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Removal of phosphate from surface and wastewater via electrocoagulation
Ecological Engineering xxx (xxxx) xxx–xxx
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Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Removal of phosphate from surface and wastewater via electrocoagulation Daniel Francoa, Jabari Leea, Sebastian Arbelaeza, Nicole Cohenb, Jong-Yeop Kima, a b
⁎
Florida Gulf Coast University, Civil and Environmental Engineering Department, 10501 FGCU Blvd South Fort Myers, FL 33965-6565, United States John Hopkins University, Department of Environmental Health and Engineering, United States
A R T I C L E I N F O
A B S T R A C T
Keywords: Electrocoagulation Aluminum electrode Phosphorus Phosphorus removal Surface water Wastewater Wastewater effluent Phosphate
Water with excessive nutrients are continuously released into water bodies, the resulting eutrophication causes public health, environmental, and economic problems. Phosphorus (P) impairment of fresh surface waters is a major concern in the USA and worldwide. The aim of this study is to use a bench scale P removal system that utilizes electrocoagulation (EC) to address this water quality problem. This study examined the effects of treatment parameters (initial pH, initial conductivity, power input, and initial P concentration) on the ability of the EC process to remove P in solutions with initial P concentrations less than 2 mg/L. It also investigated the ability of EC to reduce concentrations of P in surface water and treated wastewater. P concentrations in phosphate solutions, surface water, and wastewater effluent were reduced by 99% in under 60 min. The removal efficiency was demonstrated to be directly proportional to the conductivity and power supplied.
1. Introduction
developed. Some methods utilize physio-chemical processes such as adsorption, ion-exchange, and chemical precipitation. Enhanced biological phosphorus removal processes, which utilize microorganisms to extract P from solutions, have also been employed (Lacasa et al., 2011). Nevertheless, disadvantages such as high residence time and cost, and low removal efficiencies are persistent throughout most of these treatment methods (Mahvi et al., 2011). Investigations into electrocoagulation (EC) treatment processes have gained interest among researcher’s due to its ability to remove a variety of contaminates, such as heavy metals, organic matter, oils, suspended particles, dissolved particles, and various chemical compounds (Mollah et al., 2004; Holt et al., 2005). EC permits the removal of dissolved P in a solution by having a current applied to submerged electrodes. The electrodes are usually made of iron or aluminum. The electric current applied to the electrodes causes the release of metal cations in the contaminated water. These metal cations can form polymeric metal hydroxide species which neutralize negatively charged contaminates, such as PO43−. These particles aggregate together to form floc and settle out of the solution. The metal cations can also directly bind to the suspended P contaminant and precipitate out of the solution (Mollah et al., 2001). During EC, removal of P by amorphous metal hydroxides and formation of metal phosphate occurs simultaneously (Lacasa et al., 2011). Equations 1–4 illustrate the chemical reactions that take place at the anode, cathode, and in the solution. Chemical Reaction at Anode:
Phosphorous (P) plays a critical role in the survival of living organisms. This nutrient is mainly found as phosphate in animals and plants, where it is essential for the formation of Adenosine Triphosphate and the creation of nucleotides. Nevertheless, phosphate is a widelyused fertilizer in agriculture and animal supplements. Excess P in farming areas is directly discharged to water bodies where P concentrations increase dramatically (Vasudevan et al., 2008a). High P loads into surface water leads to eutrophication of the water. Eutrophication of water bodies has harmful ecological effects such as toxic algal blooms and the development of oxygen depleted or hypoxic zones (Carpenter et al., 1998). Both toxic algal blooms and hypoxic zones harm aquatic organisms and can lead to fish kills (Bennett et al., 2001). Eutrophication of water bodies can also lead to a change in plant and animal species composition, loss of biodiversity, and disruption of food webs (Carpenter et al., 1998). The total amount of P allowed to be discharged into water bodies varies greatly from state to state. Numerous states have established numeric nutrient criteria to determine the maximum amount of P and nitrogen a water body can receive without impairing water quality. These nutrient criteria were then used to establish National Pollutant Discharge Elimination System (NPDES) discharge permits and for the development of total maximum daily loads (TMDL) to limit the release of nutrients into impaired water bodies (USEPA, 2016). To reduce the amount of P being released into water bodies from point source discharges several treatment methods have been ⁎
− Al(s) → Al3+ (aq) + 3e
Corresponding author. E-mail address: [email protected] (J.-Y. Kim).
http://dx.doi.org/10.1016/j.ecoleng.2017.07.031 Received 31 March 2017; Received in revised form 25 July 2017; Accepted 26 July 2017 0925-8574/ Published by Elsevier B.V.
Please cite this article as: Franco, D., Ecological Engineering (2017), http://dx.doi.org/10.1016/j.ecoleng.2017.07.031
(1)
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orthophosphate concentration was measured using PhosVer® 3 Phosphate Reagent Powder Pillows (HACH DOC316.53.01119) and a spectrophotometer (Thermoscientific). Soluble reactive P concentrations were measured because it provides a good estimation of the P that can be easily utilized algae and other aquatic organisms (Busman et al., 2009). Prior to the surface and wastewater EC tests, a series of preliminary EC experiments on phosphate solutions were conducted to determine the capabilities of EC to remove P in solutions with initial P concentrations less than 2 mg/L under various operating parameters such as initial pH, initial conductivity, and power applied. Tests were conducted for low initial P concentrations of 0.07–0.15 mg/L (Low P) and high initial P concentrations of 1.5 mg/L ± 0.25 mg/L (High P). The study of differing initial P concentrations was done with the purpose of emulating the typical concentrations of P in wastewater and surface water.
Chemical Reaction at Cathode:
3e− + 3H2 O →
3 H2(g) + 3OH− 2
(2)
Chemical Reaction in Solution: + Al3+ (aq) + 3H2O → Al(OH)3(s) + 3H(aq)
Al3+ (aq)
+
PO43− (aq)
→ AlPO4(s)
(3) (4)
Numerous publications have analyzed the effects of several operating parameters such as the initial pH, initial conductivity, current density, and initial concentration of P, on the efficiency of the EC process (Attour et al., 2014; Irdemez et al., 2006a,b,c; Lacasa et al., 2011; Vasudevan et al., 2008a). 1.1. Objectives 1. Determine the capabilities of EC to remove P in solutions with initial P concentrations less than 2 mg/L under various operating parameters (initial pH, initial conductivity, and applied power). 2. Determine the extent to which EC can reduce the P concentration in surface water and wastewater without negatively impacting pH, conductivity, turbidity, and alkalinity.
