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; alkalinity; calcium-modified zeolite; electrooxidation; organic matter.