Electrochemical Ferrate(VI) Synthesis with Cast Iron

Electrochemical Ferrate(VI) Synthesis with Cast Iron Shavings and Its Potential Application for Household Graywater Recycling

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Sibel Barışçı 1

Abstract: This paper deals with a laboratory-based investigation for the treatment of graywater generated from public housing in Turkey. In the first part of the study, ferrate(VI) has been synthesized electrochemically. The current efficiency (CE), energy consumption (EC), and ferrate(VI) yield during the electrochemical synthesis of ferrate(VI) was measured using cast iron shavings as anode materials. In terms of the highest CE, the lowest EC, and ferrate(VI) yield, 16-M NaOH media, applied current of 3 A, and 90 min of electrolysis time were found as optimum conditions for electrochemical synthesis of ferrate(VI) with cast iron shavings. This reactor configuration with cast iron shavings provided much higher CE values compared with the other studies. Ferrate(VI) was quite effective for the removal of constituents in graywater. Applying 75 mg=L ferrate(VI) dose at pH 7 was successful at removing organic pollutants and total coliforms (TCs). Besides, more than 73% anionic surfactant degradation was achieved at the same conditions. According to reuse regulations, treated graywater by electrosynthesized ferrate(VI) can be used for unrestricted reuse options. Additionally, the greater removal of organics by ferrate(VI) reduced the potential of bacterial regrowth and additional chemical disinfectant demand. DOI: 10.1061/(ASCE)EE.1943-7870.0001430. © 2018 American Society of Civil Engineers. Author keywords: Ferrate(VI); Iron shavings; Electrochemical method; Graywater; Recycling.

Introduction Conservation of water resources has a great importance due to gradually increasing need for clean water. The reuse of wastewater for nonpotable purposes can reduce the pressure on drinking water supplies (Bani-Melhem et al. 2015). Graywater that comes from kitchen sinks, laundries, bathrooms, and washing machines, i.e., wastewater excluding the sewage inputs, can be a good reuse alternative. It can be reused in several applications, such as toilet flushing, car washing, and garden irrigation, which do not require drinking water quality (Oh et al. 2018). However, graywater should be treated effectively to ensure its safe and sustainable reuse (Oron et al. 2014). Graywater usually contains surfactants, suspended solids, nutrients, pathogens, and microbial indicators (Donner et al. 2010). For the successful implementation of graywater recycling, those parameters should be considered and minimized in terms of the public health and environmental risks. Several treatment technologies have been investigated for graywater recycling in the literature such as electrocoagulation (Bani-Melhem and Smith 2012; Vakil et al. 2014), photocatalytic oxidation (Li et al. 2004; Sanchez et al. 2010), membrane bioreactors (Melin et al. 2006; Merz et al. 2007), and ultraviolet ðUVÞ=H2 O2 (Chin et al. 2009; Tony et al. 2016). Ferrate(VI) as an advanced oxidation process (iron oxidation state of þ6) with high oxidation capability and coagulation and disinfection properties can be another alternative for graywater treatment

(Song et al. 2017). Also, ferrate(VI) does not produce toxic by-products compared with the other technologies. Ferrate(VI) can be synthesized chemically or electrochemically. Electrochemical ferrate(VI) synthesis has many advantages compared with chemical synthesis (Alsheyab et al. 2009) such as simple procedure, lower need of chemicals, and nontoxic by-products. The electrochemical synthesis of ferrate(VI) consists of an electrolysis cell containing a sacrificial iron anode and a strong alkaline media to oxidize the iron(0) to ferrate(VI). In this study, a new reactor configuration has been used for electrochemical ferrate(VI) synthesis using cast iron shavings. The cast iron shavings were made of gray cast iron and the iron content of the iron shavings was 99.195%. The other components of the iron shavings were 0.07% C, 0.59% Mn, 0.01% Si, 0.005% S, 0.03% Cr, 0.04% Ni, 0.01% Cu, 0.033% Al, 0.003% Mo and 0.004% V. The effect of parameters such as applied current, electrolyte (NaOH) concentration, and electrolysis time have been investigated and optimized. This study was also extended to evaluate the potential of electrosynthesized ferrate(VI) for graywater treatment. The recycling potential of graywater and also storage conditions have been investigated under various parameters.

