Next Article in Journal
Spatio-Temporal Variations of Hydrochemical and Microbial Characteristics in Karst Water in Samcheok, South Korea
Previous Article in Journal
Evaluating the Impacts of Future Urban Expansion on Surface Runoff in an Alpine Basin by Coupling the LUSD-Urban and SCS-CN Models
Article

New Approach to Remove Heavy Metals from Wastewater by the Coagulation of Alginate-Rhamnolipid Solution with Aluminum Sulfate

by 1 and 2,3,*
1
Department of Civil and Environmental Engineering, Seoul National University, Seoul 08826, Korea
2
Marine Environmental Research Center, Korea Institute of Ocean Science and Technology, Busan 49111, Korea
3
Ocean Science, KIOST School, University of Science and Technology, Busan 49111, Korea
*
Author to whom correspondence should be addressed.
Water 2020, 12(12), 3406; https://doi.org/10.3390/w12123406
Received: 26 October 2020 / Revised: 25 November 2020 / Accepted: 30 November 2020 / Published: 3 December 2020
(This article belongs to the Section Wastewater Treatment and Reuse)

Abstract

This study was conducted using alginate-rhamnolipid (Alg-Rh) solutions on copper ions (Cu2+) as an application of coagulation with aluminum sulfate (Al2(SO4)3). The results show that solid phases were rapidly formed as an output of the reaction between Alg-Rh and Al2(SO4)3. It could be considered that the Al2(SO4)3 concentration and the existence of Cu2+ have an impact on forming hard coagulation, in that the total volume has been increased with increasing Al2(SO4)3 and the existence of Cu2+. The number of ions of aluminum (Al3+) and sulfate (SO42−) were also increased with Al2(SO4)3. The efficiency of Cu2+ removal was constant above 75.0%, hence the average value was 76.8%.
Keywords: heavy metals; remediation; rhamnolipid; alginate; coagulation heavy metals; remediation; rhamnolipid; alginate; coagulation

1. Introduction

Water is one of the most important resources in the world. It is already known that 71% of the Earth’s surface is covered with water and only 2.5% of it is freshwater [1]. Nowadays, seawater has been found to be converted to freshwater, but freshwater is still an important resource for living organisms, including humans [2,3]. Despite such an important resource, water pollution has been induced by a variety of contaminants, such as heavy metals and organic pollutants [4,5,6,7]. In particular, the pollution by heavy metals has been increasing with the development of industry, and it has already been proved that a high concentration of heavy metals has a dangerous impact on living organisms and the environment as hazardous materials [8,9,10]. It can be accumulated in living organisms and inhibit their metabolism to the point of death [11,12]. Accordingly, water treatment has been essentially required, in that water quality should be improved for water resource recirculation in conditions of limited water resources. Moreover, the treatment of wastewater that contains solid material should include a separation process. Recently, various wastewater treatment technologies have been developed using biological, chemical, and physical methods but we have yet to develop high-efficiency remediation technology [13,14,15].
Alginate has been mainly used to form a capsulated medicine as a raw material to be connected with divalent ions for its special property [16]. This novel property makes it possible for various applications such as coagulation to remove heavy metals [17]. Rhamnololipids, a biosurfactant, also have proved their novel property to remediate heavy metals [18,19,20,21]. Both materials are bio-derived and have relatively long chains [22,23]. Their combined properties and longer molecular chain would be expected to improve the efficiency of solid/liquid separation and heavy metal removal.
In view of the above, Alg-Rh complexes would form a longer chain than a simple alginate or rhamnolipid molecule. This molecular structure can coagulate with heavy metals as a long polymer by connecting together. Heavy metals are usually divalent ions or trivalent ions, and they are substituted with more than two sodium ions of sodium alginate to form a relatively round shape. Moreover, adding aluminum ions makes it more aggregated as supporting strong flocculation. The solid phase would form only one mass, and the mass does not tend to be fluid. Therefore, it would be much easier to separate the solid phase with a liquid phase.
Herein, we would like to suggest the possibility of using Alg-Rh complexes as a green coagulant for heavy metals and improve their efficiency for solid and liquid separation. Moreover, the water removing heavy metals would be investigated for characterization as a preliminary study.

