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Issue link: http://wateronline.epubxp.com/i/672151
By Michele Braas and Jason Wert A s more organizations, municipalities, and companies turn to water reuse as a means to decrease their water and energy footprints and reduce costs, these groups implement technologies that often involve low- and high-pressure membrane filtration. A common challenge of membrane filtration is biofouling, which is the colonization of the membranes by bacteriological growth, resulting in decreased performance of the membrane system. Biofouling particularly concerns municipal wastewater operators in their reclamation processes. These operators must consider the cost-effective application of technology to control biofouling while ensuring the technology provides other benefits such as advanced oxidation. At the University Area Joint Authority (UAJA), serving an area in central Pennsylvania, leaders have implemented an advanced oxidation process (AOP) to control biofouling of its reverse osmosis (RO) system. The additional system simultaneously improves the Authority's ability to remove contaminants of concern. The University Area Joint Authority Surrounding Pennsylvania State University and the Borough of State College, UAJA provides wastewater collection, treatment, and water reuse to more than 80,000 residents. While not providing wastewater services to the university's entire campus, the Authority manages the surrounding growing community's need for long- term sustainability and watershed protection. Nearby flow the headwaters of Spring Creek, a high-quality, cold-water fishery. Because of its designation as "high quality" and the potential for temperature impacts from the heat within wastewater discharge, the Pennsylvania Department of Environmental Protection (PADEP) places strict limitations on both the quality and volume of treated effluent discharge allowed from the Authority. The UAJA facility meets tertiary effluence standards with some of the most stringent discharge limits in the state, including a 0.13 mg/L total dissolved phosphorus standard. First constructed in 1969 with a hydraulic design capacity of 3.84 MGD, the Authority upgraded its facility first in 1992 and again in 2002. The PADEP also granted re-ratings in 1993 and 2013. Today, the site is rated for a maximum monthly flow of 10.56 MGD and 50,000 pounds per day of organic loading. To meet the PADEP's regulatory restrictions, the Authority implemented an award-winning water reuse program in 2002 and began operations with its new facility in 2005. It now reclaims a portion of its treated wastewater effluent to Spring Creek with water quality exceeding state and federal limits for drinking water. The Authority also provides 1.0 MGD of beneficial reuse water to the community for swimming pools, laundromats, car washes, turf grass irrigation, heating and cooling supplies, and stream augmentation. This not only reduces the volume headed to Spring Creek but also offsets the potable water requirements within the community. Advanced Water Treatment The UAJA Beneficial Reuse Project Advanced Water Treatment Building houses a series of processes that transform secondary clarifier effluent into a water supply that meets all federal and state requirements for drinking water. Originally, the processes consisted of microfiltration, RO, pH stabilization, UV disinfection, and chlorination for distribution residual. After the most recent system update began operating, the Authority discovered the planned intermittent biocide treatment for water prior to its entry into RO did not sufficiently control biofouling. To stabilize pressure gains, the Authority installed a combination of chlorination and dechlorination steps prior to RO, with supplemental biocide application every few weeks. During a periodic performance review in 2013, the Authority noted elevated salt passage and nitrogen concentrations in its reuse water. The resulting discharge was still within the required limits; however, the RO membranes had exceeded their usable life. The Authority elected to replace those membranes in 2015. With new membranes as part of the process, the organization decided to review all of its costs associated with the membrane operations, finding that its biofouling costs had risen dramatically throughout the years. Additionally, the Authority found that its equipment for on-site generation of sodium hypochlorite was worn and likely in need of a significant capital upgrade. 8 wateronline.com n Water Innovations The Cure For Membrane Biofouling After reviewing multiple methods, engineers and operators at a Pennsylvania water reclamation facility discover a winning pretreatment formula for reverse osmosis biofouling control. Chemical Use Approximate Costs Sodium Hydroxide pH Adjustment $34,000 Salt Sodium Hypochlorite Production $14,000 Reverse Osmosis Chemicals Clean in Place $10,000 Biological Control Chlorination/ Dechlorination and Biocide $262,000 Table 1. CY 2012 Costs For Chemicals Associated With RO