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.
Highlights
The South African (SA) population has grown from 36 million in 1990 to an estimated 55 million in 2016, according to the latest census
For both the basic and reactive dyes a linear relationship exists between osmotic pressure (OP) and dye concentration; as well as between OP and molecular weight (Mw)
The seawater collected from the Indian Ocean seaboard (IOSB), containing an average of 50 292 mg/L NaCl, produced an average OP of 2 613 kPa
Summary
The South African (SA) population has grown from 36 million in 1990 to an estimated 55 million in 2016, according to the latest census. SA’s water and energy resources are under immense pressure due to its growing population, expanding economy and changing rainfall patterns (Von Bormann and Gulati, 2014). It has been predicted that SA will suffer serious water shortages by 2020 (Fioramonti, 2015). It has been reported that SA is already using 98% of its available water supply and 40% of its wastewater treatment is in a critical state (Fioramonti, 2015). There is a strong demand for low-energy and low-cost water treatment methods. The growing awareness of water scarcity and energy shortages in SA has sparked a renewed interest in finding suitable and sustainable solutions
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