Study on anaerobic and aerobic degradation of different non-ionic surfactants

Six alcohol ethoxylates (C5E2, C6E4, C7E4, C8E2, C8E4, C10E4) and two fatty acid esters were tested at lab-scale for degradation in anaerobic and aerobic conditions and oxygen uptake rate (OUR). Anaerobic removal of C5E2, C6E4 and C7E4 improved with increasing number of ethoxy groups (E) and decreasing length of the alkyl chain (C). Their aerobic removal was also great but lower than the anaerobic values. C8E2, C8E4 and C10E4 were adsorbed on sludge but not degraded in anaerobic conditions, while they were efficiently removed under aerobiosis. The fatty acid esters were removed to a level between the two alcohol ethoxylates groups in both anaerobiosis and aerobiosis. The measured OUR confirmed the different behaviours of the three groups of compounds.