3. Results and discussion 3.1. Effects of initial pH The initial pH has been reported to have a significant effect on the performance of the EC treatment process (Attour et al., 2014; Behbahani, 2011; Kobyaa et al., 2009; Vasudevan et al., 2008a). As seen in Fig. 1, the P removal efficiency varied significantly depending on the initial pH of the batch. For both High P tests, the solutions with initial pH of about 7.5 were observed to have fastest P removal rate, with 99% reduction achieved by 15 min of reaction time. For both High P tests, solutions with initial pH around 5-5.7 had the second fastest P removal rate and tests with initial pH 8.12-8.83 had the third fastest P removal. 99% reduction of P concentration by 60 min of reaction time for High P tests was achieved for the solutions with pH 5–8.83. Similar removal efficiencies were obtained by other studies with initial pH 5–10 (Attour et al., 2014; Behbahani, 2011; Bektas et al., 2004; Chen et al., 2014; Kobya et al., 2009; Kuokkanen et al., 2014; Mahvi et al., 2011; Vasudevan et al., 2008a). For Low P concentration, the results were found to be similar. However, the reactor with a pH of about 8.83 displayed the fastest removal efficiency, removing 99% of P in less than 10 min of reaction time. Solutions in the Low P and High P tests with an initial pH of 3 did not remove any P. These results conflicted with many studies that reported 60–100% reduction in P concentration with an initial pH of 3 (Attour et al., 2014; Behbahani, 2011; Irdemez et al., 2006a; Kobya et al., 2009). The lack of P removal at this initial pH compared to other studies may be attributed to differences in electrode materials used, power levels applied, initial conductivity, and submerged electrode area, all of which are important parameters for P reduction using EC (Chen, 2004). Thus, it was determined that the use of EC for the reduction of P was feasible over a wide range of initial pH.
2. Materials and methods 2.1. Phosphate solutions, surface water, and wastewater samples Synthetic phosphate solutions were prepared from KH2PO4 using distilled water. To prepare a completely mixed solution a magnetic stirrer plate was used. The solution’s initial pH was adjusted to pH ranging from 3 to 9 using 0.5 M HCl and 0.5 M NaOH. Initial conductivity was adjusted to 150–880 μS/cm by dissolving 0.01 M KCl into the solution. Wastewater effluent from the Three Oaks Waste Water Treatment (WWTP) plant clarifiers, as well as surface water samples from Billy Creek were collected and tested. The Three Oaks WWTP is in Estero, Florida, and Billy Creek, a tributary of the Caloosahatchee River, is in North Fort Myers. The numeric nutrient criteria for total phosphorous in rivers and streams in peninsular Florida of 0.12 mg/L applies to Billy Creek and the Caloosahatchee River (USEPA, 2016). 2.2. Experiment configuration and testing The EC reactors consisted of a square Plexiglas container capable of holding 1 L of liquid. Two pre-weighed aluminum electrodes, 50 mm × 82 mm each, were used for the anode and cathode in each reactor. The electrodes were held 2.5 cm apart. A portion of the electrode surface area, 13.32 cm2, was submerged in the solution held in the 1 L Plexiglas container. A 30 V/5A Single-Output DC Power Supply 110 V/220 V Switchable, with alligator clips, was used to apply a predetermined current and voltage to the electrodes. The container was placed on a magnetic stir plate to allow the solution to be continuously mixed, at the lowest speed, as power was applied to the electrodes. All tests were conducted for 50 or 60 min at room temperature. 20 mL samples were extracted at specific time intervals (0, 2,6, 10, 15, 20, 30, 40, 50, and 60 min). The pH and conductivity of the samples were measured using a pH meter (Oakton) and conductivity meter (Oakton). 10 mL from each 20 mL sample was filtered through a syringe membrane 25 mm filter with the pore diameter of 0.45 μm and then analyzed for the P concentration. All tests were conducted at room temperature. Turbidity of the surface water and wastewater were analyzed before and after each EC test using a turbidity meter (Clarkson 600100). Alkalinity testing was carried out on 50 mL samples of surface water and wastewater collected prior to and immediately after EC testing. Alkalinity testing was carried out per standard methods for examination of water (Clesceri et al., 1999). Dissolve reactive P or
3.2. Effects of initial conductivity Deionized water has been known to be ineffective at conducting electricity due to the lack of ions in the solution. The conductivity of surface and wastewater is usually dependent on the amount of total dissolved solids. Therefore, KCl was added to the Low P and High P solutions to create mixtures with approximate conductivity of 146–225 μS/cm, 314–345 μS/cm, and 681–880 μS/cm as shown in Fig. 2. These values were selected with the purpose of covering typical conductivities of surface and wastewater. Lake Trafford, a surface water body near Immokalee, FL, has a conductivity of approximately 280 μS/ cm (Cabezas and Tomasko, 2009), which falls within the range tested. Similarly, as presented later in this report, surface water channels near the Fort Myers area such as Billy Creek, have a conductivity of 500 μS/ cm. Regarding wastewater, the conductivity measured varied from 700 to 800 μS/cm. 2
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Fig. 1. Change of P concentrations and pH as a function of EC reaction time under different initial pH and applied power.
for the removal of P, higher conductivities favor the faster removal of P. These results agreed with other studies where the higher conductivity was demonstrated to have a higher P removal efficiency (Attour et al., 2014; Zhang et al., 2013). As seen in Fig. 2, the P concentrations in the Low P tests were reduced by 81% at roughly the same rate regardless of the conductivities by 10 min of reaction time. The fact that the reduction of P concentration leveled off after 10 min suggests that there may
The effects of conductivity on the reduction of P for Low P and High P tests were shown in Fig. 2. For the High P tests, the highest conductivity showed the fastest reduction of the P and the lowest conductivity had the slowest reduction in P. Overall, P concentrations were reduced by 99% in 30 min of reaction time for all High P tests. The higher conductivity resulted in a larger amount of electrode cations released into the solution. Since the electrode cations are responsible
Fig. 2. Change of P concentrations and pH as a function of EC reaction time under different initial conductivity and applied power.
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Fig. 3. Change of P concentrations and pH as a function of EC reaction time under distinct levels applied power.
often feed into and negatively impact large surface water bodies of economic, social, and environmental importance. Three 1-l samples of this surface water were tested simultaneously at three different power levels (0.5, 1 and 3 W, respectively). Fig. 4 illustrates the change in P concentrations at these different power levels as a function of EC reaction time. A similar rate of P reduction was observed for all three power levels. At a reaction time of 10 min the P concentrations were reduced by 90%, 92%, and 90% for reactors with 3 W, 1 W, and 0.5 W of applied power respectively. This reduction in P concentration is significant because the same P reduction were achieved in the reactors that operated at a third and a sixth of the 3 W applied to one reactor. The highest reduction in P concentration, 98%, was achieved at 30 min of reaction time in all three reactors. After 30 min, the P concentration in the three reactors fluctuated slightly but remained below 5% of the initial concentration for the remaining reaction time. Other studies have reported fluctuations in the P concentrations during EC reaction time (Attour et al., 2014; Behbahani, 2011). These fluctuations were attributed to the limited adsorption capacity of metallic hydroxide flocs under certain operating conditions (Behbahani, 2011). During testing of the surface water, the pH, alkalinity, and conductivity were measured. Fig. 5 depicts the change in pH throughout testing. pH increased gradually by 0.03–0.07 units over the 60 min of reaction time in all three reactors. This increase in pH was expected due to the hydrogen evolution and production of OH− at the cathodes (Chen, 2004) and was consistent with the results of other studies that examined P removal by EC (Attour et al., 2014; Behbahani, 2011; Bektas et al., 2004; Irdemez et al., 2006a; Vasudevan et al., 2008a,b). This gradual increase in pH is promising because a sudden change in pH can have negative effect on water quality and aquatic ecosystems. Fig. 4 shows the change in conductivity over the course of testing. A slight decrease in the conductivity during testing is shown. This small
exist a limit for the P removal rate and removal efficiency achieved when treating waters with low initial P concentration. It was determined that using EC to reduce P concentrations was feasible when waters with 146–880 μS/cm of conductivity and 0.07–1.6 mg/L of P were treated. 3.3. Effects of applied power Fig. 3 shows the change of P concentration and pH as a function of EC reaction time under different applied powers 5 W, 12 W, and 30 W for reactors with Low and High P concentration. The graphs for both P concentrations show that the highest power applied achieved the fastest P removal rate. It was shown that when 5 W and 12 W of power were applied to solutions containing Low and High P concentrations that a similar rate of removal was achieved. This suggests that there may exist a threshold for power applied and the P removal rate and removal efficiency achieved. Overall, 99% reduction of P concentration was attained for all 3 power levels in both High P and Low P concentrations. These results confirmed with all the publications studied that the greater the applied power the greater the P removal efficiency. (Attour et al., 2014; Behbahani, 2011; Bektas et al., 2004; Chen et al., 2014; Irdemez et al., 2006b,c; Kobya et al., 2009; Mahvi et al., 2011; Vasudevan et al., 2008a,b). Thus, it was determined that using EC to reduce P concentrations was feasible at various applied power levels. 3.4. Surface water Billy Creek had a history of having P concentrations ranging from 0.2 to 0.5 mg/L, which exceeds the total P nutrient threshold of 0.12 mg/L (USEPA, 2016). It was important to determine if EC could be used to reduce P concentrations in surface water because, like Billy Creek, many creeks that are contaminated with high P concentrations
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Fig. 4. Change of P concentration, conductivity, and pH as a function of EC reaction time in surface water (left) and wastewater effluent (right) under distinct levels of applied power.
