Project Case Study: Balancing growth and the environment

July 2006 » Feature Articles
A Pennsylvania community implements advanced water reuse, pushing the bounds of conventional wastewater treatment.
Jason D.Wert, P.E., DEE

A Pennsylvania community implements advanced water reuse, pushing the bounds of conventional wastewater treatment

Project: Beneficial wastewater reuse system
Civil engineer: Herbert, Rowland & Grubic, Inc., State College, Pa.
Product application: Microfiltration and reverse osmosis allow wastewater reuse to sustain growth with limited impact to groundwater and surface water resources.

During the past decade, communities have faced an increasing commitment to provide reliable and clean supplies of potable water to their citizens, coupled with environmentally friendly wastewater disposal practices to protect sensitive waterways. While these admirable goals continue to be a driving force in the municipal market, the cost of providing these separate services can have a negative impact upon the community's economic vitality.

As water and wastewater infrastructure costs are rising, communities have begun to explore alternative solutions to the traditional methods of potable water production and wastewater disposal. At the forefront, communities are considering and implementing water reuse projects that reclaim valuable wastewater discharges, substituting for drinking water supplies in a wide variety of potable and industrial uses. While numerous, high-profile projects have been implemented successfully in areas with limited high-quality water supplies, such as the Western United States and Florida, the technologies have advanced such that areas that were fortunate to have abundant water supplies are now actively considering water reuse in lieu of developing additional potable supplies.

One such community is the Centre Region, a council of local governments that surrounds and includes the borough of State College and the Pennsylvania State University, Centre County, Pa.

After almost 10 years of planning, design, and construction, this community's advanced water reuse project has become a reality and continues to push the bounds of conventional treatment practices.

Background

The Centre Region of Pennsylvania refers to the communities surrounding the borough of State College and the Pennsylvania State University. The six local governmental entities comprise a Council of Governments with a dedicated staff of professionals that provide a variety of services, including wastewater planning.

Sanitary sewer collection and treatment is provided by the University Area Joint Authority (UAJA) at its Spring Creek Pollution Control Facility. The Spring Creek Pollution Control Facility, a 10.6 million-gallon-per-day (mgd) advanced wastewater treatment plant, discharges to Spring Creek, a world-renowned brown trout fishery. Recent studies estimate that recreation associated with Spring Creek results in more than $1 million in tourism to Centre County annually.

Unfortunately, Spring Creek, a tributary to the Susquehanna River and Chesapeake Bay, is the only perennial water source that is large enough to provide an adequate discharge point for the majority of the treated effluent produced in the Centre Region.

With an average flow of approximately 45 mgd, Spring Creek can be significantly affected by the region's discharge, which currently accounts for an average of 12 percent of its flow, and is approximately 40 percent of total flow during low baseflow conditions.

Because of the high quality of this water resource and the significant flow impacts, UAJA has stringent tertiary discharge limits, including flow-based temperature limitations.

Additionally, the Centre Region is faced with a unique set of conditions for the management of water resources. First, the area has an extremely large, highquality groundwater source. Approximately 100 mgd of groundwater pass through the Spring Creek Watershed. Currently, the Centre Region has the ability to withdraw approximately 15 mgd of potable water from the various well fields scattered west and south of State College Borough.

Since the Centre Region only withdraws approximately 6.5 mgd of groundwater, it would appear that drinking water resources are sustainable well into the next century. However, groundwater provides baseflow, through seeps and springs, to the region's streams. As groundwater withdrawal increases in the Centre Region, a reduction in the groundwater baseflow is inevitable. In 1992, the Susquehanna River Basin Commission (SRBC) imposed a 7.3-mgd water withdrawal limitation for a portion of the region because of concerns surrounding the possible reduction, or elimination, of flow within tributaries to Spring Creek. While the region can withdraw drinking water safely from other areas, groundwater withdrawal and the potential impact upon Spring Creek and its tributaries will be a concern as the area grows.

With current growth estimates and the continued reliance upon Spring Creek as the sole discharge point, the region's discharge would account for an average of 15 percent of combined flow by the end of the year 2020. Coupled with increased groundwater withdrawal, the Centre Region faced a difficult problem. As the region grew, larger quantities of groundwater would be required to provide sufficient potable supplies; however, this would reduce flow within Spring Creek and exacerbate the impacts of wastewater discharge.

Because of these impacts on the water supplies and resources of the Centre Region, the community decided to explore a wastewater reuse project for the predicted increase in wastewater flow. If the additional wastewater generated could be reused within the community, the reliance upon groundwater supplies and the increasing discharge to the environment could be mitigated or possibly reversed. After a three-year study and public relations campaign, the Centre Region endorsed the Beneficial Reuse Alternative.

