Water Reuse Plans for DOD Facilities
At Naval Support Activity Annapolis, a study was conducted to determine the feasibility of re-using municipal wastewater effluent at military installations.
By David Ammerman, P.E., and Diana Maimone, CFM
Municipalities throughout the nation are struggling with the challenges of managing ever-increasing wastewater flows and the associated nutrient loads. At the same time, many regions are finding that the easily accessible, low-cost raw water supplies had been used to their full extent and the next best source of water available will be substantially more expensive to treat and transport to the demand centers.
Historically, utilities have been able to manage both water supply and wastewater disposal requirements with increased levels of treatment and the construction of transmission piping systems. These approaches are still available—but the associated energy requirements and capital expense open the door for a new approach to managing water supplies and wastewater disposal. Faced with increasingly stringent effluent discharge requirements, Naval Support Activity Annapolis (NSAA) included an analysis of the recycling highly treated municipal effluents for non-potable uses in their recent effluent management studies in addition to the traditional approach of upgrades to the treatment process.
NSAA is located across the Severn River from the U.S. Naval Academy in Maryland and provides base operating support services to tenant commands. The North Severn Complex has numerous facilities in support of local Navy operations. The Naval Academy Wastewater Treatment Plant (WWTP) serves the North Severn complex area and currently treats an average of 0.120-million-gal-per day. The treatment plant provides secondary treatment, disinfection prior to discharging to a tributary to Chesapeake Bay. Intense regulatory attention has come to bare on all activities contributing nutrients to the Bay with a focus on WWTP discharges.
The U.S. Navy and Maryland Department of the Environment (MDE) have signed a memorandum of understanding that federal wastewater facilities would comply with the Chesapeake Bay’s nutrient reduction program. The Navy has completed a study and piloting of additional treatment process to meet the nutrient removal requirements. NSAA also evaluated land application and beneficial reuse of the treated effluent as a means of diverting nutrients from the Bay. This strategy has a long history of success in states including California, Arizona, Texas and Florida. Referred to as reuse or recycled water, using effluent as a water supply for non-potable needs has a proven track record of reducing nutrient loadings to surface waters and serving as a new supply for non-potable uses.
While reduction in nutrients discharged to Chesapeake Bay is the primary driver for the reuse study, conservation of groundwater supplies may also be important in the near future. As shown in Fig. 1 (Source) ground water levels have dropped 20-ft between 1976 and 2006—raising the potential for future restrictions on this water source.
Recently, AECOM conducted a feasibility study considering the use of land application and beneficial reuse as a discharge management strategy. The primary goals of this study were to:
- Approach or achieve zero treatment plant discharge by reusing the highest volume of reclaimed water feasible.
- Assess the quality of reclaimed water and site characteristics with respect to reuse feasibility.
- Reduce groundwater dependency for irrigation.
- If determined to be feasible, complete a conceptual level design of a reclaimed water system with estimated construction costs not to exceed $2 million.
Fig. 2: Average Water Use and Resulting Nutrient Removed from the Bay through Golf Course Irrigation
Identifying Reuse and Land Application Opportunities
The feasibility of reuse and land application is highly dependent on land use in proximity to the WWTP. All potential reuse opportunities were evaluated with respect to their ability to reduce nutrient loadings and decrease high quality potable or groundwater consumption for non-potable purposes. Cost also was a factor. Working with NSAA staff, AECOM developed a process to identify and evaluate potential reuse/land application strategies.
The initial inventory of potential effluent uses was intentionally broad. It included diverse water uses such as cooling water towers, an ice rink at a sports complex, a car wash, supply for a compost wetting system and irrigation. The highest scoring sites in the first round of screening were the rifle ranges, golf course, the compost site and Greenbury Point, respectively. Ultimately, the golf course was selected as the site providing the greatest benefits to NSAA due to favorable regulations, volume of water required, proximity of the course to the WWTP, and the presence of an existing irrigation system. The AECOM/NSAA project team initiated discussions with the golf course superintendent and where able to demonstrate to the Superintendent that reclaimed water would be an acceptable alternative to ground water as a supply of irrigation.
