|Mirna Lubis||Chemical Engineering Department, Engineering Faculty, Syiah Kuala University, Jl. Syech Abdurrauf No.7, Darussalam, Banda Aceh 23111, Indonesia|
|Dwinta Fujianti||Chemical Engineering Department, Engineering Faculty, Syiah Kuala University, Jl. Syech Abdurrauf No.7, Darussalam, Banda Aceh 23111, Indonesia|
|Rita Zahara||Chemical Engineering Department, Engineering Faculty, Syiah Kuala University, Jl. Syech Abdurrauf No.7, Darussalam, Banda Aceh 23111, Indonesia|
Unmanageable industrial wastewater will have an impact on the environment. One of the alternative wastewater treatment technologies is electrocoagulation. This study investigates the effects of voltage, time, and NaCl concentrations on wastewater through electrocoagulation–specifically, how they affect the total suspended solid (TSS), the total dissolved solid (TDS), and the chemical oxygen demand (COD) reduction of palm oil mill effluent (POME)–with response surface methodology. An iron electrode was used with a time variation of 15, 30, and 45 minutes; a voltage variation of 10, 15, and 20 volts; and NaCl concentrations of 0.0, 0.5, and 1.0 M. A Box-Behnken design in the response surface method formed the model and optimized the electrocoagulation. Optimization of COD, TSS, and TDS reductions with the response surface methodology was accomplished at 93.12%, 97.70%, and 41.06% respectively, in 37 minutes with 20 volts, and no NaCl concentration. The analysis of variance (ANOVA) showed that the quadratic model, with the R2 coefficients of COD, TSS, and TDS at 0.99, 0.97, and 0.92, respectively, and the adjusted-R2 values at 0.97, 0.94, and 0.83, respectively. Conformity testing for the optimum conditions proved the model’s validity, yielding COD, TSS, and TDS reduction efficiency at 93.27%, 97.64%, and 40.78%, respectively. The results of this study were useful for predicting and controlling the COD, TSS, and TDS removal efficiencies in different conditions, and they will provide information on wastewater disposal’s impact on the environment without going through the first processing stage. Therefore, electrocoagulation is a more economical POME processing technique.
Box-Behnken; Electrocoagulation; POME; Response surface method
Wastewater is water-carried wastes that combine with surface water, groundwater, and stormwater. Many types of equipment has been made for treating wastewater, such as settling basins, strainers, filters, and reactors. Furthermore, many technologies can remove pollutants from wastewater, including membrane filtration, an ion exchange, and precipitation (Lee et al., 2014). Regulations compel the industry to keep pollutants within tolerable limits in the environment. The number of microorganisms in wastewater is a measure of the water’s quality. The palm oil industry is the most developed industry in the world because palm oil extraction results in palm kernel oil and crude palm oil (CPO). Indonesian law allows people to dispose of wastes as the standard. As such, Indonesia produces 47% of the world’s CPO, making it the largest CPO producer globally after Malaysia (Carter et al., 2007). A palm bunch consists of 20% oil, 6% kernel, 15% fibers, 7% shells, 20% bunches, and wastewater (Ozturk et al., 2017).
POME is black and contains grease, plant nutrients, total suspended solid (TSS), biochemical oxygen demand (BOD), and chemical oxygen demand (COD); (Mohammed et al., 2014). It has a maximum COD of 80,000 ppm, a BOD of 40,000 mg/l, a solid of 95,000 mg/l, and a TSS of 50,000 mg/l (Chairunnisak et al., 2018). The Indonesian Regulation of Environment states that the maximal limits are a pH of 6–9, a COD of 350 mg/l, a TSS of 250 mg/l, and a BOD5 of 100 mg/l for this pollutant. Many POME processes use anaerobic ponds, a combination of open-waste ponds and land, various membrane materials (Faisal et al., 2016), and adsorbents (Kusrini et al., 2016). These processes have problems related to the large open reactors, large surplus sludge, low process efficiency, and high energy. Therefore, this study tried an alternative, using an electrocoagulation technique or method to process POME from the second aerobic pond effluent in PT Syaukat Sejahtera, Bireuen, Aceh, Indonesia.
