Some of the most practical methods for processing post-production water wastes from water-based flexographic printing include:
- Chemical splitting in continuous or batch process.
- Continuous effluent treatment.
- Microfiltration, ultrafiltration, nanofiltration and reverse osmosis
- Biologically absorptive treatment using activated brown carbon; recycling with part or full stream desalination and reactivation of the carbon (mixed slope-reactors, flotation, filtration, softening, reverse osmosis, revolving cylindrical furnace).
- Oxidation technology through modular systems offering oxidation, ozone/UV oxidation, UV/H2O2 oxidation.
Quality and quantity of wastewater to be treated are generally the determining criteria for choosing which treatment method is best for a particular production scenario. For nearly all flexo producers of wastewater, chemical splitting is appropriate and the least expensive short and long-term solution for reducing or eliminating wastewater problems. The target quality of treated water is determined by the local discharge limits and/or if the printer plans to reuse the water for cleaning or other purposes.
While many printers elect to process only their wastewater and handle waste ink disposal as a separate component of waste management, some opt to add waste inks directly to their wastewater. This will generally increase the amount of suspended solids in the waste stream requiring a more effective and costly way to process the sludge resulting from the chemical treatment. In the end, more wastewater may need to be processed.
Best Management Practices & Pollution Prevention
It is useful to determine where and how much water is being used. Develop a plant water diagram (flow chart of water usage) and water balance (how much in/out) that is periodically reviewed, updated and used to develop further conservation methods. Use the diagram to develop a written water conservation program that utilizes elements given below that apply to your facility.
Ideally, install water meters at key usage points in the plant and take readings at regular intervals (first of month & end of month) to account for all water used. Key usage points may include the primary incoming water. This may be split into industrial water and sanitary water.
The installation of water meters may also aid in resolving environmental compliance issues associated with industrial discharges of waste water should they arise. Sanitary water usage is typically minimal compared to industrial water usage and is generally not of concern in terms of water usage and wastewater discharge environmental compliance issues. If this is the case, consider placing a water meter on the industrial water line only.
Other key usage points may include the point where industrial waste water enters into the sanitary sewer (as long as this is on the printer’s property). If the sanitary and industrial waste water combine into one pipe prior to discharging into the sanitary sewer a water meter installed upstream of this connection to measure the flow of industrial waste water may be in order.
Waste Water Minimization
In order to reduce the volume of waste water that must be treated, various measures such as installing flow restrictors on water lines, installing fan type spray heads, using pressurized water for cleaning will help minimize the amount of water consumed.
Additional water use minimization activities include printing job scheduling to minimize the number of times or number of print decks that must be cleaned at the end of a run by scheduling jobs back to back that print like colors.
Form a multi-disciplinary water conservation team to review all facets of plant operation to develop a plant water budget that is tracked and followed. Determine the costs associated with the volume of waste generated as a result of cleaning and correlate this back to plant personnel. An example would be to explain their company profit sharing benefits being reduced as a result of high waste disposal costs.
Multi-stage cleaning processes involve semi-dirty water (previously interim rinse water) to remove the first layer of ink and soil on the press and press parts. Then utilizing water recovered from the previous final rinse to be used in the interim or middle stage of the cleaning process. And finally using fresh water for final rinse of the press and press parts.
Fresh Water from Final Rinse → Water from Previous Final Rinse → Dirty Water for Initial Rinse
The amount of water used in the cleaning process can be reduced by training press operators to:
- Drain as much ink as possible into containers.
- Clean press parts immediately after coming off press to avoid ink drying. The longer the ink sits will increase cleaning efforts required.
- Use detergents (caustic) and additives according to manufacturers recommendations to avoid excessive rinsing due to using too concentrated solutions.
- Thoroughly scrape press parts before any water is used for cleaning.
- Increase cleaning efficiency by cleaning ink stations promptly (before the ink begins to dry).
- Use low flow spray nozzles on hoses.
- Use water flow restrictors.
- Modify press cleaning activities to an organized multi-stage cleaning process to reuse waste water.
Waste Water Treatment
A wastewater treatment system or filtration system may be cost effective in reducing waste disposal costs. Some companies have found that filtered wastewater, depending on its degree of contamination, may be used to dilute inks when necessary.
For access to vendors who may supply alternative materials and equipment, see the PNEAC Vendor Directory.
A wastewater treatment equipment operating permit may be required by state or local regulations.
A waste treatment equipment operator license may be required by state or local regulations.
An industrial wastewater discharge permit may be required by state or local regulations.
Treatment chemicals used in chemical separation systems may be subject to EPA SARA reporting and/or EPA CAA RMP Requirements (Section 112R).