Phthalates (PAEs) are commonly detected in discharge of municipal wastewater treatment plants. This study investigated the removal of six typical PAEs with activated sludge and the results revealed that concentrations of aqueous PAEs decreased rapidly during the beginning 15 min and reached equilibrium within 2 hours due to the adsorption of activated sludge. The process followed first-order kinetic equation, except for dioctyl phthalate (DOP). The factors influencing the adsorption were also evaluated and it was found that higher initial concentrations of PAEs enhanced the removal but affected little the adsorption equilibrium time. The adsorption of PAEs favored lower operating temperature (the optimum temperature was approximately 25°C in this research), which could be an exothermic process. Additionally, lower aqueous pH could also benefit the adsorption.
Phthalates (PAEs), a group of artificial chemicals, are characterized with low water solubility, low volatility, and low temperature resistance, which are widely used in agriculture, cosmetics, coatings, and so forth [
To control the pollutants, adsorption is a popular and effective method to separate PAEs from aqueous phase and many sorbents have been considered, such as activated carbon, polymeric adsorbent, carbon nanotube, chitosan, and seaweed. The adsorption of DBP on activated carbon is spontaneous and endothermic and favors higher temperatures [
One substitution would be activated sludge, yellowish-brown flocculants and particulates, which was confirmed to adsorb and accumulate PAEs from municipal wastewater [
This research symmetrically investigated the adsorption of six PAEs on activated sludge and the influencing factors to improve the removal rate. The partitions between sludge and water were also studied.
The regents used in this research were listed as follows: 2000
Experimental water and activated sludge: The experimental water was made with glucose as carbon source, NH4Cl as nitrogen source, certain amount of Mg, P, Fe, Ca, and Zn ions as trace nutrients, and sodium azide as inhibitor, following the instructions of pervious research [
Quantitation information of PAEs for GC-MS.
PAEs | Retention time (min) | Qualitative ion ( | Quantitative ion ( | Auxiliary quantitative ion ( |
---|---|---|---|---|
DMP | 5.27 | 163 : 164 : 92 : 194 | 163 | 164, 92 |
DEP | 6.72 | 149 : 177 : 150 : 105 | 149 | 177 |
DBP | 10.53 | 149 : 150 : 223 : 205 | 149 | 150 |
BBP | 14.09 | 149 : 206 : 91 : 123 | 149 | 91 |
DEHP | 15.58 | 149 : 167 : 279 : 113 | 149 | 167 |
DOP | 17.07 | 149 : 279 : 150 : 390 | 149 | 150 |
For the purpose of QA/QC, all the experimental processes were triplicated to minimize operational error. The detection limits were concentrations when signal/noise was three. The spiked recovery of PAEs was 83.20%–111.78% with standard deviation of 2.29%–8.99%.
Different initial concentrations of adsorption experiments were chosen as 40
The change of PAEs in water phase over time with initial concentration of 40
Figure
The change of PAEs in sludge phase over time with initial concentration of 40
In this research, the process of activated sludge adsorbing PAEs was fitted to first-order kinetics equation as follows:
Equation (
The rate constants and half-life of activated sludge adsorbing PAEs fitting first-order reaction (initial PAE concentration was 80
Phthalate ester | Kinetic equations | | | |
---|---|---|---|---|
DMP | | 2.486 | 0.279 | 0.9657 |
DEP | | 1.872 | 0.370 | 0.9380 |
DBP | | 1.599 | 0.433 | 0.9958 |
DEHP | | 0.697 | 0.994 | 0.9754 |
DOP | | 1.023 | 0.677 | 0.5657 |
BBP | | 4.629 | 0.150 | 0.9630 |
Except for DOP, the removal process of other five PAEs basically was in accord with the first-order kinetics equation, while the half-life and degradation rate constant were significantly different. The degradation rate constants were sorted in order:
The mass balance analysis after 8 hr adsorption is shown in Table
Mass balance analysis in one-liter mixture solution.
Phthalate ester | Initial mass ( | Remains in sludge ( | Remains in water ( | Loss ( |
---|---|---|---|---|
DMP | 80 | 16.4 | 24.49 | 39.11 |
DEP | 80 | 20.12 | 6.85 | 53.03 |
DBP | 80 | 20.12 | 29.82 | 30.06 |
DEHP | 80 | 40.04 | 25.04 | 14.92 |
DOP | 80 | 28 | 7.16 | 44.84 |
BBP | 80 | 24.2 | 0 | 55.8 |
The temperature effect is shown in Figure
The concentrations of PAEs in sludge (a) and water (b) at different temperatures (initial concentration = 80
Different pH values might inhibit the activity of activated sludge adsorption of PAEs. The results are shown in Figure
The concentrations of PAEs in sludge (a) and water (b) at different pH (initial concentration = 80
As shown in Figure
The adsorption capacity of activated sludge was higher with the initial PAEs concentration of 80
The adsorption of PAEs on activated sludge favored 25°C in this study, and only DEP and DMP out of six PAEs were influenced significantly by temperature.
The aqueous PAEs concentrations decreased significantly in the pH range of 5–9 and kept relatively constant when the pH was in the range of 9–11.
The authors declare that they have no competing interests.
Funds for this work were provided by the National Natural Science Foundation of China (no. 21407097) and the Shandong Natural and Science Foundation (ZR2014EEM009).