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Jurnal Litbang Industri
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The treatment of automotive workshop wastewater using electrocoagulation process
Pengolahan limbah cair bengkel dengan proses elektrokoagulasi
Monik Kasman*1, Salmariza Sy2, Anggrika Riyanti1, Hendi Matalata1, Irpan Firfansyah1
1 Departement of Environmental Engieering University of Batanghari Jl. Slamet Riyadi, Broni, Jambi, 36122, Indonesia
2 Center for Standardization and Industry Services Padang Jl. Raya LIK No. 23 Ulu Gadut Padang 25164, Indonesia
* e-mail: [email protected]
INFO ARTIKEL ABSTRACT
Sejarah artikel: Automotive workshop activities generate waste water requiring some treatments before being discharged into receiving water surface. One of the wastewater treatment methods for is the electrocoagulation method. This study aims to observe the effectiveness of the electrocoagulation method in treating wastewater from automotive workshop activities.
Observations were limited to the effect of current density on the efficiency of removal of pollutants from wastewater from automotive workshop activities, including pH, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) ,oil and grease Current density were varied into 62 A/m2, 53 A/m 2, and 31 A/m 2. The results showed that the highest removal efficiency for the pollutant parameters BOD, COD, and oil and grease respectively were 91.53%, 94.90%, and 81,38% at current density 62 A/m 2. The electrocoagulation process was strongly influenced by the current density, where the higher the current density, the higher the removal efficiency.
Diterima : 23 Februari 2023 Direvisi : 26 Juni 2023 Diterbitkan : 30 Juni 2023
Keywords:
automotive workshop wastewataer;
current density;
electrocoagualation
ABSTRAK
Kata kunci: Kegiatan usaha perbengkelan menghasilkan limbah cair yang memerlukan pengolahan sebelum dibuang ke badan air penerima. Salah satu metode pengolahan limbah cair usaha perbengkelan adalah metode elektrokoagulasi. Penelitian ini bertujuan mengamati efektifitas metode elektrokoagulasi dalam mengolah limbah cair kegiatan usaha perbengkelan. Pengamatan dibatasi pada pengaruh kerapatan arus terhadap efisiensi penyisihan polutan limbah cair kegiatan usaha perbengkelan, meliputi pH, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) dan minyak lemak. Variasi kerapatan arus meliputi 62 A/m2, 53 A/m2 dan 31 A/m2. Hasil penelitian menunjukkan bahwa efisiensi penyisihan tertinggi untuk parameter polutan BOD, COD, dan minyak lemak secara berurut adalah 91,53%, 94,90%, dan 81,38% pada kerapatan arus 62 A/m2. Proses elektrokoagulsi sangat dipengaruhi oleh kerapatan arus, dimana semakin tinggi kerapatan arus, semakin tinggi efisiensi penyisihan.
Limbah cair bengkel;
kerapatan arus;
elektrokoagulasi
© 2023 Penulis. Dipublikasikan oleh BSPJI Padang. Akses terbuka dibawah lisensi CC BY-NC-SA
1. Introduction
Automotive workshop wastewater was increased by increasing of amount of motorized vehicles. Central Bureau of Statistics for Province of Jambi noted that the number of motorized vehicles at 2020 reached 1,779,594 units. It encourages the growth of automotive workshop activities which includes washing, repair, maintenance of motorized vehicle as well as domestics activities.
Possibly, its wastewater contains oil particles (lubricating oils and oil and grease), fuel left over from spare part’s washing and traces of mechanic’s hand washing. If its wastewater is immediately disposed without any treatment, it can pollutes or contaminates receiving water surface (Rubí-juárez et al., 2017).
Automotive workshop wastewater contains BOD of 100.5 mg/L; COD of 334.6 mg/L; TSS of 106 mg/L; oil and grease of 3.7 mg/L and Iron (Fe) of 2.689 mg/L (Priliandana et al., 2021).
In recent years, electrochemical methods have been applied for automotive workshop wastewater treatment instead of conventional methods. Most popular electrochemical method is electrocoagulation process due to its typical advantages such as simple equipment;
ease of automation; ease of scale up, selectivity, environment compatibility and less or no chemical aid and less sludge. Eelectrocoagulation process is effective for contaminats of organic and inorganic material removal (Sutanto et al, 2019)(Sravanth et al., 2019).
Actually, electrocoagulation uses electrodes as a coagulant in floculation-coagulation process. Principally, its process includes several stages: the equalization process, the electrochemical process (flocculation- coagulation) and the sedimentation process. The equalization processs is intended to uniform the wastewater to be processed, especially the pH condition.
