Using waste water for agricultural irrigation : challenges and solutions

Is irrigating crops using waste water a challenge for the future ? Irstea researchers have developed a new irrigation emitter, patented jointly with Phytorem. The aim : to prevent the emitter from clogging due to particles in the waste water or the development of biofilms. Let's take a closer look.

Faced with the growing demand for water resources for agricultural irrigation, reusing waste water is a good alternative. This water, also referred to as effluent, is generated by domestic, industrial, agricultural and similar uses. However, because it has been polluted, it usually needs to be treated before it can be reused. Using it for irrigation would ease the pressure on surface and groundwater resources. So even though this does offer a solution, it is also a challenge from a regulatory [1], health, environmental and technical standpoint.

At Irstea's Laboratory for Testing and Research on Irrigation Equipment (LERMI – GEAU JRU) [2], researchers are working on the sustainability and optimisation of equipment, including irrigation emitters for treated waste water. Laboratory manager Bruno Molle explains: "Generally for this type of network, the problem is accelerated ageing", caused by blockages arising from several sources:

  • The particles carried by and contained in the partially treated effluent can stagnate, sediment and become permanently trapped.
  • The development of biofilm [3] in the areas where the fluid velocity is lowest can strongly affect the flow, even to the point of clogging.
  • Finally, chemical reactions mainly due to the water's mineral content can occur, causing mineral salts to precipitate and creating deposits that can clog the system.

What is the scientific response to these 'bottlenecks' ? It can be summarised in just a few letters: DA-EU, which stands for Irrigation Emitter for Treated Waste Water.

From thesis to patent

The project began with a thesis [4] which led to the development of the first prototype. Subsequently, a device was developed whose purpose was to "evenly distribute over large farm plots waste water that was nutrient-rich but had a high particulate load, while avoiding any risk of clogging," says Molle.

DA-EU membrane © Bruno Molle / IrsteaThe device is based on controlling the internal flow across a wide pressure range, from 0.5 to 5 bars, the challenge being to distribute the water evenly. ; "For the moment we are running at around one hundred litres per hour, but hopefully we will be able to reduce this to thirty [5]." The secret ? Researchers have developed a resilient silicone membrane which can change its shape to either partially limit or increase the flow downstream, thus acting as a regulator.

The emitter can be used with minimally treated waste water and low toxicity effluent carrying no health risks or heavy metals. For example, this effluent is decanted or filtered through reed beds. They can then be spread on plots of bamboo or fast-growing wood. "The purification process is thus carried out by the soil (if the soil’s biological activity is capable of treating the pollution contained in the effluent), and the nutrients promote production (e.g. wood, fibre, flax, fodder etc." This process is similar to fertigation (fertilisation + irrigation).

The researchers plan to use this new irrigation emitter in a full-scale experiment (in collaboration with the Irstea centre at Lyon-Villeurbanne) scheduled for April 2014 : 4.5 hectares of fast-growing eucalyptus and poplar irrigated with effluent from septic tanks.

Meanwhile, the emitter has been tested in the field for 6 months with domestic waste water and the results were convincing. Patent applications have been filed in France [6] (co-ownership with Phytorem) and internationally with the PCT (Patent Cooperation Treaty).

3D Prototypes

The DA-EU device is at the pre-industrial prototype stage and will continue to be developed as part of the European W4C (Water for Crops [7]). Tests on resistance to fibre clogging and the development of biofilms are scheduled. "We are currently working with a company specialising in 3D printing of various aspects of the device such as membrane characteristics and resistance." This is an important milestone that will soon lead to the production of an industrial prototype. To be continued.

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[1] France has published its first specific regulation (decree of 2 August 2010) on using treated waste water for irrigation, which greatly restricts use and project development. Following the ANSES report published in 2012 and written by a group of experts (including Bruno Molle), this regulation is expected to be revised in 2014.

[2] Irstea team: Bruno Molle, Mathieu Audouard, Séverine Tomas and Jean Borgarino. Phytorem team: Frédéric Panfili and Marion Delanoay.

[3] Clusters of micro-organisms (bacteria, algae and fungi) that develop most frequently in water. Further information on our website.

[4] Thesis by Julien Deborde, presented at the end of 2011 and co-financed by Irstea, the Paca Region and the Phytorem.

[5] Equivalent to drip irrigation with a drip of 8 to 10 litres per hour.

[6] Patent PCT/FR2013/052056 and no. 12.58962 "Self-regulating drip irrigation emitter and its use" (Irstea, Phytorem)

[7] Water4Crops Project: Water Use Efficiency to Support the Green Economy in EU and India. Further information on the official website.