Hydraulic performance of drip irrigation subunits using WWTP effluents

The hydraulic performance of three drip irrigation subunits using effluents from a WWTP (Waste Water Treatment Plant) was studied. Each subunit had four laterals, 40 m in length with 1.9 l/h drip emitters spaced at 0.3 m intervals. Two subunits, one with a 130 μm disk filter and the other with a 130 μm screen filter, were supplied with secondary effluent from an activated sludge treatment. The third subunit, which had a 130 μm screen filter, was supplied with the effluent that had undergone tertiary treatment based on filtration with sand cells and disinfection by ultraviolet light and chlorination. All the subunits operated intermittently for a total of 750 h–10 h per day, 5 days per week. Water was analyzed periodically at the points of entry and exit of each filter, and at the location of the first and last emitters of a lateral. The emission and pressure uniformity and the variation coefficients were determined every 50 h. The laterals and emitters were cut open and analyzed with microscopic techniques once the field experiment was finished. The action of the filters and emitters did not result in significant changes in the water composition. However, with secondary effluent, uniformity in the subunit diminished considerably, because the emitters became clogged. The main causes observed regarding the clogging of the emitters were biological. The subunit with secondary effluent and a disk filter showed the worst values of uniformity. In contrast, uniformity was stable throughout the trials with tertiary effluent.