Decision Question
What storm flows and pollutant loads reached the works, how did the existing HST respond, and what duty should inform the new side-stream treatment design?
Capturing storm first-flush loads to inform treatment-capacity decisions.
Temporary high-frequency monitoring captured storm loads that conventional sampling had missed. The evidence helped the project team assess solids capture, review design assumptions and consider whether additional settlement capacity was required.
Site / Asset Snapshot
Site Type And Scale
Biological filter works Approx. 22,500 PE
Main Treatment
Primary settlement, biological filters, HSTs, nitrifying filters and tertiary filtration
Project Stage
Design and optioneering
Monitoring Scope
Two temporary Optimisers at the works inlet and HST outlet
Process And Monitoring Points
Two Optimisers provided a time-aligned view across the treatment stage.
WORKS INLET
PRIMARY SETTLEMENT
BIOLOGICAL FILTERS
HUMUS SETTLEMENT
NITRIFYING + TERTIARY
FINAL EFFLUENT
1 Works inlet 2 HST outlet
Project Need
Primary Driver
An increased full-flow-to-treatment requirement and the need to develop new side-stream storm treatment
Evidence Gap
Earlier sampling had not captured storm onset, first-flush loading or longer events, leaving the design basis uncertain
Why It Mattered
Observed evidence was needed to assess settlement capacity and headroom, and quantify the storm duty informing the new side-stream process
BI-Zen Delivery, Evidence And Decision Informed
Two temporary Optimisers aligned inlet loading, client flow data and HST response during live storm conditions.
BI-Zen Delivery
Deployment
Two temporary Optimisers at the works inlet and HST outlet.
Measured
COD, ammonium, nitrate, turbidity, redox, pH and temperature.
Aligned With
Client flow information through a live site dashboard.
Service Provided
Deployment, maintenance, data-quality checks and access to usable evidence while monitoring remained live.
HST Performance During Storm Loading
What Became Clearer
High-frequency monitoring captured storm onset, first-flush loading and longer events that conventional sampling had missed. By aligning works inlet load, flow and HST outlet turbidity, BI-Zen quantified the actual storm duty reaching the works and showed how the existing settlement stage responded.
The evidence confirmed that the HSTs maintained effective solids capture across the monitored hydraulic range, avoiding unnecessary investment in additional settlement capacity. Crucially, it also showed that the proposed side-stream treatment process would have been undersized against the observed storm duty. Anglian Water was therefore able to revise the design before construction, avoiding the cost, disruption and performance risks associated with correcting an undersized solution later.
Decision Informed
Anglian Water used the measured site evidence to revise the side-stream storm treatment design. The completed scheme reflects the observed storm loads.
The smaller option developed from the earlier design basis would not have met the monitored duty.