Fatty alcohol polyoxyethylene ether sodium sulfate (SLES) is a commonly used anionic surfactant derived from sulfation and neutralization of fatty alcohol polyoxyethylene ether (AEO). SLES exhibits excellent properties in washing, emulsifying, dispersing, dissolving, foaming, wetting, and other applications. It finds wide usage in daily chemical washing products such as shampoo, body wash, laundry detergent, dishwashing liquid etc. However, the use and discharge of SLES can also have certain environmental and biological impacts. Therefore it is necessary to understand its biodegradability and environmental impact for achieving sustainable development and utilization.
The biodegradability of SLES refers to its ability to be decomposed by microorganisms into harmless inorganic substances like carbon dioxide, water, sulfate ions etc., in the natural environment. The biodegradability of SLES depends on its molecular structure primarily determined by the balance between hydrophobic groups (fatty alcohol groups) and hydrophilic groups (polyoxyethylene ether sulfate groups). In general terms: longer hydrophobic group length combined with shorter hydrophilic group length leads to poorer biodegradability while vice versa results in better biodegradability. Additionally structures like unsaturated bonds or branched chains or aromatic rings within molecules can also affect their biodegradability negatively.
According to international standards different methods are employed for evaluating the biodegradability of SLES including chemical oxygen demand (COD), biochemical oxygen demand (BOD), dissolved organic carbon (DOC), biodegradation rate (BD) etc. Generally speaking it is believed that SLES possesses good biodegradability with primary degradation rate exceeding 90% indicating significant destruction of surfactant’s molecular structure; final degradation rate surpassing 80% signifies substantial oxidation into inorganic substances.
