Effects of nano-copper oxide fertilizer concentration on emitter clogging in reclaimed water drip irrigation systems

The use of reclaimed water in drip irrigation has become an important approach for alleviating freshwater scarcity and improving irrigation sustainability, particularly in arid and semi-arid regions. However, emitter clogging remains a major constraint on the wider adoption of this technology. Nano-copper oxide fertilizer may help mitigate emitter clogging while simultaneously supplying Cu as an essential micronutrient for crop growth. Nevertheless, the optimal concentration of nano-copper oxide fertilizer for this purpose remains unclear. This study evaluated the effects of five nano-copper oxide fertilizer concentrations (0, 0.5, 1.0, 1.5, and 2.0 mg/L) on emitter clogging in reclaimed water drip irrigation systems over a 630 h operating period. The results showed that nano-copper oxide fertilizer mitigated emitter clogging at all tested concentrations, although the extent of mitigation was strongly concentration-dependent. Low to moderate concentrations (0.5–1.0 mg/L) showed better overall anti-clogging performance, with 1.0 mg/L being the most effective treatment. This concentration effectively reduced biological deposits and chemical precipitates while maintaining particulate deposits at a relatively low level. By contrast, although higher concentrations (1.5–2.0 mg/L) further reduced biological deposits and precipitation-related deposits, they also enhanced particle aggregation and deposition, which progressively weakened the net anti-clogging effect. These findings provide new mechanistic insight by demonstrating that the effect of nano-copper oxide fertilizer on emitter clogging is not unidirectional, but is governed by a novel concentration-dependent balance among biological deposits, chemical precipitates, and particulate deposits. Under the tested reclaimed water quality and experimental conditions, 1.0 mg/L was identified as the most effective concentration, achieving the best balance among biological, chemical, and particulate fouling. This study provides practical guidance for the concentration-optimized use of nano-copper oxide fertilizer and supports the safe and efficient application of reclaimed water in drip irrigation.