and alkalinity. All three power levels tested proved to work equally well at reducing P concentrations to by this amount.
decrease in conductivity is promising because it demonstrates that the EC process, when applied at these power levels, will not significantly alter the conductivity of the water. The alkalinity prior to EC testing, noted as “Pre-EC”, and after testing, noted by power applied to the reactor, are displayed in Fig. 5. From this figure, the data shows that alkalinity decreased by 5–14 mg/L as CaCO3. This decrease was not expected and may have been due to errors during measurement. This decrease was acceptable since the alkalinity remained in the range of what is typically found for surface water bodies in the region (Omernik et al., 1988). Fig. 5 also illustrates the turbidity of the surface water before and after treatment. The water in the reactor where 1 W was applied increased in turbidity by 0.8 NTU while the remaining reactors had a turbidity equal to the initial. Turbidity didn’t change significantly after EC. This slight increase in turbidity after EC is explained due by the visible formation of floc that hadn’t settled out of the solution. EC has been proven to be able reduce P concentrations in surface water by 98% without negatively impacting pH, turbidity, conductivity,
3.5. Wastewater effluent Fig. 4 illustrates how the P concentration, conductivity, and pH changed during EC for the wastewater effluent. A similar rate of decrease in P concentration was observed for all three-power levels. At a reaction time of 10 min the P concentrations were reduced by 93%, 99%, and 98% for reactors where 30 W, 12 W, and 5.0 W of power were applied respectively. This reduction in P concentration is significant because a 98% to 99% reduction was achieved in reactors that operated on less than half and a sixth of the 30 W applied to one reactor. At 20 min of reaction time all three reactors achieved a 99% reduction in P concentration. The rate of P removal in these reactors was greater than the removal rate achieved when testing the surface water. This was attributed to the greater power levels applied and the higher conductivity of the wastewater. Prior testing conducted by the authors and
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Fig. 5. Turbidity (top row) and Alkalinity (bottom row) of EC treated surface water (left) and wastewater effluent (right) after 60 min of EC reaction time under distinct levels of applied power.
wastewater effluent 99% without negatively impacting pH, turbidity, conductivity, and alkalinity. All three power levels tested proved to work equally well at reducing P concentrations to by this amount.
other studies have confirmed that the greater the conductivity and power applied the higher the P removal efficiency (Attour et al., 2014; Zhang et al., 2013). The pH of the wastewater effluent in all three reactors increased as depicted in Fig. 4. The pH increased by 0.91–0.98 units during the 60 min of reaction time to a final pH of 8.18–8.20. Up until 40 min of reaction time the pH in the three reactors remained below 8.0. This was important because wastewater effluent from the clarifier at Three Oaks WWTP was filtered through a slow sand filter, disinfected, then used as reclaimed water for irrigating lawns. The optimal pH range for reclaimed water used for irrigation was 6.5–8.0 (Toor and Lusk, 2011). Thus, the pH of the wastewater effluent treated using the EC process was not negatively impacted and could still be used for irrigation. As seen in Fig. 4 the conductivity in the three reactors containing wastewater effluent remained roughly the same. The lack of decrease in conductivity is acceptable as the conductivity of the water was already at an acceptable level for use as reclaimed water by the WWTP. The alkalinity of the water in the reactor that had 5 W applied was about the same as the untreated wastewater effluent, while the alkalinity of the water in reactors with 12 W and 30 W applied were 5 mg/L less than that of the untreated water (Fig. 5). Overall, alkalinity of the water was not significantly affected by the EC process which is important because a certain amount of alkalinity is necessary to prevent sudden changes in the pH. Turbidity of the wastewater effluent, as seen in Fig. 5, increased with the amount of power applied. This slight increase in turbidity after EC was due by the visible formation of flocculation particles. EC has been proven to be able reduce P concentrations in
3.6. Phosphorus removal efficiencies comparison A P removal efficiency of up to 99% was obtained by the authors for phosphate solutions, surface water, and wastewater that were treated using EC. Similar P removal efficiencies were obtained in many other studies that utilized EC for P removal. The removal efficiencies achieved and the accompanying operating parameters are displayed in Table 1. 4. Conclusion From the tests performed in this study, P concentrations of a variety of solutions were reduced by up to 99% under a variety of water quality parameters. Furthermore, the effects of initial conductivity, power supplied, and initial pH on the P removal efficiency were characterized. As power and conductivity increased, the removal efficiency and rate of P increased. 99% removal of P was achieved in solutions with initial pH 5–8.8. EC reduced the P concentration of surface water and wastewater effluent by 98% and 99% respectively in under 20 min, without negatively impacting pH, turbidity, conductivity, and alkalinity. The results of this study and other studies indicated that EC can be feasibly used to remove P from surface water, wastewater effluent, and other types of waters (Kuokkanen et al., 2013; Mahvi et al., 2011). This technology has the potential to be implemented within wastewater
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Batch
Batch
50–100
66–99
60–98
0.9
Batch
78–100
0.9
Batch with Recirculating Flow Batch 61–99
0.85
2
Batch Batch 0–99 65–100
0.85
1 1.8
Type of Reactor
Acknowledgements The authors would like to thank Florida Gulf Coast University’s U.A.Whitaker College of Engineering’sDepartment of Environmental and Civil Engineering for making this research possible. Publication was assisted by U.S. National Science Foundation grant number 1619948 with project title: U.S. Science International Collaborations and Contributions to EcoSummit 2016 Sustainability: Engineering Change.
