It is the most efficient and economical solution to treat wastewater containing biodegradable compounds. This plant is based on the use of bacteria and microorganisms, which can destroy organic and polluting matter if they are kept under specific environmental conditions. CO2, water, mineral salts and inorganic compounds are the final products of the metabolism of organic matter that also produces the growth and development of activated biomass.


In addition to a biological plant, they include a series of advanced treatments that permit to remove specific organic or inorganic pollutants, in order to reuse part of the effluent in other industrial processes (the recycling effluent is used as “process water of process”).


They are plants that do not include any liquid discharge, related neither to service water nor to process one. The ZLD is the result of a total recycling of the water discharged from the industrial process, in conjunction with a total reuse of treated water and a partial recycling of some chemical components contained in it. The final residue is composed of the crystals of dissolved salts and a part of the organic and not biodegradable components.


They are plants designed for the primary water treatment. They include simple solutions such as water softening, iron removal, de-chlorination, etc. and more advanced solutions such as demineralization, production of ultra-pure water and water with very low conductivity.


Europrogetti S.r.l. is a company that, for more than 30 years, offers to customers its expertise in the design, installation and management of plants for treatment, purification and reuse of civil and industrial water sewage. We can offer solutions which allow the recycling of more than 90% of treated water and we also guarantee the lowest running costs thanks to the implementation of the most efficient and advanced technologies in the field.

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When the climatic conditions are not suitable (high humidity, low temperature) or it is necessary to reach the solution’s saturation, the only possible solution is the traditional evaporation system, such as the Multiply Effect Evaporator (MEE), also if the management costs (€/m3 of water evaporated) are 4 - 6 times higher than forced air evaporators.

mee1In the case of MEE, the evaporation of a solution is carried out by boiling in some evaporator units with gradually decreasing pressures and connected each other, so that the steam developed in one of them is the heating fluid of the next unit.
The circulation of liquids from one unit to another one can take place in the same direction of the circulation of steam (co-current) or in opposite directions (counter current). The choice of feeding method depends on several factors: in case of evaporation in co-current, the maximum concentration of the solution is reached in correspondence of the lower temperature (and this is advantageous in case of heat-sensitive solutes). Instead, if we work in countercurrent, the maximum concentration is obtained at higher temperatures (and this allows limiting the increase of viscosity of the concentrated solution, benefiting the heat transfer.
The optimal number of evaporators in series (effects, n) to be used in a plant of this type results from an economic balance between the cost due to consumption of energy (which decreases if n increases) and the investment cost (which increases if n increases).

Compared to the air forced evaporators, the MEE allows recovering part of the evaporated water by condensation and obtaining a saturated solution (mother liquor), easily crystallizable through next steps of cooling and heating, in order to form a solid composed of atoms neatly disposed.

mee2To accelerate and manage the formation of salt’s crystals contained in the mother water, one of the most efficient system is the Chiller.
This technology, if used correctly, allows the recovery of sodium sulphate (Glauber Salt) for subsequent uses in the phases of dyeing. Given the high cost of Na2SO4, its recycling can cover up to 90% of management costs of MEE.

This technology is used as an integral part of the treatment process in a Zero Liquid Discharge Plant.


Generally, in the treatment of wastewater, the evaporation is used to increase the concentration of a solution, separating a part of the water in the form of water steam, or to reduce the solute in the crystalline form.
The technologies normally used are all quite expensive, both from the point of view of energy consumption and investment costs. Therefore, when it needs this type of system, it is desirable to minimize the quantity of effluent to be treated, supplying it with previously concentrated solutions.

evaporazione1A method certainly cheaper is the forced air evaporation, which simply accelerates the natural evaporation. This phenomenon, that is the passage of a body from the liquid to the gaseous state, with a consequent decrease of the liquid itself, involves only the surface of the liquid and occurs at any temperature. However, it is more enhanced under the following conditions
a)    a) Low humidity;
b)    b) High air speed;
c)    c) High temperature.

Thanks to its internal energy (enthalpy), the air mass maintains in balance the dry bulb temperature with the wet bulb, through water evaporation, thus increasing the relative humidity and reducing the dry-bulb temperature.
The dry bulb temperature is the one measured by a common bulb thermometer, while the temperature of the wet bulb is that obtained with the bulb of the thermometer wrapped in a damp cloth. In case the air is not saturated, the dry bulb temperature is higher than the one measured with wet bulb. This means that, for a certain value of enthalpy (kcal or kJ per cubic meter of air), if the air is not yet steam saturated and there is the presence of liquid water, the air tends to absorb water to approach equilibrium conditions.

In order to accelerate the natural phenomenon, some special panels in HDPE with strongly alveolar structure are used, in the way to increase the surface of evaporation, resulting in approximately 120 m2 of surface evaporation in 1 m3 of volume. In this way, you are working with a film of water of the order of about 4 to 5 microns and a ? potential tending to zero, exponentially increasing the evaporative effect.
To further implement this phenomenon, fans artificially produce a forced ventilation.
The number of evaporative modules are calculated according to the quantity of water to be concentrated and the climatic conditions of the place. The sizing considers that, with a relative humidity of 40-45% and a temperature of about 30°C, each module is able to evaporate approximately 6-7 m3 per day, with energy costs comprised between 15 and 17 kWh/m3 of water to be evaporated.

In addition to being an economic solution, the system does not produce spray emissions of pollutants or gas (only air and moisture) and is practically free from any kind of maintenance, since the particular composition of the polyethylene net prevents the permanent adhesion of concentrated molecules, avoiding possible clogging phenomena.
A further advantage of using this technology comes from the reduction of CO2 emissions (benefits in terms of "carbon credits"). In fact, the production of CO2, using our air forced evaporators, is approximately 14.5 kg of CO2 for 1 m3 of evaporated water, against the 168/205 kg produced by the traditional systems of evaporation steam, i.e. approximately 12/18 times lower.

This technology is used as an integral part of the treatment process in a Zero Liquid Discharge Plant.

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