A closed loop washrack wastewater recycling system offers activities an alternative that can achieve compliance with discharge limits while reducing water and detergent usage. As environmental regulations continue to set more stringent discharge limits for wastewater contaminants, recycling becomes even more lucrative since regulatory agencies grant permitting exemptions to activities that recycle wastewater on-site.

Numerous systems are commercially available including one developed by the Naval Facilities Engineering Service Center. In general, systems are purported as capable of removing contaminants from the wastewater to the following concentrations: oil to less than 10 ppm, heavy metals to less than 0.1 ppm, and suspended solids to 1 ppm.

Although each system is unique in configuration and operations, all use one or more of the following treatment processes; chemical precipitation, flocculation, filtration, absorption, oxidation, and gravity separation. In addition, all require appurtenance including sumps, tanks, pipes, and pumps. For illustrative purposes the Navy’s recycle system is described in the following paragraphs.

Vehicle, equipment, or aircraft wash and rinse water is collected from a wash pad and pumped via a sump pump to the treatment system’s load equalization tank (LET) until sufficient water is collected to begin processing. The wastewater from the LET is then pumped to the treatment system. Inside the treatment system a corrugated parallel plate separator removes free oil. Next, the system adds a demulsifier to treat emulsified oils, sodium hydroxide to precipitate heavy metals, and hydrogen peroxide as a disinfectant. Following the chemical additions, the solids generated by the chemistries are removed through an automated diatomaceous earth pre-coat indexing filter. The treated water is then stored in a holding tank to be utilized for washing and preliminary rinse of aircraft or discharged directly into a Publicly Owned Treatment Works.

Closed loop wastewater recycling systems require scheduled maintenance to insure satisfactory performance. This may include replacing or cleaning filters, transferring chemicals, or collecting water samples. The Navy’s closed loop wash rack systems are installed with automated controls and sensors to ease operation and maintenance.

System capital and recurring costs are important factors when determining the feasibility of installing a recycling system at a particular activity. Recycling systems are not always the most cost-effective way to manage washrack wastewater. However, certain pre-existing conditions may make recycling a cost-effective alternative. Favorable conditions include activities that promote water conservation, remote areas that lack readily available disposal alternatives, or when a permit under Resource Conservation and Recovery Act Part B is required for treatment prior to discharging into a sanitary sewer.

The compliance benefits listed here are only meant to be used as a general guideline and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g. the amount of workload involved.

Recycling systems are relatively safe systems that can be operated for years if properly maintained. With any new system all operators should receive proper training and guidance. Since many systems utilize chemical agents in the recycling process, special consideration should be taken when handling chemicals and/or detergents. They are irritants to the skin, eyes, and mucous membranes. Inhalation of the fumes can also be dangerous, therefore, proper personal protection equipment and procedures should be heavily stressed.

Consult your local Industrial Hygienist, local health and safety personnel, and acquire appropriate MSDSs prior to implementing any closed loop recycling system.

Since all systems require electrical power, only trained professionals should undertake electrical troubleshooting and repair.

• Complies with discharge requirements.
• Reduces annual quantity of water used to wash vehicles, equipment, and aircraft.
• Reduces annual detergent used to wash vehicles, equipment, and aircraft.
• Reduces loading on wastewater treatment plants.

• Requires additional space to store holding tanks.
• Require additional resources to operate and maintain system.

Closed loop wash racks are specifically sized to meet the needs of the facility. System design varies on the number and types of vehicles, equipment, and/or aircraft washed at the specific facility. Consequently, the purchase, installation, and operation cost of a closed loop system varies significantly from activity to activity. The following illustrates the fixed costs and recurring costs for the Navy’s closed loop system as described in the overview section. Costs based on an estimated 500,000 gallons of wastewater generated in one year.

Approval is controlled locally and should be implemented only after engineering and environmental approval has been granted. Major Claimant approval is advisable.