2. Materials and Methods

2.1. Materials

Sodium alginate was supplied by Junsei Chemical Co., Ltd. (Tokyo, Japan), and the rhamnolipids (R90–100G) were purchased from AGAE Technologies (Corvallis, Oregon, USA). Additionally, copper standards (Kanto Chemical Co., Inc., Tokyo, Japan) were adjusted to make a 100 mg/L copper solution. A small amount of nitric acid (504–756 mg/L) is contained in the standard solution (980–1020 mg/L). Aluminum sulfate from Kanto Chemical Co., Inc., Tokyo, Japan, was also used as a coagulant.

2.2. Experimental Methods

Alginate solution (4% w/v) was mixed with a rhamanolipid solution (0.1% w/v) at 80 °C for 2 h, and then a copper standards solution was put into the mixture (Figure 1) [24,25,26,27]. A small amount of copper standard solution, 5 mL of 100 mg/L, was adopted for this preliminary study. To identify the effects of heavy metal in the mixture, samples have been also made without Cu2+. Aluminum sulfate (Al2(SO4)3) solution at 0.1%, 0.3%, and 0.5% w/v of total volume was added as an additive to support coagulation. All the experiments for coagulation were conducted in 250 mL glass beakers. Then, a mass wrapped in a thin layer was formed and the liquid phase (water) was separated from the solid phase by gravity. The final step in this experiment is filtering the water using a 0.45 μm acrylic-based filter.

2.3. Analysis

After the reaction, the samples were analyzed using ion chromatography (Dionex™ Aquion™ Ion Chromatography (IC) System, Thermo Fisher scientific, Waltham, MA, USA) to investigate the sulfate ions. An inductively coupled plasma optical emission spectrometer (ICP/OES) (Optima 7300DV, Perkin Elmer, Waltham, MA, USA) was also used for Cu2+ and Al3+. The total organic carbon (TOC) was determined using a UV-vis spectrophotometer (DR-5000, Hach, Loveland, CO, USA), followed by US EPA (United States Environmental Protection Agency) methods (method 10129).

3. Results and Discussion

3.1. Characterization of the Purified Water

Several distinct characteristics of the purified water will be discussed in detail. As explained above, the water has been separated from the formed mass, the solid phase, by gravity. The mass shows a different degree of rigidity with different concentrations of the coagulant (Figure 2). The pressure generated in the separation process causes the formed mass to break and the liquid contents wrapped in a thin layer to flow out. Eventually, the separation process could no longer proceed. In the case of the busted sample, the obtained water contained lots of organic matter and heavy metals that flowed out from the mass. Therefore, the samples were excluded from the exact analysis. Figure 2a shows that the liquid in the mass spilled into the water because of the weak bond of the mass surface. The sample without Cu2+ was observed to be busted easily compared to the other samples. The sample with 0.1% Al2(SO4)3 and Cu2+ made two separated phases which are not distinguishable in macroscopic view. However, the sticky liquid wrapped in the thin layer has been discovered to be separated (Figure 2b). In the case of Figure 2c, a remarkable change in the solid phase has been shown. The liquid in the mass has a sticky property because of the alginate and it makes lots of small bubbles inside the layer. The liquid has not been observed to be spilled to the water. The samples with 0.3% and 0.5% Al2(SO4)3 solution are comparatively hard (Figure 2d). The image was taken in tilted form for a more distinctive change from the others. The separated water was observed to be very transparent.
Figure 3 shows the different volume of the liquid phase depending on samples which have different Cu2+ and Al2(SO4)3 concentrations. The sample without Cu2+ shows the smallest total volume because it is difficult to separate the water without bursting the mass. The total volume of the samples with Cu2+ has been increased with increasing Al2(SO4)3, and the obtained volume remained stable from 0.2% Al2(SO4)3 sample. It would be considered that Cu2+ also has an impact on coagulation behavior. Divalent ions have already proved their property to substitute two sodium ions in alginate since they have been discovered [28].
TOC contents are also distinctive features in this experiment. Alginate and rhamnolipids have many carbons on their own, so it can be an important indicator of the remediation degree of the Alg-Rh complexes. As shown in Table 1, the highest TOC contents were observed in sample 1. The results indicate that Cu2+ works as another coagulant with Al2(SO4)3. The bond of Al3+ or Cu2+ with alginate has been proved [29,30,31]. As Al3+ and Cu2+ ions gather the alginate and rhamnolipid more tightly, carbon would not be spilled out of the mass to liquid phase.
The concentration of sulfate ions (SO42−) has been detected as a dominant material. The existence of Cu2+ played an important role, in that the SO42− concentration in sample 1 was 1.43 times higher. This indicates that Cu2+, the only controlled factor, is an important substance to support coagulation. The higher effects would be expected with higher contents of heavy metals inside the Alg-Rh solution. Not only Cu2+ but also other heavy metals with a strong ionic strength could be applied to this study. Except for sample 1, this is an increasing tendency among the samples. In comparison with sample 2, sample 3 and 4 have 3.39 and 5.71 times higher in SO42− concentrations. Higher Al2(SO4)3 shows higher sulfate ions. We can assume that Al3+ would react more extremely at higher Al2(SO4)3 contents, suggesting a higher efficiency.