Beneficial reuse

The Beneficial Reuse Project was envisioned in three phases, lasting the predicted 20 years of accelerated growth within the region. The first phase consisted of the modification of the existing UAJA treatment facility and construction of the advanced water treatment facilities necessary for production of a potable-grade product. Also during the initial phase, a small distribution system would be constructed to an adjacent industrial park. During the initial phase, UAJA would have the capability to produce approximately 1.0 mgd of reuse water for industrial and commercial reuse.

The second and third phases of the project would be the further development of the distribution system and the addition of further reuse capacity at the treatment facility. The incremental nature of membrane technologies allowed the region to invest in its reuse project as growth occurred, deferring a portion of the capital cost to later years. The second and third phases included significant expansion of the availability of the reuse water, as well as several restoration projects for local waterways. These secondary phases would include several constructed wetlands to act as discharge points for additional baseflow in the smaller tributaries of Spring Creek that had been impacted by groundwater pumping.

After detailed hydrogeologic study, however, it was discovered that these wetlands would release the water into the active withdrawal wells, and the reuse water could comprise as much as 20 percent of the potable supply for the region. With the high possibility of indirect potable reuse, the project was envisioned to produce a product that met the nation's most stringent water reuse regulations as Pennsylvania was just developing its own regulations.

System upgrades

The upgrades at the existing facility were completed over a three-year period and included construction of a biological nutrient removal system for the hydraulic train of the existing UAJA facility, an upgrade of the award-winning biosolids composting facility, and construction of the advanced water treatment building.

The biological nutrient removal system was selected to meet predicted Chesapeake Bay discharge standards and can produce an effluent meeting UAJA's goals of less than 8.0 mg/l of total nitrogen and 0.13 mg/l of total phosphorus when combined with chemical precipitation.

Other improvements to the facility included construction of fine screening and grit removal, expansion of the primary and secondary clarifiers, installation of centrifuges and automated sludge-handling mechanisms, and installation of ultraviolet disinfection on the plant outfall. Total project costs for the conventional facility upgrades and addition of reuse water production was approximately $64 million, with a total capital cost investment for the remaining phases of nearly $90 million.

To produce the reuse water, UAJA had examined other successful projects, and in conjunction with its consultant, Herbert, Rowland & Grubic, Inc., developed a multiple-barrier approach to produce an exceptional quality product while ensuring adequate safeguards to reduce the potential for the production of a nonpotable product. Using secondary clarified wastewater as a raw product, the advanced water treatment process first provides prescreening with a 500-micron wedge wire strainer. Straining protects the expensive membrane units from particulate and algae damage and produces a consistent product for treatment.

Following straining, primary treatment is accomplished through microfiltration. Since a reverse osmosis system is the ultimate barrier for the advanced water treatment train, UAJA wanted to ensure the highest quality feedwater to enhance the performance and reduce the operating costs of the reverse osmosis system. After significant field trials, the microfiltration system was proven to provide the highest quality water with the lowest operating and maintenance costs. The fully automated microfiltration system incorporates backwash treatment to recover 99 percent of the product water for feed to the reverse osmosis system.

With a potable water product goal, UAJA had reviewed numerous processes for tertiary treatment of the wastewater effluent.

Reverse osmosis was the only process identified that could economically and reliably meet a stringent goal of less than 1.0 mg/l of total organic carbon, and a product water that met all current state and federal limits for drinking water. The reverse osmosis system at UAJA uses ultra-low-pressure, thin film composite membranes to produce a continuous supply of reuse water. With current performance of less than 30 mg/l of total dissolved solids and less than 0.5 mg/l of total organic carbon, the system is operational and meeting all water quality goals.

Following reverse osmosis, UAJA uses a two-step disinfection process for the final barrier. Utilizing medium-pressure, ultraviolet light disinfection, followed by sodium hypochlorite disinfection and chemical stabilization for corrosion control, UAJA then stores the reuse water for resale within its newly constructed distribution system. With a second phase of construction underway, the distribution system is being extended to a total of 11 miles of pipeline to serve the businesses and industries of the region. Numerous industries are preparing to receive the reuse water, including a commercial laundry, a concrete batch plant, and a local golf course that intends to irrigate with 0.4 to 0.6 mgd of reuse water daily.

Future of reuse

With a total capacity of 10.6 mgd in hydraulic treatment, and an ultimate reuse capacity of 3.0 mgd, the University Area Joint Authority and Centre Region are poised to meet their growth, while limiting their impacts to the groundwater and surface water resources of the community. As the second phase of construction nears completion, the region will have its largest customer to-date in operation and have approximately 50 percent of the total pipeline installed for the envisioned distribution system, with a commitment for one-third of the total reuse water production.

Actively marketing their high-quality resource, the Centre Region is hoping to attract additional users and industries that desire an exceptional quality source for a wide variety of end uses.

Jason Wert, P.E., DEE, a senior project manager with Herbert, Rowland & Grubic, Inc., State College, Pa., is involved in the design of alternative technologies for potable water and water reclamation, including low- and high-pressure membrane filtration systems. He can be contacted at 1-814-238-7117 or via e-mail at jwert@hrg-inc.com.


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