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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 583-592 in On-Site Wastewater Treatment, Proc. Ninth Natl. Symp. on Individual and Small Community Sewage Systems (11-14 March 2001, Fort Worth, Texas, USA), ed. K. Mancl., St. Joseph, Mich. ASAE  701P0009.(doi:10.13031/2013.6065)
Authors:   S.J. Berkowitz
Keywords:   Drip irrigation, Wastewater, Subsurface distribution, Hydraulic characteristics

Subsurface drip is a wastewater management technology which optimally makes use of the shallow soil environment, allowing for effective utilization of the landscape for handling small to large wastewater inputs. This system allows for both the assimilation of wastewater and nutrient attenuation. Critical to long-term operational success is the continuing effective hydraulic performance of the drip tubing. Effluent flow rate from all emitters must remain near design values for the life of the system. Constituents of the effluent or surrounding soil must not clog the emitters, and the tubing interior must not become blocked. This is typically addressed through emitter design, use of chemicals impregnated into the emitters and/or tubing, air venting, and by prescreening delivered effluent and routine flushing of the distribution network. A field assessment is presented of long-term hydraulic performance of drip tubing at five large subsurface wastewater systems operating in North Carolina six or more years. Field measurements collected periodically since system start-up include irrigation flow rates, flushing flow rates and flushing head losses. The computer program DRIPNET, previously developed by the author, is used to compare field measurements with design predictions to evaluate factors that have changed over time. The relationship of pretreatment method (septic tank-vs-sand filter), flushing regime and other design factors to hydraulic performance is presented. Long-term hydraulic performance of the systems was generally found to be excellent. Emitter clogging was observed at only two of the five sites, with the maximum reduction in emitter flow rate at any site measured to be 23 %. Optimal hydraulic performance was found to be associated with minimum initial flushing velocities in excess of 0.91 m/s (3 ft/s) with septic tank effluent and 0.46 m/s (1.5 ft/s) with sand filter effluent.

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