100 60 DNS 10 5 2–12 600 Vasudevan et al. (2008b)
Aluminum/ Aluminum Alloy/ Iron Mild Steel
Iron or Aluminum Aluminum
Attour, A., Touati, M., Tlili, M., Ben Amor, M., Lapicque, F., Leclerc, J.-P., 2014. Influence of operating parameters on phosphate removal from water by electrocoagulation using aluminum electrodes. Seperation Purif. Technol. 123, 124–129. Behbahani, M.A., 2011. A comparison between aluminum and iron electrodes on removal ofPhosphate from aqueous solutions by electrocoagulation process. Int. J. Environ. Res. 5, 403–412. Bektas, N., Akbulut, H., Inan, H., Dimoglo, A., 2004. Removal of phosphate from aqueous solutions by electro-coagulation. J. Hazard. Mater. 106B, 101–105. Bennett, E., Carpenter, S., Caraco, N., 2001. Human impact on erodable phosphorus and eutrophication: a global perspective. Bioscience 51 (3), 227–234. Busman, L., Lamb, J., Randall, G., Rehm, G., Schmitt, M., 2009. The nature of phosphorus in soils. Retrieved from University of Minnesota Extension: http://www.extension. umn.edu/agriculture/nutrient-management/phosphorus/the-nature-of-phosphorus/. Cabezas, M., Tomasko, D., 2009. Water Quality and Ecological Assessment of Lake Trafford. Mac Hatcher, Tampa, FL. Carpenter, S., Caraco, N., Correll, D., Howarth, R., Sharpley, A., Smith, V., 1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Issues Ecol. 8, 559–568. Chen, G., 2004. Electrochemical technologies in wastewater treatment. Sep. Purif. Technol. 38, 11–41. Chen, S., Shi, Y., Wang, W., Li, Z., Gao, J., Bao, K., Zhang, R., 2014. Phosphorus removal from continuous phosphate- contaminated water by electrocoagulation using aluminum and iron plates alternately as electrodes. Sep. Sci. Technol. 49, 939–945. Clesceri, L., Greenberg, A., Eaton, A., 1999. Standard Methods for the Examination of Water and Wastewater, 20th Edition. American Public Health Association. Holt, P., Barton, G., Mitchell, C., 2005. The future for electrocoagulation as a localised water treatment technology. Chemosphere 59, 355–367. Irdemez, S., Demircioglu, N., Yildiz, Y.S., 2006a. The effects of pH on phosphate removal from wastewater by electrocoagulation with iron plate electrodes. J. Hazard. Mater. B17, 1231–1235. Irdemez, S., Demircioglu, N., Yıldız, Y.S., Bingul, Z., 2006b. The effects of current density and phosphate concentration on phosphate removal from wastewater by electrocoagulation using aluminum and iron plate electrodes. Sep. Purif. Technol. 52, 218–223. Irdemez, S., Yildiz, Y., Tosunoglu, V., 2006c. Optimization of phosphate removal from wastewater by electrocoagulation with aluminum plate electrodes. Sep. Purif. Technol. 52, 394–401. Kobya, M., Demirbas, E., Dedeli, A., Sensoy, M., 2009. Treatment of rinse water from zinc phosphate coating by batch and continuous electrocoagulation processes. J. Hazard. Mater. 173, 326–334. Kuokkanen, V., Kuokkanen, T., Rämö, J., Lassi, U., 2013. Recent applications of electrocoagulation in treatment of water and WastewateräA review. Green Sustainable Chem. 3, 89–121. Kuokkanen, V., Kuokkanen, T., Rämö, J., Lassi, U., Roininen, J., 2014. Removal of phosphate from wastewaters for further utilization using electrocoagulation with hybrid electrodes ? Techno-economic studies. J. Water Process Eng. 94, 1–8. Lacasa, E., Canizares, P., Sáez, C., Fernández, F., Rodrigo, M., 2011. Electrochemical phosphates removal using iron and aluminium electrodes. Chem. Eng. J. 172, 137–143. Mahvi, A., Ebrahimi, S.-D., Mesdaghinia, A., Gharibi, H., Sowlat, M., 2011. Performance evaluation of a continuous bipolar electrocoagulation/electrooxidation–electroflotation (ECEO–EF) reactor designed for simultaneous removal of ammonia and phosphate from wastewater effluent. J. Hazard. Mater. 192, 1267–1274. Mollah, M., Morkovsky, P., Gomes, J., Kesmez, M., Parga, J., Cocke, D., 2004. Fundamentals, present and future perspectives of electrocoagulation. J. Hazard. Mater. 114, 199–210. Mollah, M., Schennach, R., Parga, J., Cocke, D., 2001. Electrocoagulation (EC)—science and applications. J. Hazard. Mater. 84, 29–41. Omernik, J., Griffith, G., Irish, J., Johnson, C., 1988. Total Alkalinity of Surface Waters. (Retrieved from USGS: https://water.usgs.gov/owq/alkus.pdf).
Stainless Steel
100 30 DNS 10 5 600 Stainless Steel
3–10
50–500 100 0–3.09 0.375–1.5 4–7 1500
5
25–150 40 0.1–0.7 0.375–1.125 3 1500
5
10–160 60 11.3 0.48–1.92 10 4–10 Aluminum/Iron
960
Iron/ Aluminum Iron or Aluminum Aluminum
0.07–1.75 100 50–60 140 0.15–0.88 0.8–3.2 0.10–2.00 0.10–0.90 2.5 5–20 3–9 2–11 Aluminum Aluminum Aluminum Aluminum
Present Study Attour et al. (2014) Chen et al. (2014) Irdemez et al. (2006b) Irdemez et al. (2006c) Vasudevan et al. (2008a)
13.32 50
Initial Conductivity (mS/ cm) Electric Current (Amps) Distance between Electrodes (mm) Initial pH Effective Surface Area of Electrodes (cm2) Material of Anode
Material of Cathode
treatment plants, specifically in the clarifiers that contain wastewater effluent that has undergone primary and secondary treatment. When used for treating surface water, EC has the potential to be implemented at the outflow treatment wetlands or detention ponds. Future research should involve designing an in-situ pilot scale reactor for treating surface water and a pilot scale design for utilizing EC directly in the WWTP.
References
Studies
Table 1 Comparison of phosphorus removal efficiencies achieved and the associated operating parameters using electrocoagulation. DNS = Did Not Specify.
Time (min)
Initial Phosphorus Concentration (mg/L)
P Removal Efficiency (%)
Volume Treated per Reactor (L)
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mild steel anodes. J. Hazard. Mater. 3, 1480–1486. Vasudevan, S., Sozhan, G., Ravichandran, S., Jayaraj, J., Lakshmi, J., Sheela, S., 2008b. Studies on the removal of phosphate from drinking water by electrocoagulation process. Ind. Eng. Chem. Res. 47, 2018–2023. Zhang, S., Zhang, J., Wang, W., Li, F., Cheng, X., 2013. Removal of phosphate from landscape water using an electrocoagulation process powered directly by photovoltaic solar modules. Solar Energy Mater. Solar Cells 117, 73–80.
