Management of emitter clogging with municipal wastewater

Drip systems, mainly if buried in soil, are suitable for wastewater reuse because they minimise the health risks to farmers and product consumers. Drip irrigation is, however, limited by emitter clogging. Clogging and mitigation procedures are closely related to the quality of the water used. Field tests using wastewater showed that suspended solids and organic matter content can cause emitter clogging, discouraging wastewater reuse in drip systems, mainly in Southern areas where advanced wastewater treatment is not used. The paper discusses some drip irrigation system management problems according to the performance of emitters and filters shown in trials conducted in Sicily (Italy) using six kinds of municipal wastewater that has not undergone previous advanced treatment. Nine kinds of filters (gravel media, disk and screen) and five types of drip emitters (vortex, labyrinth and long-path) were tested. The performance of the emitters and filters tested depends on the quality of the wastewater: pH and total suspended solids, organic matter, calcium and magnesium content influence the percentage of totally clogged emitters, the emission uniformity coefficient, the reduction in mean discharge, and the operating time of the filters between cleaning operations. Total suspended solids and pH are the water characteristics best correlated to emitter and filter performance. Vortex emitters were more sensitive to clogging than labyrinth emitters. To obtain acceptable performance, it is necessary to remove any particles larger than almost one-quarter the diameter of the flow passages of the long-path and labyrinth-type emitters, using disk filters. The optimal performance of emitters buried in soil shows the feasibility of drip sub-irrigation, which reduces health risks related to wastewater reuse. The gravel media filter guaranteed the best performance, but the disk filter, which is cheaper and more simple to manage, assured performance similar to that of the gravel media filter. Screen filters were shown to be unsuitable for use with wastewater. The short operating times of most filters cause management problems. An empirical equation is proposed to estimate the frequency of cleaning operations depending on the solid discharge (calculated as the product between TSS and water discharge).