Materials and Method Chemicals

1

Postdoctoral Fellow, Dept. of Civil and Environmental Engineering, Water and Environmental Technology Center, Temple Univ., 1947 N 12th St., Philadelphia, PA 19122. Email: [email protected] Note. This manuscript was submitted on February 13, 2018; approved on March 26, 2018; published online on June 20, 2018. Discussion period open until November 20, 2018; separate discussions must be submitted for individual papers. This paper is part of the Journal of Environmental Engineering, © ASCE, ISSN 0733-9372. © ASCE

Potassium ferrate (K2 FeO4 , purity of 97%) and sodium hydroxide (pellets, anhydrous, purity of ≥98%) were supplied by SigmaAldrich (Turkey). The buffers used for the pH adjustment in the study included C8 H5 KO4 -HCl solution (pH 4), C8 H5 KO4 -NaOH solution (pH 5), KH2 PO4 -NaOH solution (pH 6, 7, and 8), Na2 B4 O7 · 10H2 O-HCl solution (pH 9), and Na2 B4 O7 · 10H2 O-NaOH solution (pH 10).

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Table 1. Characteristics of domestic graywater samples Parameter

Value

Standard deviation

pH Chemical oxygen demand (COD) (mg=L) Biochemical oxygen demand (BOD5 ) (mg=L) Total organic carbon (TOC) (mg=L) Turbidity (NTU) Total Kjeldahl nitrogen (TKN) (mg=L) Total phosphorus (TP) (mg=L) Anionic surfactant [methylene blue active substance (MBAS)] (mg=L) Total coliform (cfu=100 mL)

7.2 270 120 42.2 50.1 9.1 3.55 12

0.12 5.10 4.80 0.76 3.45 0.20 0.16 2.60

>105

1.27

Graywater Samples Graywater samples were collected from a public housing in Gebze, Turkey. All samples were taken on the same day and at the same time during a 5-month period and stored at 4°C, then analyzed within 48 h. Graywater samples were analyzed after each collection and standard deviation were calculated. The brief characterization of the graywater samples can be found in Table 1. Electrochemical Ferrate(VI) Synthesis The electrosynthesis of ferrate(VI) was conducted in a plexiglass electrochemical cell. The dimensions of the cell were 22 × 14 × 10 cm, and the wall thickness was 0.4 cm. Insulant plastic material with 20 holes (1 cm in diameter) was placed at the bottom of the reactor from 1 cm above. These holes let electrolytes enter the reactor from the bottom. The inlet and outlet of the electrolyte were controlled with a valve. Then iron shavings as anode were located on this insulant plastic material. A removable stainless steel cathode with a handle and the same dimensions was positioned in the top part of the reactor. Insulant plastic with the same dimensions was placed between the cathode and cast iron shavings to prevent a short circuit. For stirring the electrolyte (NaOH), air from an air compressor was provided from a silicone pipe from the bottom of the reactor. With the movement of the cathode, electrosynthesized ferrate(VI) was taken from the top of the reactor. Ferrate(VI) Treatment Procedures Ferrate(VI) was generated in situ and the generated ferrate(VI) was applied directly for graywater treatment. A total of 1 L of the graywater was placed in a glass reactor. After ferrate(VI) was added, pH was modified to the final pH (4, 5, 6, 7, 8, 9, and 10) with the buffers. A rapid mix at 400 rpm for 30 s was applied using a magnetic stirrer. The sample was then slowly mixed for an additional 20 min at 40 rpm and allowed to settle for 60 min. The experiments were conducted using different ferrate(VI) doses (2, 5, 10, 20, 50, 75, and 100 mg=L). This range of ferrate(VI) doses was chosen according to the preliminary studies (Barışçı et al. 2016). At the end of each experiment, the treated water was filtered through 0.45-μm cellulose acetate membrane syringe filters (VWR, Turkey) for the measurements.

The microbial analyses were conducted in accordance with standard methods (APHA 2005). In addition, the regrowth of bacteria for the treated graywater samples was also analyzed at 12 h after ferrate(VI) treatment because it characterizes the residence time of graywater effluent in typical reuse systems.

