Tibebe et al. BMC Chemistry (2019) 13:107 https://doi.org/10.1186/s13065-019-0628-1 BMC Chemistry RESEARCH ARTICLE Open Access Treatment and characterization of phosphorus from synthetic wastewater using aluminum plate electrodes in the electrocoagulation process Dessie Tibebe1* , Yezbie Kassa2 and Ashok N. Bhaskarwar3 Abstract The main objective of this study is treatment and characterization of phosphorus from synthetic wastewater using aluminum electrodes in the electrocoagulation process. EC experimental setups were designed and diferent parameters were optimized. The maximum amounts of phosphorus removal efciencies were observed at pH 7. The phosphorus removal efciency increases from 85.16 to 97.65% as the temperature increases from 15 to 45 °C, beyond this temperature, there is small efect on removal efciency. Pollutant removal efciency increases with an increase in the electrolysis time. At lower initial concentrations the removal efciencies reached to their maximum values while at the highest initial concentration, the phosphorus removal efciency was decreased. The increase of current density improves the efciency of phosphorus removal. Energy and aluminum consumption decreases with increasing initial concentration of phosphorus. Field Emission Scanning Electron Microscope (FESEM) image analysis demonstrated very fne structures for aluminum hydroxide/oxyhydroxides and aluminum phosphate. The existence of the diferent elemental composition in the sludge was proved by the help of Energy Dispersive X-ray Analysis (EDXS), indicat- ing that the aluminum, oxygen and phosphorus were present in the product. From X-ray difraction (XRD), Fourier- transform infrared spectroscopy (FT-IR) and Raman analyses of the sludge product, it is concluded that the chemical speciation of the by-products can be mostly aluminum hydroxide and aluminum phosphate. Keywords: Wastewater treatment, Electrocoagulation, Characterization, Aluminum electrode Introduction as in the case electrodialysis or reverse osmosis [2]. In One of the main problems in the twenty-frst century is a biological treatment plant, it is necessary to transfer the provision of adequate treated water free from pol- phosphorus from liquid to sludge phase, removal ef- lutants. At the beginning of 2000, one-sixth of the global ciency usually doesn´t exceed 30%, which means that population was without access to a clean water supply, the remaining phosphorus should be removed by other leaving over 1 billion people in Asia and Africa alone technologies. Terefore, the treatment is not enough to with a polluted water system [1]. Tere are various tech- assure complete pretreatment and refning technolo- nologies used for the removal of pollutants from waste- gies should be added to the treatment process with other water in particular to phosphorus. Tese technologies advanced technologies which are not economically fea- are mainly divided into physical, chemical and biologi- sible. Because of the high capital and expensive costs of cal methods. Physical methods are usually too expensive, these techniques, there is a need to use more efcient and cheap methods which requires minimum chemical and energy consumptions [3]. Now a day, electrocoagu- *Correspondence: [email protected] 1 Department of Chemistry, College of Natural and Computational lation (EC) method gives great attention in wastewater Sciences, University of Gondar, P. O. box 196, Gondar, Ethiopia treatment. Tis technology has been successfully used Full list of author information is available at the end of the article to remove diferent kinds of pollutants like phosphorus © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Tibebe et al. BMC Chemistry (2019) 13:107 Page 2 of 14 from wastewater [4]. A signifcant contribution to the understanding of the removal of phosphorus using coag- ulation was given by [5]. Tey suggested that the Al– OH–Al and the Al–PO4–Al linkages tend to integrate. Tus, the precipitation is governed by the integrated particles giving the formation of aluminium-hydroxyl- phosphate complexes, Al(OH)3-x(PO4)x, rather than the individual AlPO4 and Al(OH)3 species. Tese complexes either adsorb onto positively charged aluminium hydrol- ysis species or act as further centers of precipitation or nucleation points for aluminum hydrolysis products [5, 6]. Furthermore, this technology is a promising tech- nique for phosphorus removal from wastewater because it is simple, selective, efective, ability in multi-pollutant removal and