WO2009087259A1 - Method for the treatment of water originating from the washing of agricultural products - Google Patents

Abstract

The invention relates to a method for the treatment of water originating from the washing of agricultural products in fruit and vegetable processing industries, particularly for the treatment of water originating from olive-washing machines in mills, enabling the water to be reused following the effective removal of suspended matter and pesticide residues. The method is based on a clarification process comprising the addition of a coagulant in order to remove the suspended matter and the use of an adsorbent in order to remove the pesticide residues. Said method can be used to remove pesticides from water originating from machines used to wash agricultural products. Consequently, the invention can be used to obtain pesticide-free, clean, clear water which can be reused in the aforementioned washing process or discharged.

Description

 Procedure for the treatment of water from the washing of agricultural products

SECTOR OF THE TECHNIQUE

Wastewater treatment from the washing of agricultural products.

STATE OF THE TECHNIQUE

The main source of liquid waste generation in the fruit and vegetable processing industry is the process of washing them and the machinery and equipment of the production line. The discharge, without prior treatment, of liquid waste from the fruit and vegetable products processing industry can cause significant contamination of the receiving waters. Since the organic material constitutes the main pollutant, the problems of water pollution will be related mainly to the decomposition of said material, which can result in a decrease in water oxygen, fish death, biogas production and emission and formation of a floating material layer. Likewise, if the liquid discharges have a high concentration of solids, a layer of sediment may form at the bottom of the receiving waters, where anaerobic degradation can occur with the consequent formation of malodorous gases. To solve this problem, most of the industries carry out a wastewater treatment, consisting of the application of the following physical-chemical processes: coagulation, flocculation, sedimentation and / or filtration. An additional problem presented by these wash waters is the presence of pesticides and other agrochemical compounds from the cultivation of raw materials. These substances can reach un tolerated concentrations depending on the subsequent use that will be given to those waters, either their recirculation to the washing process or their discharge to receiving waters. The elimination of these agrochemical compounds is more complex and requires specific chemical treatments that allow their elimination. Despite the existence of this double problem, in the state of the art there are no known procedures that allow the joint elimination of suspended matter and agrochemical compounds, in particular pesticides, in wastewater from the fruit and / or vegetable processing industrial . In particular, to the olive processing industry, especially the one that aims to obtain olive oil, this fruit sometimes reaches the oil mills with residues of different pesticides, in addition to traces of soil (10-15% can be reached in soil weight accompanying harvested olives), branches, stones, leaves, etc. This occurs as a result of the application of pre-emergency herbicides in the months of October to November, before winter rains and prior to the annual germination of weeds. After harvesting, residues of different agrochemical compounds are detected in olives, including diuron, oxyfluorfen, simazine and terbutylazine herbicides, as well as the endosulfan insecticide and the product resulting from its degradation, endosulfan sulfate. This is due, as stated above, to the use of these compounds so close to the harvesting campaign, together with their persistence, which maximizes the risk of surface contamination of this fruit. To solve this problem, and thus avoid that these compounds can be incorporated into the oil from the milling of the olives, they are properly washed in the washing machines of the oil mills. Ideally, the wash water would have to be changed with a frequency such that the concentration of pesticides reached was tolerated, but in general these changes are not made as many times as necessary, because fundamentally to two reasons; first, the large amount of water needed (around 20,000 liters of water per wash cycle), in regions that typically have a great shortage of this water resource; and second, the need to frequently stop the production process to effect water change.

In this way, as more fruits and / or vegetables are washed, in particular more olives, there is a progressive contamination of this water, which causes a progressive decrease in washing efficiency, to the point that in certain Circumstances, olives show higher concentrations of pesticides after washing than at the beginning.

In practice, it has been observed that olives exempt from these compounds, for example from crops where the harvesting is carried out directly on the tree (the olive deposited in the soil is not collected), have become contaminated in the washing machine. Some methods have been described for the purification of waste water from the washing of olives in the oil mills, as well as the vegetation water (water contained in the olive) from the production of olive oil, but none of them treats the elimination of pesticide residues. All these procedures are focused on the optimization of pH, concentration of polyphenols and / or chemical oxygen demand (COD).

The present invention provides a solution to this double problem of the washing waters from the fruit and / or vegetable processing industry, allowing its integral treatment, so that the final effluent can be reused or discharged. EXPLANATION OF THE INVENTION Object of the invention

The present invention has as its object the development of a process for the treatment of washing waters of the fruit and vegetable processing industries, particularly for the treatment of water from olive washing machines in oil mills, thus allowing their subsequent reuse after effective disposal both of suspended materials and pesticide residues. The proposed method is based on a clarification process by adding a coagulating agent for the elimination of suspended matter, together with the use of an adsorbent for the elimination of pesticide residues. With this procedure, pesticides are eliminated from the water from the washing machines of agricultural products. Thus, the proposed invention makes it possible to obtain a transparent, clean and pesticide-free water, which can be recirculated to the same washing process or discharged.

