The Innovative Use of Electrocoagulation-Microwave Techniques for the Removal of Pollutants from Water

Electrocoagulation (EC) is an effective water and wastewater treatment technology; where the coagulants are generated in-situ by electrolytic oxidation of a sacrificial anode. In this technique, pollutant removal is done without adding chemicals; therefore, it remarkably reduces the sludge produced, and consequently reduces the cost of sludge handling. This method has been efficiently used to remove, up to 99%, of a wide range of pollutants such as heavy metals, oil, dyes, and fluoride. However, the EC technology still has a deficiency in the variety of reactor design, and its performance is highly influenced by the chemistry of the water being treated, especially the presence of organic matter (OM), as this inhibits heavy metal removal due to the formation OM-heavy metals complexes. The presence of heavy metals and OM in water resources is one of the most problematic pollutants in Hilla River, Babylon city, Iraq, which inhibits the application of the EC method in that area. Thus, the current study has been devoted to develop a new hybrid EC rector that can be applied to treat water drawn from Hilla River especially, and to treat water containing OM-heavy metals complexes. The aims of this study are therefore; firstly to examine the removal of heavy metals from drinking water in the presence of OM-heavy metal complexes using a new hybrid treatment method that utilises a combination of microwave-electrocoagulation (MW assisted-EC method). Secondly, to present a new configuration for an electrocoagulation reactor (FCER) that employs perforated plate flow columns (which are widely used in the chemical industry) to achieve water mixing, aeration, and temperature control processes. Additionally, the development of statistical models for the EC performance, recovery of hydrogen gas, and the removal of biological pollutants are other targets in the present project. Initially, the performance of the new flow column EC reactor (FCER) was validated in terms of water mixing efficiency, water aeration, and temperature controllability. The results were compared to those of traditional EC reactors. Then, the ability of the FCER to work as an EC unit was validated by treating different pollutants such as fluoride, nitrate, iron, and reactive black 5 (RB-5) dye from drinking water. Then, the ability of the new MW assisted-EC method to remove OM-heavy metal complexes was experimentally proved by treating synthetic water samples contain iron (Fe2+) ions and ethylenediaminetetraacetic acid (EDTA) (C10H16N2O8) (as organic matter). The results obtained showed that FCER achieved a complete water mixing efficiency, and increased the dissolved oxygen (DO) concentration by 110.6% within 10 min, and kept the temperature of water being treated within the range of 22-28 oC for 30 min of electrolysing. While the traditional reactors achieved water-mixing efficiency of 96.5%, increased the DO by 52.2%, and the temperature increased to about 32 oC over the same treatment period. Additionally, FCER was able to reduce fluoride, iron, nitrate, and RB-5 dye concentrations by 98%, 99.6%, 95.2%, 98.6%, respectively. In terms of OM-heavy metal complex removal (the novelty of the present work), the results obtained demonstrated that this novel method removes 92% of this refractory complex within 35 min of treatment at a power of 100 W, temperature of 100 oC, initial pH of 6, ID of 5 mm, and CD of 1.5 mA/cm2. While, the traditional treatment (EC only) removed only 69.6% of this complex under the same operating conditions. It is noteworthy to mention, the new MW assisted-EC method achieved 100% removal of culture-able activated sludge microorganisms ASM from drinking water, which could eliminate the need for costly separated biological treatment units. Statistically, empirical models were developed to reproduce the performance of FCER in terms of fluoride, nitrate, RB-5 dye, iron, and iron-EDTA complex removal. The R2 value for the models of fluoride, nitrate, RB-5 dye, iron, and iron-EDTA complex removal were, respectively, 0.823, 0.848, 0.798, 0.868, and 0.923. Economically, it has been found that the preliminary operating cost of the MW assisted-EC method is 0.628 US $/m3. Additionally, it has been found that the generated hydrogen gas from this new method could be used to reproduce about 2.82 kW/m3 of power, which is a promising amount of power on field scale plants. In conclusion, according to the obtained results, the new MW assisted-EC method is a safe promising alternative to the complicated, expensive, and time consuming traditional treatment methods, as it removes heavy metals in the presence of OM in a relatively short time without the need for chemical additives. Economically, the MW assisted-EC method reduces the need for separated biological treatment unit that require space, money, equipment, and time, because drinking water will be sterilised as it passes through the microwave field. The latter merit makes this new method a cost-effective alternative. Additionally, FCER reduces the need for external mixing and aeration devices that require extra power to work, which makes FCER a cost-effective alternative for traditional lab-scale EC units