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Wastewater Recovery Process – Drying Plant

Eng. Guillermo Bossio
Sustainability; Environment
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Strategic decision: Plant location

Argenti Lemon’s Drying Plant is located in Leales, Tucumán, Argentina, 55 km from the industrial plant. Why is the distance relevant? It’s worth analyzing to understand.
In general, lemon processing industries have a scheme with the following chained processes:

  • Fresh fruit sorting and packing for export.
  • Industrialization to obtain essential oil, lemon juice and lemon dehydrated peel .

During the process of peel dehydration, solid waste and wastewater are generated with high levels of acidity. In some companies, this type of waste is used to generate gas using biodigesters.

In our case, it was determined that from the wastewater generated during the process, vegetable water would be used for irrigation and soil improvement on sugar cane farms, replacing part of the well water normally used for this purpose. With this objective in mind, in 2015 Argenti Lemon defined that the Drying Plant would be located on a sugar cane farm owned by the company, and distant from the Industry Plant.

Lemon Dehydrated Peel

The process of lemon dehydrated peel has 3 stages: washing, pressing, and drying.

First stage: Washing – Counter-current system

Coming from the industrial plant, the moist peel is received in tipper trucks, and it is discharged into a 60-ton hopper.
Moist peel is removed from the hopper by means of screw piles and then carried to a blade mill.
Once it passes through the mill, the peel is taken to a drain, and pumped into a reactor where the first washing takes place. Then, it overflows and falls into a static Johnson sieve N°1
In this sieve, water is filtered and sent to the waste drain while the peel is pumped into a vertical washing tank N° 1. In its upper part, this tank overflows onto sieve N°2, where once more, the peel is separated from water and sent to the mill drain.
The peel obtained from sieve N° 2 is moistened with clean water and is introduced into the washing tank N°2; its overflow is connected to sieve N° 3. At this point, the peel and the water are separated again and this latter is sent to sieve N° 1 drain.

 

Second stage: Pressing

First pressing:
Peel collected from sieve N° 3 is placed in a screw pile
that feeds the first line of the pressing process. This process is made by a
screw press, extracting the remaining water in the peel after the washing stage.

Second pressing:
Peel obtained from the primary pressing output is collected by another screw pile, thus feeding the secondary press. In this case, bed dryers are used for the same purpose as the first press: reducing peel moisture.

Water obtained from first and second press, added to the washing line water, constitute the wastewater generated in the plant; this effluent is pumped into some filters for treatment, separating solid from liquid waste.


Third stage: Drying

Drying must be progressive to avoid the peel getting any burnt particles. That is why this stage requests a pre-drying and a final-drying.

Pre-drying:
Moist peel released from the second press is collected by screw piles feeding the pre-dryers. These are one-stage rotary heaters drying peel with hot air.

Final drying:
The peel obtained from the pre-dryers is introduced into a heating drum with the same drying principle, though this stage is three-folded.

How can we recover 100% of wastewater in the drying peel plant?

According to this process, either the washing or the pressing stages generate wastewater. The plant has only one current of industrial waste coming from the washing peel circuits (raw material) and facilities in general. This current is pre-treated to separate the solid material in suspension by means of filters. The solid material, once sorted out, is used for soil improvement, or cattle food; and the vegetable water is disposed for irrigation.

After being filtered, vegetable water is sent to the irrigation system comprising 4 storage tanks distributed on a sugar cane farm located around the drying plant. Total storage capacity is about 1,760 m3; every tank has
a pumping room; all of them are interconnected by means of an aqueduct.

The aqueduct is extended with a piping system of 25 km. On this piping system, there are 200 sprinklers placed for irrigation, connected to 4 rolapi tubes with a capacity of 80m3/hour. They are arranged on the aqueduct in released areas, after
the sugar cane harvest takes place.

The system is flexible enough and may irrigate with water recovered from the industrial process or clean water obtained from the existing wells at the same time in different pieces of land. During the harvest, this recovery system allows us to cover 1,350 hectares. The irrigation system uses clean water from the well when the drying plant is not working, since these crops need supplemental irrigation.

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