Characterization of wastewater subsurface drip emitters and design approaches concerning system application uniformity
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Subsurface drip distribution is an important on-site wastewater treatment technique which is widely used with various soil types and restricted site conditions. It can distribute pretreated wastewater uniformly into soil. Some recent field applications showed low application uniformities, which was reflected in overloading of the field near the supply manifold while low emitter discharge rates occurred at the end of lateral. Designers are seeking appropriate operation pressures and drip zone configurations to improve system application uniformity. This research was conducted to test some popular wastewater drip products in both lab and field-scale experiments. The first goal of this study was to evaluate the performance of five subsurface drip products under eight operational pressures ranging from 0 to 310 kPa (45 psi). After evaluation of each group of 60 emitters, results showed that Netafim Bioline pressure compensating (PC) emitters exhibited a uniformity coefficient (UC) of 95% with a coefficient of variance (Cv) of 4.9%. The average UC of Geoflow Wasteflow products is 94.4% and Cv value is 6.8%. Flow rate and pressure relationships (Q-H curves) were developed for each drip emitter tested. By analyzing low and normal operational pressure ranges, Q-H curves were fitted to the data and resulted in R2 values ranging from 1.000 to 0.414. Geoflow pressure compensating products possess the features of non-pressure compensating emitters under low pressure head. Netafim PC products are characterized as pressure compensating over the full range of operational pressures and emit water with nominal uniformity during low pressure range. To evaluate drip zone configurations with respect to distribution uniformity, a field-scale experiment was set up and three drip tubing products were tested in different dosing and operation schemes. Three factors of wastewater drip system design were tested. System operation pressure (138 kPa/20 psi and 276 kPa/40 psi); different pressure control components (pressure regulator/recirculation valve) and schemes (continuous flushing/intermittent flushing); and supply line length (7.6 m/25 ft, 15.2 m/50 ft, and 30.4 m/100 ft) were evaluated to compare their influence on water application uniformity. It was concluded that, for Geoflow PC and NPC products, among all three factors, system operational pressure has the greatest effect on drip system application uniformity; supply line length has the least influence. For Netafim PC tubing, pressure control scheme has the greatest effect on drip system application uniformity; supply line length has the least influence. The optimal combination of the three factors could save more than 10 minutes of dosing time to meet the required dosing application uniformity. An engineering computation example on system fill time was presented and compared to experimental results to demonstrate the possible gap between typical design processes and real field application.
Duan, Xiaojing (2006). Characterization of wastewater subsurface drip emitters and design approaches concerning system application uniformity. Master's thesis, Texas A&M University. Available electronically from