Wastewater reuse by drip irrigation

Agriculture is the main user of water in Italy, as in most regions of the world. Particularly in southern regions, where it is more difficult to meet the agricultural water demand with conventional resources, wastewater (WW) reuse represents a viable option. In northern and central regions, where conventional resources are usually sufficient, WW reuse plays an important role in controlling surface water pollution. Drip irrigation is particularly suitable for WW reuse because it minimises the health risks to farmers and product consumers due to contact with the WW. The performance of drip irrigation systems using WW is mainly limited by emitter clogging, and this discourages farmers from introducing it. The paper gives the results of experimental trials on the behaviour of the three kinds of filter (screen, gravel and disk) most commonly used in irrigation systems around the world and two commercial types of drip emitters (vortex and labyrinth) using dilute and non-dilute municipal WW. The results substantially confirm the possibility of using WW in drip irrigation, even if the quality of the effluent is very poor. The performance of the emitters and filters tested depends on the quality of the WW. With non-dilute raw WW drip irrigation is possible using labyrinth emitters protected by gravel filtration only. With dilute WW both vortex and labyrinth emitters assure good performance. The operating time of the filters also depends on WW quality: cleaning is required more than once a day using non-dilute WW and once a day for dilute WW.