Removal Of Aox In Activated Sludge And Processing Wastewater Of Chemical Pharmaceutical Industry With Fenton Oxidation

Adsorbable organic halogens?AOX?refer to all organic chemicals with chloro,bromo or iodo substituents and could be adsorbed onto activated carbon.Organic halides are widely applied in industries such as pharmaceutical and dyestuff manufacture,and their emission to environment poses high risk to human health and eco-safety owing to their toxic and refractory nature.Since AOX chemicals are in a great variety and it is of great difficult to monitor and manage each single chemical species,AOX was worldwide used as a comprehensive indicator to limit the environmental emissions of organic halides.Fenton reagent showed potential to remove AOX because that it owns the advantage of strong oxidation capacity,short reaction time,simple operation and easy to control.Fenton oxidation was used to remove AOX in aerobic activated sludge and processing wastewater in a chemical pharmaceutical factory.The influence from initial pH,H₂O₂ dosage,Fe²⁺to H₂O₂ molar ratio and reaction times were investigated.The optimized conditions for AOX removal in processing wastewater were initial pH of 9.25,H₂O₂ dosage of0.29 mol/L,n(Fe²⁺):n?H₂O₂?of 1:10 and reaction time of 1.5 h.Under the above conditions,AOX in the wastewater was removed as high as 95.1%⁹5.7%,and thereby the AOX concentration entering the activated sludge system was greatly cut off.The optimized conditions for AOX removal in activated sludge were initial pH of 7.16,H₂O₂ dosage of 0.9 mol/L,n(Fe²⁺):n?H₂O₂?of 1:20 and reaction time of 2 h.Under the above conditions,AOX was removed70.7%⁷1.1%in the sludge and 78.5%⁸0.8%in the supernatant.Addition of Fenton reagent in the study caused greatly decreased pH in wastewater and activated sludge.The initial pH was 9.3 in wastewater and 7.2 in sludge.After the addition of Fenton reagent,the pH sharply drop to 3.9 and 2.5,respectively,and the final pH at the end of Fenton reaction was 3.0 in the wastewater and 2.2 in the sludge.Neutralization was required after Fenton reaction.GC-MS analysis of semi-volatile organic chemicals was carried out for wastewater and sludge before and after Fenton reaction.The results showed that halogenated chemicals such as fluorinated and chlorinated acetophenones,2,4-dichloro-fluorophenyland2,6-dichloro-4-?1,1-dimethylethyl?phenol were almost completely removed in the wastewater.Chlorinated hydrocarbons and chlorinated esters,as well as non-halogenated toxic compounds such as p-Xylene and diisobutyl phthalate were efficiently removed in the sludge.Based on the above,Fenton oxidation was considered as effective method to remove AOX and other toxic organics in order to detoxify the wastewater and sludge.