3.2. Respective Correlation

As explained above, the Alg-Rh solution has high contents of carbon, and the contents are closely related to the reaction with Al2(SO4)3. Therefore, the contents of Al3+, SO42−, and Cu2+ in the water are also expected to have a correlation with TOC as the result of the reaction. As shown in Figure 4, the sulfate ions have been increased with increasing Al2(SO4)3. This does not seem to have a correlation with TOC without Cu2+, in that there is not a dramatic change comparing the significant change in TOC between sample 1 and 2. With Cu2+, the concentrations have been increased in multiples, as explained above, not showing a specific relation with TOC. Indeed, the TOC contents of sample 2 and 3 decreased 0.48 and 0.44 times compared to sample 1, contrary to the constantly increased SO42−.
Al3+ concentrations also have been constantly increased similar to SO42− (Figure 5). A difference is that Al3+ was used to form coagulation as an effective coagulant, so the contents are definitely lower than those of SO42−. The concentrations are respectively remarked at 0.360, 0.236, 0.854, and 1.400 g/l. Compared to sample 1, more Al3+ in sample 2 is expected to react with the Alg-Rh solutions, detecting a lower Al3+ in sample 2.
Figure 6 shows the Cu2+ concentrations with a change in Al2(SO4)3. This is not remarked at sample 1 because Cu2+ was not put into sample 1. They are remarked at 23.150 (±1.485), 26.850 (±2.616), and 23.500 (±0.281) with sample 2, 3, and 4. Cu2+ in samples 2 and 4 are quite similar, but sample 2 has more or less high value compared to them. The standard deviation of sample 2 is high. This indicates that there is a possibility to get a similar value with sample 2 and 4 during repeated experiments. However, the values show quite constant values, even though the TOC contents were decreased. Therefore, it is considered that Cu2+ has an effect on improving the efficiency to coagulate the solution with Al3+, but the Al2(SO4)3 and TOC contents do not affect the Cu2+ removal. There would be high potential to remove not only copper but also other di- and trivalent ions. this indicates that a bridging effect would be expected using heavy metals as a bridge and then it results in heavy metal removal. Moreover, as shown, Al3+ has a large effect on the Cu2+ removal. With these results, other heavy metals in wastewater may successfully replace the role of Al3+. Therefore, it could be suggested that a variety of heavy metals in wastewater can be also removed at the same time.
Each effect of the factors is explained using regression analysis and expressed in Table 2. As discussed above, decreasing TOC indicates that Alg-Rh complexes are combined with heavy metals, resulting in carbon being decreased in the samples. However, aluminum and sulfate ions are evaluated to have relatively little influence. This is considered because the Alg-Rh complexes are also combined with copper ions.

