Archives of

The irregular detergent entry into groundwater and surface water resources is causing serious environmental problems, including the eutrophication phenomenon and production of synthetic foam (1-3). Household cleaning products and detergents in sewage are major sources of phosphorus (4-8). In order to remove phosphorus detergent compounds in the treatment basin, the use of different and expensive units such as complex systems, aeration, pumping, treatment and disposal of the resulting sludge will require (9). Most detergents are slow biodegradable and there is no fast break in conventional treatment (10,11). Because of the availability conditions, especially in the pond aeration and mixing, foam is produced which disturbs the treatment process because of the high volume and also creates many risks for the refinery workers (12,13). Therefore, treatment is particularly important for detergents and phosphorus wastewater to prevent environmental pollution, prevent degradation of groundwater, surface water resources and improve the performance treatment plants of municipal sewage (13-15). A wide range of water and wastewater treatment processes, including physical operations, biological, physical-chemical and chemical processes (such as chemical precipitation) have been identified to remove contaminants (16-19). In recent years due to environmental compatibility and the possibility of purification of liquids, gases and solids, the use of direct electricity in the water and wastewater treatment plants is developed; also, it is known as an attractive method for coagulation or sedimentation as an electrocoagulation/electrochemical method (10, 20-25). This method can be used widely for wastewater treatment containing BOD, COD, proteins, oils, detergents, paints and solutions containing heavy metals (13,17,21,26-27). Electrocoagulation is a process that consists of creating a drainage metal hydroxide fluke electrical due to dissolution of soluble anodes which are usually iron or aluminum. This was met with limited success in the twentieth century; this method is accepted recently due to environmental restrictions on output wastewater (17,21,26). Studies on the use of EC in wastewater treatment have increased during recent decades about the kind of consumer electrodes and the effective factors which have been used. In a similar work, Mansoorian et al. studied the removal of lead and zinc from battery industry wastewater, using electrocoagulation process; the effect of direct and alternating current, using iron and stainless steel rod electrodes (25). Malakootian et al in their study had shown the relationship between electrocoagulation process, using iron-rod electrodes and removing hardness from drinking water (10). Jay et al. offered a new bipolar electrocoagulation and electro-flotation process for wastewater laundry treatment. The electrocoagulation and electro-flotation processes were performed in a single reactor simultaneously. Performance parameters such as primary pH, hydraulic retention time (HRT) and flow intensity were examined (23). Irdimz et al. used the Taguchi method to determine the optimum conditions, phosphate removal from wastewater by EC with flat aluminum electrodes. Removal efficiency and a laboratory of phosphate from wastewater by electrocoagulation and flat aluminum electrodes are 99.9 and 100%, respectively (27). Önder et al. studied the possibility of removal of the surface-active agents (surfactants) from the solution model and polluted water sample with EC method by Fe²⁺ ions. In these tests, the efficiency of surface-active substances removal with a concentration of surfactant of 10 mg/L was reached to 100 % (26). In order to remove the COD, phosphate, fat and turbidity from sewage treatment in the presence of hydrogen peroxide (H₂O₂) and poly aluminum chloride (PAC) as a coagulant aid method, Un et al. used an electrochemical method with soluble aluminum or iron electrodes. COD removal efficiency was in the range of 62% to 86%, while the removal rates of oil, fat and turbidity was reached up to 100% (28). Sengil et al. studied the removal of COD, phosphate and fats from dairy wastewater by EC with direct current (DC). The removal efficiency of COD and grease was 98 and 98%, respectively (29). Mahvi et al. studied the usability of the electrocoagulation process, using aluminum electrodes to remove heavy metal chromium in aquatic environments. The test results showed that the highest removal efficiency of chromium ions is at pH=3, and a potential difference of 40 v (20). Bani-Melhem et al. studied the efficiency of submerged membrane bioreactor system on the real grey water treatment. (21).
Aims of the study: In the present study, we investigate the influence of type of electrodes with different arrangements, voltage, PH and retention time in removal of detergent and phosphate from car wash wastewater.
 