There is no chemical reaction occurred in this stage. In the electrochemical process, Al3+ will be released from the electrode plate (anode) to form a complex Al(OH)3
hydroxide floc which is able to bind contaminants and particle in the waste (G et al., 2016).
In this paper, the discussion is focused on the use of electrocoagulation process in pollutants removal from the automotive workshop wastewater. Futhermore, the
influencing factors which must be controlled in this experiment was observed and analyzed. Our previous experiment comfirmed earlier researchers finding that electrocoagulation process is most influenced by applied current density, electrode distance and retention time (Kuokkanen et al., 2013). The distance between the electrodes affects the speed of electron transfer between the anode which accepts electrons and the cathode wher the reduction process occurs. The electrode distance determines the current density. It greatly affects electrolysis rate of anode metal and the production of electrolytic bubbles at the cathode (An et al., 2016).
However, the floc formation is also related to retention time or treatment time. The longer the electrocoagulation process occurs, the more colloids will be bound to form large flocs or upward flotation (Mollah et al., 2001)(Prabowo et al., 2012). The pollutant’s parameters observed refers to the regulation of the minister of environment No.5 of 2014, annex XLVII concerning wastewater quality standard. The parameters includepH, COD (Chemical Oxygen Demand), BOD (Biochemical Oxygen Demand), oil and grease .
2. Method 2.1. Materials
Automotive workshop activities wastewater was treated by electrocoagulation process. The batch experiment was conducted in a laboratory scale reactor.
A set of electocoagulation reactor consisted of reactor and a DC (direct current) power supply. The reactor was made of cubed glass of 5 mm thickness within 12 liters capacity. It was designed at 20 cm x 25 cm x 20 cm size.
Four pieces of aluminium with dimensions of 20 cm x 19 cm x 0,2 cm used as electrodes. The electrode plates consist of catode and anode were connected to DC power supply. They serve as conductor which supplies electical current into wastewater contained in reactor, as electrolite. The electrode plates were set submerged in wastewater with the height of 17 cm from the wastewater surface. The electrocoagulation reactor is illustrated in Figure 1.
Figure 1. A schematic of electrocoagulation reactor Real wastewater sample was obtained from
equalization tank effluent of Sewage Treatment Plant of Automotive Workshop nearby Jambi City. Initial
concentration of sample was tested to determine of pollutant’s parameters refers to the regulation of the minister of environment No.5 of 2014, annex XLVII
DC power suplpy
Parallel anode Wastewater
Parallel cathode
Outlet
concerning wastewater quality standard. The parameters include BOD, COD, Oil and grease and Fe (iron). The initial characteristics of wastewater are shown in Table 1.
2.2. Experiment
The experiment was preceeded by some preparations including experimental device set up and wastewater sampling. The main experiment was done in batch system which varied current density in to 62 A/m2, 53 A/m2 dan 31 A/m2. Current density was indicated as extremely effecting factors according to previous researches. A 16 voltage of electrics was supplied into wastewater using electrodes with the distances of between electordes were 2 cm, 4 cm and 6 cm. The treated samples were collected after retention time regulated 15 minutes, 30 minutes, 45 minutes, and 60 minutes.
Pollutant’s removals (%) were calculated using mathematical equation 1, where C intial is initial concentration and C final is final concentration. The effects of current density were analyzed.
(1) 3. Results and discussions
3.1. Characterictics of automotive workshop activities wastewater
Physically, automotive workshop activities wastewater has a black color and a strong bad smell.
Chemically, five tested pollutant’s parameters include pH, COD (Chemical Oxygen Demand), BOD (Biochemical Oxygen Demand), and oil and grease. The results are showed in Table 1. Based on Table 1, BOD and COD concentration were above the threshold value refers to the regulation of the minister of environment No.5 of 2014, annex XLVII.
Table 1.
Characterictics of automotive workshop activities wastewater
*the regulation of the minister of environment No.5 of 2014, annex XLVII
3.2. The experimental results
The three variants of current density were determined by adjusting electrode plate’s distance. The distance of electrode for each current was 2 cm, 4 cm and 6 cm for current density of 62 A/m2, 53 A/m2 and 31 A/m2 respectively. Table 2 shows the experimental results of the parameter test for wastewater from automotive workshop activities after processing using the electrocoagulation method.
3.3. Parameter of pH
Figure 1 shows the effect of current density (CD) to pH value of aumototive workshop wastewater in regulated retention time. Electrocoagulation was actually influenced by current density and retention time.