Analytical Methods Ferrate(VI) concentrations were measured by ultraviolet–visible (UV/VIS) spectrophotometer (Hach DR-5000, Turkey) at the wavelength of 505 nm. Chemical oxygen demand (COD) and anionic surfactant, as methylene blue active substance (MBAS), were analyzed with Lange cuvette tests (LCK 332 and LCK 114, Hach, Turkey, respectively) based on standard methods with a Hach spectrophotometer (Hach Lange DR-2800). Biochemical oxygen demand (BOD5 ) (5210 B), total Kjeldahl nitrogen (TKN) (2540 B), and total phosphorus (TP) (4500 P manual digestion and flow injection) were also measured according to standard methods (APHA 2005). Turbidity was measured using a 2100P ISO turbidimeter (Hach, Istanbul, Turkey). Total organic carbon (TOC) measurements were performed by a TOC analyzer (TOC-VCPH, Shimadzu, Japan; Istanbul, Turkey) calibrated with standard potassium hydrogen phthalate solutions. The pH was determined using a WTW (Turkey) Inolab Multi 9310 IDS pH meter.

Results and Discussion This part of the study has been conducted to determine optimum ferrate(VI) synthesis conditions using iron shavings with a different reactor configuration. This reactor configuration was beneficial with providing higher current efficiency (CE) because it has high surface area. Besides, using cast iron as an anode material may provide low cost in real-scale applications.

Effect of Electrolyte Concentration The surface layer of an anode is affected by concentration and composition of the electrolyte (Bouzek et al. 1999). It is known that both surface layer disintegration and ferrate(VI) stability are increased by using more concentrated OH− solution (Čekerevac et al. 2009; Híveš et al. 2006). Also, increasing alkalinity of anolyte provides more solubility of iron species with lower valence. The effect of electrolyte (NaOH) concentration on electrochemical synthesis of ferrate(VI) can be seen in Fig. 1(a). As seen in Fig. 1(a), increasing NaOH molarity provided more concentrated ferrate(VI) solution. While only 0.23 mM ferrate(VI) was synthesized with 5-M NaOH media, 2.26 mM ferrate(VI) was produced in 20-M NaOH media. A total of 1.4, 1.45, 1.82, 1.85, 1.98, and 2.01 mM ferrate(VI) were synthesized in 10-, 12-, 14-, 16-, and 18-M NaOH media, respectively. In Fig. 1(b), CEs and energy consumptions (ECs) according to electrolyte concentration are shown. CEs and ECs were calculated according to the following equations: CE ð%Þ ¼

Determination of Bacterial Cell Count

EC ðkWh=kgÞ ¼

Escherichia coli (E. coli) was analyzed by pour plate method using eosin methylene blue (EMB) agar (incubation at 37°C for 24 h) and results were expressed as colony-forming units (cfu) per 100 mL. © ASCE

½FeðVIÞexp × 100 ½FeðVIÞtheo V×i×t m

ð1Þ ð2Þ

where ½FeðVIÞexp and ½FeðVIÞtheo = experimental and theoretical ferrate(VI) concentrations, respectively; V = cell voltage (V);

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Fig. 1. Effect of NaOH concentration on (a) Fe(VI) yield; and (b) current efficiencies and energy consumptions according to electrolyte (NaOH) concentration. Experimental conditions were i ¼ 3 A, electrolysis time = 90 min, and temperature ¼ 30 1°C.

i = applied current (A); t = process time (h); and m = amount of ferrate(VI) produced (kg). Theoretical ferrate(VI) concentration was calculated according to Faraday’s law. Current efficiency was very low in 5- and 10-M NaOH media. It can be said that increasing molarity of NaOH provided better current efficiencies. It was observed that CE decreased and EC increased with 14-M NaOH media. This is possibly due to crystallization of the iron anode dissolution products [ferrate(VI) and other iron species] directly on the anode surface. A total of 72.98% CE and only 2.798 kwh=kg EC were gained in 16-M NaOH media. More than 70% CE and less than 2.9 kwh=kg EC were obtained in 16-, 18-, and 20-M NaOH media. In many studies, iron plate or wire electrodes were used, and the current efficiencies achieved ranged between 4.8 and 55% (Denvir and Pletcher 1996; Mácová and Bouzek 2011; Mácová et al. 2010). In Barışçı et al. (2014), where iron plates were used, CE was around 65% in 16-M NaOH media. This reactor configuration with cast iron shavings provided relatively high CE and low EC values compared with the other configurations. It can be concluded that higher surface area allows higher dissolution rates, which enhances the CE values and lowers the EC values.