Detailed description of the invention

The two stages necessary for the treatment of washing water from fruit and / or vegetable processing industries are described below. These two stages can be performed simultaneously or consecutively.

First stage: The washing water contaminated with suspended matter and agrochemical compounds, kept under stirring, is subjected to a coagulation / flocculation process by the addition under suitable conditions of a coagulating agent, preferably between 10 and 1000 mg of AI ₂ ( SO ₄ ) ₃ or FeCI ₃ per liter of water. The mixture is made by stirring slowly for a time between 10 seconds and 10 minutes, after which it is allowed to settle for 1 to 100 minutes. In that time the flocs can be easily separated, leaving the water transparent, free of suspended particles.

Second stage: An optimum amount of a suitable adsorbent material, such as activated carbon, diatomaceous earth, etc., is added to the water. Preferably, between 10 and 1000 mg of activated carbon sprayed per liter of initial wastewater are added, mixing slowly for a time ranging from 10 seconds to 10 minutes. Subsequently, it is allowed to settle for 1 to 100 minutes. The adsorbent effectively retains the residues of agrochemical compounds present, particularly pesticides, ultimately resulting in water that can be recirculated to the washing process or discharged abroad.

If the steps described above are performed successively, the liquid resulting from the first stage must be kept under stirring. When the sludge content of the wash water is very high, between the first and the second stage an optionally filtering phase can be inserted for the elimination of the flocs formed in the first stage. In this case, it would be possible to reuse the active carbon after the desorption of the pesticides.

If the stages are carried out simultaneously, adding the coagulant and the adsorbent at the same time, it is only necessary to perform a single sedimentation phase.

Preferred Embodiment

First stage: To the wash water from olive mill processing, subjected to mechanical agitation, 300 mg of FeCI ₃ per liter of water was added as coagulant. The mixture was stirred slowly for 1 minute and allowed to settle for 10 minutes, after which a clear water, free of suspended matter, was obtained by decantation. Second stage: Next, to the water resulting from the previous stage, maintained under mechanical agitation, 200 mg of activated carbon sprayed per liter of initial water was added as adsorbent, stirring again for 1 minute. The mixture was allowed to settle for 10 minutes. After this time, a water free of solids and pesticide residues was obtained by decantation. The analyzes of the treated water showed an efficient elimination of the herbicides diuron, terbutylazine and oxyfluorfen; and of the insecticide endosulfan and its degradation product endosulfan sulfate.

Claims

L- Procedure for the treatment of water for washing agricultural products characterized by comprising two stages, successive or simultaneous, one of them being coagulation / flocculation of suspended matter and the other adsorption of agrochemical compounds. 2. Method according to claim 1, characterized in that in the coagulation / flocculation stage a coagulating agent is added, preferably AI ₂ (SO ₄ ) ₃ or FeCI _3, stirring slowly for a time that varies between 10 seconds and 10 minutes and It is then allowed to settle for a time that varies between 1 and 100 minutes. 3. Method according to claim 2, which uses between 10 and 1000 mg of AI ₂ (SO ₄ ) ₃ or FeCI ₃ per liter of water. A - Procedure according to claims 2 or 3, characterized by the addition of 300 mg of FeCI ₃ per liter of water, stirring slowly for 1 minute and allowing to settle for 10 minutes. 5. Method according to claim 1, characterized in that the adsorption step comprises the addition of an adsorbent agent, preferably between 10 and 1000 mg of activated carbon sprayed per liter of water, mixing slowly for a time between 10 seconds and 10 minutes and leaving sediment for a time between 1 and 100 minutes. 6. Method according to claim 5, characterized by the addition of 200 mg of activated carbon sprayed per liter of water, stirring slowly for 1 minute and allowing to settle for 10 minutes. 7. Method according to any of the preceding claims, characterized in that the coagulation / flocculation and adsorption steps are carried out simultaneously, adding the coagulating agent and the adsorbent agent thereto. time, being necessary a single phase of sedimentation during a time between 1 and 100 minutes. 8. Method according to claims 1 or 2, characterized in that after the coagulation / flocculation stage a filtering phase is carried out for the elimination of the formed flocs. 9. Method according to any of the preceding claims in which the water subjected to treatment comes from the washing of olives and / or the production of olive oil in oil mills.