Effect of newly synthesized salts and three common micropollutants on the biochemical activity of nitrifiers

Abstract

Often, different types of contaminants in wastewater are suspected of adversely affecting the treatment efficiency of a wastewater treatment plant (WWTP). Therefore, it is essential to study the effects of newly synthesized substances on the activity of activated sludge microorganisms. The aim of this study was to determine the effect of innovative biosurfactants, i.e., sophorolipids quaternary ammonium salts (SQAS), and three common micropollutants (MPs), i.e., diclofenac (DCP), 17α-ethynylestradiol (EE2), and 4-nonylenol (4-NP), on the biochemical activity of activated sludge microorganisms. The effect of all tested substances was more significant on nitrite-oxidizing bacteria (NOB) than on ammonia-oxidizing bacteria (AOB), and least on the respiratory activity of heterotrophic organisms (HET). SQAS inhibited nitrification even at the lowest concentration tested (5 mg L−1) and the inhibition degree was in the range of 37% to 78%; at the highest concentration of SQAS studied (160 mg L−1), it was about 45–96%. In most cases, the degree of inhibition increased when the SQAS concentration approached 80–160 mg L−1. MPs influenced the activity of nitrifiers to a lower extent than SQAS. The inhibition degree varied from 25% to 75%, depending on the micropollutant tested and its concentration.