Abstract
In this study, the contribution of liquid and powder detergents to the composition of domestic laundry graywater was evaluated. Dosages recommended by the manufacturers were used to prepare detergent solutions and generate laundry graywater. Solutions and graywater were characterized in terms of total solids (TS), total suspended solids (TSS), total dissolved solids (TDS), chemical oxygen demand (COD), total organic carbon (TOC), and concentration of Linear Alkylbenzene Sulfonates (LAS’s). Additionally, the effect of the type of detergent on the treatment performance was also assessed. The coagulation–flocculation process was selected as a potential alternative for treating domestic laundry graywater. Treatment performance was assessed based on the removals of TS, TSS, TDS, turbidity, COD, and electrical conductivity (EC). Optimum coagulant dosages and mixing conditions for flocculation were determined. The results indicate a differential contribution of the type of detergent to the domestic laundry graywater composition. Liquid detergents contributed with more COD and TOC and fewer solids and LAS’s, in comparison with powder detergents. Soiled clothes increased the solids and organic loads of laundry graywater; furthermore, the laundry process reduced the LAS concentration of graywater by 77% for the liquid detergent and 47% for the powder detergent. On the other hand, the coagulation–flocculation process was more effective in treating powder detergent graywater even though the liquid detergent graywater was less polluted. Removal efficiencies on the order of 95% for turbidity and 75% for TSS were achieved for powder detergent graywater; meanwhile, for liquid detergent graywater, the removals were 73% for turbidity and 51% for TSS.
Highlights
The use of detergents in washing and cleaning processes is so familiar and normal in our modern lifestyle that we do not pay attention to the way we use such substances
The results indicate a differential contribution of the type of detergent to domestic laundry graywater composition
The coagulation–flocculation process was more effective in treating powder detergent graywater
Summary
The use of detergents in washing and cleaning processes is so familiar and normal in our modern lifestyle that we do not pay attention to the way we use such substances. The indiscriminate and intensive use of detergents has caused the disposal of huge amounts of xenobiotic compounds into water and soil environments. Graywater from domestic laundry is one of the major contributors of surfactants contained in domestic wastewater. The washing process represents a complex interaction between soiled laundry, water, mechanical and thermal energy, and detergents. Graywater is a troublesome byproduct that has the potential to cause a number of undesirable effects in sewage treatment plants and in the environment. All of the clean water brought into the process is later released to the sewage system in the form of contaminated wastewater containing additional energy, soil from laundry, lint, dyes, finishing agents, and detergents.
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