Adaptability of biogas slurry–water ratio and emitter types in biogas slurry drip irrigation system
Haitao Wang, Jiandong Wang, Chuanjuan Wang, Shuji Wang, Xuefeng Qiu, Guangyong Li
Abstract
Biogas slurry drip irrigation (BSDI) can not only save water, but also reduce the use of chemical fertilizers. Determining the appropriate biogas slurry–water ratio (BSWR) and emitter types can ensure long-term stable operation of systems. Therefore, this study proposes an obtaining the BSWR suitable for crop irrigation conductivity method based on conductivity biogas slurry and clean water. The three conductivity levels（1.3, 2.3 and 3.3 mS/cm）are set based on their suitability for crop growth. The corresponding BSWR is determined using the proposed method, i.e.,1:20, 1:8, and 1:4. The clogging dynamic process, clogging location, and characteristic parameters are analyzed using a hydraulic test, an industrial camera and the ordered regression method for three common emitters under three BSWR. The results show that the proposed method relative error is approximately 10%, which is considered feasible. Over time, the discharge and uniformity of emitters decrease, and subsequently remain constant. As the slurry concentration increases, the emitters clog more rapidly, and internal patch emitters (IPEs) show the lowest adaptability to BSDI systems. The pressure compensation (PCEs) and single-wing labyrinth emitters (SWLEs) is better than IPEs on anti-clogging performance. Clogging mainly occurs at the inlet grid, and the SWLEs are clogged at the internal flow channel and outlet. Moreover, the inlet grid and pressure compensation are key characteristic parameters affecting clogging. The adaptability of emitters can be improved by changing the inlet grid layout, increasing the cross-sectional area of the flow channel, and/or reducing the pathway length. Based on irrigation uniformity and economic cost, large discharge SWLEs and PCEs are recommended for one-time field crops and multi-year cash crops respectively. Furthermore, the BSWR should be at least 1:4, and ratios of 1:8–1:20 are most conducive to stable operation. This study serves as a guideline for future development of BSDI systems.