3.3. Efficiency of Heavy Metal Removal

Herein, the efficiency of Cu removal would be discussed as one of the important objectives to obtain clean water (Figure 7). As explained above, the Cu2+ contents were not extremely changed with the change in Al2(SO4)3 concentrations. The efficiency of Cu removal is also depicted similarly, respectively at 78.7, 75.3 and 76.5%. Most of the removed Cu2+ concentrations would be considered to react with Alg-Rh solutions and Al2(SO4)3. They are considered to be quite high amounts and deserve to be researched more in detail. Furthermore, a higher concentration of Cu2+ might have an impact on coagulation, and it also improves the efficiency to increase the Cu removal. As discussed above, other heavy metals with similar ionic states might be expected to have a similar role to that of Cu2+. There were not observed to be a dramatic effect depending on the concentration of aluminum sulfate. However, both the concentration and kind of heavy metals would affect the degree of heavy metal removal. Further studies about these factors would be needed.

4. Conclusions

In this research, we studied Alg-Rh solutions reacting with Al2(SO4)3 to remove Cu2+ by coagulation. The total volume of the liquid phase separated from the solid phase has been increased with the existence of Cu2+ and the concentration of Al2(SO4)3. Al3+ and SO42− have been also increased with the concentration of Al2(SO4)3. Furthermore, the efficiency of the Cu2+ removal constantly stayed above 75.0%. Therefore, this indicates that the existence of Cu2+ has an impact on tighter coagulation with Al2(SO4)3 but Al2(SO4)3 does not extremely affect removing Cu2+. This knowledge is worth applying to other heavy metals. More detailed studies should be researched about the effect of Cu2+ and Alg-Rh concentration changes.

