Azo textile dyes wastewater treatment with constructed wetlands : design and operation of experimental vertical-flow constructed wetlands applied for the treatment of azo textile dyes (with/without artificial wastewater)

Hussein, A 2017, Azo textile dyes wastewater treatment with constructed wetlands : design and operation of experimental vertical-flow constructed wetlands applied for the treatment of azo textile dyes (with/without artificial wastewater) , PhD thesis, University of Salford.

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Abstract

Wetlands have long played a significant role as natural purification systems. Textile industry processes are among the most environmentally unsustainable industrial processes, because they produce coloured effluents in large quantities polluting water. The aim of this study is to assess the performance of VFCWs to treat two different azo textile dyes with and without artificial wastewater for long periods of time through different operation modes such as contact and resting times, and loading rates, which has rarely been considered in previous research works. The corresponding key objectives are (a) to assess the role of gravel (as a control wetland) and plants on dye reduction and other pollutants; (b) to determine the influence of two groups of dyes (acid (AB113) and basic (BR46)), each dye having a different molecular weight and chemical structure, at two different concentrations (7 mg/l and 215 mg/l); (c) to evaluate the impact of the mixture of both dyes on the performance of vertical-flow constructed wetlands in terms of dye reduction with/without artificial wastewater; (d) to determine the annual and seasonal reduction; and (e) to assess the influence of operational parameters such as contact time (48h and 84h), resting time and mass loading rate on dye reduction and other pollutants for a long period.

The first phase dealt with treating the two azo textile dyes only during the period between 1 June 2015 and 31 May 2016, while the second phase dealt with artificial wastewater containing the two azo textile dyes during the period between 1 June 2016 and 31 May 2017. According to the first phase, for the low concentration of BR46, there was no significant (p≥0.05) difference between the wetlands in terms of dye reductions. However, for chemical oxygen demand (COD), the reduction percentages were 50%, 59% and 67% for the control and for the wetlands with short and long contact times, respectively. All reductions were statistically significant (p<0.05). For the high concentration of BR46, the reduction percentages for the dyes were 94% and 82%, and for COD, they were 89% and 74% for the long and short contact times, correspondingly. A good reduction was noted for total suspended solids for long and short contact times. For the low concentration of AB113, the percentage reductions for the dye were 71%, 68% and 80%, and for COD, they were 5%, 7% and 16% for the control, and the short and long contact times, respectively. For the high concentration of AB113, the percentage reductions for the dye were 72% and 73%, and for COD, they were 54% and 55% for the 48 h and 96 h contact times in this order. Regarding ortho-phosphate-phosphorous for the low concentrations of BR46 and AB113, the reduction percentages for wetlands, which have high contact times, were significantly (p<0.05) better than those of the control wetlands, as well as wetlands, which have low contact times. In the case of high concentration regarding BR46, the reduction percentages of wetlands with low loading rates were significantly (p<0.05) better than wetlands with high loading rates, while for AB113, the reduction percentages of wetlands with high loading rate were significantly (p<0.05) better than those for wetlands with low loading rates. In the case of ammonia-nitrogen for the high concentration of dyes, there were no significant (p≥0.05) differences between wetlands. Regarding nitrate-nitrogen reduction for low and high concentration of BR46 and AB113, the reduction percentages for wetlands with long contact times were better than those for wetlands having short contact times.

In the case of phase two, the presence of plants had no effect on the dye and COD reductions. For the low concentration of BR46, the percentage reductions for the dye were 92%, 89% and 91%, and for COD, they were 69%, 82% and 70% for the control, and the short and long contact times, respectively. All reductions were statistically significant (p<0.05). For the high concentration of BR46, the reduction percentages for the dyes were 73% and 33%, and for COD, they were 56% and 39% for the long and short contact times, respectively. For the low concentration of AB113, the percentage reductions for the dye were 85%, 77% and 82%, and for COD, they were 76%, 81% and 62% for the control, and the short and long contact times in this order. For the high concentration of AB113, the percentage reductions for the dye were 44% and 54%, and for COD, they were 40% and 56% for the 48 h and 96 h contact times, correspondingly. Regarding ortho-phosphate-phosphorous for the low concentrations in the case of AB113 and BR46 and the mixture of both dyes, the reduction percentage in wetlands with high contact time was significantly (p<0.05) better than those of the control wetlands and wetlands with low contact time. For the high concentration of BR46, AB113 and the mixture of both of them, wetlands with high resting and contact times had lower ortho-phosphate-phosphorous effluent concentrations when compared with wetlands with low resting and contact times. Regarding ammonia-nitrogen reduction percentages for low concentrations of BR46 and AB113 and the mixture of both dyes, wetlands with high resting times had better reduction percentages (p<0.05) when compared with the control wetlands as well as wetlands with low resting times. In the case of high concentrations for BR46, AB113 and the mixture of both of them, wetlands with low loading rates had a better reduction percentage when compared with wetlands with a high loading rate. Regarding nitrate-nitrogen reductions for low and high concentrations of BR46, AB113 and the mixture of both of them, the reduction percentages for all wetlands were in the range from 75 to 100%. Regarding aromatic amine compound reductions, wetlands with long contact times showed significant (p<0.05) differences when compared with the control and wetlands with short contact times for the low concentrations of BR46 and AB113. For the high concentration of BR46 and AB113, wetlands with low loading rates showed a significant difference (p<0.05) when compared with wetlands with a high loading rate. The researcher recommended that using HPLC combined with FTIR to investigate the reduction in aromatic amines and working on modelling of the results should help the designer in improving the construction of wetlands on an industrial scale.

Item Type: Thesis (PhD)
Schools: Schools > School of Computing, Science and Engineering
Funders: Iraqi Cultural Attache
Depositing User: amjad Hussein
Date Deposited: 23 Feb 2018 14:19
Last Modified: 23 Mar 2018 01:38
URI: http://usir.salford.ac.uk/id/eprint/43774

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