Laboratory experiment on drip emitter clogging with fresh water and treated sewage effluent

A laboratory experiment was carried out to study the emitter performance of three commonly used emitter types with the application of freshwater and treated sewage effluent (TSE). The three emitter types are the inline-labyrinth types of emitters with a turbulent flow (E1) and a laminar flow (E2) and the online pressure-compensation type of emitters (E3). The qualities of freshwater and TSE were measured, and the emitter performance was evaluated, using the relative emitter discharge, the reduction of emitter discharge (q_reduction), the coefficient of variation of emitter discharge (CV), the emission uniformity (EU), Christiansen uniformity coefficient (CU), and the percentage of emitter clogging (P_clog). Results showed that all indices were affected by water quality, emitter type and time of operation. The values of q_reduction, CV and P_clog for the TSE treatments were greater than those for the freshwater treatments. The values of EU and CU for the TSE treatment were lower than those for the freshwater treatments. The q_reduction, CV and P_clog increased and the EU and CU decreased as operational time increasing for the TSE treatment. For both freshwater and TSE treatments, the emitter clogging was more severe, the CV was greater, and the EU and CU were smaller for emitter type E2 than those for emitter types E1 and E3. Thus a more severe clogging was found for emitter type E2 due to its smaller flow-path dimension and higher manufacturing coefficient of variation in addition to the high pH values and relatively high total dissolved solids (TDS) values of the used water. Analyses of water quality and the precipitation components inside and at the outlet of emitters revealed that chemical precipitation was the main reason for emitter clogging due to high pH and ions’ concentration, especially in the TSE. Flushing emitters and drip pipes did not efficiently alleviate emitter clogging caused by chemical precipitation. In a conclusion, emitter type E3 showed a better anti-clogging function than emitter types E1 and E2 and was recommended for irrigation with TSE in the Beijing area of China.