Abstract
In the present study, the optimization of electrocoagulation (EC) conditions for the purification of olive debittering wastewater (ODW) was investigated by response surface methodology (RSM). For this purpose, a central composite design (CCD) was employed to optimize the process variables including current density (3.0–30.0 mA/cm2) and EC time (10.0–60.0 min). The results showed a significant effect of current density and EC time on the removal efficiency of total phenolic compounds (TPC) and chemical oxygen demand (COD). The best models obtained using the central composite design were quadratic polynomial for TPC (R2 = 0.993), COD (R2 = 0.982), and the inverse square root of turbidity (R2 = 0.926). Additionally, the square root of electrode consumption and energy consumption were appropriately fitted to the two-factor interaction (2FI) model (R2 = 0.977) and quadratic polynomial (R2 = 0.966) model, respectively. The predicted optimum conditions based on the highest removal efficiency for TPC were a current density of 21.1 mA cm−2 and an EC time of 58.9 min, in which the obtained model predicted 82.6% removal for TPC. This prediction was in agreement with the laboratory result (83.5%). The amount of energy consumption and the operating cost in these conditions was estimated to be 14.92 kWh and USD 6.49 m−3 per ODW, respectively.
Highlights
Olive food products are known for nutritional and health benefits
The results showed that chemical coagulation brought a considerable decrease in chemical oxygen demand (COD), suspended solids and chlorides, the extent of the decrease in the total dissolved solids (TDS) was only 14.05% using aluminum and 26.3% using FeCl3
Obtained by response surface methodology (RSM) and the corresponding responses. This table reveals the total phenolic compounds (TPC) and COD contents and turbidity of olive debittering wastewater (ODW), as well as the amount of electrode and energy consumption after electrocoagulation treatment according to RSM runs
Summary
The fruits are widely used for the extraction of oil and are consumed in processed forms. In 2018, an amount of 2.87 million metric tons of table olive was produced worldwide, of which 108,895 tons belonged to Iran according to agriculture statistics [1]. Virgin olive oil and its fruits have a characteristic taste because they contain phenolic compounds that are derived from oleuropein hydrolysis [2,3]. The processing of fruits includes cleaning, debittering, and fermentation. The whole process consumes a large quantity of water, which is entirely converted to the waste stream [4]. Olive industries use about 0.4–0.8 m3 water per ton of green olives in the debittering stage. The generated discharge contains different organic compounds such as phenolic compounds, as well as inorganic compounds with
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