Defluoridation of drinking water by magnesium and aluminum electrocoagulation in continuous flow-rate: a response surface design.

The goal of this research is to apply an electrocoagulation process in continuous flow for the defluoridation of drinking water. Two sampling sites were studied, Temascalcingo (T), Mexico state and Jerecuaro (J), Guanajuato, with fluoride (F-) concentrations above the norms (2.3 mg L-1 and 4.5 mg L-1, respectively). In addition, a second Temascalcingo sample was enriched (TE) to 9.2 mg L-1 F- to study the effect of the F- concentration. A response surface design was proposed through a Box-Behnken model, and the variables studied were electrode system, flow-rate and current intensity. 51 experiments were performed with T-site to determine the best operating conditions for the system. These conditions were applied to the J-site. The experiments for T, Al/Al system achieves an F- concentration within permissible limits (0.72 mg L-1 F-) at 10 min of treatment, 0.2 A (Current density j 48.78 A m-2) and 10 mL min-1 with a removal efficiency of 68.69%, and after 160 min, the removal increased to 99.56%. AlMg/AlMg needs 10 min to achieve a concentration of 0.75 mg L-1 F- at 0.2 A (j 25 A m-2), 16 mL min-1 with a removal efficiency of 67.39%, and after 100 min, the removal is increased to 92.17%. An important and novel advantage is the use of AlMg allows an acceptable removal of F- (<1.5 mg L-1) at high and low concentrations in short periods of time; this also allows save energy costs and the effluent is free of residual aluminum, avoiding side effects.

Industrial wastewater treatment using magnesium electrocoagulation in batch and continuous mode.

In the present study, the electrocoagulation (EC) performance of a Mg-Mg system was applied for the industrial wastewater treatment, from an industrial park that covers different activities such as: food, automotive, pharmaceutical, chemistry and cosmetics, after primary clarification. The effects of major operating parameters such as pH, reaction time, and current density were investigated for chemical oxygen demand (COD), color, and turbidity removal efficiency. The batch system was found convenient, achieving 63.52% COD, 96% color, and 99.32% turbidity removal at optimized operating conditions of pH 7.12, reaction time of 75 min, and current density of 201.5 A/m2. On the other hand, for continuous EC, the process removed approximately 46.58%, 95.96%, and 87.19% of the COD, color, and turbidity respectively, at 90 min of retention time, current density 440 A/m2, and a rate of 20 mL/min. Additionally, concerning nutrient removal (N and P), the EC system with Mg electrodes was highly efficient; batch treatment removed 97% of total phosphorus and 67% of ammoniacal nitrogen, whereas the continuous treatment removed 98.5% of total phosphorus and 83% of ammoniacal nitrogen. The sludge characterization before and after EC treatment was made by SEM, EDS, Fluorescence spectroscopy, IR spectroscopy. Minerals such as chlorite, crossite, richterite, pyroaurite, langbeinite as weel as aliphatic and polysubstituted aromatics compounds, sulfates and phosphates inorganic ions, and organic phosphorus were reduced. The energy cost in the batch EC is US$0.05/m3. A numerical CFD model was used to estimate the velocity fields and guarantee the presence of turbulent kinetic energy within a continuous flow reactor.

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

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.