Pre-treatment of soft drink wastewater with a calcium-modified zeolite to improve electrooxidation of organic matter

Abstract

Wastewater from soft drink manufacturing, having a high organic load (chemical oxygen demand (COD) = 4,500 mg L⁻¹) and high alkalinity (2,653.7 mg L⁻¹ CaCO₃; pH 12), was pretreated with a calcium-modified zeolite to reduce the alkalinity and improve the electrooxidation of organic matter. The natural zeolite clinoptilolite was modified in various ways with Ca(OH)₂ and CaCl₂. The CaCl₂-modified zeolite (ZSACaCl-72h) was more effective for the treatment of soft drink wastewater than the congener modified with Ca(OH)₂, where the former reduced the alkalinity by 86% after 8 h. Electrooxidation of soft drink wastewater without zeolite pre-treatment was carried out with boron-doped diamond (BDD) electrodes under the optimal conditions (current intensity: 3 A; sample pH: 12), with 98% and 94.05% reduction of the COD and total organic carbon (TOC), respectively, after 14 h of treatment. Soft drink wastewater pretreated with calcium-modified clinoptilolite was also electrooxidized using the BDD system. The results showed that the pre-treatment was extremely convenient, reducing the treatment time to 6 h compared to the electrooxidation of wastewater. At a current intensity of 3 A, the treatment time was 8 h, with 100% reduction of colour and COD and 97.5% reduction of TOC.

Keywords:

• Soft drink wastewater
• calcium-modified zeolite
• alkalinity
• electrooxidation
• organic matter

Acknowledgement

The authors thank the Secretary of Research and Advanced Studies of the Autonomous University of the State of Mexico for financial support granted through research project grant 4482/2018/CI and PRODEP-SEP for the postdoctoral scholarship for Almazán-Sánchez.

Additional information

Funding

This work was supported by the Secretary of Research and Advanced Studies of the Autonomous University of the State of Mexico [grant number 4482/2018/CI].