Although the treatment technology of sulfamethoxazole has been investigated widely, there are various issues such as the high cost, inefficiency, and secondary pollution which restricted its application. Bioflocculant, as a novel method, is proposed to improve the removal efficiency of PPCPs, which has an advantage over other methods. Bioflocculant MFX, composed by high polymer polysaccharide and protein, is the metabolism product generated and secreted by
In recent decades, the use of pharmaceutical and personal care products (PPCPs) has increased dramatically [
The strain was screened by our laboratory from activated sludge in municipal wastewater treatment plants and preserved in China General Microbiological Culture Collection Center (CGMCC number 6243).
Peptone 10, NaCl 5, beef extract 3, agar 15~18, water 1000 mL, pH 7.0~7.2; Flocuclant fermentation medium (g/L): glucose 10, yeast extract 0.5, urea 0.5, MgSO4·7H2O 0.2, NaCl 0.1, K2HPO4 5, KH2PO4 2, H2O 1000 mL, pH 7.2~7.5.
Flocculating rate: 5.0 g chemically pure kaolin clay, 1000 mL tap water, and 1.5 mL 10% CaCl2 liquid are added into a beaker, pH is adjusted to 7.2 by adding NaOH, then 10 mL flocculant is added, compared with control without flocculant addition. Flocculator is applied during the experiment, after 40 s fast mixing, and changed into slow mixing for 4 minutes, after 20 min settling, and the absorbance of the supernatant is measured under 550 nm by 721 UV spectrometer [
The removal efficiency of sulfamethoxazole is calculated by the following equation:
Polysaccharide measurement: Phenol-sulphuric acid method [ Protein measurement: Coomassie light blue [
Add 2x volume absolute alcohol (precooled under 4°C) to fermentation liquid, and filter and collect the white flocs after mixing. Add 1x volume absolute alcohol to filtered liquid, and then collect the white flocs again. Add small amount of DI water to collected flocs, after uniformly dissolving, freeze the flocculants in the ultralow temperature freezer for 24 h, and then put them into freeze drying to change the flocculants into dry powder.
Chromatographic column: C18 (
Add flocculants into 1 mg/L sulfamethoxazothe liquid with dosage 0 mL, 1 mL, 3 mL, 5 mL, 7 mL, and 9 mL; set the coagulant aids dosage as 0 mL, 0.5 mL, 1 mL, 1.5 mL, and 2 mL; adjust pH value to 4, 5, 6, 7, and 8 under 5°C, 15°C, 25°C, 35°C, 45°C, and 55°C; change the reaction time as 0 h, 0.25 h, 0.5 h, 0.75 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, and 12 h; calculate the removal rate.
Based on the preliminary obtained optimum condition, flocculant dosage, coagulant-aid dosage, pH, reaction time, and temperature are considered as influencing parameters. The design of experiment is shown in Table
Factors and levels of orthogonal test.
Levels |
|
|
|
|
---|---|---|---|---|
1 | 5 | 2 | 0 | 0.5 |
2 | 6 | 5 | 0.2 | 1 |
3 | 7 | 8 | 0.5 | 1.5 |
Mix the flocculant MFX and sulfamethoxazole with initial concentration as 0.8 mg/L, 1 mg/L, 1.2 mg/L, 1.4 mg/L, 1.6 mg/L, and 1.8 mg/L separately, under different temperature condition as 15°C, 35°C, put on 140 rpm shaking table with constant temperature, conduct adsorption isotherm experiment, and adsorption time is 1 h.
The strain J1 was short rod-shaped, cream-colored, viscous, smooth, and Gram-positive. J1 was identified as
Distribution of flocculent active ingredients.
Table
Qualitative analysis of flocculent active ingredients.
Reaction type | Analytical method | Phenomenon |
---|---|---|
Polysaccharide | Molish reaction | + |
Anthrone reaction | + | |
Seliwanoff reaction | − | |
| ||
Protein | Ninhydrin reaction | + |
Biuret reaction | + | |
Xanthoprotein reaction | + |
After the enzymatic digestion of EPS, polysaccharides were removed, while proteins remained. The proteins accounted for 15.05% (cellulase), 61.9% (
Enzymatic digestion of flocculent active ingredients.
Reaction type | Enzym | Flocculation rate after enzymatic digestion | Floc |
---|---|---|---|
Polysaccharide | Cellulase | 15.05% | Small |
|
61.90% | Big | |
|
11.4% | Small | |
| |||
Protein | Trifluoroacetic acid | Negative | None |
Pepsase | Negative | None | |
Trypsin | Negative | None |
Five parameters: pH value, flocculant dosage, coagulation aid ratio, flocculation time, and temperature are measured to see the effects of these factors on sulfamethoxazole removal efficiency. Along with the changes of pH value, the removal efficiency increases firstly then decrease, and changes sharply, from where we could know that pH does affect removal ratio a lot. It is shown in Figure
The influence of ecological factor on removal rate. (a) is the influence of pH; (b) is the influence of MFX dosage; (c) is the influence of CaCl2 dosage; (d) is the influence of temperature; (e) is the influence of time on removal rate.
In conclusion, the optimum flocculation condition is pH 5, flocculant dosage 5 mL, coagulant aid dosage 0.5 mL, flocculant reaction time 1 h, and temperature 35°C. Under this condition, the highest removal efficiency is reached, which is 67.82%. It is reported that the removal efficiency using conventional water treatment process including preoxidation, coagulation, and sand filtration is 36% [
In order to evaluate the removal effect of bioflocculant MFX on sulfamethoxazole in actual wastewater, domestic wastewater is used, with sulfamethoxazole concentration as 23.26 ug/L. 9 sets of experiments are conducted according to the orthogonal design table L9 (34), and results are shown in Table
Orthogonal test result and visual analysis.
