Potential of dyes as draw solutions in forward osmosis for the South African textile industry

Abstract

The textile industry produces large volumes of wastewater that requires appropriate treatment before being released into the environment. Research globally has focused on advanced desalination technologies to augment the limited freshwater resources. Forward osmosis (FO) technology has gained substantial interest as a possible lower-energy desalination technology. However, challenges such as the availability of effective draw solutions (DS) have limited its implementation. This study evaluated alternative feed water resources and assessed the potential of dye solutions as DS. The aim is to dilute a concentrated dye DS to a target concentration for direct dye-batch use, thereby reclaiming water resources. The measured osmotic pressure (OP) of the alternative feed solutions (synthetic brackish water; syntethic seawater; seawater from the Atlantic and Indian Oceans; and wastewater from two textile factories) were 414, 2 761, 2 580, 2 614; 1 716 and 7 822 kPa, respectively. Three basic dyes (Maxilon Turquoise, Red and Blue) and three reactive dyes (Carmine, Olive Green and Black) were selected based on common use in the South African textile industry. The dye samples were prepared without and with lt at different concentrations and different dye-to-salt mass ratios ranging from 1:10 to 1:60. The OP trends for the basic dyes followed Blue >> Red > Turquoise and for the reactive dyes Black >> Olive > Carmine. The overall OP trend was Black > Olive > Carmine > Blue > Red > Turquoise. The OP at different dye concentrations and different dye-to-salt ratios was mostly influenced by the dye chemistry and molecular weight (Mw) rather than the type of dye, i.e., reactive vs basic.The OP trend for the dye-to-salt ratios was 1:60 > 1:50 > 1:40 > 1:30 > 1:20 > 1:10. For both the basic and reactive dyes a linear relationship exists between OP and dye concentration; as well as between OP and Mw. The dye DS exhibited larger OP compared to that of the FS evaluated, thus rendering them suitable DS.

Fashion designers' attitude-behaviour inconsistencies towards a sustainable business model: a neutralisation theory perspective

“…This is despite the prevalence of massive pollution of Durban and Cape Town coastal areas from wastewater discharged from the textile industry (May, 2019). In particular, the dyes used by the fashion industry contribute more to water pollution, hence the analogy of “flowing colourful rivers” (Sheldon et al , 2018). Although the negative effects of fast fashion are a cause for concern in South Africa, the majority of fashion designers seem to have an apathetic disposition towards the sustainability theme (Steyn, 2014; May, 2019).…”

“…Thus, the first research question asks: What are South African fashion designers' attitudes towards sustainable fashion as a business model? The concern of South African fashion designers for environmental sustainability is established in literature (Cimatti et al , 2017; Sheldon et al , 2018). However, it remains unknown why fashion designers in South Africa are reluctant to embrace sustainable fashion (Steyn, 2014; May, 2019).…”

“…Previous studies on sustainable behaviour (Gifford, 2011; Barbarossa and De Pelsmacker, 2016) suggest that psychological factors related to worldviews and conflicting value orientations have the potential to explain the complexities associated with performance of sustainable behaviours. A focus on this research strand is important in South Africa as the fashion industry continue to consume more water, discharge more greenhouse gases and discard more apparel waste in landfills (Cao et al , 2017; Sheldon et al , 2018). For instance, it remains unknown how fashion designers manage the possibility of cognitive conflict and dissonance associated with not behaving in an environmentally sustainable manner.…”

“…In this sense, an understanding of how sustainable fashion can assist in repositioning struggling brands especially in the minds of environmentally conscious shoppers is important. 2) South Africa is ranked as one of the countries with a high carbon and water footprint (Sheldon et al , 2018). Thus, a transition to sustainable fashion is a potential solution to address this challenge.…”

“…Thus, a transition to sustainable fashion is a potential solution to address this challenge. 3) The majority of textile industries in South Africa are situated in coastal areas in Western Cape and KwaZulu Natal (Sheldon et al , 2018). Hence, embracing sustainable fashion offers the possibility of reducing contamination of coastal areas.…”