Effect of Applied Current Applied current has a significant effect on the synthesis efficiency (Tomic et al. 2017). It is related to the applied electrode potential and thus to the reactions taking place at the anode surface. As seen in Fig. 2(a), ferrate(VI) concentration increased with increasing current. A total of 0.6, 0.65, 1.2, 1.54, 1.67, 2.13, 2.26, and 2.8 mM ferrate(VI) in alkaline media were synthesized with applied currents of 0.5, 0.8, 1, 1.2, 1.5, 2, 3, and 5 A, respectively. To find an optimum current for electrochemical synthesis of ferrate(VI) ions with the reactor configuration in which cast iron shavings were used, it is important to know CE and EC, not only produced ferrate(VI) concentration. According to Fig. 2(b), lower applied currents (0.5, 0.8, and 1 A) provided lower CE and higher EC. When current was increased to 1.2, 1.5, 2, and 3 A, higher CE and lower EC were obtained. However, the applied current of 5 A provided very low CE of 38.97%. This can be due to oxygen evolution. Ferrate(VI) formation takes place in the transpassive potential region of iron dissolution and it competes with oxygen evolution. The increasing potential represents higher involvement of this parasitic reaction in the overall electric current consumption, which reduces the CE. The decrease of the ferrate(VI) formation

Fig. 2. Effect of current on (a) Fe(VI) yield; and (b) current efficiencies and energy consumptions for applied currents. Experimental conditions were NaOH concentration = 16 M, electrolysis time = 90 min, and temperature ¼ 30 1°C. © ASCE

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long-term effect of the electric field. This represents a serious obstacle for industrial production of ferrate(VI) because economic advantages should be considered. Finally, the electrochemical reaction mechanism consists of a chemical step in the ferrate(VI) formation, which suggests a certain time elapses after current load before generation of the initial ferrate(VI) product. This indicates an ideal electrolysis time.

Graywater Recycling by Electrosynthesized Ferrate(VI)


This part of the study evaluates the potential application of electrosynthesized ferrate(VI) for graywater recycling and demonstrates the effect of parameters on the treatment of graywater. Fig. 3. Effect of electrolysis time on Fe(VI) yield. Experimental conditions were NaOH concentration = 16 M, i ¼ 3 A, and temperature ¼ 30 1°C.

rate at higher anodic potentials is caused by improved deactivation of the anode surface (Vogt 2013). At insufficient anodic potentials, the kinetics of ferrate(VI) formation are limited by the rate of formation of the intermediates, which may be removed from the anode.

Effect of Electrolysis Time The efficiency of ferrate(VI) formation is also influenced by the electrolysis time (Bouzek and Roušar 1997; Mácová et al. 2009) because ferrate(VI) is reasonably unstable in an aqueous solution. According to Fig. 3, a measurable ferrate(VI) concentration was obtained in 10 min with 0.43-mM concentration. As seen in Fig. 3, increasing electrolysis time until 90 min increased the produced amount of ferrate(VI). However, after 90 min, produced ferrate(VI) concentration started to decrease with increasing electrolysis time. The maximum ferrate(VI) concentration was achieved at 90 min because the amount of ferrate(VI) was 2.26 mM. Increasing the electrolysis time decreased the amount of ferrate (VI) because of its instability and then its decomposition. Additionally, the electrode is gradually deactivated during electrochemical synthesis. The surface layers of anode consolidate as a result of the

