Chemical Clogging Behavior in Drip Irrigation Systems Using Reclaimed Water

Abstract

Abstract. Reusing reclaimed water in agricultural irrigation has become an effective way to alleviate water shortages in agriculture. However, the multiple substances in reclaimed water and their coupling effects easily lead to emitter clogging when using drip irrigation technology. The microorganisms present in reclaimed effluents secrete extracellular substances and absorb large amounts of solid particles, ions, nutrients, and organic matter and thus become the main part of the clogging substance. Meanwhile, traditional drip irrigation systems converted from irrigation to both irrigation and fertilization and the water-fertilizer coupling effects result in more chemical precipitation. Determining whether the chemical process has a significant impact on clogging and understanding the mechanism of this process was considered a difficult and important research question. For this reason, an indoor experiment, under a controllable environment, for drip irrigation emitter clogging using both reclaimed water with three Ca2++Mg2+ concentrations and groundwater was carried out. Several precise testing methods, such as x-ray diffraction, were applied to identify the mineral components in the clogging substances, and their characteristics and impacts on clogging were systematically explored. The results indicated that the emitter clogging characteristics were coincident under different treatments when using reclaimed water, and chemical precipitates were found in all treatments. Higher Ca2++Mg2+ concentrations led to more serious emitter clogging. The discharge ratio variation and Christiansen coefficient of uniformity for the reclaimed water treatments were lower than those for the groundwater treatment. Meanwhile, the total weights of the clogging substances were 5.6% to 58.8% higher. There were sufficient mineral components in the clogging substances, and they were identified as quartz, silicate, carbonate, and salt. Their contents all showed significant linear correlations with the degree of emitter clogging (R2 > 0.64, p < 0.05), which indicated that mineral components increased as the system continued operation. Among them, salt and silicate were linearly correlated to quartz contents, as they mainly originated from the water used for drip irrigation. However, carbonate contents increased in an exponential pattern with quartz contents (R2 > 0.67, p < 0.01), which demonstrated that carbonate was the main mineral component formed during the clogging process and the key component that increased clogging. The results obtained in this study provided insights into the chemical clogging process and the targeted chemical precipitates to be dealt with when using reclaimed water for drip irrigation. Keywords: Chemical precipitation, Emitter, Microirrigation clogging, Reclaimed water application.