Water Reuse Project Provides Advanced Water Treatment
The region surrounding State College, PA, faced a problem: population growth had led to increased water use, but the lack of a major river meant options for disposing of the resulting wastewater were restricted.
Construction underway at the University Area Joint Authority treatment plant
The region surrounding State College, PA, faced a problem: population growth had led to increased water use, but the lack of a major river meant options for disposing of the resulting wastewater were restricted. And since the largest waterway in the region, Spring Creek, is a renowned and environmentally protected trout fishery, the solution to the problem had to be innovative. The University Area Joint Authority (UAJA), together with local engineers Herbert, Rowland & Grubic (HRG), decided in the early 1990s to address the problem via beneficial reuse.
Beneficial reuse, the recycling of wastewater for nonpotable consumer and industrial use, allowed UAJA to expand its treated wastewater output from 6 mgd to 10.4 mgd thanks to the addition of a biological nutrient removal (BNR) treatment system. Additionally, an advanced water treatment (AWT) system was built to withdraw a portion of this flow and produce 3.0 mgd of potable-grade quality water. The AWT system consisted of microfiltration, reverse osmosis, ultraviolet irradiation, chemical buffering and chlorine disinfection.
After extensive planning and public relations, UAJA and HRG set out to come up with a design for the plant expansion. Together they reviewed a list of operational concerns and then worked to select desirable systems that would accomplish UAJA’s goals in an efficient manner. Specific improvements included:
• Design and construction of a three-train biological nutrient removal (BNR) system to achieve BNR to a level of 8 parts per million (ppm) of total nitrogen and 1 ppm of phosphorous.
• Conversion of the disinfection system to eliminate the use of chlorine and use ultraviolet (UV).
The biggest change to the facility would be the addition of microfiltration (MF) and reverse osmosis (RO). Even though the recycled water was primarily earmarked for nonpotable consumer and industrial use, the water would be discharged to a local waterway in periods of off-peak use. As this waterway was part of the local raw water supply, the recycled water had to meet the most stringent requirements of state and federal drinking water regulations.
In order to prove its safety as well as familiarize UAJA with membrane filtration technologies and select the equipment for microfiltration and reverse osmosis, HRG set up a two-tiered pilot test. This competitive analysis allowed UAJA to procure the most cost-effective and operable equipment for full-scale implementation.
The project involved the design and construction of a three-train biological nutrient removal (BNR) system to achieve BNR to a level of 8 ppm of total nitrogen and 1 ppm of phosphorous.
Since the ultimate project would include two stages of treatment - MF followed by RO - a two-tiered test was necessary to determine the best equipment for each individual stage. If multiple manufacturers of MF and RO were competing simultaneously, the proper interpretation of water quality data and present worth operation costs would be difficult. Thus, Phase I of the pilot test included a competitive analysis between MF and UF manufacturers and kept the subsequent RO units homogeneous. A second pilot testing period (Phase II) took place after the completion of Phase I testing and the selection of the most advantageous MF/UF unit. The pilot testing facilities and water quality analysis protocols were thus tailored to multiple pilot tests.
While the water quality of the MF/UF effluents alone did not comply with all water quality goals set for the final product water, all three MF/UF units were able to produce water that met the intermediate goals of the first stage of the two-stage treatment process. After microfiltration, water analysis demonstrated that trace contaminants were nonexistent, but three parameters in particular did require further treatment by reverse osmosis: nitrates (NO3-), Total Dissolved Solids (TDS) and Total Organic Carbon (TOC).
The total nitrogen and nitrates that remained were too high for immediate distribution without further treatment. With the upgrading of the UAJA facility as part of the overall Beneficial Reuse Project, biological nutrient removal (BNR) would be incorporated, an addition that would greatly reduce total nitrogen and remove this parameter from the feed water. Still, reverse osmosis can also treat for this compound and results of the final water met desired limits.
The second parameter of concern was total dissolved solids (TDS). While TDS is not an indicator of pathogenic or viral activity, it is an aesthetic parameter established by the Environmental Protection Agency (EPA) and Pennsylvania Department of Environmental Protection (DEP). UAJA’s Phase I recycled water exceeded the Maximum Contaminant Level (MCL-500 mg/l) by approximately 150 mg/l and also required further treatment after microfiltration. Typical treatment methods include lime softening, ion exchange columns, nanofiltration and reverse osmosis. Since RO was anticipated as a necessity, this result was not cause for concern.
A series of pilot tests examined the performance of various membrane systems.
The final water quality parameter was Total Organic Carbon (TOC). TOC is often used in reuse projects as an overall indicator of water quality; however, little scientific background has been established on this topic. UAJA, the Beneficial Reuse Project Management Team (PMT), and local water authorities had set a goal of 1.0 mg/l of TOC for the recycled water. TOCs averaged between 6.0 and 7.0 mg/l for the various MF and UF units. Further treatment would be required to reduce TOC - typical methods include coagulation and filtration, activated carbon, nanofiltration and reverse osmosis.
Based upon the operation of the pilot facility and analysis of water quality and process parameters, HRG concluded that microfiltration used in conjunction with reverse osmosis produced recycled water that exceeded all established water quality limits. The RO units that followed the MF/UF units met all established water quality limits, reducing total dissolved solids and total organic carbon below 100 mg/l and 1.0 mg/l respectively. Additionally, no synthetic organics or volatile organics were found to be present in the RO permeate.
Upon completion of the design phase and pilot testing, UAJA and HRG embarked upon construction. The expanded wastewater treatment plant was completed in the spring of 2005 and as a result, a world-class trout fishery was preserved, a community’s water resources were replenished and the State College region is equipped for growth in the 21st century. WW
About the Authors:
Brian L. Book, Regional Manager for Herbert, Rowland & Grubic, Inc. (HRG) in State College, PA, served as Project Manager for the UAJA Beneficial Reuse Project. Jason D. Wert of HRG served as Assistant Project Manager. Adam Wilson, also from HRG, assisted with the article. For more information, contact HRG in State College at 814-238-7117.