This demonstration project was conducted to evaluate a shipboard wastewater treatment system that could potentially meet the restrictive requirements of Department of Defense (DoD) vessel design and operation and meet current and future effluent discharge standards. Commercial systems are available, but are challenged by the high strength wastewater, the need for fast startup in meeting effluent quality standards quickly, and the lack of highly trained operators dedicated to a treatment system. All these factors, as well as size and weight restrictions, create barriers for seamless integration of commercial systems. Shipboard treatment versus the use of a holding tank will allow more mission flexibility, reduce or eliminate disposal costs, and reduce security risks in foreign ports. The Navalis Orion™ Advanced Oxidation Wastewater Treatment System employs advanced oxidation as its primary process technology.
The overall objective was to demonstrate that advanced oxidation technology is applicable to DoD vessel wastewater, and to evaluate the system installation and operation in a realistic shipboard environment. The criteria included treatment capacity, reduction of key effluent quality parameters to meet the environmental regulations, startup time and the absence of critical component failures.
The Navalis Orion™ system is designed for a maximum flow rate of 5 gallons per minute or 7200 gallons per day (gpd). The manufacturer information is based on testing with nominal influent of 500 milligrams per liter (mg/L) five-day Biochemical Oxygen Demand (BOD5) and 1500 mg/L Total Suspended Solids (TSS). The manufacturer designed the system to treat a combination of shipboard generated wastewater (vacuum-collected blackwater combined with gravity-collected graywater) produced by approximately 150 people.
The system was purchased for full-scale evaluation and installed at the Non-Oily Wastewater Laboratory, a liquid waste laboratory facility at Naval Surface Warfare Center, Carderock Division (NSWCCD) in West Bethesda, Maryland. The laboratory evaluation consisted of two phases. Phase 1 evaluated the treatment system performance while processing combined blackwater and graywater. Phase 2 evaluated the treatment system performance while processing blackwater alone. The full-scale laboratory test followed the inspections and system checks listed in the military performance specification, MIL-PRF-30099.
In Phase 1 testing, the Navalis Orion™ system processed combined blackwater and graywater. The effluent BOD5 and Chemical Oxygen Demand (COD) values were consistently higher than the desired standards, while both effluent TSS and Fecal Coliform (FC) thresholds were met. Even with effective solids removal, the effluent BOD5 and COD levels remained high. The high BOD5 and COD values are an indication that the advanced oxidation step did not oxidize the organic contents sufficiently. The fact that TSS levels were low in the effluent shows that precipitated solids were not the source of organics. The system averaged 22 hours of daily operation throughout the Phase 1 evaluation. The daily average capacity of the system was 4023 gpd, which was not as high as estimated at 6600 gpd. The average and maximum processing rates of 6600 gpd and 7200 gpd were not attained. A large impairment of the system operation was due to the Solids Separation Zone.
The purpose of the evaluation was not to perform a detailed analysis of each unit operation in the system, but to test a commercial system as a whole in automatic mode with little operator interaction. However, with the unexpected performance in Phase 1and issues with individual components, some modifications were made to the system to improve performance for Phase 2. With BOD5 and COD values remaining high after the advanced oxidation step, the ozone levels in the reactor were suspect. To improve the efficiency of the ozone generator, an air dryer was installed to provide oil-free, dry compressed air. In order to improve dissolved ozone levels in the reactor, a higher capacity ozone dissolving pump was installed for the reactor recirculation and ozone additions for Phase 2 testing. To improve processing capacity and reduce sludge generation, the backwash source was changed from the Finishing Tank to the membrane permeate. Different sizes of Shaker Screen and bag filter media were tested.
In Phase 2 testing, the Navalis Orion™ system processed blackwater alone. All effluent quality parameter thresholds were met. The Ultraviolet (UV) unit experienced issues and shutdown for days. The system averaged 24 hours of daily operation throughout the Phase 2 evaluation. The daily average capacity of the system was 1500 gpd, which was not as high as estimated at 6600 gpd. The average and maximum processing rates of 6600 gpd and 7200 gpd were not attained. The capacity of the system processing blackwater was much lower than estimated. The same reasons from Phase 1 can be cited for reduced throughput. In addition, the flocculent was not optimal for a blackwater influent leading to more solids removed by the bag filters and increased backwash frequency. Sludge generation was also greater than expected at an average of 297 gpd. The system generated 23% of the processed volume as sludge, which was higher than estimated by the manufacturer. The excessive sludge generation caused the system to slow down the processing rate due to lack of influent. The Navalis Orion™ system did not meet the minimum startup time in either test phase, since the capacity was not met.
In both phases, the system required operator involvement to operate and maintain the system for several hours per day. The details of daily operation and troubleshooting were documented in the laboratory logbook. Each installation will need to judge whether or not the documented labor level is acceptable based on labor force available and mission. No critical components failed in Phase 1, meeting the max time-to-repair requirement. Although it did not affect the effluent performance of Phase 2, the UV unit experienced inconsistent operation for days which exceeded the max time-to-repair requirement.
Overall, the evaluation has demonstrated that advanced oxidation using ozone and ultraviolet light is a potential technology for the treatment of blackwater and graywater generated on a military vessel and warrants further testing. To help improve the system performance and correct issues, optimization is needed.
A formal cost/benefit analysis could not be performed. Comparing the cost of purchasing, installing and operating a holding tank cannot be compared to the same costs for a treatment system. The treatment system is an additional capability with higher associated costs. The Life Cycle Cost (LCC) estimated by Navalis Environmental Systems was evaluated and a new LCC was estimated based on experience during the laboratory testing and shipboard estimates. The new LCC was calculated to be more than two times greater than the Navalis estimate primarily due to the higher labor requirements for operation, maintenance and repair of the complex system.