The objective of this project was to demonstrate that on-site water reclamation is technically feasible and cost-effective. Current and future water shortages and degraded water quality are and will continue to jeopardize the ability of the Department of Defense (DoD) to maintain training capacity and military readiness. Specific technical objectives of the project were to:
A number of technologies are available; however, on-site water reclamation is particularly attractive because it is relatively easy to implement and it captures and reuses water that has already been delivered and paid for. On-site treatment of wastewater can also be integrated into existing or future construction with concomitant reductions in water and sewer costs.
Operationally, the Living Machine mimics tidal wetland ecology; at regular intervals blackwater (i.e., sewage) is pumped into media-filled treatment cells, allowed to react, and then subsequently drained. A typical cycle (fill, react, and drain) takes approximately 40 minutes. An innovative feature of the Living Machine is that as the treatment cells drain, air is drawn into the media, which eliminates the need to operate a costly aeration system. As the wastewater passes through the treatment cells, most of the organic compounds along with ammonia are captured and consumed by a diverse microbial population that grows as a biofilm on the surface of the media. To enhance the aesthetics of the aboveground portion of the cells, an upper layer of gravel (10-12 inches deep) in each treatment cell is planted with a variety of hydrophytic vegetation. The plants remove some nutrients, promote microbial growth, and the roots help maintain treatment layer porosity. The highly flexible cells may be aesthetically integrated into exterior landscaping or buildings.
At the Marine Corps Recruit Depot (MCRD) in San Diego, California, there are four treatment cells: two primary or Stage 1 cells filled with a coarse media that is less susceptible to plugging by solids in the incoming blackwater, and two secondary or Stage 2 treatment cells filled with a less coarse higher surface area media. Following secondary treatment, the treated water is sent to a disinfection unit (filtration, ultraviolet light, and chlorinator) and stored on site in a clean water tank. The treated clean water is then plumed into a new sub-terrain irrigation system that provides enough water to sustain approximately 2 acres of adjacent grass lawn.
The Living Machine is producing approximately 8,500 gallons of clean water per day at an average energy consumption of 0.006 kilowatt hours (kWh) per gallon of water treated. Because the nitrogen loading (total Kjeldahl nitrogen [TKN]) was significantly higher (average 180 parts per million [ppm]) than expected (≤ 100 ppm), incoming blackwater was diluted with recycled treated water. The higher TKN value appears to be due to the extreme heterogeneity of the blackwater at MCRD. With this adjustment, all analytes commonly used as indicators of organic matter degradation were reduced by more than 95%. The exceptions are residual color and phosphate along with total nitrogen, which remains elevated because ammonia is converted to nitrate (and an insignificant quantity of nitrite). Performance objectives were met, and results are summarized below.
Reduced contaminant levels in the effluent
Effluent water quality compared to influent
Meet treatment goals
Volume of wastewater treated per day
Total - 10,000 gpd
Wastewater - 8,500 gpd
Lost/Recycle -1,500 gpd
Volume of water recovered
Volume of water reclaimed
Water recovery ≥ 90%
Wastewater recovery per day 85%
Return on Investment
Capital and O&M costs
Costs for system purchase, installation and O&M
8-10 year return on investment
Estimated 9.7 years based on current and projected utility rates
Contaminant levels in the effluent
Effluent water quality
Meet reuse requirements
Did not meet POTW discharge limits for Phosphate and Nitrogen. However, the system met and is permitted under General Waste Discharge Requirements by the SDRWQCB
Total hours of operation and hours of downtime
Hours system is operating with adequate performance over total hours of system operation
>95% once the system is fully operational
% – percent BOD – biochemical oxygen demandCOD – chemical oxygen demandgpd – gallons per dayNH3 – AmmoniaO&M – operation and maintenancePOTW – Publicly Owned Treatment WorksSDRWQCB – San Diego Regional Water Quality Control BoardTN – total nitrogenTOC – total organic carbonTP – total petroleum
The system did not meet POTW discharge limits, which was selected at the beginning of the project because it was more stringent. However, it turns out that POTW limits is not the most applicable discharge standard for the system. The system meets the California water reuse standards for water reuse. The system also meets the General Waste Discharge Requirements for Small Domestic Wastewater Treatment Systems (General Order) under SDRWQCB. Based on this order, the effluent limits specified in the table above do not apply because the flow rate is below 20,000 gpd. In November 2014, the SDRWQCB issued a permit to MCRD that allows the treated reclaimed water to be used for subsurface irrigation.
Although DoD agencies have mandates to reduce water usage and promote water reuse, funding is difficult to obtain especially for items with large capital cost. With budget cuts, furloughs, and uncertainties in future budgets, it is more difficult to champion a new technology or system. Even if a technology is proven to work in certain DoD applications, there is a strong reluctance to take a chance on the new system because of uncertainties it brings (e.g., O&M procedures).