Organics Degradation and Removal of Turbidity Removal efficiencies for COD, BOD5 , TOC, and turbidity by electrosynthesized ferrate(VI) are shown in Fig. 4. In terms of physical impurities, the ferrate(VI) process showed excellent removal efficiencies for turbidity with all applied ferrate(VI) doses as seen in Fig. 4(a). Corresponding removal efficiencies varied between 97.8 and 99.54%. When the pH effect was considered for turbidity removal, high removal efficiencies were gained too. However, the efficiency was relatively lower for pH 10 as seen in Fig. 4(b) with 95.4%. In terms of organic matter, the treatment by electrosynthesized ferrate(VI) ion process reduced COD up to 88.67% with a 100-mg=L ferrate(VI) dose [Fig. 4(a)]. COD removal efficiency was affected by the increase of ferrate(VI) dose. Only 47.3% removal was provided with a 2-mg=L ferrate(VI) dose. TOC removal efficiency showed a similar trend of COD removal. TOC removal efficiency varied between 40.2 and 73.8% according to the applied ferrate(VI) dose. The highest TOC removal was achieved at pH 7 and 8. This can be attributed to the coagulation effect of ferrate(VI) together with the oxidizing effect. The pollutants can be removed using produced hydroxide species [mostly FeðOHÞ3 ] during Fe(VI) treatment via adsorption and/or charge neutralization and then precipitation. Treatment of domestic graywater source with ferrate(VI) showed good performance for BOD5 removal [Fig. 4(b)] as the removal efficiency reached up to 92%. The treatment appeared to be dependent on the ferrate (VI) dose and pH. Corresponding removal efficiencies varied between 70 and 92% for applied ferrate(VI)

Fig. 4. Turbidity, COD, and TOC removal efficiencies according to (a) ferrate(VI) dosage at pH 7; and (b) pH with 75-mg=L ferrate(VI) dosage. © ASCE

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performance for surfactant removal. All applied pH values provided more than 50% MBAS removal efficiency.


TKN and TP Removal

Fig. 5. Surfactant removal efficiencies.

doses, which reflects the low level of BOD5 in the influent. As mentioned, pH affected the BOD5 removal efficiency. Residual BOD5 concentrations varied between 9.6 and 37.2 mg=L under all conditions tested in terms of pH. The best performance for BOD5 removal was obtained in the pH range of 6–8, and this was similar to COD and TOC removal. Based on BOD5 removal data, it can be stated that using only a 2-mg=L ferrate(VI) dosage, the reduction of most of the organic suspended solids (70%) was obtained in domestic graywater. When the ferrate(VI) dose increased to 75 mg=L, the efficiency reached 92%. Applying a higher ferrate(VI) dose, higher BOD5 removal was achieved. Surfactants Degradation Fig. 5 specifies surfactant degradation according to ferrate(VI) dose and pH. Increasing the ferrate(VI) dose showed increasing surfactant removal efficiency. The minimum applied ferrate(VI) dose (2 mg=L) provided about 48% surfactant removal. After the 75-mg=L ferrate(VI) dose, a stable stage for the removal efficiency was observed. Almost 73% surfactant removal was gained with the ferrate(VI) treatment process. pH had a significant effect on MBAS removal. Just like organics removal, pH 7 showed the best

