The effect of sodium dodecyl sulphate (SDS) and sodium dodecylbenzene sulphonate (SBS) on activated sludge oxygen uptake rate (OUR) and nitrification

摘要

Anionic surfactants are used worldwide in detergent and household cleaning products. Due to their extensive use, surfactants can find their way into wastewater treatment plants (WWTPs), where they may be completely or partially removed. Anionic surfactants not only have adverse effects on aquatic and terrestrial environment, but also can have adverse effects on the WWTP operation and performance. Anionic surfactants are the major class used in detergent formulations. Sodium Dodecylbenzene Sulphonate (SDBS) is a member of the LAS group and Sodium Dodecyl Sulphate (SDS) is a member of the Alkyl Sulphate group. This study selected SDS and SDBS as model anionic surfactants due to their widespread use. The aim of this study is to assess the effect of the presence of anionic surfactants in the influent to WWTPs on activated sludge processes. To accomplish this aim, the effect of the presence of SDS and SDBS on activated sludge oxygen uptake rate (OUR) and nitrification was assessed according to the ISO standard methods. The OUR method facilitates estimation of the effects of anionic surfactants on activated sludge microorganisms in aerobic biological treatment systems. A nitrification inhibition test was developed by International Standard Organization and has been used by many researchers for assessing the inhibitory effects of anionic surfactants on nitrifying microorganisms in activated sludge. The morphology of activated sludge flocs was also evaluated to help investigate the effect of anionic surfactants on the settling behaviour of flocs. The results indicated that the anionic surfactants SDS and SDBS have an adverse effect on the activated sludge OUR and nitrification activities. Inhibition to OUR increased from 12.9% to 44.2% for SDS concentrations from 5 to 100 mg/L, after 30 minutes of incubation. The inhibition to OUR decreased with increased incubation time to 180 minutes reaching 6% at 5 mg/L and 27% at 100 mg/L. SDBS showed a strong inhibitory effect on activated sludge OUR where an inhibition of 19.8% to 79.1% was measured after 30 minutes, which declined reaching 15% to 69.2%, after 180 minutes, for the same concentration range. SDS and SDBS also showed an inhibitory effect on activated sludge nitrification which followed a trend that was in agreement with that observed for their inhibition to OUR. SDS and SDBS inhibition to nitrification was proportional to their initial concentrations. For example, inhibition to nitrification increased from 5.9% to 46.5% with increase SDS concentration from 5 to 100 mg/L compared with 12.9% to 53.6% for the same concentration range of SDBS. The results obtained demonstrated that the inhibitory effects of SDS and SDBS on activated sludge biological activities were intensified at low temperature, as measured in terms of OUR and nitrification. However, inhibition to nitrification decreased significantly with a temperature increase from 20ºC to 30ºC. The results showed that the presence of SDS and SDBS in the activated sludge aeration basins may lead to changes to the morphology of activated sludge flocs measured in terms of the mean projected area and perimeter.