The behavior of phosphonates in wastewater treatment plants of Switzerland

The behavior of three phosphonates in seven Swiss wastewater treatment plants was investigated. The phosphonates ATMP (aminotrismethylene-phosphonic acid) and EDTMP (ethylenediaminetetramethylenephosphonic acid) were found in the influents of wastewater treatment plants at concentrations between <0.05 μmol l−1 (detection limit) and 0.8 μmol l−1, DTPMP (diethylenetriaminepentamethylenephosphonic acid) from <0.05 to 2 μmol l−1. The highest concentration was found in the influent of a wastewater treatment plant with significant input from the textile industry. The effluent of this wastewater treatment plant contained an average DTPMP concentration of 0.12 μmol l−1, which reflects a 85% decrease from the influent concentration. The phosphonate concentrations in all other effluents were below detectable levels. As phosphonates are not biodegradable, the elimination must be due to sorption processes. The phosphonates are almost quantitatively transferred to the anaerobic digester. The investigation of the anaerobic degradation showed no evidence for mineralization. Compared to EDTA (ethylenediaminetetraacetic acid) which is not eliminated during wastewater treatment, phosphonates have less impact on the metal speciation in natural waters.