Fig. 6(a) shows the effect of ferrate(VI) dose on TKN and TP removal efficiencies for graywater treatment. According to Fig. 6(a), about 55% TKN removal and more than 90% TP removal efficiencies were gained with the 100-mg=L ferrate(VI) dose. Increasing the ferrate(VI) dose provided better efficiencies for both TKN and TP parameters. After the 50-mg=L ferrate(VI) dose, the removal of TP reached a stable stage. However, TKN removal showed an increasing trend with higher doses of ferrate(VI). According to Fig. 6(b), pH was very effective for TKN and TP removal. A neutral pH value showed the best removal efficiency for both parameters. The removal trends were almost similar for TKN and TP removal. The efficiencies increased up to pH 7 and then decreased with increasing pH values. In the literature, the studies on graywater treatment by using alum and iron chloride indicate that 420-mg=L alum concentration provided 14.93 and 94.58% TKN and TP removal, respectively, and 150 mg=L FeCl3 provided 8.96 and 96.39% TKN and TP removal, respectively (Pidou et al. 2008). In this case, as mentioned, higher removal efficiencies were gained with relatively low ferrate(VI) doses, particularly for TKN. Only a 2-mg=L ferrate(VI) dosage delivered more than 10% TKN removal from graywater samples, while almost 20% TKN removal was gained with using a 5-mg=L ferrate(VI) dosage. This proves that ferrate(VI), with coagulation properties together with high oxidizing capacity, can be used instead of well-known coagulants in water and wastewater treatment. Removal of Pathogens Attempts to identify pathogens in domestic graywater revealed that total coliform (TC) was present in all the graywater samples tested at a mean concentration of 5.2 0.34 log10 cfu=100 mL. TC survival in ferrate(VI)-treated graywater was greater with increasing contact time. The studies were conducted at pH 7 and 75-mg=L ferrate(VI) dose. As seen in Fig. 7(a), TC reduced to 4.1 from 5.2 log10 cfu=100 mL at 1 min, meaning that only 21.2% removal was provided. However, TC reduced to 0.052 and 0.0052 log10 cfu= 100 mL with 99 and 99.9% removal at 9 and 10 min, respectively. Longer ferrate(VI) contact times resulted in less TC survival in domestic graywater. Ferrate(VI) was very successful for inactivation

Fig. 6. TKN and TP removal efficiencies according to applied: (a) Fe(VI) dose at pH 7; and (b) the change of pH at 75-mg=L Fe(VI) dose. © ASCE

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Fig. 7. (a) Effect of contact time for inactivation of TC by Fe(VI) (experimental conditions: 75-mg=L Fe(VI) dose and pH 7); (b) effect of Fe(VI) dose for inactivation of TC (experimental conditions: 10-min contact time and pH 7); and (c) TC concentrations as a function of Fe(VI) dose and storage time (before and after treatment).

of TC. The process of ferrate(VI) can be used for wastewater disinfection according to the results. In Fig. 7(b), the effect of the ferrate(VI) dose can be seen. The experiments were conducted at pH 7, and a 10-min contact time was applied to the samples. The lowest ferrate(VI) dose (2 mg=L) gave the poorest removal of indicator bacteria. To illustrate, TC reduced to 4.5 log10 cfu=100 mL from the mean value of 5.2 log10 cfu=100 mL in 10 min of contact time. Although the ferrate(VI) dose increased to only 5 mg=L, TC reduced to 2.4 log10 cfu=100 mL. TC removal by higher doses of ferrate(VI) such as 10 and 20 mg=L seemed to be efficient for providing some type of reuse standards. To illustrate, TC reduced to 1.1 and 0.84 log10 cfu=100 mL with 10- and 20-mg=L ferrate(VI) doses, respectively. Bacterial Regrowth Graywater treatment and disinfection used in practice should be determined by risk assessment considering the potential of pathogen spread from graywater reuse applications (Newcomer et al. 2017). The different risks associated with urban water reuse applications are revealed in many guidelines, with an increasing possibility of public exposure typically having stricter criteria. Disinfection of all treated effluents would be obligatory to guarantee the strictest microbiological standards for reuse options (Benami et al. 2016). The quality of the treated effluents also affects the following disinfection process and regrowth of bacteria (Teh et al. 2015). © ASCE

Regrowth of TC bacteria was investigated for 0.5, 3, 6, and 12 h after ferrate(VI) treatment and for untreated graywater samples. As seen in Fig. 7(c), TC did not exhibit regrowth ability after treatment for all applied ferrate(VI) doses. When only a 2-mg=L ferrate(VI) dose was used for disinfection of domestic graywater, after 0.5 h TC remained at the same value and after 12 h TC increased to 4.93 log10 cfu=100 mL from 4.5 log10 cfu=100 mL. TC increased to 2.78, 1.45, and 0.95 log10 cfu=100 mL from 2.4, 1.1, and 0.84 log10 cfu=100 mL with 10-, 20-, and 50-mg=L applied ferrate(VI) doses, respectively. The 75- and 100-mg=L ferrate(VI) doses did not cause any regrowth. However, TC regrowth showed a significantly increasing trend for untreated graywater. TC increased to 5.4, 5.8, 6.1, and 6.45 log10 cfu=100 mL from 5.2 log10 cfu= 100 mL in untreated stored graywater after 0.5, 3, 6, and 12 h, respectively. Available carbon sources and nutrients in untreated graywater samples may cause TC regrowth with lower ferrate(VI) doses. Some previous studies also examined the regrowth ability of microorganisms in treated graywater effluents. For instance, coliform bacteria regrowth was significant after UV irradiation (Gilboa and Friedler 2008). Another study showed that even with 88.5–99.9% bacteria removal by rotating biological reactor, it was observed 6 h after treatment (Friedler et al. 2011). In conclusion, electrosynthesized ferrate(VI), preventing regrowth of bacteria, can be used effectively for graywater treatment. The reuse potential of treated graywater considering the reuse guidelines can be found in Table 2.

