Surfactants can interfere with the biological wastewater treatment processes. They contribute to the changes in activated sludge floes structure. In order to quantify the influence of surfactants on sludge floes morphology the series of experiments in the flow continuous system were conducted. Sodium dodccyl sulphate, which belongs to the most ubiquitous anionic surfactant in everyday use, was selected to be the object of investigations. The results of its biodegradation in continuous flow system at influent concentration of 250 mg -dm' are presented. It turned out that SDS diminished the mean projected area of floes from 50 OOO to 15 OOO μm' with the increase of dilution rate from 0.029 to 0.192 h·1• At the same time the obtained data confirmed that there was a correlation between the morphological parameters of floes and other biomass indicators. The linear relation between mean projected area of floes and volatile suspended solids was found.

In this study the effect of anionic surfactants on the morphology of activated sludge floes and biomass activity is quantitatively described. Three anionic surfactants: sodium dodecyl sulphate, sodium alkylbenzene sulphonate and sodium alkyltrioxyethylene sulphate were tested. The batch experiments were performed for a wide range of initial concentrations of anionics in wastewater from 2.5 to 2500 mgdm3. In spite of different chemical structure the action of all tested anionic surfactants resulted in the decrease of activated sludge floes dimensions at the similar level. It occurred that in the range of anionics concentrations, which are typical for domestic wastewater (2.5-25 mgdm3), they contributed to the decrease of mean projected area of floes by about 30%, whereas at the concentrations of 250 and 2500 mg-dm3 mean projected area decreased usually by 50-60%. Sodium alkylbenzene sulphonate exerted the strongest inhibition effect on dehydrogenase activity of activated sludge biomass. This effect coincided with the decreased degrees of removal for this surfactant and its biodegradation products, especially at its lower initial concentrations in wastewater.

This study investigates the influence of four imidazolium ionic liquids (ILs) present in wastewater on the activated sludge process. In addition, experiments with inactivated sludge to assess the capacity of this sorbent to remove ILs from the wastewater were conducted. It occurred that the presence of ionic liquids in wastewater reduces biomass growth and size of the sludge flocs. The strongest effect has been found for IL 6 (1-hexyl-2H-3-methyl-4,5-dimethylimidazolium iodide) with the longest alkyl chain length. Also, the degree of ILs removal increases with the alkyl chain length and decreases with the increase of initial concentration of ILs in wastewater. IL 6 reaches the highest degree of ILs removal from wastewater but inhibits the biomass growth and growth of sludge flocs in a greater extent than other tested compounds. Moreover, it was confirmed that newly synthesized ionic liquids can be adsorbed onto inactivated sludge. IL 6 could be adsorbed in a higher degree than other ionic liquids. This adsorption was described by Langmuir isotherm, whereas adsorption of other ionic liquids was described by Freundlich isotherm.