Conference Agenda

Biological phosphorus removal (BPR) is a powerful method to meet effluent phosphorus requirements. At Clean Water Services (CWS), BPR is capable of producing effluent ortho-phosphorus concentrations below 0.1 mg/L, however at times, the performance degrades and effluent phosphorus concentrations can exceed 2 mg/L. Previous CWS work has shown measurements of the phosphorus uptake rate at the end of the aeration, which we’ve termed the residual phosphorus uptake rate (RPU), correlate well with BPR stability. Higher RPU rates correspond to more stable BPR and decreases in RPU can predict impending increases in the secondary effluent orthophosphate concentration. Because phosphorus uptake in some phosphorus accumulating organisms is driven by the amount of stored polyhydroxyalkanoate (PHA), it was hypothesized that the health of the BPR process is related to the biomass’ ability to store excess PHA, allowing them to better manage variable loading conditions. CWS has recently optimized a PHA analysis method, allowing us to investigate this hypothesis further and to ask wider questions into the behavior of the BPR process.

For approximately 6 months, the PHA content of the biomass has been measured with each RPU batch test. Contrary to our original hypothesis, there does not appear to be a consistent relationship between RPU and the total amount of PHA in the biomass. We have therefore started characterizing the relationship between phosphorus uptake rate and PHA content at other locations along the basins. A more clearly defined relationship was identified between uptake rates measured early in the aeration basin and the polyhydroxyvalerate (PHV) concentration. We continue to explore the dynamics of phosphorus uptake and PHA content along the length of the aeration basins to build a better understanding of the relationships and variability that may be observed.

PHA data can provide further information into the behavior of the BPR process and suggest shortcomings in our understanding of key operational parameters. This paper will present the current status of the CWS PHA research and investigate other factors that may be influencing the interrelationship between phosphorus uptake rates, PHA storage and PHA utilization.

Stringent nutrient limits can be achieved while also providing for energy efficient process operation. The secondary upgrade at the Budd Inlet Treatment Plant (BITP) owned and operated by LOTT Clean Water Alliance in Olympia, Washington is a prime example. Upgrades to the instrumentation, aeration system, and controls associated with ammonia-based aeration control (ABAC) enabled staff to implement low-DO simultaneous nitrification and denitrification. This resulted in improved effluent quality, approximately 50% lower methanol use for nitrate polishing, and reduced aeration demand in the second aeration step. This presentation will describe the upgrades and how they can achieve extremely good nitrogen removal in the first stage of treatment, reducing loading to the second stage as an example for how similar success can be achieved at other plants in the area.

The BITP has stringent total inorganic nitrogen (TIN) limits of 3 mg/L in spring through fall, as well as total maximum daily load limits which are potentially more restrictive, depending on flow. Before and after the recent upgrades, treatment was accomplished with a 4-stage Bardenpho process. Prior to the upgrades, the first anoxic and first aeration zones were in separate tanks and aeration was controlled on a per-treatment-train basis. The upgrades combined the first anoxic and aeration stages into the old aeration tank, including new swing zones to adjust aerated volume, significantly reducing the energy required for mixed liquor recycle and reducing the treatment volume. Additional instrumentation and control were added to the new process, including influent and mid-train ammonia probes as well as dissolved oxygen (DO) probes and airflow control in each zone.

These changes provided the operators great flexibility and insight into the control of their process. Come learn how the staff put the improvements to use as they dialed down the oxygen supply using ABAC control, adjustable recycle ratios, and the swing zones. Eventually, the process moved into simultaneous nitrification denitrification (SND) giving further reductions in energy and methanol use in the second stage. Effluent TIN was maintained at 1.5 mg/l or less throughout.