Author Contributions

Conceptualization, A.L. and K.K.; investigation, A.L.; data analysis, A.L. and K.K.; methodology, A.L. and K.K.; writing—original draft, A.L.; writing—review and editing, A.L. and K.K.; project administration, A.L.; supervision, K.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Korea Institute of Ocean Science and Technology under Grant (PE99723 and PE99823), Republic of Korea.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Sivakami, M.S.; Gomathi, T.; Venkatesan, J.; Jeong, H.; Kim, S.; Sudha, P.N. Preparation and characterization of nano chitosan for treatment wastewaters. Int. J. Biol. Macromol. 2013, 57, 204–212. [Google Scholar] [CrossRef]
  2. Qasim, M.; Badrelzaman, M.; Darwish, N.N.; Darwish, N.A.; Hidal, N. Reverse osmosis desalination: A state-of-the-art review. Desalination 2019, 459, 59–104. [Google Scholar] [CrossRef]
  3. Yoon, J.; Do, V.; Pham, V.; Han, J. Return flow ion concentration polarization desalination: A new way to enhance electromembrane desalination. Water Res. 2019, 159, 501–510. [Google Scholar] [CrossRef]
  4. Yan, Z.; Pan, J.; Gao, F.; An, Z.; Liu, H.; Huang, Y.; Wang, X. Seawater quality criteria derivation and ecological risk assessment for oil pollution in China. Mar. Pollut. Bull. 2019, 142, 25–30. [Google Scholar] [CrossRef] [PubMed]
  5. Quesada, H.; Baptista, A.; Cusioli, L.; Seibert, D.; Bezerra, C.; Bergamasco, R. Surface water pollution by pharmaceuticals and an alternative ofremoval by low-cost adsorbents: A review. Chemosphere 2019, 222, 766–780. [Google Scholar] [CrossRef]
  6. Chu, Z.; Fan, X.; Wang, W.; Huang, W. Quantitative evaluation of heavy metals’ pollution hazards andestimation of heavy metals’ environmental costs in leachate during foodwaste composting. Waste Manag. 2019, 84, 119–128. [Google Scholar] [CrossRef]
  7. Zhang, L.; Zhu, G.; Ge, X.; Xu, G.; Guan, Y. Novel insights into heavy metal pollution of farmland based on reactiveheavy metals (RHMs): Pollution characteristics, predictive models, andquantitative source apportionment. J. Hazard. Mater. 2018, 360, 32–42. [Google Scholar] [CrossRef]
  8. Zhang, Y.; Li, S.; Lai, Y.; Wang, L.; Wang, F.; Chen, Z. Predicting future contents of soil heavy metals and related health risks by combining the models of source apportionment, soil metal accumulation and industrial economic theory. Ecotoxicol. Environ. Saf. 2019, 171, 211–221. [Google Scholar] [CrossRef]
  9. Rai, P.; Lee, S.; Zhang, M.; Tsang, Y.; Kim, K. Heavy metals in food crops: Health risks, fate, mechanisms, and management. Environ. Int. 2019, 125, 365–385. [Google Scholar] [CrossRef]
  10. Carolin, C.F.; Kumar, P.S.; Saravanan, A.; Joshiba, G.; Naushad, M. Efficient techniques for the removal of toxic heavy metals from aquaticenvironment: A review. J. Environ. Chem. Eng. 2017, 5, 2782–2799. [Google Scholar] [CrossRef]
  11. Peterson, B.; Tietböhl, T.; Marqueze, A. Interference of heavy metals present in the water of the Lagoa Tramandaí/RS on the carbohydrate metabolism of the GURI Sea Catfish (G. genidens) and Bay whiff (C. spilopterus). Comp. Biochem. Physiol. Part C 2019, 219, 42–49. [Google Scholar] [CrossRef]
  12. Houri, T.; Khairallah, Y.; Zahab, A.; Osta, B.; Romanos, D.; Haddad, G. Heavy Metals Accumulation Effects on the Photosynthetic Performance of Geophytes in Mediterranean Reserve. J. King Saud Univ. 2019. [Google Scholar] [CrossRef]
  13. Meena, R.; Kannah, Y.; Sindhu, J.; Ragavi, J.; Kumar, G.; Gunasekaran, M.; Rajesh, J. Trends and resource recovery in biological wastewater treatment system. Bioresour. Technol. Rep. 2019, 7, 100235. [Google Scholar] [CrossRef]