Materials & Methods

Laboratory materials
In this experimental study that conducted in a pilot project in the chemical laboratory, pH, voltage, retention time and the effects of variables of electrode type were measured. Potassium dichromate (K₂Cr₂O₇), Potassium permanganate (KMnO₄), potassium hydroxide (KOH), potassium hydrogen phthalate (C₈H₅KO₄), silver sulfate (Ag₂SO₄), mercury sulfate (HgSO₄), sulfuric acid (H₂SO₄), 3-methyl-2-benzothiazoline hydrazine and Formaldehyde (HCHO) used in this study. Equipment that used in this study were photo spectrophotometric meter DR/5000, the AC power supply Tracking Dual JPS-302D, glass reactor electro coagulation, iron and aluminum plate electrodes, oven and magnetic mixer.
Sampling
Samples of wastewater were collected from different car washes in the city and transferred to the laboratory. Tests of phosphate and detergent were done on initial samples, and initial concentration was determined. To adjust the primary pH of the solution, the sulfuric acid and one-tenth normal sodium hydroxide were used. Table 1 shows the factors which were affect the electrocoagulation process including characteristics of the raw carwash wastewater, voltage, primary pH and retention time (Table 1).
Experimental apparatus
A lab-scale reactor with diameters of 15cm×15cm×15cm was used for doing this experiment. This reactor was made of glass with a thickness of 10mm with iron and aluminum electrodes with dimensions 12cm×10cm×2mm that were upright and a distance of 2cm from together that the end of each was connected to the DC power supply. Sewage mixing was done, using a magnetic stirrer with a constant speed of 100rpm. Hydrochloric acid, with a weight of 15%, was used to clean the electrodes before starting the procedure. The test was assessed in the voltage range of 10, 20, 30 and arrangements of AL-AL, AL-Fe, Fe-Fe in the pH domains of 3, 7 and 11 with 2 cm intervals and the contact time of 30, 60 and 90 min for each set of pairs of electrodes. In these tests due to the transmission voltage, flow rates were varied between 0.5 to 2 amps. In each set of experiments, samples were taken from the liquid inside of the reactor at specified times; and after filtration, according to the DR5000 UV- Vis HACH spectrophotometer, the samples were prepared for testing the parameters; then, their values were determined, using wavelengths specified by the device.
Table 1) Parameters measured and their range

Parameter	Range	Unit	Raw wastewater Mean ± S.D
pH	3,7,11	---	0.03±7.08
Steering time	30,60,90	Minutes	-
Voltage	10,20,30	Volt	-
Electrode Type	Al-AlFe- Fe،AL-Fe	---	-
Conductivity	-	(mS/cm)	2.4±7.6
Detergent	-	(mgL−1)	8.3±23
Phosphate	-	(mgL−1)	8.8±17

 
 

Results

In this study, voltage (10, 20, 30 V), contact time (30, 60, 90 minutes), type of electrode (AL-AL, AL-Fe, Fe-Fe), pH (11, 7, 3), turbidity and organic matter has evaluation. The results of various arrangements under optimal conditions is shown in Figures 1 to 6.
Changes in phosphate due to variations in input voltage during EC:
Figure 1 shows that increase in the removal of phosphate in the EC with an optimum pH=7 with aluminum electrode have been from 73% phosphate removal (in the 10 voltage) to 100% phosphate removal (in the 30 voltage), respectively.
According to Figure 2, phosphate removal in the EC with aluminum-iron electrode with an optimum pH=7 has been from 34% (in the 10 voltage) to 78% (in the 30 voltage), respectively.
 

Figure 1) Phosphate changes in the EC with aluminum electrodes in the optimum pH =7
 

Figure 2) Changes in phosphate in the EC with electrodes made of aluminum – iron at the optimum pH=7

According to Figure 3, the removal of phosphate in the EC with aluminum-iron electrode with an optimum pH=7 has been from 34% (in the 10 voltage) to 63% (in the 30 voltage), respectively. According to Figure 4, percentage of detergent removal in the EC with aluminum electrode with an optimum pH=7 has been from 51% (in the 10 voltage) to 80% (in the 30 voltage), respectively. According to Figure 4, percentage of detergent removal in the EC with aluminum-iron electrode with an optimum pH=7 has been from 68% (in the 10 voltage) to 94% (in the 30 voltage), respectively.
 

Figure 3) Changes in phosphate in the EC with iron electrodes in the optimum pH=7
 

Figure 4) concentration of detergent in the EC with aluminum electrodes in the optimum pH=7

According to Figure 5, percentage of detergent removal in the EC with aluminum-iron electrode with an optimum pH=7 has been from 41% (in the 10 voltage) to 72% (in the 30 voltage), respectively. According to Figure 6, percentage of detergent removal in the EC with aluminum-iron electrode with an optimum pH=7 has been from 68% (in the 10 voltage) to 94% (in the 30 voltage), respectively. 

 

Figure 5) Changes in detergent concentration in the EC with aluminum-iron at the optimum pH electrode=7
 

Figure 6) Changes in detergent concentration in the EC iron electrodes in the optimum pH=7