Treatment of laundry wastewater by biological and electrocoagulation methods Terelle Ramcharan and Ajay Bissessur ABSTRACT 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. Terelle Ramcharan Ajay Bissessur (corresponding author) School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa E-mail: bissessura@ukzn.ac.za Key words | biological, Biospinners, electrocoagulation, laundry wastewater, linear alkylbenzene sulphonates INTRODUCTION Water is a vital component for the sustainability of life on earth. With an increase in the world population and urban- isation, the demand for fresh potable water has escalated (Marcucci et al. ). This has accelerated the need for the development of new and more efficient wastewater recy- cling systems. Laundry wastewater (LWW) can be considered to be relatively less chemically polluted when compared to other industrial effluents; hence its purification and recycling would become pivotal in decreasing the demand for fresh potable water (Schouten et al. ). Targeting the development of new and economical treat- ment methods for LWW should not only be geared toward efficiency in the recycling ability but also incorporate mini- mal consumption of chemicals and energy. The typical composition of LWW consists primarily of the laundry detergent, inorganic species, minor organic compounds and dirt removed from soiled items (St Laurent et al. ). The characteristic chemicals found in laundry deter- gents chiefly include surfactants, builders, bleach and co-builders. Laundry detergents to a large extent contain a higher percentage of anionic surfactants and builders in comparison to other minor ingredients. Sodium dodecylben- zene sulphonate (SDS) and sodium aluminium silicates (more commonly known as zeolites) are the most common anionic surfactants and builders, respectively, utilised in laundry detergents (Duarte et al. ). The hydrophobic head and hydrophilic tail of the surfactant ensure effective removal of most inorganic species from LWW regardless of its hydrophobic or hydrophilic nature. On the other hand builders prevent water hardness by exchanging sodium ions with smaller cations such as magnesium and calcium. For the implementation of the recycling of LWW it is imperative to routinely monitor and analyse the surfac- tant level, as this is the major component of the detergent’s ingredients and is indicative of its efficacy in the removal of dirt. Most laundering facilities require a single wash cycle and two rinse cycles for the effective cleaning of soiled items. The sampling and purification of LWW after the 84 © IWA Publishing 2017 Water Science & Technology | 75.1 | 2017 doi: 10.2166/wst.2016.464 Downloaded from https://iwaponline.com/wst/article-pdf/75/1/84/456517/wst075010084.pdf by guest on 01 November 2018