A lack of natural water resources and an increase in the demand for fresh potable water has shifted focus to the possible reuse of recycled laundry wastewater water that is considered to be relatively clean. Organic components such as linear alkylbenzene sulfonates (LAS) are the major and most abundant contributing anionic surfactant constituents found in laundry detergents. The development and reliability of treatment methods targeted at purification of laundry wastewater necessitates a fast and accurate method for quantification of LAS. This paper focuses on a comparative study for the quantification of LAS based on traditional liquid–liquid extraction (LLE) and HPLC–UV methods. In the case of LLE, the anionic surfactant LAS complexes via ion association to a methylene blue (MB) cationic dye resulting in the formation of an anionic surfactant–methylene blue (AS–MB) complex. The AS–MB complex extracted with chloroform absorbs at a λ max of 653 nm. Optimized conditions for quantification of a single eluted LAS peak using HPLC–UV were obtained by isocratic elution on a C18 column with a 95 % acetonitrile and 5 % 0.7 M acetic acid mobile phase. Both methods displayed percentage recoveries >90 % and statistically showed reproducibility and precision in the quantitation of LAS. HPLC–UV prevailed over UV–Vis as the method of choice for LAS determinations given the ease of sample preparation and applicability to a wider range of samples. Typical levels of LAS in laundry samples assessed in this study ranged between 116 and 454 mg L−1.
The present study describes an improvement in the current electrocoagulation treatment process and focuses on a comparative study for the clean-up of laundry wastewater (LWW) after each wash and rinse cycle by biological and electrocoagulation treatment methods. For biological treatment, the wastewater was treated with a Bacillus strain of aerobic bacteria especially suited for the degradation of fats, lipids, protein, detergents and hydrocarbons. Treatment of the LWW by electrocoagulation involved the oxidation of aluminium metal upon the application of a controlled voltage which produces various aluminium hydroxy species capable of adsorbing pollutants from the wastewater. The efficiency of the clean-up of LWW using each method was assessed by determination of surfactant concentration, chemical oxygen demand and total dissolved solids. A rapid decrease in surfactant concentration was noted within 0.5 hour of electrocoagulation, whereas a notable decrease in the surfactant concentration was observed only after 12 hour of biological treatment. The rapid generation of aluminium hydroxy species in the electrocoagulation cell allowed adsorption of pollutants at a faster rate when compared to the aerobic degradation of the surfactant; hence a reduced period of time is required for treatment of LWW by electrocoagulation.
The greater demand for potable water, both locally and worldwide, has directed a huge interest amongst researchers to investigate the possibility of recycling and reusing wastewater from laundry run-offs. The advantage of using recycling wastewater from such sources is mainly due to the fact that these bulk volumes of wastewater are considered to be less chemically polluted in comparison to those discarded from industrial effluents and wastewater sources. Almost all laundry detergents contain surfactants, whose main function serves to remove dirt/soil from contaminated items. Thus, an analysis of the surfactant levels before and after a treatment process is important to confirm that the surfactant has in fact carried out its intended purpose. Electrocoagulative treatment of wastewater, a well-researched and well-documented clean-up process that involves the production of aluminium hydroxy species by oxidation of aluminium metal upon the application of a controlled voltage which adsorbs fine particulate matter and pollutants from the wastewater has been investigated as a clean-up application to the treatment of laundry wastewater. The use of a biological treatment process which entails treating the wastewater with aerobic bacterial specie specifically designed to degrade fats, lipids, protein, detergents and hydrocarbons has also been investigated.
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