Cleaning and decontamination challenges in modern sprayers

The necessary optimization of resources available in agricultural production has led the sector to adopt more economical and more efficient technologies in controlling damage agents. Among them, new ways of using agrochemicals and the equipment that applies them.

The adoption of these technologies aimed at controlling weeds in crops resistant to certain herbicides provided versatility, savings and efficiency in post-emergence management. It also motivated the diversification of herbicide options applied post-emergence with selectivity, such as glyphosate, 2,4-D, dicamba and glufosinate.

With regard to sprayers, there has been a notable evolution in their size and level of sophistication, replacing part of the tractor-driven and small equipment with self-propelled ones with greater operational performance and automated control and recording systems.

Although the association of these advances has contributed to the evolution of the sector, it has also brought new concerns to users. Among them, the fact that the application of these herbicides should be carried out exclusively on resistant crops, even on properties with a diversity of species, hybrids and varieties. It also showed that the use of highly complex hydraulic circuit machines would make cleaning or decontamination difficult.

Therefore, there are operational challenges that are still being studied and understood, and which will be addressed below from the perspective of recent experiences, which may guide actions to prevent cross-contamination from sprayers from harming the productive potential of crops or, even even discourage the use of chemical and mechanical resources necessary for the growth of Brazilian and global agribusiness.

Cleaning agents

Some products have the function of removing agrochemical residues from the hydraulic circuit, without promoting inactivation of the active ingredient. These products are characterized by the authors as cleaning agents.

Detergents represent the majority of this group and can help remove residues adsorbed in pores, surfaces, crusts, crystals and floccules. Some, however, have the disadvantage of producing foam due to their own characteristics and the turbulence of the liquid when washing, which does not affect the cleaning of equipment with a simple hydraulic circuit, but makes it difficult for those with a complex circuit.

Although this result has been frequently observed, the true reason has not yet been determined. It is believed that the foam, by occupying the interior of the restriction points (filters, anti-drip, nozzle holders, flow meters, valves, connections, etc.), reduces the occupation of water during rinses, favoring the permanence of residues in these spaces. 

It should also be considered that these products are generally cheaper and rarely cause corrosion problems in the components of the hydraulic circuit, meaning there are no restrictions regarding their use in different equipment. Furthermore, good products can be used effectively to clean machines used to apply various herbicides, without requiring specific products for each active ingredient.

The effectiveness of the product in cleaning can be proven by collecting the liquid resulting from rinsing the machine during its triple wash and spraying it on plants sensitive to the herbicides last used in the sprayer. If the plant shows signs of phytotoxicity, it will indicate that the sprayer cleaning was not effective and another product or cleaning method should be used. Although this method is effective, it requires time for the herbicide to take effect on the sensitive plant.

Decontaminants

These products have the function of inactivating the active ingredient molecules present in the sprayer's hydraulic circuit. They are also called inactivators and, although they do not have the function of removing residues from the equipment, they greatly minimize the risks of phytotoxicity in subsequent spraying. In general, decontaminants act more specifically on some active ingredients, therefore requiring prior tests on the agrochemical intended to be inactivated to confirm its action and the necessary concentration.

Among the products historically used are ammonia (which despite its inactivating effect, has restrictions on acquisition and chemically attacks copper components), hydrogen peroxide (which, due to its high oxidation potential, also inactivates a series of molecules, but can also attack metallic parts and lower density rubbers of the sprayer) and ozone (which acts in the same way as hydrogen peroxide, but depends on specific equipment for its generation and insertion into the solution).

Recently, some chemical products designed exclusively for spray decontamination have shown the ability to inactivate various herbicides, and can be applied for this purpose as long as there is information or experience about their quality and the concentration required to inactivate each herbicide.

Factors Affecting Cleanliness

The effectiveness in cleaning sprayers directly depends on the method and product used, in addition to the complexity of the hydraulic circuit, the number of restriction points through which the spray passes and the quality and porosity of components such as the tank, rubbers and hoses. These components can only be evaluated after disassembly and microscopic analysis of their internal surface, therefore depending on specialized instruments and personnel. The complexity of the circuit can be determined with simple observation.

Type of equipment

To better understand the complexity of hydraulic circuits, they will be divided into three groups: simple, combined and complex hydraulic circuits.

Less sophisticated equipment with few restriction points, such as knapsack sprayers, represents the first group. Kitchen detergents combined with simple procedures such as triple washing with water are sufficient to achieve good cleaning. Furthermore, as these are small-capacity equipment, the volume of residual liquid from triple washing does not represent a major problem in disposal. This residual liquid must be discarded in the agricultural area where the agrochemical was applied or in a management area. 

Tractorized sprayers, such as mounted and trailed sprayers, represent the group of combined hydraulic circuits well. They have some restriction points such as filters, anti-drip valves and possibly flow meters, which must be removed and cleaned separately to improve the process. Common cleaning products inserted in the first washing stage followed by two washes with water are sufficient to carry out a good cleaning.

The group of complex hydraulic circuits is the most difficult to ensure effective cleaning, regardless of the method or product used. The most sophisticated self-propelled sprayers represent this group. It is suggested, in this case, that at the end of the daily work shift, the sprayer is cleaned before the machine is stored or, at least, that it is filled with water to prevent residues from drying inside, making it easier to clean later. 

When considering that cleaning will be carried out at least in three stages (triple washing) and in the case of equipment with a high tank capacity, the residual volume will, in the same way, be quite high, requiring time and sufficient agricultural or management area for the due disposal.

Cleaning procedure

Step 1

For machines with polyethylene and stainless steel tanks, add half a tank of water. For machines with a fiberglass tank, fill the tank with water up to its nominal capacity. Add the cleaning agent at the recommended concentration to the tank and stir the liquid for 20 minutes throughout the hydraulic circuit. Turn on spraying until the tank contents are completely exhausted.

Step 2

Remove spray tips, nozzle filters, suction filters, line filters, boom segment drains (except for machines with circulating segment) and clean them separately. The syrup ballast must also be removed.

Step 3

Assemble the suction filters, line filters and spray tips. Do not install nozzle filters or bar segment drains (except for machines with circulating segments). 

For machines with polyethylene and stainless steel tanks, add half a water tank. For machines with a fiberglass tank, top up the tank to its nominal capacity. Turn on spraying until the tank contents are completely exhausted. 

Note that the absence of nozzle filters and bar segment drains will cause the liquid to drain quickly through the bars, which will facilitate the removal of solid waste from the circuit.

Step 4

Assemble the entire circuit and wash once again with water, for machines with polyethylene and stainless steel tanks, add half a tank of water and for machines with fiberglass tanks, top up the tank to its nominal capacity.

Final considerations

Although there are recommended procedures and products for satisfactory cleaning, knowledge of the difficulties and limitations of each equipment and the adoption of specific measures for these cases can be more efficient than general measures. It must also be considered that the market will continue to offer new agrochemicals, which will have greater risks of sprayer contamination than current products, added to the fact that the complexity of sprayer hydraulic circuits will continue to increase, requiring the user to take special care not only in its calibration, configuration and operation, but also in the form of cleaning.

This new reality will require greater attention from mechanical engineering in the design of hydraulic circuits, roughness, durability and porosity of materials. It will also challenge chemical engineering in the development of cleaning or decontaminating agents that eliminate the risk of injury due to contamination in equipment in an economical and rapid way.  

*Per Ulisses Delvaz Gandolfo, from the Dashen Institute, and Marco Antonio Gandolfo, from Uenp Campus Luiz Meneghel