  14. Bora, A.; Dutta, R. Removal of metals (Pb, Cd, Cu, Cr, Ni, and Co) from drinking water by oxidation-coagulation-absorption at optimized pH. J. Water Process Eng. 2019, 31, 100839. [Google Scholar] [CrossRef]
  15. Yun, Y.; Lee, E.; Kim, K.; Han, J. Sulfate reducing bacteria-based wastewater treatment system integrated with sulfide fuel cell for simultaneous wastewater treatment and electricity generation. Chemosphere 2019. [Google Scholar] [CrossRef]
  16. Kazi, C.; Yamamoto, O. Effectiveness of the sodium alginate as surgical sealant materials. Wound Med. 2019, 24, 18–23. [Google Scholar] [CrossRef]
  17. Bang, S.; Choi, J.; Cho, K.; Chung, C.; Kang, H.; Hong, S. Simultaneous reduction of copper and toxicity in semiconductor wastewater using protonated alginate beads. Chem. Eng. J. 2016, 288, 525–531. [Google Scholar] [CrossRef]
  18. Wang, S.; Mulligan, C.N. Rhamnolipid biosurfactant-enhanced soil flushing for the removal of arsenic and heavy metals from mine tailings. Process Biochem. 2009, 44, 296–301. [Google Scholar] [CrossRef]
  19. Di Palma, L.; Petrucci, E.; Pietrangeli, B. Environmental effects of using chelating agents in polluted sediment remediation. Bull. Environ. Contam. Toxicol. 2015, 94, 340–344. [Google Scholar] [CrossRef]
  20. Mao, X.; Jiang, R.; Xiao, W.; Yu, J. Use of surfactants for the remediation of contaminated soils: A review. J. Hazard. Mater. 2015, 285, 419–435. [Google Scholar] [CrossRef]
  21. Chen, W.; Qu, Y.; Xu, Z.; He, F.; Chen, Z.; Huang, S.; Li, Y. Heavy metal (Cu, Cd, Pb, Cr) washing from river sediment using biosurfactant rhamnolipid. Environ. Sci. Pollut. Res. 2017, 24, 16344–16350. [Google Scholar] [CrossRef] [PubMed]
  22. Kim, G.; Seo, Y.; Kim, I.; Han, J. Co-production of biodiesel and alginate from Laminaria japonica. Sci. Total Environ. 2019, 673, 750–755. [Google Scholar] [CrossRef] [PubMed]
  23. Zeftawy, M.A.; Mulligan, C. Use of rhamnolipid to remove heavy metals from wastewater by micellar-enhanced ultrafiltration (MEUF). Sep. Purif. Technol. 2011, 77, 120–127. [Google Scholar] [CrossRef]
  24. Kaygusuz, H.; Uzaşçı, S.; Erim, F.B. Removal of Fluoride from Aqueous Solution Using Aluminum Alginate Beads. Clean-Soil Air Water 2014, 43, 724–730. [Google Scholar] [CrossRef]
  25. Wang, M.; Yang, Q.; Zhao, X.; Wang, Z. Highly efficient removal of copper ions from water by using a novel alginate-polyethyleneimine hybrid aerogel. Int. J. Biol. Macromol. 2019, 138, 1079–1086. [Google Scholar] [CrossRef]
  26. Li, Y.; Xia, B.; Zhao, Q.; Liu, F.; Zhang, P.; Du, Q.; Wang, D.; Li, D.; Wang, Z.; Zia, Y. Removal of copper ions from aqueous solution by calcium alginate immobilized kaolin. J. Environ. Sci. 2011, 23, 404–411. [Google Scholar] [CrossRef]
  27. Papageorgiou, S.; Katsaros, F.; Kouvelos, E.; Nolan, J.; Deit, H.; Kanellopoulos, N. Heavy metal sorption by calcium alginate beads from Laminaria digitate. J. Hazard. Mater. B 2006, 137, 1765–1772. [Google Scholar] [CrossRef]
  28. Blando, A.; Macias, M.; Cantero, D. Formation of calcium alginate gel capsules: Influence of sodium alginate and CaCl2 concentration on gelation kinetics. J. Biosci. Bioeng. 1999, 88, 686–689. [Google Scholar] [CrossRef]
  29. He, X.; Abdoli, L.; Li, H. Participation of copper ions in formation of alginate conditioning layer: Evolved structure and regulated microbial adhesion. Colloids Surf. B Biointerfaces 2018, 162, 220–227. [Google Scholar] [CrossRef]
  30. Liu, Y.; Li, Z.; Wang, J.; Zhu, P.; Zhao, J.; Zhang, C.; Guo, Y.; Jin, X. Thermal degradation and pyrolysis behavior of aluminum alginate investigated by TG-FTIR-MS and Py-GC-MS. Polym. Degrad. Stab. 2015, 118, 59–68. [Google Scholar] [CrossRef]
  31. Zhou, Q.; Xiaoyan, L.; Bin, L.; Xuegang, L. Fluoride adsorption from aqueous solution by aluminum alginate particles prepared via electrostatic spinning device. Chem. Eng. J. 2014, 256, 306–315. [Google Scholar] [CrossRef]
