Abstract
The widespread use of detergents has raised concern with regard to the environmental pollution caused by their active substances, which are biorefractory, toxic or persistent. Even though anionic and non-ionic surfactants often used in commercial detergents composition are reasonably degradable under aerobic conditions and not particularly toxic at low concentrations, high concentration of surfactants influenced the activated sludge activity and are harmful for the aquatic environment. In the literature, data on the biodegradability and/or ecotoxicity of a certain type of surfactant (anionic, nonionic, cationic) are usually presented. Our study aimed to assess the biodegradability of a mixture of two types of surfactants (anionic mixed with non-ionic) and also, effects caused by their presence of elevated concentrations to the activated sludge micro-organisms, within a batch experiment. We performed a biodegradability test (according Zahn-Wellens method) on 2 synthetic solutions with high concentrations of anionic surfactant �methyl dodecylbenzene sulfonate (15-25 mg/L) and non-ionic surfactant -4-nonylphenyl-polyethylene glycol (10 mg/L). The study established different percent of biodegradability (measured by COD decrease and surfactants removal) depending on initial concentrations of anionic and nonionic surfactants in the tested solutions. High surfactants concentrations modulated the activity and morphology of activated sludge, so its degradation efficiency of the organic substrate has decreased. Surfactant solutions resulting from biodegradability experiment have been tested for toxicity to planktonic crustaceans (Daphnia magna).
Highlights
The widespread use of detergents has raised concern with regard to the environmental pollution caused by their active substances, which are biorefractory, toxic or persistent
Similar with results obtained for Chemical Oxygen Demand (COD) elimination, the surfactants removal (Table 2) during experimental period (21 days) was higher for mixture A (86% removal of total content of surfactants) comparative with mixture B, where removal was less than 80%, which represents a minimum level of primary biodegradability for surfactants, according to European Regulation No 648/2004 [31]
The values of COD and surfactants removal obtained within Zahn-Wellens test indicated that biodegradation process occurred at concentration of 25 mg/L anionic surfactant, mixed with 10mg/L non-ionic surfactant and this mixture may be considered readily biodegradable in the aquatic environment
Summary
The widespread use of detergents has raised concern with regard to the environmental pollution caused by their active substances, which are biorefractory, toxic or persistent. Even though anionic and non-ionic surfactants often used in commercial detergents composition are reasonably degradable under aerobic conditions and not toxic at low concentrations, high concentration of surfactants influenced the activated sludge activity and are harmful for the aquatic environment. Surfactants ( called surface-active agents) are a wide group of chemical compounds which have a large number of applications due to their solubility properties, detergency, endurance of water hardness, as well as emulsifying, dispersing and wetting properties. They have numerous applications in humans lives, being used in household cleaning detergents, personal-care products, textiles, paints, polymers, pesticides, pharmaceuticals, mining, oil recovery, pulp and paper industries, coatings and processing aids [1]. The surfactants spread in the aquatic systems, especially LAS could damage fish grills triggering excessive mucus secretion and a decreased respiration rate in the common goby [8]
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