Technical Report No. 163
IMPROVED EMITTER AND NETWORK SYSTEM DESIGN FOR WASTEWATER REUSE IN DRIP IRRIGATION
Donald R. McDonald, L. Stephen Lau, I-Pai Wu, Henry K. Gee, Stephen C.H. Young
July 1984
ABSTRACT
The problem of emitter (orifice) plugging inherent in drip irrigation systems was investigated. Plugging not only reduces the effectiveness of this most water conservative method but also excludes the use of low quality waters unless first processed with costly water treatment. A problem-solution approach was used to develop simple emitters and a network system that would minimize plugging to acceptable levels. Tests using secondary treated municipal effluent from the Mililani Wastewater Treatment Plant on Oahu, Hawaii, consisted of numerous plugging experiments supplemented by theoretical and laboratory studies. Tests showed that plugging, up to 25% or less, can be controlled by using size emitters and passing the effluent through a stationary 40 and 80-mesh screen; critical-size emitters are 0.03 in. for microjets and 0.019 in. for monotubes; higher operating pressure further reduces plugging percentages; flexible 0.15 in. slit orifices (at 15 psi) perform as well as the critical size rigid orifice but another round flexible orifice (rubber tube) was less successful; a multiple-inlet network design with critical-size emitters can minimize pressure and emitter flow variations along the drip laterals and was ideal for systems with large flow rates; and plugging was attributed to particles and fibers in the effluent.