Toor, G. S., & Lusk, M., 2011. Reclaimed Water Use in the Landscape: Understanding Landscape Irrigation Water Quality Tests. Retrieved from EDIS IFAS: https://edis. ifas.ufl.edu/ss546#TABLE_4. USEPA., 2016. State Development of Numeric Criteria for Nitrogen and Phosphorus Pollution. Retrieved from US EPA: https://www.epa.gov/nutrient-policy-data/statedevelopment-numeric-criteria-nitrogen-and-phosphorus-pollution. Vasudevan, S., Lakshmi, J., Jayaraj, J., Sozhan, G., 2008a. Remediation of phosphatecontaminated water by electrocoagulation with aluminium, aluminium alloy and
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Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Removal of phosphate from surface and wastewater via electrocoagulation Daniel Francoa, Jabari Leea, Sebastian Arbelaeza, Nicole Cohenb, Jong-Yeop Kima, a b
⁎
Florida Gulf Coast University, Civil and Environmental Engineering Department, 10501 FGCU Blvd South Fort Myers, FL 33965-6565, United States John Hopkins University, Department of Environmental Health and Engineering, United States
A R T I C L E I N F O
A B S T R A C T
Keywords: Electrocoagulation Aluminum electrode Phosphorus Phosphorus removal Surface water Wastewater Wastewater effluent Phosphate
Water with excessive nutrients are continuously released into water bodies, the resulting eutrophication causes public health, environmental, and economic problems. Phosphorus (P) impairment of fresh surface waters is a major concern in the USA and worldwide. The aim of this study is to use a bench scale P removal system that utilizes electrocoagulation (EC) to address this water quality problem. This study examined the effects of treatment parameters (initial pH, initial conductivity, power input, and initial P concentration) on the ability of the EC process to remove P in solutions with initial P concentrations less than 2 mg/L. It also investigated the ability of EC to reduce concentrations of P in surface water and treated wastewater. P concentrations in phosphate solutions, surface water, and wastewater effluent were reduced by 99% in under 60 min. The removal efficiency was demonstrated to be directly proportional to the conductivity and power supplied.
1. Introduction
developed. Some methods utilize physio-chemical processes such as adsorption, ion-exchange, and chemical precipitation. Enhanced biological phosphorus removal processes, which utilize microorganisms to extract P from solutions, have also been employed (Lacasa et al., 2011). Nevertheless, disadvantages such as high residence time and cost, and low removal efficiencies are persistent throughout most of these treatment methods (Mahvi et al., 2011). Investigations into electrocoagulation (EC) treatment processes have gained interest among researcher’s due to its ability to remove a variety of contaminates, such as heavy metals, organic matter, oils, suspended particles, dissolved particles, and various chemical compounds (Mollah et al., 2004; Holt et al., 2005). EC permits the removal of dissolved P in a solution by having a current applied to submerged electrodes. The electrodes are usually made of iron or aluminum. The electric current applied to the electrodes causes the release of metal cations in the contaminated water. These metal cations can form polymeric metal hydroxide species which neutralize negatively charged contaminates, such as PO43−. These particles aggregate together to form floc and settle out of the solution. The metal cations can also directly bind to the suspended P contaminant and precipitate out of the solution (Mollah et al., 2001). During EC, removal of P by amorphous metal hydroxides and formation of metal phosphate occurs simultaneously (Lacasa et al., 2011). Equations 1–4 illustrate the chemical reactions that take place at the anode, cathode, and in the solution. Chemical Reaction at Anode:
Phosphorous (P) plays a critical role in the survival of living organisms. This nutrient is mainly found as phosphate in animals and plants, where it is essential for the formation of Adenosine Triphosphate and the creation of nucleotides. Nevertheless, phosphate is a widelyused fertilizer in agriculture and animal supplements. Excess P in farming areas is directly discharged to water bodies where P concentrations increase dramatically (Vasudevan et al., 2008a). High P loads into surface water leads to eutrophication of the water. Eutrophication of water bodies has harmful ecological effects such as toxic algal blooms and the development of oxygen depleted or hypoxic zones (Carpenter et al., 1998). Both toxic algal blooms and hypoxic zones harm aquatic organisms and can lead to fish kills (Bennett et al., 2001). Eutrophication of water bodies can also lead to a change in plant and animal species composition, loss of biodiversity, and disruption of food webs (Carpenter et al., 1998). The total amount of P allowed to be discharged into water bodies varies greatly from state to state. Numerous states have established numeric nutrient criteria to determine the maximum amount of P and nitrogen a water body can receive without impairing water quality. These nutrient criteria were then used to establish National Pollutant Discharge Elimination System (NPDES) discharge permits and for the development of total maximum daily loads (TMDL) to limit the release of nutrients into impaired water bodies (USEPA, 2016). To reduce the amount of P being released into water bodies from point source discharges several treatment methods have been ⁎
− Al(s) → Al3+ (aq) + 3e
Corresponding author. E-mail address: [email protected] (J.-Y. Kim).
http://dx.doi.org/10.1016/j.ecoleng.2017.07.031 Received 31 March 2017; Received in revised form 25 July 2017; Accepted 26 July 2017 0925-8574/ Published by Elsevier B.V.
Please cite this article as: Franco, D., Ecological Engineering (2017), http://dx.doi.org/10.1016/j.ecoleng.2017.07.031
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orthophosphate concentration was measured using PhosVer® 3 Phosphate Reagent Powder Pillows (HACH DOC316.53.01119) and a spectrophotometer (Thermoscientific). Soluble reactive P concentrations were measured because it provides a good estimation of the P that can be easily utilized algae and other aquatic organisms (Busman et al., 2009). Prior to the surface and wastewater EC tests, a series of preliminary EC experiments on phosphate solutions were conducted to determine the capabilities of EC to remove P in solutions with initial P concentrations less than 2 mg/L under various operating parameters such as initial pH, initial conductivity, and power applied. Tests were conducted for low initial P concentrations of 0.07–0.15 mg/L (Low P) and high initial P concentrations of 1.5 mg/L ± 0.25 mg/L (High P). The study of differing initial P concentrations was done with the purpose of emulating the typical concentrations of P in wastewater and surface water.
Chemical Reaction at Cathode:
3e− + 3H2 O →
3 H2(g) + 3OH− 2
(2)
Chemical Reaction in Solution: + Al3+ (aq) + 3H2O → Al(OH)3(s) + 3H(aq)
Al3+ (aq)
+
PO43− (aq)
→ AlPO4(s)
(3) (4)
Numerous publications have analyzed the effects of several operating parameters such as the initial pH, initial conductivity, current density, and initial concentration of P, on the efficiency of the EC process (Attour et al., 2014; Irdemez et al., 2006a,b,c; Lacasa et al., 2011; Vasudevan et al., 2008a). 1.1. Objectives 1. Determine the capabilities of EC to remove P in solutions with initial P concentrations less than 2 mg/L under various operating parameters (initial pH, initial conductivity, and applied power). 2. Determine the extent to which EC can reduce the P concentration in surface water and wastewater without negatively impacting pH, conductivity, turbidity, and alkalinity.
