Achieving Biological Phosphorus Removal Stability and Optimizing the System through Online Controls Provides Reliability and Savings

The Durham Advanced Wastewater Treatment Facility (AWWTF) has a history of continued evolution in its Enhanced Biological Phosphorus Removal Process (EBPR). Following the initial transition to EBPR, a sludge fermenter was installed to increase volatile fatty acids. Subsequent refinements were made to the basin configuration to improve aerobic uptake of phosphorus in the activated sludge process. In 2009, a struvite recovery facility was installed to reduce recycle phosphorus and improve EBPR stability. Throughout this time the facility had periodic upsets in EBPR, which increased dependence on chemicals to meet the low effluent total phosphorus limit (0.11 mg/L). To increase understanding of the EPBR process and provide the ability to respond to diurnal variations, a suite of online instrumentation was installed during the summer of 2013. The installed instrumentation included solids and blanket measurements to assist in control of the SRT and RAS flow rates. Other instruments include measurement of the phosphorus release in the anaerobic zone and nitrate removal in the anoxic zone, and influent ammonia, VFAs and ortho-phosphorus. The first challenge of adding these instruments was the requirement to validate the results and incorporate instrumentation maintenance to gain comfort in their reliability. Most discrepancies during this initial period could be traced back to maintenance or physical difficulties. The results show diurnal relationships that could not be observed using daily composite samples. Control loops to improve overall treatment control and performance have been drafted and will be implemented during the next phase of this project.