Tests |
|
|
|
|
Removal efficiency (%) |
---|---|---|---|---|---|
1 | 1 | 1 | 1 | 1 | 40.64 |
2 | 1 | 2 | 2 | 2 | 48.38 |
3 | 1 | 3 | 3 | 3 | 50.13 |
4 | 2 | 1 | 2 | 2 | 36.91 |
5 | 2 | 2 | 3 | 1 | 30.26 |
6 | 2 | 3 | 1 | 3 | 44.27 |
7 | 3 | 1 | 3 | 2 | 29.86 |
8 | 3 | 2 | 1 | 3 | 35.03 |
9 | 3 | 3 | 2 | 1 | 41.70 |
Average 1 | 46.383 | 35.803 | 39.980 | 37.533 | |
Average 2 | 37.147 | 37.890 | 42.330 | 40.837 | |
Average 3 | 35.530 | 45.367 | 36.750 | 40.690 | |
Variance | 10.853 | 9.564 | 5.580 | 3.304 |
As is shown in Table
By comparing the extremums, we may reach a conclusion that the effect degrees of factors obey the following order:
In the research of removal mechanism of sulfamethoxazole aqueous solution, the highest removal efficiency is more than 60%, but, in the removal of sulfamethoxazole in wastewater, the highest removal efficiency under optimum condition is only 53.27%. This may be caused by the relatively low concentration of sulfamethoxazole in wastewater, which is 23.26 ug/L. The limitation of measurement methods may lead to potential systematic errors. On the other hand, domestic wastewater has complex component, and there exists reversible and irreversible competitions among substrates, liming the combination of flocculant and sulfamethoxazole. What is more, some unknown ions and organic compounds may also decrease the removal efficiency.
The dry power of MFX is white, sparses and reticulate, while the aqueous solution is milky white, ropy, and turbid. The material of MFX adsorbent is glycoprotein which has hydrophobicity and displays a wide range of sorption behavior for hydrophobic organic compounds in aqueous solutions [
Freundlich isotherm parameters at different temperature.
|
Freundlich equation |
|
|
|
---|---|---|---|---|
15 |
|
82.1486 | 0.8820 | 2.07 |
35 |
|
176.6445 | 0.9641 | 3.18 |
Adsorption isotherms of sulfamethoxazole by MFX adsorbent in 15°C (a) and 35°C (b).
The results show that MFX exhibited high-adsorption capacities for sulfamethoxazole in water. A maximum adsorption capacity (
This is due to the effect of temperature on chemical reaction and molecular movement, which finally promote or restrain flocculent effect. On the one hand, providing appropriate temperature, colloidal particle is bombarded intensively by molecules of flocculation to form a whole. If temperature is excessively low, molecular movement slows down, and reaction rate lessens, leading to bad adsorptive property. On the other hand, some active groups between bioflocculant and sulfamethoxazole start the chemical reaction to separate out of aqueous solution system. What is more, when hydrophobic chain polymer-bioflocculation MFX comes into sulfamethoxazole aqueous solution system, with the help of appropriate pH and Ca2+, sulfamethoxazole becomes unstable rapidly, passing into flocculation phase.
Driven by such mechanism, the adsorption on MFX does not rely on a high porosity and a resultant high specific surface area to reach a high adsorption capacity, as for most activated carbon and polymeric adsorbents. This result implies that hydrophobic partitioning is an important factor in determining the adsorption capacity of MFX for sulfamethoxazole solutes in water; meanwhile, some chemical reaction probably occurs.
This work demonstrates the efficient removal of sulfamethoxazole from water using bioflocculant MFX as adsorbents. The findings are summarized as follows. The active flocculent constituents of MFX are EPS which is composed by polysaccharides and proteins fermented by J1. Proteins mainly accounted for the flocculation activity. The MFX displays great sorption behavior for sulfamethoxazole in aqueous solutions. The optimum condition is 5 mg/L bioflocculant, 0.5 mg/L coagulant aid, initial pH 5, and 1 h reaction time, and the removal efficiency could reach 67.82%. Using MFX, the removal rate of sulfamethoxazole in domestic wastewater can reach 53.27%. The effect size of ecological factor is as follow: pH > flocculant dosage > coagulant aid > reaction time. It is efficient for MFX to remove sulfamethoxazole in aqueous environment in 35°C. And the process obeys Freundlich equation.
The study shows that bioflocculation MFX can be used as an efficient alternative adsorbent for the removal of sulfamethoxazole in water, with high-adsorption capacities observed in actual wastewater. Further studies are underway to make mathematical models of the relationship between flocculant and contaminant. When many PPCPs coexist, the research on removal efficiency with bioflocculant is more significant.
This work was supported by Grants from the National High Technology Research and Development Program of China (863 Program) (no. 2009AA062906), the National Creative Research Group from the National Natural Science Foundation of China (no. 51121062), the National Natural Science Foundation of China (Nos. 51108120 and 51178139), the Key Projects of National Water Pollution Control and Management of China (nos. 2012ZX07212-001 and 2012ZX07201-003) and the State Key Lab of Urban Water Resource and Environment, Harbin Institute of Technology (nos. 2010TX03 and 2010DX09).