3. Results and discussion 3.1. Effects of initial pH The initial pH has been reported to have a significant effect on the performance of the EC treatment process (Attour et al., 2014; Behbahani, 2011; Kobyaa et al., 2009; Vasudevan et al., 2008a). As seen in Fig. 1, the P removal efficiency varied significantly depending on the initial pH of the batch. For both High P tests, the solutions with initial pH of about 7.5 were observed to have fastest P removal rate, with 99% reduction achieved by 15 min of reaction time. For both High P tests, solutions with initial pH around 5-5.7 had the second fastest P removal rate and tests with initial pH 8.12-8.83 had the third fastest P removal. 99% reduction of P concentration by 60 min of reaction time for High P tests was achieved for the solutions with pH 5–8.83. Similar removal efficiencies were obtained by other studies with initial pH 5–10 (Attour et al., 2014; Behbahani, 2011; Bektas et al., 2004; Chen et al., 2014; Kobya et al., 2009; Kuokkanen et al., 2014; Mahvi et al., 2011; Vasudevan et al., 2008a). For Low P concentration, the results were found to be similar. However, the reactor with a pH of about 8.83 displayed the fastest removal efficiency, removing 99% of P in less than 10 min of reaction time. Solutions in the Low P and High P tests with an initial pH of 3 did not remove any P. These results conflicted with many studies that reported 60–100% reduction in P concentration with an initial pH of 3 (Attour et al., 2014; Behbahani, 2011; Irdemez et al., 2006a; Kobya et al., 2009). The lack of P removal at this initial pH compared to other studies may be attributed to differences in electrode materials used, power levels applied, initial conductivity, and submerged electrode area, all of which are important parameters for P reduction using EC (Chen, 2004). Thus, it was determined that the use of EC for the reduction of P was feasible over a wide range of initial pH.
2. Materials and methods 2.1. Phosphate solutions, surface water, and wastewater samples Synthetic phosphate solutions were prepared from KH2PO4 using distilled water. To prepare a completely mixed solution a magnetic stirrer plate was used. The solution’s initial pH was adjusted to pH ranging from 3 to 9 using 0.5 M HCl and 0.5 M NaOH. Initial conductivity was adjusted to 150–880 μS/cm by dissolving 0.01 M KCl into the solution. Wastewater effluent from the Three Oaks Waste Water Treatment (WWTP) plant clarifiers, as well as surface water samples from Billy Creek were collected and tested. The Three Oaks WWTP is in Estero, Florida, and Billy Creek, a tributary of the Caloosahatchee River, is in North Fort Myers. The numeric nutrient criteria for total phosphorous in rivers and streams in peninsular Florida of 0.12 mg/L applies to Billy Creek and the Caloosahatchee River (USEPA, 2016). 2.2. Experiment configuration and testing The EC reactors consisted of a square Plexiglas container capable of holding 1 L of liquid. Two pre-weighed aluminum electrodes, 50 mm × 82 mm each, were used for the anode and cathode in each reactor. The electrodes were held 2.5 cm apart. A portion of the electrode surface area, 13.32 cm2, was submerged in the solution held in the 1 L Plexiglas container. A 30 V/5A Single-Output DC Power Supply 110 V/220 V Switchable, with alligator clips, was used to apply a predetermined current and voltage to the electrodes. The container was placed on a magnetic stir plate to allow the solution to be continuously mixed, at the lowest speed, as power was applied to the electrodes. All tests were conducted for 50 or 60 min at room temperature. 20 mL samples were extracted at specific time intervals (0, 2,6, 10, 15, 20, 30, 40, 50, and 60 min). The pH and conductivity of the samples were measured using a pH meter (Oakton) and conductivity meter (Oakton). 10 mL from each 20 mL sample was filtered through a syringe membrane 25 mm filter with the pore diameter of 0.45 μm and then analyzed for the P concentration. All tests were conducted at room temperature. Turbidity of the surface water and wastewater were analyzed before and after each EC test using a turbidity meter (Clarkson 600100). Alkalinity testing was carried out on 50 mL samples of surface water and wastewater collected prior to and immediately after EC testing. Alkalinity testing was carried out per standard methods for examination of water (Clesceri et al., 1999). Dissolve reactive P or
3.2. Effects of initial conductivity Deionized water has been known to be ineffective at conducting electricity due to the lack of ions in the solution. The conductivity of surface and wastewater is usually dependent on the amount of total dissolved solids. Therefore, KCl was added to the Low P and High P solutions to create mixtures with approximate conductivity of 146–225 μS/cm, 314–345 μS/cm, and 681–880 μS/cm as shown in Fig. 2. These values were selected with the purpose of covering typical conductivities of surface and wastewater. Lake Trafford, a surface water body near Immokalee, FL, has a conductivity of approximately 280 μS/ cm (Cabezas and Tomasko, 2009), which falls within the range tested. Similarly, as presented later in this report, surface water channels near the Fort Myers area such as Billy Creek, have a conductivity of 500 μS/ cm. Regarding wastewater, the conductivity measured varied from 700 to 800 μS/cm. 2
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Fig. 1. Change of P concentrations and pH as a function of EC reaction time under different initial pH and applied power.
for the removal of P, higher conductivities favor the faster removal of P. These results agreed with other studies where the higher conductivity was demonstrated to have a higher P removal efficiency (Attour et al., 2014; Zhang et al., 2013). As seen in Fig. 2, the P concentrations in the Low P tests were reduced by 81% at roughly the same rate regardless of the conductivities by 10 min of reaction time. The fact that the reduction of P concentration leveled off after 10 min suggests that there may
The effects of conductivity on the reduction of P for Low P and High P tests were shown in Fig. 2. For the High P tests, the highest conductivity showed the fastest reduction of the P and the lowest conductivity had the slowest reduction in P. Overall, P concentrations were reduced by 99% in 30 min of reaction time for all High P tests. The higher conductivity resulted in a larger amount of electrode cations released into the solution. Since the electrode cations are responsible
Fig. 2. Change of P concentrations and pH as a function of EC reaction time under different initial conductivity and applied power.
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Fig. 3. Change of P concentrations and pH as a function of EC reaction time under distinct levels applied power.
often feed into and negatively impact large surface water bodies of economic, social, and environmental importance. Three 1-l samples of this surface water were tested simultaneously at three different power levels (0.5, 1 and 3 W, respectively). Fig. 4 illustrates the change in P concentrations at these different power levels as a function of EC reaction time. A similar rate of P reduction was observed for all three power levels. At a reaction time of 10 min the P concentrations were reduced by 90%, 92%, and 90% for reactors with 3 W, 1 W, and 0.5 W of applied power respectively. This reduction in P concentration is significant because the same P reduction were achieved in the reactors that operated at a third and a sixth of the 3 W applied to one reactor. The highest reduction in P concentration, 98%, was achieved at 30 min of reaction time in all three reactors. After 30 min, the P concentration in the three reactors fluctuated slightly but remained below 5% of the initial concentration for the remaining reaction time. Other studies have reported fluctuations in the P concentrations during EC reaction time (Attour et al., 2014; Behbahani, 2011). These fluctuations were attributed to the limited adsorption capacity of metallic hydroxide flocs under certain operating conditions (Behbahani, 2011). During testing of the surface water, the pH, alkalinity, and conductivity were measured. Fig. 5 depicts the change in pH throughout testing. pH increased gradually by 0.03–0.07 units over the 60 min of reaction time in all three reactors. This increase in pH was expected due to the hydrogen evolution and production of OH− at the cathodes (Chen, 2004) and was consistent with the results of other studies that examined P removal by EC (Attour et al., 2014; Behbahani, 2011; Bektas et al., 2004; Irdemez et al., 2006a; Vasudevan et al., 2008a,b). This gradual increase in pH is promising because a sudden change in pH can have negative effect on water quality and aquatic ecosystems. Fig. 4 shows the change in conductivity over the course of testing. A slight decrease in the conductivity during testing is shown. This small
exist a limit for the P removal rate and removal efficiency achieved when treating waters with low initial P concentration. It was determined that using EC to reduce P concentrations was feasible when waters with 146–880 μS/cm of conductivity and 0.07–1.6 mg/L of P were treated. 3.3. Effects of applied power Fig. 3 shows the change of P concentration and pH as a function of EC reaction time under different applied powers 5 W, 12 W, and 30 W for reactors with Low and High P concentration. The graphs for both P concentrations show that the highest power applied achieved the fastest P removal rate. It was shown that when 5 W and 12 W of power were applied to solutions containing Low and High P concentrations that a similar rate of removal was achieved. This suggests that there may exist a threshold for power applied and the P removal rate and removal efficiency achieved. Overall, 99% reduction of P concentration was attained for all 3 power levels in both High P and Low P concentrations. These results confirmed with all the publications studied that the greater the applied power the greater the P removal efficiency. (Attour et al., 2014; Behbahani, 2011; Bektas et al., 2004; Chen et al., 2014; Irdemez et al., 2006b,c; Kobya et al., 2009; Mahvi et al., 2011; Vasudevan et al., 2008a,b). Thus, it was determined that using EC to reduce P concentrations was feasible at various applied power levels. 3.4. Surface water Billy Creek had a history of having P concentrations ranging from 0.2 to 0.5 mg/L, which exceeds the total P nutrient threshold of 0.12 mg/L (USEPA, 2016). It was important to determine if EC could be used to reduce P concentrations in surface water because, like Billy Creek, many creeks that are contaminated with high P concentrations
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Fig. 4. Change of P concentration, conductivity, and pH as a function of EC reaction time in surface water (left) and wastewater effluent (right) under distinct levels of applied power.