Electrocoagulation process reduced the acidity of wastewater, and tend to be neutral which was indicated by pH value. It seems the pH value rose with the increasing of current density in 60 minutes of retention time. The pH values for each retention time in 60 minutes of retention were 7.88, 7.41 and 7.38.
The increase in the pH value was due to the increase in the accumulation of hydroxide ions (OH-) during the
electrocoagulation process. According to (Tchamango et al., 2020), the reaction that occurs at the cathode: 2H2O + 2e- → H2 + 2OH- and the reaction at the anode: Al + 3H2O → Al(OH)3 + 3H+ + 3e. The higher the current density, the greater the rate of fight of Al3+ ions at the anode and the formation of hydroxyl ions (OH-) at the cathode. In the Al3+ cation solution, the oxidation product of aluminum metal at the anode will be associated with hydroxyl ions (OH-). Thus, the formation of Al(OH) near the anode may lead to the decrease of pH.
On the other hand, it has also been reported that ultimate pH values increase rapidly during electrocoagulation such that the ultimate pH values reached at the end of electrocoagulation are always greater than 8–9. This is not surprising, since continuous hydroxyl ion production occurs at the cathode. Under alkaline conditions, the formation of Al(OH) complexes is the major reason for a decrease in pH. Moreover, hydrogen bubbles produced at the cathode are smallest and finest at neutral pH, providing sufficient surface area for gas–liquid–solid interfaces and mixing efficiency to favor the aggregation of tiny destabilized particles and colloids (G et al., 2016).
Pollutant
parameter Unit Concentration Treshold value*
pH - 6,80 6-9
BOD mg/L 71,32 50
COD mg/L 226,50 100
Oil and grease mg/L 8 10
Figure 2. The effect of current density to parameter of pH
3.4. Parameter of BOD
The BOD value is indicated how much oxygen used by microorganisms in decomposing organic materials in waste. The efficiency of BOD pollutant removal parameters using the electrocoagulation process can be seen in Table 2 and Figure 3. Figure 3 shows the current density and the longer the retention time, the higher the removal efficiency for BOD concentration in wastewater.
BOD removals at a current density of 62 A/m2 with a regulated retention time of 15, 30, 45, and 60 minutes were 63.59%, 74.26%, 77.44%, and 91.53%
respectively. At current density of 53 A/m2 with a regulated retention time of 15, 30, 45, and 60 minutes, BOD removals were obtained 49.58%, 66.45%, 69.32%
and 79.99% respectively. While, at the current density of 31 A/m2 with retention time 15, 30, 45, and 60 minutes, respected BOD removals obtained were 44.49%, 55.54%, 68.90% and 74.64%.
Treatment of wastewater from automotive workshop activities using the electrocoagulation process is considered effective in reducing the BOD pollutant parameter, where the highest removal is at a current density of 62 A/m2 and retention time of 60 minutes.
These results indicate that the longer the regulated retention time and the higher the current density used in the electrocoagulation process, the higher the efficiency of BOD reduction.
The removal of BOD is caused by aluminum ions Al3+ functioning as a coagulant which can form flocs which will precipitate, so that the waste becomes clearer than before, so the organic compounds left in the liquid waste become more easily degraded by microorganisms (Setianingrum et al., 2017). At the anode, an oxidation reaction occurs, namely the formation of oxygen as a result of the reaction: 4OH- → 2H2O + O2 + 4e- (Rubí- juárez et al., 2017). The removal of BOD in wastewater is caused by more organic matter being bound to the flocs, so that it is oxidized due to the presence of a strong oxidizing agent, namely oxygen (O2). At the anode, an oxidation reaction occurs, namely the formation of oxygen as a result of the reaction: 4OH- → 2H2O + O2 + 4e-. The removal of BOD in wastewater is caused by more and more organic matter being bound to the floc, so that it is oxidized due to the presence of a strong oxidizing agent, namely oxygen (O2). The more oxygen in the wastewater, the oxygen needs for microorganisms in decomposing organic matter will be fulfilled (Gustiana and Widayatno, 2020)
Table 2.
