Wastewater valorization and resources recovery

Often, the waste generated in industrial activities is considered a problem to be dealt with at the end of the production process. However, what is considered waste in one process can be used as a resource in another. The implementation of a waste treatment and valorization plant offers numerous advantages, both environmental and economic, including:

• Reduction of costs associated with the management of final waste.
• Lower environmental impact resulting from industrial activity.
• More responsible use of natural resources.
• Reduced investment in raw materials.
• Income from the sale of valorized by-products.
• Avoidance of fines resulting from non-compliance with environmental laws.
• Improved public image of the company.

Waste valorization involves a set of processes that involve the utilization and transformation of materials considered as waste or garbage into raw materials, by-products, energy, or other resources. The primary goal of waste valorization is to reduce the amount of waste sent to landfills or incinerators, thus minimizing environmental impact and promoting a more sustainable approach to waste management.

There are several forms of waste valorization, including:

• Recycling: Involves collecting, processing, and transforming materials like paper, cardboard, glass, plastic, and metals into new products, reducing the need to extract and produce virgin raw materials.
• Composting: Involves breaking down organic matter, such as food scraps and plant waste, in a controlled environment to produce compost, a natural soil enricher and fertilizer.
• Energy production: Some waste, like organic waste unsuitable for composting, can be used as an energy source through processes like anaerobic digestion to generate biogas or controlled incineration to produce electricity.
• Energy valorization: Involves converting waste into heat or electricity through controlled burning, which can be useful in disposing of non-recyclable or non-compostable waste.
• Reuse: Involves using products or components of waste in their original or slightly modified form to extend their lifespan and reduce the need to produce new items.
• Upcycling: Involves transforming waste into higher-value or higher-quality products, often involving a creative and artistic process.

The valorization of industrial wastewater aims to recover valuable resources from liquid effluents while minimizing environmental impact and reducing costs associated with waste management. There are various ways to valorize industrial effluent, including:

• Water reuse by reintegrating it into the production process or for other purposes.
• Recovery of chemicals for reuse within the industry or in other processes.
• Recovery of valuable salts, such as metal salts, nutrient salts, chemical salts, or saline water salts. Their reuse reduces the need to extract and process salts from natural sources.
• Separation of oils and fats that can be reused in the industry for the same purposes or transformed into secondary products like biodiesel or chemicals.
• Energy production, mainly through anaerobic digestion of wastewater, which generates biogas that can be used for heat and electricity generation.
• Production of high-quality organic fertilizers, provided the wastewater has a high nutrient content, such as nitrogen and phosphorus.
• Recovery of various metals, including high-value metals like gold, silver, or copper.
• Recovery of acids and other materials from different types of exhausted baths, such as degreasing and phosphodegreasing baths, anodic oxidation baths, pickling baths containing hydrochloric acid, zinc, and caustic soda, or baths with other acidic compounds. These baths can be treated for bath regeneration or material valorization.
• Recycling of organic solvents, including turpentine, acetone, ethanol, and ethyl acetate. While they can be valorized energetically due to their high calorific value, recycling is a more economically and environmentally efficient option.
• Utilization of residual heat generated in some industrial processes, which can be used to preheat water before entering treatment processes.

Vacuum evaporation offers high efficiency for material recovery and solution concentration in wastewater from various industries. In a vacuum evaporator, wastewater is heated to high temperatures under vacuum conditions to facilitate the evaporation of water and the concentration of solutes in the solution. As water evaporates, dissolved solids and other materials become more concentrated, facilitating their recovery and valorization.

Vacuum evaporation can achieve high levels of solute concentration in the solution, making it easier to recover and reuse valuable products in the industrial process or for commercial purposes. By concentrating wastewater components, the amount of water needing treatment or disposal is reduced, leading to significant savings and simplification of management and disposal.

On the other hand, vacuum crystallization allows efficient recovery of valuable salts present in wastewater, such as precious metal salts (e.g., gold, silver) or specific chemical salts used in industrial processes. These recovered salts can have significant economic value and can be reused within the industry or sold on the market.

Crystallization is a process that produces high-purity products, which is especially important in the chemical and pharmaceutical industries where impurities can be critical. In addition to valuable salts, crystallization can generate useful by-products such as purified water and secondary crystals that may have additional applications or value in the market.

There are various efficient technologies for valorizing wastewater, and the choice of one depends on the composition and volume of wastewater, available energy sources, valorization goals, and specific industry conditions. It is common for wastewater valorization plants to include multiple treatment stages with different technologies, with membrane technologies and evaporation typically found at the end of the process for effective recovery of valuable products.

In addition to evaporation and crystallization, here are some of the most efficient technologies for wastewater valorization:

• Membrane Systems: Include technologies such as ultrafiltration, nanofiltration, and reverse osmosis. These technologies allow the separation of solids, organic matter, and contaminants present in wastewater, which can facilitate water reuse and the recovery of valuable products.
• Anaerobic Digestion: This biological process breaks down organic matter in wastewater in the absence of oxygen, generating biogas (mainly methane and carbon dioxide). Biogas can be used as an energy source.
• Advanced Wastewater Treatment (AWT): These technologies combine biological, chemical, and physical processes to remove specific contaminants from wastewater, such as nutrients and chemicals. Examples include nitrogen and phosphorus removal systems.
• Granular Media Filtration: Uses filtration beds to remove particles and organic matter from wastewater. Filter media can be replaced periodically, and the removed material can be valorized or disposed of properly.
• Electrocoagulation and Electro-oxidation: Use electrochemical reactions to precipitate and remove substances from wastewater. They can also assist in disinfection and the removal of organic compounds.