| The textile dyeing wastewater was one of the main industrial wastewater in China, and it was characteristic of large quantity, strong alkaline, high chroma, high concentrations of organics, complex composition, poor biodegradability and so on. The treatment of textile dyeing wastewater is causing extensive concern, and only COD, NH3-N, chroma and SS are regarded as primary contaminants and are generally employed to assess the treatment technology now. However, there are other toxic or carcinogenic organics in the textile dyeing wastewater, and it is short of systematic research reports. In the study, according to the priority controlled contaminants list in China, benzene series (BTEX) and polycyclic aromatic hydrocarbons (PAHs) were chosen as target contaminants in textile dyeing wastewater. Moreover, both BTEX and PAHs are toxic or carcinogenic organics, and can cause harm to human and eco-environment. The main research conclusion is as follows:In this work, textile dyeing wastewater treatment plants (TDWTPs) located in Pearl River Delta were selected for study. Furthermore, BTEX and PAHs in wastewater and sludge were measured by GC-MS. These results were used to analyze removal characteristic of BTEX during textile dyeing wastewater treatment process, and discuss the occurrence and removal of PAHs in representative textile dyeing wastewater, and evaluate ecological risk of PAHs in textile dyeing sludge.The average TEX concentration in raw textile dyeing wastewater (RW) was 6.735± 8.59 μg/L, which was much lower than that in oilfield produced water and coking wastewater. The raw materials, production process, output and wastewater composition were different between the TDWTPs. As a result, the ∑TEX concentrations in RW from 6 TDWTPs were different. Among the selected TDWTPs, the highest TEX concentration of 23.839±2.20 μg/L was detected in the TDWTP-F RW, and the lowest ∑TEX concentration of 1.161±0.19 μg/L was detected in the TDWTP-C RW. BTEX removal efficiency of the different treatment processes was guaranteed, and it was achieved between 76.5% and 93.1%. Therefore, the average TEX concentration in final effluent (FE) was only 0.652±0.23 μg/L. In addition, the toluene and xylenes contributed a notable proportion of BTEX in textile dyeing wastewater, which accounted for 37±13% and 47±15%, respectively. The proportion of ethylbenzene (about 10%) was relatively steady, followed by benzene, styrene and isopropylbenzene. The component distribution of BTEX in FEs was similar to RWs.In the wastewater treatment system, the aerobic process played an important role of BTEX removal. Overall,78.3% and 82.2% of the elimination of the EBTEX in the aqueous phase occurred in aerobic process of TDWTP-A and TDWTP-E, respectively. The major BTEX removal mechanisms in aerobic process were bio-degradation and aeration stripping. Moreover, both anaerobic process and flocculation of TDWTP-A and TDWTP-E played a supporting role in BTEX removal, and 21.6% and 16.4% of the elimination of the ∑BTEX were achieved respectively.The total PAHs concentration in the typical and integrated textile dyeing wastewater was 1349.51±35.77 ng/L, and 88% of PAHs were mainly adsorbed onto the suspended particles presented in RW. The dominant compounds were 3-6 ring PAHs in RW, while 2-3 ring PAHs predominated in FE. The physicochemical treatment+ pulse circulating fluidized bed system of TDWTP-G removed 95% of PAHs in wastewater efficiently, and ∑6PAHs concentration in FE was reduced to 65.81±20.99 ng/L. The significant removal mechanisms for PAHs during wastewater treatment process were bio-degradation and sludge sorption. Actually, ∑16PAHs concentration of the dry sludge was 2996.10±151.00 ng/g. The PAHs ecological risk probability of textile dyeing sludge was lower than 10%, however, these 7 compounds (acenaphthene, fluorene, phenanthrene, benzo(b)fluoranthene, benzo(k)fluoranthene, indeno(1,2,3-cd)pyrene, benzo(ghi)perylene) have toxic side effects to biology. Therefore, The landfill and agricultural reuse of the textile dyeing sludge may cause a potential risk to ecosystem. |
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