Emitter and filter tests for wastewater reuse by drip irrigation

Agriculture is the main user of water in Italy, as in most regions of the world. Particularly in Mediterranean regions, where it is more difficult to meet the agricultural water demand with conventional resources, wastewater reuse represents a viable option. Drip irrigation is particularly suitable for wastewater reuse because it minimises the health risks to farmers and product consumers due to contact with the wastewater. The performance of drip irrigation systems using wastewater 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 six kinds of filters (gravel media, disk and screen) and four types of drip emitters (vortex and labyrinth) using five kinds of municipal wastewater that have not undergone previous advanced treatment. The performance of the emitters and filters tested depends on the quality of the wastewater: total suspended solids and organic matter content influence the percentage of totally clogged emitters, the mean discharge emitted, the emission uniformity coefficient, and the operating time of the filter between cleaning operations. Vortex emitters were more sensitive to clogging than labyrinth emitters. The gravel media filter guaranteed the best performance, but the disk filter, which is cheaper and simpler to manage, assured performance similar to that of the gavel media filter. The test showed the importance of the technology used in manufacturing disk filters. Screen filters were shown to be unsuitable for use with wastewater, with the exception of diluted and settled wastewater. The theoretical discharge of filters, suggested by the manufacturers for clean water, is not adequate for wastewater of the kind used in the trials (suspended solids greater than 78 mg/l and BOD5 more than 25 mg/l of O2). The operating times of the filters between cleaning operations, less than 1 h in most trials, suggest the use of automatic cleaning systems. The existing clogging risk classifications proposed for clean water can only be considered reliable for wastewater when labyrinth emitters and gravel or good quality disk filters (such as Arkal) are used; they are not adequate for vortex emitters or screen filters.