Electrocoagulation uses aluminum and iron electrodes because they have good coagulant property, and they are non-toxic, effective, cheap, and easy to procure. Iron electrodes are washed with distilled water prior to implementation to dispose impurities, such as oil and pollutants. The method is electrolysis by oxidation and reduction, when the electric current flows into an electrolyte solution (Kuokkanen et al., 2013), which is helpful because the equipment is simple, easy to run, low energy, and relatively low cost. Electrocoagulation can also neutralize a large pH, purify wastewater content, and precipitate the smallest colloid. Furthermore, electrocoagulation treats textile dyes, heavy metals, oil, and organic compounds in wastewater. This method is reliable, effective, simple, and friendly, as a result of no added chemicals. The method is extremely physical, but more economical because the little electricity is used. The advantage and efficiency make it possible to achieve optimum results by decreasing the response on a larger scale. This reduction of COD, TDS, and TSS by electrocoagulation, using iron as an electrode, is highly attractive for researchers to investigate. This study aims to determine the optimum conditions for reducing COD, TSS, and TDS.
Studies on the use of electrocoagulation to produce safer POME have been conducted to treat industrial textile wastewater containing Direct Red 81. Factors that influence electrocoagulation include time, voltage, electrode type, inter-electrode distance, and electrolyte concentration. Studies have shown that higher voltage and time increase COD, TSS, and TDS reduction. A few researchers focused on electrocoagulation to achieve more effective voltage, time, and electrolyte concentrations. However, few studies have focused on the effect that voltage, time, and electrolyte concentration have on these reductions. Furthermore, the previous research has not investigated the optimum voltage, time, and electrolyte concentrations to reduce COD, TSS, and TDS simultaneously using the response surface methodology (RSM). The present study, therefore, investigates the effects of the optimum time, voltage, and NaCl concentrations on POME COD, TSS, and TDS reduction from a second aerobic pond utilizing RSM.
Without RSM, research would be ineffective because it would require repetition, a higher price, and a longer time. Optimization uses many response surface designs, such as the Doehlert and the Box-Behnken design (BBD). Research took place randomly to diminish the error systematically. The BBD was appropriate because it uses a formula that consists of a simple combination. The resulting design was extremely effective in deciding the amount of research that should be carried out. The present study investigated the optimal electrocoagulation method for iron electrodes as well as the time, voltage, and electrolyte concentrations for reducing pollutants of COD, TSS, and TDS. It employed an electrolyte to guide the flow of ions from the POME by adding sodium chloride to stimulate electrical current. This study focused on wastewater disposal in the environment without passing a primary treatment. The method could be a POME-processing alternative with more economical, simple, and friendly properties than other POME processes. The study‘s results are expected to be a reference for investigations that focus on wastewater processing techniques, specifically the POME process.
Time and voltage were more influential in POME electrocoagulation than the electrolytes. A longer time and a higher voltage resulted in higher COD reduction, but not in higher TSS and TDS reduction. As contact time is longer and the voltage is too high, the reduction of TSS and TDS is less. This study’s electrocoagulation reduced the COD, TSS, and TDS from the second pond’s effluent. The highest results obtained were 95.01%, 97.27%, and 44.11%, respectively. The TSS (130 mg/l) fulfilled the Permen LH No. 5 standard from 2014. The optimum conditions using BBD were comprised of 37 minutes, 20 V, and without the NaCl, resulting in COD, TSS, and TDS reductions of 93.12%, 97.70% and 41.06%, respectively. These values show that iron electrodes are well suited to this kind of electrocoagulation. Such conditions were implemented to treat the POME from the second pond effluent. Nevertheless, the COD did not meet the standard, TSS fulfilled it, and TDS was not required. Therefore, the optimization needs improvement, referring to other electrodes and the energy consumed.
Thanks to Ms. Aula Chairunnisak, PT. Syaukat Sejahtera, and the laboratory staff of Bapedal Sigli for their help as well as to the Unsyiah Grant (Project No. 267/UN11.2/PP/SP3/2016).
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