Physical-chemical wastewater treatment plants

At Condorchem Envitech, we design and install state-of-the-art plants for the physicochemical treatment of wastewater that are tailored to the specific needs and objectives of each client, taking into consideration parameters such as the volume and composition of the wastewater to be treated.

We have extensive experience in wastewater characterization, allowing us to guarantee the highest quality standards in the design, manufacturing, installation, commissioning, and operation monitoring of various physicochemical processes for treating wastewater generated in industrial processes.

Depending on the production of effluents, the most appropriate option may vary from a compact purifier prepared to work intermittently, a continuous treatment plant or a purifier that works sequentially (SBR).

Physical-chemical plants are designed for treating effluents that contain one or several of the following pollutants:

• Suspended solids.
• Heavy metals.
• Oils and fats.
• Color.
• Recalcitrant organic compounds.
• Toxic compounds (hexavalent chromium, cyanides, pesticides, etc.).
• High concentration of salts (brines).

The companies that generally produce effluents with these pollutants usually belong to the chemical, pharmaceutical, cosmetic, textile, food (abattoirs, dairies, canning, wineries, pickling), metallurgical, plastic and leather industries, among others.

The processes that must be implemented in the physical-chemical purifier to eliminate the pollutants will vary according to these and they shall be some of those that are described below:

Floatation: Floatation is used to separate all the substances that are less dense than water; this is true of oils and fats. Depending on the concentrations of oils and fats and on the available space, it may be necessary to add through the bottom of the system an airflow. This accelerates the ascent of the drops of oil and fat particles to the surface.

Decantation: Decantation or sedimentation makes it possible for the particles that are suspended in the water to be deposited on the bottom of the container thanks to the difference in densities. Sometimes this process is used in isolation, for example to separate suspended solids that are already present in the effluent, but it is generally used as the second stage of a precipitation or coagulation-flocculation process, in which it is desirable to separate the particles whose formation was forced in the first stage.

Precipitation: Precipitation transforms the pollutants, which are soluble, into other, insoluble substances which precipitate. Often, the chemical reaction that makes it possible to form an insoluble compound, also manages to change the nature of the pollutant, reducing its toxicity. This process may be used to eliminate from the effluent pollutants such as hexavalent chromium and other heavy metals, cyanides, etc.

Coagulation-flocculation: If the effluent has colloidal pollutants, a coagulation-flocculation process will be necessary. These particles (of a size between 0.001 and 1 mm) are highly stable in suspension and it is impossible to separate them by floating, decantation or filtration. The cause of this stability is that the colloids has surface electrostatic charges of the same sign, a fact that cause the appearance of repellent forces between them, which impedes their agglomeration to deposit.

Coagulation consists of the destabilisation of the colloids when neutralising their electrostatic charges, forming a floccule. This is achieved by adding an electrolyte (coagulant) to the water.

Flocculation consists of causing the floccules that have already formed to join together to acquire sufficient critical mass for them to decant in a reasonable time. To do so, a chemical agent, the flocculent, is dosed, which helps to bring together the individual floccules by forming agglomerates of greater size and weight.

Neutralisation: Neutralisation consists of adjusting the pH of the effluent. Though it may be an independent process, it is usually accompanied by a precipitation process. Many pollutants are soluble at acid or alkaline pH and a neutral pH change form and their solubility is notable reduced.

Adsorption: Adsorption makes it possible for the pollutant molecules to adhere superficially and reversibly to the adsorbent particles. The absorbent is a porous material that has a large specific surface. The commonly used adsorbent is active coal, though there are others that are also very effective such as the zeolites, etc. Normally, on increasing the temperature the pollutant is desorbed, having the regenerated adsorbent to be able to be reused.  This process may be used to eliminate pollutants from the effluent such as the colour, halogenated organic compounds, heavy metals, etc.

Filtration: Filtration makes it possible to separate macroscopic particles from the effluent. It may be done by gravity (gravel, sand or active coal filters) or under pressure (press filters). The most suitable option will vary depending on the effluent flows to be treated and on the particles to be separated.

Electrocoagulation: Electrocoagulation consists of destabilising colloids, but rather than being due to the addition of a coagulating agent, it is caused by the action of a low-voltage direct electrical current and by the action of sacrificial metallic electrodes, normally aluminium/iron. The electrocoagulation treatment cost is extremely low, including electricity consumption, electrodes replacement, labour, etc.

Advanced oxidation: Advanced oxidation chemical process uses oxidative reagents to eliminate the pollutants. These reagents are usually ozone, hydrogen peroxide, hypochlorite, Fenton reagent, ultraviolet radiation and ozone, and ultraviolet radiation and hydrogen peroxide, among others. Some or others of these will be used depending on the characteristics of the effluent.

Advanced oxidation processes are suitable when the pollutants of the effluent are recalcitrant organic compounds, toxic compounds or colour, among others.