Demonstrating that the reclaimed water was suitable for golf course irrigation was an involved process, and included connecting the superintendent of the North Severn golf course with golf course superintendents elsewhere in the area as well as in other states who had experience in using reclaimed water. AECOM’s scope of work also included testing and comparison of reclaimed water quality with the ground water that is currently used to irrigate the course. The results of the comparison indicated that all water quality parameters of concern were well within the limits of suitability for turf application. Finally, NSAA worked with the course superintendent to develop a small pilot study on the golf course site to use reclaimed water trucked from the WWTP for turf irrigation. As a result of these efforts the golf course agreed to move forward with the conceptual design of a reclaimed water system for use as irrigation.
Conceptual Design and Preliminary Project Costs
The conceptual design of water reuse system involves combining two enterprises with very different objectives. Municipal wastewater treatment plants are an essential service and are charged with collecting, treating and discharging effluent subject to regulatory water quality limitations. Golfing on the other hand is completely discretionary. The financial success of the site is wholly dependent on the challenge and aesthetics of the site. While effluent from the WWTP must be dependably disposed of every day, irrigation of the golf course is only required in the summer months when rainfall is not sufficient to maintain turf at the optimum conditions for play. Based on long-term average water use the golf course will require approximately 18,000,000-gal of water per year. However, water use varies significantly throughout the year as shown in Fig. 2. Expected reductions in nitrogen loadings to the Bay will be approximately 35 percent under current and future flow and nutrient concentration conditions.
Fig. 3 provides a schematic of the conceptual design for the delivery reclaimed water to the golf course. Planning level cost estimates indicated the capital cost of approximately $1.5 million. How does it compare to the cost of upgrading treatment processes to reduce nitrogen concentrations in the effluent? The golf course reuse system was slightly less expensive than the proposed plant upgrades. Additional treatment was estimated to cost $1,680/lb of nitrogen removed. The golf course reuse system would provide nitrogen removal at a cost of approximately $1,200/lb. Reuse systems can be cost competitive to traditional plant upgrades as a means of reducing discharge and energy consumption and even more competitive when the value of offsetting potable and groundwater use for irrigation are included.
At this time, NSAA is upgrading the WWTP to reduce effluent nitrogen concentrations while keeping the golf course reuse irrigation project on hold, mostly due to funding restrictions. However, reuse has been included in NSAA’s Master Plan and the WWTP’s Environmental Assessment. It is reasonable to anticipate that some form of reuse will ultimately be implemented.
Moreover, the golf course reuse system evaluated in this study demonstrated the potential of reducing nutrient discharges to the Bay at costs less than that of traditional treatment. Further restrictions in nutrient loads from the wastewater treatment plant are likely and will necessitate even higher and more costly plant upgrades. This will serve to make reuse even more financially attractive to the utility. From the standpoint of water supplies, reclaimed water may become a valuable resource as traditional water supplies are used to the maximum extent possible. While this study did not consider charging end-users for reclaimed water service, this has become standard practice in states such as Florida and California where reclaimed water has become an indispensable part of the total water supply. Once given away for free as part of an effluent disposal strategy, utilities now routinely charge rates ranging from a flat monthly fee to use based charges including inclining rates to encourage responsible use of this valuable resource. There are no standard methods for setting rates but some utilities are charging customers 80 percent of the cost for potable water for reclaimed water service.
The benefits to the reclaimed water customer can also make for a compelling argument to consider this new supply. Reclaimed water is essentially drought proof and therefore more reliable than traditional supplies. When used for irrigation, reclaimed water also provides nutrients essential for plant growth. Reclaimed water may be more reliable and less expensive from a mechanical stand point than the customer’s existing water supply system.
Golf courses, for instance, often are responsible for the construction, operations and maintenance of water supply wells, pumps and transmission systems. Customers are able to eliminate the costs and responsibilities of securing traditional water supplies where reclaimed water is provided. The pressures to reduce nutrients discharged to the environment and secure additional water supplies are an inevitable result of increasing population densities. Recycling municipal effluents for non-potable uses has proven to be a successful strategy for addressing both of these imperatives and can provide benefits to utilities and reclaimed water customers alike.