and alkalinity. All three power levels tested proved to work equally well at reducing P concentrations to by this amount.
decrease in conductivity is promising because it demonstrates that the EC process, when applied at these power levels, will not significantly alter the conductivity of the water. The alkalinity prior to EC testing, noted as “Pre-EC”, and after testing, noted by power applied to the reactor, are displayed in Fig. 5. From this figure, the data shows that alkalinity decreased by 5–14 mg/L as CaCO3. This decrease was not expected and may have been due to errors during measurement. This decrease was acceptable since the alkalinity remained in the range of what is typically found for surface water bodies in the region (Omernik et al., 1988). Fig. 5 also illustrates the turbidity of the surface water before and after treatment. The water in the reactor where 1 W was applied increased in turbidity by 0.8 NTU while the remaining reactors had a turbidity equal to the initial. Turbidity didn’t change significantly after EC. This slight increase in turbidity after EC is explained due by the visible formation of floc that hadn’t settled out of the solution. EC has been proven to be able reduce P concentrations in surface water by 98% without negatively impacting pH, turbidity, conductivity,
3.5. Wastewater effluent Fig. 4 illustrates how the P concentration, conductivity, and pH changed during EC for the wastewater effluent. A similar rate of decrease in P concentration was observed for all three-power levels. At a reaction time of 10 min the P concentrations were reduced by 93%, 99%, and 98% for reactors where 30 W, 12 W, and 5.0 W of power were applied respectively. This reduction in P concentration is significant because a 98% to 99% reduction was achieved in reactors that operated on less than half and a sixth of the 30 W applied to one reactor. At 20 min of reaction time all three reactors achieved a 99% reduction in P concentration. The rate of P removal in these reactors was greater than the removal rate achieved when testing the surface water. This was attributed to the greater power levels applied and the higher conductivity of the wastewater. Prior testing conducted by the authors and
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Fig. 5. Turbidity (top row) and Alkalinity (bottom row) of EC treated surface water (left) and wastewater effluent (right) after 60 min of EC reaction time under distinct levels of applied power.
wastewater effluent 99% without negatively impacting pH, turbidity, conductivity, and alkalinity. All three power levels tested proved to work equally well at reducing P concentrations to by this amount.
other studies have confirmed that the greater the conductivity and power applied the higher the P removal efficiency (Attour et al., 2014; Zhang et al., 2013). The pH of the wastewater effluent in all three reactors increased as depicted in Fig. 4. The pH increased by 0.91–0.98 units during the 60 min of reaction time to a final pH of 8.18–8.20. Up until 40 min of reaction time the pH in the three reactors remained below 8.0. This was important because wastewater effluent from the clarifier at Three Oaks WWTP was filtered through a slow sand filter, disinfected, then used as reclaimed water for irrigating lawns. The optimal pH range for reclaimed water used for irrigation was 6.5–8.0 (Toor and Lusk, 2011). Thus, the pH of the wastewater effluent treated using the EC process was not negatively impacted and could still be used for irrigation. As seen in Fig. 4 the conductivity in the three reactors containing wastewater effluent remained roughly the same. The lack of decrease in conductivity is acceptable as the conductivity of the water was already at an acceptable level for use as reclaimed water by the WWTP. The alkalinity of the water in the reactor that had 5 W applied was about the same as the untreated wastewater effluent, while the alkalinity of the water in reactors with 12 W and 30 W applied were 5 mg/L less than that of the untreated water (Fig. 5). Overall, alkalinity of the water was not significantly affected by the EC process which is important because a certain amount of alkalinity is necessary to prevent sudden changes in the pH. Turbidity of the wastewater effluent, as seen in Fig. 5, increased with the amount of power applied. This slight increase in turbidity after EC was due by the visible formation of flocculation particles. EC has been proven to be able reduce P concentrations in
3.6. Phosphorus removal efficiencies comparison A P removal efficiency of up to 99% was obtained by the authors for phosphate solutions, surface water, and wastewater that were treated using EC. Similar P removal efficiencies were obtained in many other studies that utilized EC for P removal. The removal efficiencies achieved and the accompanying operating parameters are displayed in Table 1. 4. Conclusion From the tests performed in this study, P concentrations of a variety of solutions were reduced by up to 99% under a variety of water quality parameters. Furthermore, the effects of initial conductivity, power supplied, and initial pH on the P removal efficiency were characterized. As power and conductivity increased, the removal efficiency and rate of P increased. 99% removal of P was achieved in solutions with initial pH 5–8.8. EC reduced the P concentration of surface water and wastewater effluent by 98% and 99% respectively in under 20 min, without negatively impacting pH, turbidity, conductivity, and alkalinity. The results of this study and other studies indicated that EC can be feasibly used to remove P from surface water, wastewater effluent, and other types of waters (Kuokkanen et al., 2013; Mahvi et al., 2011). This technology has the potential to be implemented within wastewater
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Batch
Batch
50–100
66–99
60–98
0.9
Batch
78–100
0.9
Batch with Recirculating Flow Batch 61–99
0.85
2
Batch Batch 0–99 65–100
0.85
1 1.8
Type of Reactor
Acknowledgements The authors would like to thank Florida Gulf Coast University’s U.A.Whitaker College of Engineering’sDepartment of Environmental and Civil Engineering for making this research possible. Publication was assisted by U.S. National Science Foundation grant number 1619948 with project title: U.S. Science International Collaborations and Contributions to EcoSummit 2016 Sustainability: Engineering Change.
