Sterilization and alkalinity-hardness removal effect by using electrochemical method for reclaimed water used in drip irrigation

Reclaimed water is becoming more and more important for irrigation due to water deficits, however, the ions and microbes in reclaimed water can lead to physiochemical or biological fouling of drip irrigation. There are physical, chemical, biological methods on controlling emitter clogging. In principle, electrolysis supply allows electrical forces to inhibit the formation of fouling. Electrochemical water treatment technology is a clean and environmentally friendly method to prevent emitter clogging compared to chlorination added in reclaimed water because it only uses electricity as power and few poisonous materials are produced. This study investigated the sterilization and alkalinity-hardness removal effect of electrochemical water treatment technology for reclaimed water in order to provide a possible method for reclaimed water treatment used in drip irrigation that could prevent emitter clogging. An electrochemical system was designed, which included a power supply, a pump, a cylindrical upflow low-voltage electrolysis reactor and inlet and effluent bottles. The electrolysis reactor used Ti/ SnO2+Sb2O3 and stainless steel as the anode and cathode, and the volume of electrolysis reactor was 1.5 L, the high-aspect ratio was 4:1. The following 2 experiments are designed: 1) the treatment time was 12 h, and the voltage was maintained at 0.5, 2 and 4 V; 2) the voltage was 4 V, and the treatment time was maintained at 3, 6, 12, 24, 48 h; all the experiments were repeated 3 times. The total number of bacteria, total hardness, total alkalinity, pH value, concentration of chlorine was measured before and after electrochemical water treatment. And then we calculated the sterilization rate, removal rate of hardness, the removal rate of alkalinity, the variation of chlorine to evaluate the possibility of electrochemical methods in dealing with ions and microbes. The results showed that besides the applied voltage and treatment time, the accumulated treatment time was also a key factor for electronic water treatment technology. When the accumulated treatment time was below 100 h, the amount of bacteria was very low, and the sterilization rate was more than 80%. The biggest removal rate of hardness and the alkalinity was 23.94% and 66.85%, respectively, which was found when the applied voltage was 4 V and the treatment time was 48 h, and at the same time the accumulated treatment time was 160 h. This result demonstrated that electrochemical water treatment technology had a positive effect on controlling emitter clogging. With the increasing of accumulated treatment time, especially when the accumulated treat time was more than 320 h, there was a significant decline on sterilization rate and removal rate of hardness. The amount of bacteria was increased, and the sterilization rate was below 0 correspondingly. The anode (Ti/SnO2+Sb2O3) was not stable for long-term operation especially when the accumulated treat time was more than 320 h. The sterilization rate and removal rate of hardness and alkalinity was better when the accumulative treatment time was 160 h than it was 320 h. Further study is needed to improve the robustness of the electrolysis reactor and find the reason why Ti/ SnO2+Sb2O3 anode lost effectiveness. To apply the electrochemical water treatment in practice, the improvement of anode materials and performance is also needed. The lowcost of electrochemical water treatment provides an economic basis for its application. This primary investigation demonstrated the electrochemical method has the potential for the inhibition of irrigation fouling.