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Table 2. Evaluation of electrosynthesized ferrate(VI)-treated graywater for reuse potential Category Unrestricted reuses


Restricted reuses

Unrestricted reuses

Restricted reuses

Goals for treatment

Applications

Recreational impoundments, lakes Ornamental fountains, recreational impoundments, BOD5 : ≤10 mg=L Total nitrogen: ≤1 mg=L lakes and ponds for swimming TP: ≤0.05 mg=L Turbidity: ≤2 NTU pH: 6–9 Fecal coliform: ≤10=mL Total coliform: ≤100=mL Lakes and ponds for recreation without body contact BOD5 : ≤10 mg=L Total nitrogen: ≤1 mg=L TP: ≤0.05 mg=L Total suspended solids: ≤30 mg=L pH: 6–9 Fecal coliform: ≤10=mL Total coliform: ≤100=mL Urban reuses and agricultural irrigation BOD5 : ≤10 mg=L Toilet flushing, laundry, air conditioning, process water; landscape irrigation, fire protection, Turbidity: ≤2 NTU construction, surface irrigation of food crops and pH: 6–9 vegetables (consumed uncooked), and street Fecal coliform: ≤10=mL washing Total coliform: ≤100=mL Residual chlorine: ≤1 mg=L Landscape irrigation where public access is BOD5 : ≤10 mg=L infrequent and controlled, subsurface irrigation of Surfactant (anionic): ≤1 mg=L Total suspended solids: ≤30 mg=L nonfood crops and food crops and vegetables pH: 6–9 (consumed after processing) Fecal coliform: ≤10=mL Total coliform: ≤100=mL

According to Table 2, ferrate(VI) provided sufficient treatment for the graywater reuse option. As stated by the reuse regulations, treated graywater by electrosynthesized ferrate(VI) can be used for unrestricted reuse options such as toilet flushing, air conditioning, process water, landscape irrigation, and fire protection. Moreover, the greater removal of organics by ferrate(VI) reduced the potential of bacterial regrowth, and this further reduces the chemical disinfectant demand.

Conclusion Ferrate(VI) was synthesized using cast iron shavings in this study. Optimum conditions such as electrolyte concentration, applied current, and electrolysis time were determined in this reactor configuration considering the highest CE, the lowest EC, and ferrate(VI) yield. Using cast iron shavings with high surface area provided relatively high ferrate(VI) yields and reduced the initial cost for ferrate(VI) production. The treatment of graywater effluent was investigated using optimized electrosynthesized ferrate(VI). In conclusion, it was found that the electrosynthesized ferrate(VI) performed optimally at the dose of 75 mg=L and pH 7 in graywater effluent. Besides, TC did not show regrowth ability after ferrate(VI) treatment for 12 h. The research outcomes suggested that the electrosynthesized ferrate(VI) could be potentially used for graywater recycling and it can minimize the possible public health and environmental risks in the treated graywater.

References Alsheyab, M., J.-Q. Jiang, and C. Stanford. 2009. “On-line production of ferrate with an electrochemical method and its potential application © ASCE

Treated graywater (in this study) pH: 6.8 Turbidity: 0.23 NTU COD: 30.6 mg=L BOD5 : 9.6 mg=L TP: 0.12 mg=L TKN: 4.08 mg=L Anionic surfactant: 3.1 mg=L Total coliform: