The textile and garment industry has made a remarkable contribution to the economic development of Vietnam and employs currently a large labor force of 2.5 million people.However, the textile industry is also seen as a most polluting and unsustainable industry due to the use of excessive amounts of materials and the release of large amounts of pollutants into the environment. In order to improve the environmental sustainability and effectiveness of the textile industry in Vietnam this study has looked into preventive measure, reuse/recycling options and improved end-of-pipe technologies, separately and in combination.
The end-of-pipe treatment is the last step in the greening production model. Textile wastewater is very difficult to treat, especially regarding the high color intensity. Removal of color from textile wastewater was studied by varying the pH, the application of a biological treatment step, the application of coagulation/flocculation and of Advanced Oxidation Processes (O3, O3/H2O2, Fenton’s reagent). The coagulation process was very effective in color removal of insoluble dyestuffs (98%), but this process is not so suitable for wastewater containing only soluble dyestuffs (12-55%). Of the Advanced Oxidation Processes, the Fenton’s reagent process was the most effective method for color removal (81-98%)for the four types of wastewater tested. The decolorization with the ozone process at low pH (pH 5)showed that direct oxidation by molecular ozone is much more selective in color removal than the oxidation by hydroxyl radicals. The presence of colloidal particles caused a 12-fold increase for ozone needed to obtain the same color removal efficiency as for a wastewater without colloidal particles.Each of the investigated processes could only remove one or a few types of pollutants from the wastewater, with the consequence that effluents could not meet all the discharge regulations. The combination of an activated sludge process, and a coagulation and ozone process yielded the best color (45 Pt-Co) and COD (30 mg O2/L) removal at the lowest costs (0.3 €/m3), compared with all other tested combinations.
Separate collection of wastewater streams in a factory can also strongly contribute to the efficiency and sustainability of wastewater treatment. In the wet processes of the textile industry 75% of the total water consumption is for rinsing purposes. Wastewater from most rinsing steps contains low amounts of pollutants and can be reused in other process stages or can be discharged without treatment.
An industrial ecology zone model, integrating preventive cleaner production approaches, a waste exchange network for reuse and recycling, and new end-of-pipe technologies, has been developed and assessed in two case studies: the Thanh Cong Company and the Nhon Trach 2 Industrial Zone. The greening production model developed for the Thanh Cong Company, a large-scale textile company in Hochiminh city, included the combination of cleaner production, external waste exchange and end-of-pipe technology. The dyestuffs, auxiliary chemicals, water and energy consumption can be reduced significantly when the proposed cleaner production, the external waste exchange options and the improved end-of-pipe technologies are implemented. Total benefits in savings per day can be more than 1,000 US$.
The industrial ecology zone model was designed in three steps. Firstly the greening production model developed for the Thanh Cong Company was applied to all textile enterprises in the industrial ecology zone that was considered. Secondly an outside waste exchange network was designed. The outside network includes reuse of waste plastics, waste paper and waste oil at recycling companies in the neighborhood. The last step is to treat solid waste and polluted air and to treat and reuse wastewater for irrigation (cotton cultivation), for use in sanitary systems and to water plants in the industrial zone.
The case studies of the greening production model and of the industrial ecology zone model demonstrated that a successful industrial ecology practice not only depends on the interaction between enterprises inside but also on the interaction with the actor networks outside the industrial system:the economic networks, the social networks and the policy networks. These networks can contribute in different ways to the implementation of the models. In the case study of a large textile company the economic network is very important in the implementation of the greening production model and in the case study of an industrial ecology zone the policy network play the most important role in the implementation of the industrial ecology model.
|Doctor of Philosophy
|18 Apr 2011
|Place of Publication
|Published - 18 Apr 2011
- environmental policy
- textile industry
- environmental degradation
- waste water
- water pollution
- sustainable development
- south east asia