Table of Contents
Aqueous Cleaning: Regulatory Requirements
As part of the Clean Water Act, Effluent
Guidelines and Standards for Metal Finishing (40 CFR Part 433) have
been established that limit concentrations of conventional
pollutants, and heavy metals in wastewater streams. Aqueous cleaning solutions may have a non-neutral
pH, and may contain chemical additives and/orimetal ions, depending on
their intended use. Used solutions will also contain dirt, oils and
grease. These materials can enter the wastewater through liquid dripping
off of parts, when cleaning equipment or changing solution, and from accidental
spills or leaks in equipment. Actual limits for effluent constituents
depend on the size of the operation and the amount of wastewater generated
from the facility. If the facility discharges directly to receiving
waters, these limits will be established through the facility's National
Pollutant Discharge Elimination System (NPDES) permit (40
CFR Part 122). Facilities which are indirect dischargers releasing
to a POTW must meet limits in the POTW's discharge agreement. Wastewater
streams with concentrations exceeding permit limits will require pretreatment prior to discharge to receiving waters or to a publicly
owned treatment works. Pretreatment may include separation of
liquid wastes to remove solvents, and settling or precipitation of solid
Solid and Hazardous Waste
Under the Resource Conservation and Recovery
Act (RCRA), organic finishing facilities are required to manage listed
and characteristic hazardous wastes (40 CFR Part
261). Used aqueous cleaning solutions may contain constituents
listed or characterized as hazardous wastes, such as oils and grease. Hazardous waste management (40 CFR Part 262) includes obtaining permits for the facility in order to generate wastes,
meeting accumulation limits for waste storage areas, and manifesting waste
containers for off-site disposal.
The Emergency Planning and Community Right-to-Know
Act (EPCRA) requires facilities to notify employees, customers and
the surrounding community of certain hazardous chemicals and substances
that are present on-site. Large aqueous cleaning operations may contain
hazardous substances in sufficient quantities to subject a facility to
several EPCRA requirements. Facilities may be required to inform
emergency planning committee (LEPC) and the state
emergency response commission (SERC) of the materials stored and used
on-site, devise emergency
response plans for reacting to spills, and notify authorities of accidental
spills and releases (40 CFR Parts 302 and 355). In addition, due to the materials used in organic solvent cleaning solutions,
facilities may be required to submit Material
Safety Data Sheets (MSDS) for these materials to state, regional, and
local organizations, while disposed volumes of the material may have to
be documented on annual Toxic
Release Inventory reports (40 CFR Part 372).
- Do aqueous cleaning solutions come in contact with water streams? If so, do concentrations of pollutants exceed limits established by the
facility NPDES permit or POTW discharge agreement?
- Are all aqueous cleaning solutions and wastes labeled and packaged in accordance
with 40CFR Part 262, Subpart C? Are manifest
forms completed for wastes to be shipped for disposal?
Aqueous Cleaning: Common Causes of Violations
- Has the facility participated in local, regional, or state emergency response
planning activities? Have facility response plans been developed and coordinated
with local authorities?
- Aqueous cleaning solutions are liquid materials that can contaminate water
streams. Contamination may occur accidentally, as with spilt material
entering a storm sewer. Contaminated water streams may contain pollutants,
including surfactants, residual sludges, and oils, in concentrations that
exceed the limits established by facility NPDES permits or POTW discharge
agreements. The water stream may also have a non-neutral pH. Effluent, then, may not be directly released to water systems or to publicly
owned treatment works without pretreatment.
- Aqueous cleaning solutions containing oils, grease, and other contaminants
may be classified as hazardous waste according to RCRA. These materials
must be labeled, stored, and disposed in accordance with 40CFR
Part 262, Subpart C.
Aqueous Cleaning: Sources of Pollution
- Organic solvent cleaning solutions may contain substances defined
as hazardous chemicals. Depending on the quantity of material on-site,
facilities must have an MSDS for each solution, maintain records for TRI
reporting, and cooperate with local emergency planning committees.
- Used aqueous cleaning solutions with non-neutral pH levels, and/or containing
grease, oils, phosphates, and heavy metals may spill due to improper handling
or leaks in tanks, pipes, hoses, or other containers. The liquid
material may enter storm sewers if not properly contained.
- Used aqueous cleaning solutions may contain grease, oils, and heavy metals
which would classify the solutions as hazardous waste.
- Grease, oils, and heavy metals may be separated from aqueous cleaning solutions
as sludge. The sludge may be classified as a hazardous waste and require
disposal in accordance with 40 CFR Part 262.
Aqueous Cleaning: Pollution Prevention Alternatives
- Parts experiencing flash rusting of the substrate due to incompatibility
with aqueous cleaning solutions will necessitate rework or possibly disposal.
- Aqueous cleaning may be considered a pollution prevention alternative since
it aids in proper application of coating materials thereby reducing rework
or reject parts.
- Substituting aqueous cleaners for semi-aqueous cleaners or organic solvents
reduces the problems associated with volatile organic compounds and hazardous
substances and wastes.
- Use a higher quality cleaner at a lower concentration to minimize consumption
of additive, water, and time.
- Restrict traffic in storage areas to reduce spills and accidents. Keep storage and work areas clean so that spills and leaks are more noticeable
and reaction time is reduced.
- Optimize aqueous cleaning processes to clean properly with minimal water
and additives. Proper adjustment of operating parameters, such as
time, agitation, solution concentration, temperature, and water type, will
improve cleaning without creating additional wastewater or using more additives. Modify part orientation or racking to ensure that the cleaner reaches all
- Conserve energy by operating at optimum temperature; and by covering baths,
using insulated tanks, or using waste heat from other processes to heat
- Remove contaminants from aqueous cleaning solutions to retain cleaning
effectiveness. Separate soils, dirt, oils, and other contaminants
using filtration, gravity separation, or membrane technologies (crossflow
filtration). Reducing heat and stopping agitation will promote separation
of contaminants in batch systems.
- Segregate non-hazardous wastewater and other materials from hazardous organic
solvents, and label containers to prevent mixing. Separation of the
materials reduces the amount of hazardous waste that is produced.
- Minimize water consumption by utilizing counter-current rinse baths. Backflow water from final rinse, to pre-rinse, to cleaning baths before
- Check aqueous cleaning equipment regularly for leaks and repair them. Items to check include tanks, pumps, pipes, hoses, valves, fittings, and
- Minimize accumulation of soils, dirt, and oils by practicing good housekeeping. Keep the facility clean and use proper part handling procedures to reduce
part contamination initially. Perform regular maintenance of machinery
to remove excess oil, grease, and dirt; use gloves when handling parts
to reduce oils.
- Train employees on safe handling of materials and wastes and encourage
continuous improvement. Training familiarizes workers with their
responsibilities, which reduces spills and accidents.