Figure 1. Schematic diagram of the experimental flow.
Figure 1. Schematic diagram of the experimental flow.
Water 12 03406 g001
Figure 2. The difference depending on the Cu2+ and Al2(SO4)3 concentrations ((a) 0.1% (Al2(SO4)3) without Cu2+, (b) 0.1% Al2(SO4)3 with Cu2+, (c) 0.3% Al2(SO4)3 with Cu2+, (d) 0.5% Al2(SO4)3 with Cu2+, (e) the solid phase after separation).
Figure 2. The difference depending on the Cu2+ and Al2(SO4)3 concentrations ((a) 0.1% (Al2(SO4)3) without Cu2+, (b) 0.1% Al2(SO4)3 with Cu2+, (c) 0.3% Al2(SO4)3 with Cu2+, (d) 0.5% Al2(SO4)3 with Cu2+, (e) the solid phase after separation).
Water 12 03406 g002
Figure 3. Total volume obtained from experiments in this research (1: 0.1% (Al2(SO4)3) with Cu2+, 2: 0.1% (Al2(SO4)3) with Cu2+, 3: 0.3% (Al2(SO4)3) with Cu2+, 4: the solid phase after separation).
Figure 3. Total volume obtained from experiments in this research (1: 0.1% (Al2(SO4)3) with Cu2+, 2: 0.1% (Al2(SO4)3) with Cu2+, 3: 0.3% (Al2(SO4)3) with Cu2+, 4: the solid phase after separation).
Water 12 03406 g003
Figure 4. Variation in TOC and SO42− depending on samples (Sample 1: 0.1% Al2(SO4)3 without Cu2+, Sample 2: 0.1% Al2(SO4)3 with Cu2+, Sample 3: 0.3% Al2(SO4)3 with Cu2+, Sample 4: 0.5% Al2(SO4)3 with Cu2+).
Figure 4. Variation in TOC and SO42− depending on samples (Sample 1: 0.1% Al2(SO4)3 without Cu2+, Sample 2: 0.1% Al2(SO4)3 with Cu2+, Sample 3: 0.3% Al2(SO4)3 with Cu2+, Sample 4: 0.5% Al2(SO4)3 with Cu2+).
Water 12 03406 g004
Figure 5. Change in the TOC and Al3+ depending on sample (Sample 1: 0.1% (Al2(SO4)3) without Cu2+, Sample 2: 0.1% (Al2(SO4)3) with Cu2+, Sample 3: 0.3% (Al2(SO4)3) with Cu2+, Sample 4: 0.5% (Al2(SO4)3) with Cu2+).
Figure 5. Change in the TOC and Al3+ depending on sample (Sample 1: 0.1% (Al2(SO4)3) without Cu2+, Sample 2: 0.1% (Al2(SO4)3) with Cu2+, Sample 3: 0.3% (Al2(SO4)3) with Cu2+, Sample 4: 0.5% (Al2(SO4)3) with Cu2+).
Water 12 03406 g005
Figure 6. Change in TOC and Cu2+ depending on the sample (Sample 1: 0.1% Al2(SO4)3 without Cu2+, Sample 2: 0.1% Al2(SO4)3 with Cu2+, Sample 3: 0.3% Al2(SO4)3 with Cu2+, Sample 4: 0.5% Al2(SO4)3 with Cu2+).
Figure 6. Change in TOC and Cu2+ depending on the sample (Sample 1: 0.1% Al2(SO4)3 without Cu2+, Sample 2: 0.1% Al2(SO4)3 with Cu2+, Sample 3: 0.3% Al2(SO4)3 with Cu2+, Sample 4: 0.5% Al2(SO4)3 with Cu2+).
Water 12 03406 g006
Figure 7. Removal efficiency change of Cu2+ in the liquid phase depending on the sample’s conditions (Sample 2: 0.1% Al2(SO4)3 with Cu2+, Sample 3: 0.3% (Al2(SO4)3) with Cu2+, Sample 4: 0.5% Al2(SO4)3 with Cu2+).
Figure 7. Removal efficiency change of Cu2+ in the liquid phase depending on the sample’s conditions (Sample 2: 0.1% Al2(SO4)3 with Cu2+, Sample 3: 0.3% (Al2(SO4)3) with Cu2+, Sample 4: 0.5% Al2(SO4)3 with Cu2+).
Water 12 03406 g007
Table 1. Characteristics of the liquid phase separated from the mixed phase with solid.
Table 1. Characteristics of the liquid phase separated from the mixed phase with solid.
Sample NumberTOC (mg/L)SO42− (g/L)
Sample 1116.3 (±5.3)2.244 (±0.190)
Sample 232.00 (±2.5)1.573 (±0.078)
Sample 315.50 (±4.4)5.340 (±0.184)
Sample 414.17 (±2.0)8.976 (±0.734)
Sample 1: 0.1% Al2(SO4)3 without Cu2+, Sample 2: 0.1% Al2(SO4)3 with Cu2+, Sample 3: 0.3% Al2(SO4)3 with Cu2+, Sample 4: 0.5% Al2(SO4)3 with Cu2+.
Table 2. Regression analysis.
Table 2. Regression analysis.
SpecificationTOCSO42−Al3+
R20.9480.8400.859
p value0.0040.0940.089
F value0.0260.2620.245
Note: R2 coefficient of determination; p < 0.05, indicating significant difference; F value, indicating the degree of statistical confidence.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Back to TopTop