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Aqueous Cleaning Demonstration Project

Final Report

Aqueous Cleaning Demonstration Project
City and County of San Francisco
July 1999
Hazardous Waste Management Program
Administrative Service Department


The mention and demonstration of commercial products, their source, or their use in connection with information reported herein is not to be construed as an actual or implied endorsement or recommendation of such products by the City and County of San Francisco. Identification and selection of commercial aqueous cleaning units for demonstrations was based on the available information at the time of project implementation, and is not intended to be inclusive or to exclude any commercial aqueous cleaning units in the market or in development.

Executive Summary

The City and County of San Francisco Hazardous Waste Management Program (HWMP) is assisting City departments in identifying cost-effective alternatives to petroleum-based solvent part cleaners in an effort to reduce solvent use and waste solvent generation. Under the Aqueous Cleaning Demonstration Project, the HWMP demonstrated aqueous cleaning units in selected City department facilities to determine the viability of replacing solvent cleaning with aqueous cleaning. Between February 1998 and January 1999, 14 different aqueous cleaning units were demonstrated at three Municipal Railway (MUNI) fleet maintenance facilities: the Woods diesel bus maintenance facility, the Green light rail vehicle maintenance facility, and the Potrero electric bus maintenance facility.

This final report discusses the cleaning operations at the MUNI demonstration facilities, the types of aqueous cleaning units available and their applications, the demonstration results, the waste management practices used to handle aqueous cleaning wastes, the costs of aqueous cleaning compared to those of solvent cleaning, and purchasing requirements for the City departments. The conclusions drawn from the demonstration results are summarized below according to performance criteria established for the project.

Overall Conclusions

  • MUNI facilities can convert to aqueous cleaning using a combination of two or more types of aqueous cleaning units and can realize equal, and in some cases, better cleaning results than those obtained using solvent.
  • MUNI cleaning requirements were best met by implementing two or more types of aqueous cleaning units.
  • MUNI can reduce the total number of cleaning units used by implementing spray cabinets and ultrasonic units with large cleaning capacities.
  • Based on the demonstrations of aqueous cleaning units at MUNI, results relevant to all City departments are as follows:
  • Spray cabinets have the greatest potential for application in all City department facilities because of their high cleaning performance, wide range of unit sizes available, and highly favorable economics.
  • Ultrasonic units have potential for application in all City department facilities that have parts that cannot be effectively cleaned by other aqueous cleaning units and can justify the higher capital cost.
  • Sink-top and immersion units have potential for application limited to City department facilities that perform a small volume of parts cleaning, clean primarily lightly soiled parts, or clean and replace vehicle or machinery parts immediately.

Aqueous Cleaning Performance

A total of 9 of the 14 aqueous cleaning units demonstrated were identified as meeting the overall performance requirements of MUNI facilities and as being potentially applicable to other City department facilities. These units are listed below according to unit type.

  • Microbial sink-top: ForBest IPC360 and EcoClean Bioflow20
  • Immersion unit: Mirachem PW-40S
  • Spray cabinet: Landa SJ-10, Safety-Kleen TLW-2, Safety-Kleen SJW-4, and EMC Jetsink
  • Ultrasonic unit: GlobalSonics GreaseMonkey Senior and Alpha Cleaning Systems 1818-54

One-page descriptions of these nine units are included at the end of this Executive Summary.

  • Spray cabinets were by far the most favorably reviewed aqueous cleaning units because of their high cleaning performance and automated cleaning operations.
  • Ultrasonic units were able to provide a high level of overall cleaning performance. In addition, ultrasonic units were able to perform special cleaning applications that other cleaning units could not, such as cleaning interior and hidden part surfaces, removing carbonized soils, and cleaning aluminum parts that would be damaged in a spray cabinet.
  • Sink-top and immersion units received a positive response from facility workers in light-duty cleaning applications because workers did not have to smell solvent odors, the skin on their hands did not become chapped, and the warm solution felt good on their hands. However, these units' cleaning performance was inadequate for moderately to heavily soiled parts.

Part Rusting

Despite the use of rust inhibitors in all aqueous cleaning chemistries, rusting would often occur on parts cleaned in sink-top and immersion units. Rusting was prevented, however, by wiping parts dry with a rag immediately after cleaning.

  • Rusting generally did not occur on parts cleaned in spray cabinets if the parts were removed soon after the cleaning cycle finished.
  • Parts cleaned in ultrasonic units almost never rusted.