100 60 DNS 10 5 2–12 600 Vasudevan et al. (2008b)
Aluminum/ Aluminum Alloy/ Iron Mild Steel
Iron or Aluminum Aluminum
Attour, A., Touati, M., Tlili, M., Ben Amor, M., Lapicque, F., Leclerc, J.-P., 2014. Influence of operating parameters on phosphate removal from water by electrocoagulation using aluminum electrodes. Seperation Purif. Technol. 123, 124–129. Behbahani, M.A., 2011. A comparison between aluminum and iron electrodes on removal ofPhosphate from aqueous solutions by electrocoagulation process. Int. J. Environ. Res. 5, 403–412. Bektas, N., Akbulut, H., Inan, H., Dimoglo, A., 2004. Removal of phosphate from aqueous solutions by electro-coagulation. J. Hazard. Mater. 106B, 101–105. Bennett, E., Carpenter, S., Caraco, N., 2001. Human impact on erodable phosphorus and eutrophication: a global perspective. Bioscience 51 (3), 227–234. Busman, L., Lamb, J., Randall, G., Rehm, G., Schmitt, M., 2009. The nature of phosphorus in soils. Retrieved from University of Minnesota Extension: http://www.extension. umn.edu/agriculture/nutrient-management/phosphorus/the-nature-of-phosphorus/. Cabezas, M., Tomasko, D., 2009. Water Quality and Ecological Assessment of Lake Trafford. Mac Hatcher, Tampa, FL. Carpenter, S., Caraco, N., Correll, D., Howarth, R., Sharpley, A., Smith, V., 1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Issues Ecol. 8, 559–568. Chen, G., 2004. Electrochemical technologies in wastewater treatment. Sep. Purif. Technol. 38, 11–41. Chen, S., Shi, Y., Wang, W., Li, Z., Gao, J., Bao, K., Zhang, R., 2014. Phosphorus removal from continuous phosphate- contaminated water by electrocoagulation using aluminum and iron plates alternately as electrodes. Sep. Sci. Technol. 49, 939–945. Clesceri, L., Greenberg, A., Eaton, A., 1999. Standard Methods for the Examination of Water and Wastewater, 20th Edition. American Public Health Association. Holt, P., Barton, G., Mitchell, C., 2005. The future for electrocoagulation as a localised water treatment technology. Chemosphere 59, 355–367. Irdemez, S., Demircioglu, N., Yildiz, Y.S., 2006a. The effects of pH on phosphate removal from wastewater by electrocoagulation with iron plate electrodes. J. Hazard. Mater. B17, 1231–1235. Irdemez, S., Demircioglu, N., Yıldız, Y.S., Bingul, Z., 2006b. The effects of current density and phosphate concentration on phosphate removal from wastewater by electrocoagulation using aluminum and iron plate electrodes. Sep. Purif. Technol. 52, 218–223. Irdemez, S., Yildiz, Y., Tosunoglu, V., 2006c. Optimization of phosphate removal from wastewater by electrocoagulation with aluminum plate electrodes. Sep. Purif. Technol. 52, 394–401. Kobya, M., Demirbas, E., Dedeli, A., Sensoy, M., 2009. Treatment of rinse water from zinc phosphate coating by batch and continuous electrocoagulation processes. J. Hazard. Mater. 173, 326–334. Kuokkanen, V., Kuokkanen, T., Rämö, J., Lassi, U., 2013. Recent applications of electrocoagulation in treatment of water and WastewateräA review. Green Sustainable Chem. 3, 89–121. Kuokkanen, V., Kuokkanen, T., Rämö, J., Lassi, U., Roininen, J., 2014. Removal of phosphate from wastewaters for further utilization using electrocoagulation with hybrid electrodes ? Techno-economic studies. J. Water Process Eng. 94, 1–8. Lacasa, E., Canizares, P., Sáez, C., Fernández, F., Rodrigo, M., 2011. Electrochemical phosphates removal using iron and aluminium electrodes. Chem. Eng. J. 172, 137–143. Mahvi, A., Ebrahimi, S.-D., Mesdaghinia, A., Gharibi, H., Sowlat, M., 2011. Performance evaluation of a continuous bipolar electrocoagulation/electrooxidation–electroflotation (ECEO–EF) reactor designed for simultaneous removal of ammonia and phosphate from wastewater effluent. J. Hazard. Mater. 192, 1267–1274. Mollah, M., Morkovsky, P., Gomes, J., Kesmez, M., Parga, J., Cocke, D., 2004. Fundamentals, present and future perspectives of electrocoagulation. J. Hazard. Mater. 114, 199–210. Mollah, M., Schennach, R., Parga, J., Cocke, D., 2001. Electrocoagulation (EC)—science and applications. J. Hazard. Mater. 84, 29–41. Omernik, J., Griffith, G., Irish, J., Johnson, C., 1988. Total Alkalinity of Surface Waters. (Retrieved from USGS: https://water.usgs.gov/owq/alkus.pdf).
Stainless Steel
100 30 DNS 10 5 600 Stainless Steel
3–10
50–500 100 0–3.09 0.375–1.5 4–7 1500
5
25–150 40 0.1–0.7 0.375–1.125 3 1500
5
10–160 60 11.3 0.48–1.92 10 4–10 Aluminum/Iron
960
Iron/ Aluminum Iron or Aluminum Aluminum
0.07–1.75 100 50–60 140 0.15–0.88 0.8–3.2 0.10–2.00 0.10–0.90 2.5 5–20 3–9 2–11 Aluminum Aluminum Aluminum Aluminum
Present Study Attour et al. (2014) Chen et al. (2014) Irdemez et al. (2006b) Irdemez et al. (2006c) Vasudevan et al. (2008a)
13.32 50
Initial Conductivity (mS/ cm) Electric Current (Amps) Distance between Electrodes (mm) Initial pH Effective Surface Area of Electrodes (cm2) Material of Anode
Material of Cathode
treatment plants, specifically in the clarifiers that contain wastewater effluent that has undergone primary and secondary treatment. When used for treating surface water, EC has the potential to be implemented at the outflow treatment wetlands or detention ponds. Future research should involve designing an in-situ pilot scale reactor for treating surface water and a pilot scale design for utilizing EC directly in the WWTP.
References
Studies
Table 1 Comparison of phosphorus removal efficiencies achieved and the associated operating parameters using electrocoagulation. DNS = Did Not Specify.
Time (min)
Initial Phosphorus Concentration (mg/L)
P Removal Efficiency (%)
Volume Treated per Reactor (L)
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mild steel anodes. J. Hazard. Mater. 3, 1480–1486. Vasudevan, S., Sozhan, G., Ravichandran, S., Jayaraj, J., Lakshmi, J., Sheela, S., 2008b. Studies on the removal of phosphate from drinking water by electrocoagulation process. Ind. Eng. Chem. Res. 47, 2018–2023. Zhang, S., Zhang, J., Wang, W., Li, F., Cheng, X., 2013. Removal of phosphate from landscape water using an electrocoagulation process powered directly by photovoltaic solar modules. Solar Energy Mater. Solar Cells 117, 73–80.
Toor, G. S., & Lusk, M., 2011. Reclaimed Water Use in the Landscape: Understanding Landscape Irrigation Water Quality Tests. Retrieved from EDIS IFAS: https://edis. ifas.ufl.edu/ss546#TABLE_4. USEPA., 2016. State Development of Numeric Criteria for Nitrogen and Phosphorus Pollution. Retrieved from US EPA: https://www.epa.gov/nutrient-policy-data/statedevelopment-numeric-criteria-nitrogen-and-phosphorus-pollution. Vasudevan, S., Lakshmi, J., Jayaraj, J., Sozhan, G., 2008a. Remediation of phosphatecontaminated water by electrocoagulation with aluminium, aluminium alloy and
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