economical, result in less sludge production and therefore experience minimal disposal problems [7, 8]. Fig. 1 Experimental setup for the electrocoagulation process using aluminum electrode systems Tere have been diferent studies on various aspects of the phosphate removal from wastewater using elec- trocoagulation process [2, 6, 9, 10]. However, studies on comparison between the diferent anode and cathode Al stirrer at 200 rpm. During the experiments, temperature electrode systems in both for the removal of phosphorus and pH of the synthetic wastewater was measured by a from wastewater and the characterization of the elec- pH meter (pHTestr 30). trodes before and after treatments as well as the sludge formed after the treatment using FESEM, EDXS, XRD, Calculation of removal efciency FTIR and Raman spectroscopy are very limited. Tere- Te removal efciencies for Phosphorus were calculated fore, the main objective of this study is the treatment and as follows: characterization of phosphorus from synthetic wastewa- Co − Cf ter using aluminum plate electrodes in the electrocoagu- Removal efficiency (%) = ∗ 100 C (1) lation process. o where; Co is the initial phosphorus concentration (mg/L) Materials and methods and Cf is the fnal phosphate concentration (mg/L) [9]. Experimental setup Te experimental setups for the designed EC process Chemicals and reagents were explained as follows (Fig. 1): For each run a 0.9 L All chemicals used were analytically graded and used of synthetic wastewater was mixed with 0.1 g of sodium without further treatment. Te chemicals used in the pre- chloride which was used as increasing electrical conduc- sent work were sodium hydroxide (reagent grade, ≥ 98%), tivities of the solution. Te solutions were placed into the concentrated hydrochloric acid, concentrated sulfu- 1 L beaker. NaOH and HCl solutions were used to adjust ric acid (reagent grade, 95–98%), potassium antimony the pH. In separate diferent electrode systems with the tartrate, ammonium molybdate (ACS reagent, ≥ 99%), same dimension of Aluminum electrode were used in EC ascorbic acid (ACS reagent, ≥ 99%), potassium di-hydro- technique. External power supply was applied through gen phosphate (ACS reagent, ≥ 99%), and sodium chlo- the diferent electrode systems using a DC power sup- ride (AR grade, ≥ 99%). All the working solutions were ply. A 10 mL sample solution was taken at diferent time prepared using distilled water except the cleaning of elec- intervals in each run. Te location of the drawn samples trode with 5% HCl solution. was kept constant for each run. Te submerged por- tion of an electrode was 10 × 3 × 1 cm though its actual Apparatus and equipment dimension was 20 3 1.5 cm. Te distance between the × × Te apparatus and equipments used in the experiments electrodes was kept constant at 2 cm and the efective were UV–Visible Spectrophotometer (Perkin Elmer submerged area was 30 cm2. Lambda 25, USDA); portable pH meter (pHTestr 30, During the EC process the synthetic wastewater in the China);DC Power Supply Regulator (L3210 Regulated beaker was mixed continuously with a 30 mm magnetic Tibebe et al. BMC Chemistry (2019) 13:107 Page 3 of 14 DC Power Supply 0–16 V/0–2 A, Aplab Limited, India), Al plate electrodes; Magnetic Stirrer (30 mm) with Hot Plate (Remi 5 MLH plus, India), Digital mass balance, Oven Dry (Macro Scientifc Works Pvt Ltd, India), Field Emission Scanning Electron Microscope (FESEM) (FEI Quanta 200 F SEM, Netherland), EDXS (Oxford xmax 80 mm2, Netherland), XRD, FT-IR Spectrophotometer (Nicolet 6700 FT-IR spectrometer, Termo Scientifc, India) and Raman Spectrometer (Micro Raman Spec- trometer, UK). Measurements of phosphorus concentration from synthetic wastewater Te analysis of phosphorus was measured colorimetri- cally using ascorbic acid method following the stand- ard procedures outlined in [11]. Te fltered sample was mixed with ammonium molybdate that forms molybdo- phosphoric acid with any phosphate present in the water sample. Te acid is then reduced by ascorbic acid to a blue complex known as molybdenum blue. Te color Fig. 2 Three layers formed in the beaker after the electrocoagulation process intensity, which is proportional to the concentration of phosphate in the water sample, was then measured by a UV Visible spectrophotometer at a wave length of 880 nm. Ten, concentration of phosphorus was calcu- with constant current density were explained in Table 1. lated from standard calibration curve. From the table removal efciency of