Unit Design

  • Spray cabinets and ultrasonic units are available in a wide range of capacities, from small to very large. Therefore, these units are appropriate for cleaning applications with a wide range of parts sizes and volumes.
  • Medium- to large-sized spray cabinets and ultrasonic units have cleaning capacities equivalent to multiple solvent cleaning units.
  • Solution odor was a significant factor in how staff reviewed sink-top and immersion units. In some cases, workers reacted differently to the solution odor from the same unit. Working height and sink-top size were also cited as significant factors with sink-top units.

Servicing Requirements

Servicing requirements for aqueous cleaning units were minimal, consisting of water additions, chemical additions, filter changes, and solution replacement. The frequency that these services were required varied according to the type of unit and the magnitude of its use. The range of servicing frequencies experienced during the demonstration, from least frequent to most frequent, were as follows:

  • Water additions: never (for units with automatic water fill device) to every two days
  • Chemical additions: monthly to weekly
  • Filter change: never (for units without filters) to monthly
  • Solution replacement: greater than 3 months to monthly (full life of most solutions not measured as demonstration lasted for only 3 months)
  • MUNI was able to service most of the aqueous cleaning units itself. However, MUNI staff indicated that they would prefer full servicing and waste management services if MUNI converted entirely to aqueous cleaning. Five of the vendors of aqueous cleaning units demonstrated offer full "turn-key" servicing including waste management with their units.


Performing aqueous cleaning with sink-top, immersion, spray cabinet, or ultrasonic units is less costly than performing part cleaning using solvent. The potential annual costs savings estimated from the demonstration project results for each type of unit, including the annualized capital cost of the unit, are summarized below.

Potential Savings from Different Aqueous Cleaner Units

Aqueous Cleaning Unit Implemented Number of Solvent Units Replaced Cleaning Application Potential Annual Savings
Microbial Sink-Top 1 Light-Duty $852
Immersion 1 Medium-Duty $425
Spray Cabinet 2 Heavy-Duty $21,977
Ultrasonic 2 Heavy-Duty $16,057

Spray cabinets are moderate in capital cost and ultrasonic units are high in capital cost, but both units offer significant cost savings because their large cleaning capacities allow them to replace multiple solvent units and their automated cleaning ability reduces cleaning labor requirements. These cost savings offset capital costs and result in short payback periods

For example, MUNI could realize significant cost savings by converting from solvent to aqueous cleaning. Estimated capital costs, savings, and payback periods for the MUNI Woods, Green, and Potrero facilities to convert to aqueous cleaning by purchasing aqueous cleaning units are summarized in the table below. Because servicing costs vary according to the number of units implemented and servicing frequency, these costs assume MUNI service the units themselves.

Costs and Savings from Full Conversion by MUNI Facilities
  (Woods) Heavy Duty (Woods) Preventative Maintenance Green (Entire Facility) Potrero (Entire Facility)
Capital Cost $30,400 $6,100 $39,800 $14,030
Annual Savings $134,810 $13,270 $226,200 $13,250
Payback Period < 3 months < 6 months < 3 months 1.1 years
  • Aqueous cleaning can decrease waste management costs by decreasing the amount of hazardous waste generated.
  • MUNI and other City department facilities may realize additional cost savings through a decrease in hazardous waste generator fees paid to the California State Board of Equalization. In 1998, MUNI payed $6,176 in hazardous waste generator fees.

Waste Generation

  • Aqueous cleaning generates significantly less waste than solvent cleaning. Most facilities will be able to decrease their hazardous waste generation by converting from solvent to aqueous cleaning.
  • Aqueous cleaning solutions lasted four to twelve times longer than solvent before requiring disposal. The cleaning solution in microbial sink-top units lasted longer than other aqueous cleaning solutions. All four microbial sink-top units demonstrated lasted the duration of the 3-month demonstration period without requiring solution disposal.
  • Spent solutions from three aqueous cleaning units were analyzed and determined to be hazardous because of their cadmium, chromium, silver, toluene, and xylene content. Therefore, spent aqueous solutions from all units were disposed of off site by the City Department of Public Health waste contractor or by the aqueous cleaning unit vendors.
  • Oil skimmed from aqueous cleaning units was managed as used engine oil and recycled. Spent filters from the units were disposed of by the aqueous cleaning unit vendors or were recycled with spent engine oil filters. State agencies suggest solution filters be disposed of as hazardous waste unless characterized and shown not to be a hazardous waste.
  • Five of the vendors of aqueous cleaning units demonstrated offer full "turn-key" servicing including waste management with their units.

Best Aqueous Cleaner Units Demonstrated

Based on the demonstration results, MUNI staff rated nine units as good to excellent in meeting their cleaning needs. These units represent all four aqueous cleaning unit types (sink-top, immersion, spray, and ultrasonic). A 1-page summary describes each units' specifications, demonstration performance results, design, and servicing requirements.

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