A Study On AOX Pollution In Wastewater Treatment Process Of Dyeing And Dyestuff Chemical Industries

Organic halides are toxic, refractory and in a great variety. Adsorbable oganic halogens(AOX), as an integrated indicator for the pollution level of organic halides in the environment, has been regulated in wastewater emission standards by many countries including China. However, AOX is so complex and expensive to analysis that little information has been released on its pollution status up to date.Selecting wastewater treatment plants in six large-scale dyeing enterprises, four large-scale dyestuff chemical enterprises and three industrial parks in Zhejiang province, AOX pollution was studied in the raw wastewater, and their change was studied along the wastewater treatment process. The components of AOX were then characterized by GC-MS. In addition, AOX pollution was also surveyed in two paper factories and three pharmaceutical manufacturers. The main conclusions were drawn as follows:(1) AOX concentration was low in wastewater from the dyeing enterprises, ranging 0.15 ~ 1.62 mg/L in the raw wastewater and 0.05 ~ 1.43 mg/L in the biologically treated effluent. All the biologically treated effluent met the emission limits of 8 mg/L in the Discharge Standard of Water Pollutants for Dyeing and Finishing of Textile Industry. Sludge in five factories was with AOX of below 630 mg/kg, only one factory was with high AOX concentration of 3280 mg/kg.(2) AOX concentration greatly varied between the wastewater from dyestuff chemical factories, being 1.70 mg/L to 78.72 mg/L in the raw wastewater and 1.68 mg/L to 24.45 mg/L in the biologically treated effluent. AOX concentrations in the activated sludge were as high as 960-2297 mg/kg. Chlorobenzenes, chloronitrobenzenes, chloroanilines, chlorine nitroanilines and halophenols were the typical TOX components detectable in the dyestuff chemical wastewater. Halophenols and chlorine nitroanilines could be efficiently removed. Single chloroanilines and single chloronitrobenzenes seemed to be easier removable than polychlorinated anilines and polychlorinated nitrobenzenes. Polychlorinated benzenes were also easily removal but the products chlorobenzene was hard to remove. One thing must mention is that some highly toxic halides, although trace amount, were newly formed during the biological treatment of the dyestuff chemical wastewater. Regulation on AOX emission in wastewater of dyestuff chemical industry should be established, and the risk in activated sludge should be paid much attention.(3) AOX concentrations from wastewater treatment plants of industrial parks ranged from 0.14 mg/L to 0.27 mg/L in the effluent and 320 mg/kg to 466 mg/kg in the sludge, higher than those in a sewage treatment plant. The wastewater treatment plant dealing with dyestuff wastewater demonstrated the highest AOX concentration, 1.53 ~ 1.63 mg/L in the effluent, exceeding the emission standard of 1 mg/L. Moreover, the AOX concentration in the activated sludge was as high as 1227 ~ 2752 mg/kg.(4) AOX concentration was low in wastewater from the paper enterprises, ranging 0.25 ~ 0.53 mg/L in the raw wastewater and 0.11 ~ 0.24 mg/L in the treated effluent. AOX concentration greatly varied between the wastewater from pharmaceutical enterprises, being 0.28 mg/L to 17.06 mg/L in the raw wastewater and 0.05 mg/L to 3.74 mg/L in the treated effluent. AOX concentrations in the activated sludge greatly differed. The lowest concentration was 49 mg/kg, while the highest concentration was up to 8290 mg/kg.