Behavior of PBTC, HEDP, and Aminophosphonates in the Process of Wastewater Treatment

Abstract

Ten times at intervals of 1–2 months, individual treatment stages of two wastewater treatment plants (WWTPs) were analyzed for the five quantitatively most widely used phosphonates. The total dissolved concentration of the investigated phosphonates in the influents was between 131 µg/L and 384 µg/L. The nitrogen-free phosphonates 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) and 1-hydroxyethylidene(1,1-diphosphonic acid) (HEDP) accounted for an average proportion of 83–85%. Diethylenetriaminepenta(methylene phosphonic acid) (DTPMP) contributed with 13–14%, whereas aminotris(methylphosphonic acid) (ATMP) (≤15 µg/L) and ethylenediaminetetra(methylene phosphonic acid) (EDTMP) (≤11 µg/L) contents detected in the WWTP influents were comparatively low. The application of new analytical methods allowed the quantification of phosphonates in the solid fraction of the WWTP influents for the first time. High loads of phosphonates were determined (223–2555 mg/kg), indicating that 20%–80% of the phosphonates are present in the adsorbed state. The removal of total dissolved phosphonate by secondary clarification was between 69.7% and 92.4% (medians: 90.7% and 87.7%). In both WWTPs, HEDP (medians: 89.2% and 86.4%) was slightly better eliminated than PBTC (medians: 87.2% and 82.5%). In the sand filtration stage of a WWTP, the average removal was not further improved. In contrast, an additional removal of dissolved phosphonates could be achieved by activated carbon treatment (median: 96.4%). The proportion of phosphonate-P in the dissolved unreactive phosphorus fraction was consistently between 10% and 40% throughout all treatment stages.

Influence of Wastewater Discharge on the Occurrence of PBTC, HEDP, and Aminophosphonates in Sediment, Suspended Matter, and the Aqueous Phase of Rivers

“…The fact that, in River1, the proportions of HEDP and DTPMP in the total phosphonate load increased, whereas the proportion of PBTC decreased, implies that the two polyphosphonates tend to adsorb stronger than the monophosphonate PBTC (Table 1). This hypothesis is supported by the fact that PBTC (3-25 µg/L, median: 13 µg/L) was present in similar concentrations to HEDP (7-38 µg/L, median: 13 µg/L) in the effluent of WWTP1 [12]. PBTC also had a lower adsorption potential than HEDP towards the particles in the influents of both WWTPs [12].…”

“…The maximum flow rate of WWTP1 (7.5 m 3 /s) is comparatively low compared to the typical runoff (~290 m 3 /s) of its receiving water. For more information on WWTP1, see Rott et al [12].…”

“…The strong impact of WWTP2 on River2 is illustrated in Figure 4, comparing the increase of dissolved phosphonate concentrations in the rivers with the effluent concentrations and elimination of phosphonates in the WWTPs [12]. Whereas no correlation could be observed for River1/WWTP1, a significant increase in phosphonate concentration of River2 was observed when the effluent of WWTP2 had elevated phosphonate concentrations (despite relatively low coefficients of determination of <0.46, the significance of correlation was high with p < 0.039; Table A3).…”

“…Figure 6. Increase of the sediment phosphonate loads (load behind minus load before the WWD) in both rivers as a function of the dissolved phosphonate concentrations in the WWTP effluents (WWTP data from Rott et al [12]).…”

“…In a previous study, Rott et al [12] reported a comprehensive characterization of the behavior of the above-mentioned five phosphonates in different stages of two German wastewater treatment plants (WWTPs). This study revealed that up to 80% of the phosphonates in the WWTP influent can be present in adsorbed form.…”