Experimental results of wastewater treatment fro automotive workshop activities using electrocoagulation process
No Plate distance
Current
density Parameter Unit Retention time (minute)
15 30 45 60
1 2 cm 62 A/m2
pH - 7,29 7,49 7,72 7,88
BOD mg/L 25,97 18,36 16,09 6,04
COD mg/L 86,57 32,01 54,75 11,56
Oil & grease mg/L < 1,56 < 1,56 1,61 2,26
2 4 cm 53 A/m2
pH - 7,26 7,24 7,30 7,41
BOD mg/L 35,96 23,93 21,88 14,27
COD mg/L 127,49 70,66 57,02 20,65
Oil & grease mg/L 1,96 < 1,56 2,28 2,39
3 6 cm 31 A/m2
pH - 7,22 7,33 7,24 7,38
BOD mg/L 39,59 31,71 22,18 18,09
COD mg/L 152,22 97,94 66,11 57,02
Oil & grease mg/L 4,35 2,70 1,65 4,44
Figure 3. The effect of current density to parameter of BOD 3.5. Parameter of COD
COD is one of the important parameters in wastewater. COD is the amount of oxygen needed to chemically oxidize organic materials contained in water.
Therefore, the removal of COD concentrations is important to be tested in this study. The results of COD removal can be seen in Table 2 and Figure 4. Figure 4 shows that the higher the current density and the longer the contact time, the higher the efficiency of removing COD concentrations in wastewater. At a current density of 62 A/m2 with a retention time of 15, 30, 45, and 60 minutes, the COD removals were 61.78%, 85.87%, but the removal decreased in the retention time of 45 minute by 75.83% and rose again in the 60 minutes by 94.90%.
Current density of 53 A/m2 with retention times of 15, 30, 45, and 60 minutes, COD removals reached on 43.71%, 68.80%, 74.83% and 90.88% respectively.
While at a current density of 31 A/m2 with regulated retention times of 15, 30, 45, and 60 minutes, COD decreased at efficiencies of 32.79%, 56.76%, 70.81%
and 74.83%.
Based on the experiment, the highest removal of COD occurs at a current density of 62 A/m2 at a distance of 2 cm in the 60 minutes was 94 .90%. It indicates that the longer the retention time and the higher the current density used in the electrocoagulation process, the higher the COD reduction efficiency.
The removal of COD concentration was due to the oxidation and reduction reactions that took place at the anode and cathode, at the anode the reactions that occurred were: 2H2O + 2e- → 2OH- + H2 and at the cathode: Al + 3H2O → Al(OH)3 + 3H+ + 3e-. Al3+ ions released at the anode can react with OH- ions and negatively charged colloidal particles or organic compound ions to form Al(OH)3 to form flocs in wastewater. These flocs will slowly settle to the bottom of the electrocoagulation reactor. While the oxidation- reduction reaction that occurs at the cathode produces hydrogen gas (H2) and at the anode produces oxygen (O2) which carries colloids of impurities up to the surface (flotation process). This is indicated by the presence of lots of bubbles or foam (Amri et al., 2021).
Figure 4. The effect of current density to parameter of COD
3.6. Parameter of oil and grease
Oils and fats are organic materials that are not easily decomposed by bacteria, so their concentration must be limited in water. During this experiment, the value and efficiency of removing the concentration of oil and grease pollutant parameters in the workshop wastewater
by electrocoagulation process can be seen in Table 2 and Figure 5. Figure 5 shows that the higher the current density, the higher the efficiency of removal of oil and grease concentrations in wastewater. In this study, the highest removal of oil and grease concentrations reached on 81.38% at current density of 62 A/m2.
Figure 5. The effect of current density to parameter of oil and grease The amount of Al3+ released into solution greatly
influences the interactions that occur in the oil and fat destabilization mechanism. The more Al3+ released at the anode, the higher the trapping and binding of oil and grease by the coagulant core so that the removal is also greater (Nur, 2017). The smaller the distance between the electrode plates, the higher the electric current flowing will make Al3+ ions which are oxidized in large quantities and bind with OH- to form coagulants quickly.
Oil and grease pollutant parameters in the retention time of 45 have shown a decrease in efficiency. It was due to the stabilization of the floc (coagulant) or the passitivity of the electrode, where the electrode is saturated and then the flocs fall to precipitate and react again at the aluminum anode and cathode (Amelia et al., 2019).
4. Conclusions
It can be concluded that electrocoagulation process was effective to remove pollutant from automotive workshop activities wastewater. It is indicated by the highest removal efficiency for the pollutant parameters BOD, COD, and oil and grease respectively were 91.53%, 94.90%, and 81,38% at the highest current density of 62 A/m2. Further, excluding for oil and grease removal, the removal of pollutants were being higher as the retention time being longer.
Acknowledgement
The authors appreciate to the Lembaga Penelitian dan Pengabdian Kepada Masyarakat (LPPM) of University of Batanghari, The laboratory of Engineering Faculty, PT. DIPO International Pahala Otomotive, Jambi Lestari
International Laboratory and all parties who have assisted in this research.
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