Troubleshooting Biological Phosphorus Removal – The Middle Atlantic Experience

Activated sludge biological phosphorus removal (BPR) is particularly sensitive to changes in influent characteristics and operational parameters. Several plants in the eastern United States have struggled with maintaining consistent BPR year-round, and four of these facilities were evaluated to summarize the challenges associated with achieving reliable BPR. Potential issues identified include: operation at excessive sludge ages, secondary phosphorus release, excessive anaerobic detention time, insufficient aeration capacity and aerobic dissolved oxygen (DO) levels, significant and variable influent phosphorus loads due to solids recycle streams, low pH, and mechanical issues with RAS/WAS collection. Operation at excessive solids retention time, solids recycle stream impacts and low pH operation were the most commonly indicated reasons for unreliable BPR. Readily biodegradable carbon (rbCOD) initiations decrease BPR efficacy particularly during periods of high solids recycle stream loading. SRT control and optimization, solids recycle stream treatment, DO control and alkalinity addition should be incorporated in the design of facilities to reduce the occurrence of BPR upsets.