of a Novel Fibrous Catalyst and Application for Removal of Endocrine Disrupting Compounds
Advanced oxidation processes based on Fenton’s chemistry have the potential to treat a wide range of organic pollutants. In this work, a novel catalyst underwent development for scale-up commercial production and tested for oxidative treatment of contaminants in water. In this work the existing modification process of polyacrylonitrile yarn to create the heterogeneous PAN catalyst has been optimised for the requirements of a scale-up of production in a dye bath type reactor. The concentration of sodium hydroxide, duration and temperature of alkaline treatment were optimised with respect to the physical properties of the yarn and presence of chelating functional groups. The quality of the catalyst produced after each modification was evaluated by monitoring functional groups present, total iron loading and strength of fixation. Treatment with 2.5% NaOH solution, at 60oC for 60 min resulted in a yarn similar properties to that produced using standard procedure. These conditions were appropriate for the reactor selected. The final step of production of the catalyst, i. e. introduction of Fe3+ cation to the fibre was optimised with respect to duration, composition of the impregnating solution and additional washing prior to the impregnation methodology. The solution of 6.2 g/L Fe2(SO4)3 / 14.8 g/L Na2SO4 (molar ratios of Fe3+ to co-salt anion 1:1.5) was found to be the best in terms of resultant iron loading on the yarn and the strength of iron fixation to the yarn. The highest iron loading on the yarn was found for the samples impregnated for 2 hours. Introduction of a new step of modification i. e. acidic wash after step 2 to remove entrapped NaOH did not result in better iron uptake or fixation strength to the yarn, it was therefore deemed unnecessary. Existing methods of removal of estrogenic compounds from wastewater were reviewed. The PAN catalyst produced using optimised procedure was successfully applied for removal of estrogenic compounds in the bench scale experiment. The catalyst produced from the industrial scale-up was used with H2O2 and found to be efficient in the removal of estradiol (E2) at a concentration of 1mg/L in aqueous solution, achieving 97% removal within 1 h. The optimum conditions found were pH 7, [H2O2] 75ppm, 4.2g of mesh in 100 mL of solution. The system was also very efficient in the removal of 17β-ethinylestradiol (EE2) using the same mesh to liquor ratio and [H2O2] as for E2, however the optimal pH for EE2 was pH 3. Under these conditions the removal was over 90% in 50 minutes. The removal of estrogenic compounds, pharmaceuticals, pesticides, total organic carbon, heavy metals and ammonia during two field trials of the 32 L pilot reactor at Severn Trent Water wastewater treatment plant in Longbridge were discussed.. During the first trial at a residence time of 5h, H2O2 dose app. 150 ppm and 1.48 kg of PAN catalyst the system removed on average 89 %, 93 % and 76% of E1, E2 and EE2 respectively, some pesticides (terbutryl 37 % removal), most heavy metals (with the highest removal rates for Mn, Al and PB 88 %, 82 % and 67 % respectively), total suspended solids (by 82 %) and ammonia (20.2%). During the second field trial a number of changes in the pilot plant unit regime took place (shorter RT of 2.5 h and 3.5 h, lower H2O2 dose at 40 and 75 ppm). The system was removed 19 % of atrazine and 40 % of simazine and terbutryn. The percentage removal results for metals were similar to those of the first trial. On average removal of E1 and E2 was in the second trial at 73 % and 87 % respectively whereas EE2 was at 18 % on average; however it was very uneven during the course of the trial. Biofilm formation on the catalytic mesh during extended periods of use was also investigated using SEM microscopy, sugar and protein assays. Some evidence of bacterial growth was found.
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