In this post, we will review some of the main liquid waste generated in the graphic arts sector and the most suitable technologies for their treatment.
Recovery of residual cleaning solvents through distillation
Description: The residual solvents used for cleaning can be distilled and reused. There are specific equipment for the distillation operation of these solvents.
When grease cleaning or purging systems are applied, solvents are used to clean this system after each color change. Modern ink supply equipment already incorporates recovery systems for these solvents.
Environmental benefits achieved: The environmental benefits obtained through this technique are very significant: On one hand, it reduces the amount of residual solvents, which, once used, are managed as contaminating waste. On the other hand, the use of recycled solvent reduces the amount of fresh cleaning solvent needed, leading to significant economic savings.
Adverse effects: The distillation of contaminated solvent requires energy consumption.
Operational data: The distillation equipment must be installed and operated with care.
Cleaning agents with a high flash point usually also have a high boiling point. For these solvents, only vacuum distillation equipment can be applied, so that excessively high temperatures are not reached. In this situation, however, the use of a filtration membrane may be a cheaper alternative. There are already washing machines with an integrated distillation system.
Applicability: The recovery of cleaning solvents through distillation is a technique applicable to all industrial sectors. In particular: In the gravure, flexographic, and heat-set offset printing industries, solvent recovery by distillation is commonly applied. It is especially used in plants whose consumption exceeds 200 liters of cleaning solvents per week.
Economic costs: The installation costs of solvent recovery equipment through distillation vary widely, as they depend on the necessary size of the equipment and its specific application. However, by applying this technique, considerable cost savings are also achieved due to the reuse of the solvent, as well as a minimization of the management costs of the generated waste, which are also reduced as they are smaller.
Reasons for implementation: Reduction of VOC emissions and compliance with regulations regarding them. Economic savings in raw materials through solvent recycling, and reduction of management costs for generated waste.
Distillation and evaporation of solvent-based product waste
Description: Solvent-based waste, such as inks, varnishes, and adhesives used in printing plants, can be distilled and evaporated under vacuum to recover the solvent and thus reduce the amount of hazardous waste.
Environmental benefits achieved: The amount of contaminating and/or hazardous waste is reduced, and there is a reduction in the consumption of raw materials (solvent).
Adverse effects: The distillation of contaminated solvent requires energy consumption.
Applicability: This technique is applicable in all printing facilities, both new and existing.
Economic costs: The installation costs of solvent recovery equipment through distillation vary widely, as they depend on the necessary size of the equipment and its specific application. However, by applying this technique, considerable cost savings are also achieved due to the reuse of the solvent, as well as a minimization of the management costs of the generated waste, which are also reduced as they are smaller.
Reduction and treatment of wastewater through ultra and nanofiltration
Description: With ultrafiltration and nanofiltration (UF and NF), also known as reverse osmosis, contaminated water passes through a semi-permeable membrane at high pressure, which allows small water molecules to pass but not larger molecules. The concentration of contaminating compounds on the membrane increases due to the repeated passage of contaminated water through this membrane.
Environmental benefits achieved: The volume of contaminating substances is reduced, and the water can be reused for, for example, cleaning operations, etc. The filtered waste, such as ink or paint, can be recovered and reused.
Adverse effects: The filtered water, if not reused, is discharged into the sewer system. Filtration requires energy consumption.
Applicability: This technique is commonly applied in printing plants that use large amounts of water-based inks, varnishes, and adhesives, such as packaging printing plants. It is also used in the automotive industry.
Economic costs: The installation costs of ultrafiltration or nanofiltration equipment are quite high.
Vacuum distillation
Description: This is a distillation performed by creating a vacuum in the column, so that the boiling of the solvent or the liquid to be separated occurs at a temperature lower than that which would occur at atmospheric pressure. In other respects, this technique is similar to conventional distillation.
Applicability: Applicable in the entire graphic industry.
