What Data Is Required to Design Tertiary Treatment?
The complete input checklist for engineering a tertiary treatment upgrade.
Designing a reliable tertiary treatment system requires six categories of input data: influent/effluent quality (minimum 12 months), hydraulic data (average, peak, and diurnal patterns), site and space data (surveyed footprint), existing infrastructure inventory (reuse potential), regulatory targets (concentration and efficiency limits), and operational context (staffing, budget). Missing or incomplete data is the most common cause of design delays and cost overruns. Our Plant Assessment Tool is structured around this checklist — submit what you have, and our engineers will identify the gaps.
Key Numbers
The Six Data Categories
Influent / Effluent Quality
- •Secondary effluent: TSS, BOD₅, COD, TN (NH₄-N, NO₃-N), TP
- •Minimum 12 months of composite sampling data
- •Peak, average, and 90th-percentile concentrations
- •Seasonal variation patterns (summer vs. winter)
- •Particle size distribution (if filtration is considered)
Why it matters: Sizing is based on peak loads and worst-case concentrations, not averages. Missing peak data leads to undersized systems.
Hydraulic Data
- •Average daily flow (Qₐₛ), dry-weather flow (DWF), peak wet-weather flow (Qₚₑₐₖ)
- •Diurnal flow pattern (hourly variation)
- •Frequency and duration of storm flow events
- •Available hydraulic head between secondary clarifier and discharge point
- •Existing pumping station capacities
Why it matters: Tertiary treatment must handle peak flows without bypass. Hydraulic head determines whether gravity feed is possible (critical for OPEX).
Site & Space Data
- •Site plan with available footprint (surveyed, with levels)
- •Geotechnical conditions (groundwater level, soil bearing capacity)
- •Underground services (pipes, cables, culverts)
- •Access routes for construction vehicles and deliveries
- •Distance to nearest residential area (noise/odour constraints)
Why it matters: The footprint determines the technology shortlist. Geotechnical surprises are the most common cause of retrofit cost overruns.
Existing Infrastructure
- •Secondary clarifier dimensions and performance
- •Decommissioned or underused tanks/basins (potential for reuse)
- •Electrical supply: transformer capacity, MCC spare ways
- •Control system type and available I/O points
- •Chemical storage and delivery infrastructure
Why it matters: Reusing existing structures can reduce CAPEX by 30–50 %. Knowing the electrical and control capacity avoids costly surprises.
Regulatory Targets
- •Required effluent limits: TSS, TN, TP, BOD₅, COD (annual average and/or absolute)
- •Efficiency requirements (e.g. ≥87.5 % P removal)
- •Compliance deadline (2033, 2036, or 2039 depending on plant size)
- •Receiving water sensitivity classification
- •Any additional local/regional requirements beyond the EU Directive
Why it matters: The gap between current performance and target defines the treatment challenge. Efficiency-based limits can be harder to meet than concentration limits.
Operational & Financial Context
- •Current operating staff (number, qualifications)
- •Annual operating budget (energy, chemicals, maintenance)
- •Preferred project delivery model (EPC, design-bid-build, design & build)
- •Available capital budget or funding mechanism
- •Planned maintenance shutdowns or process changes in the next 3–5 years
Why it matters: Technology selection must match operational reality. A high-tech solution is wrong if the plant lacks staff to maintain it.
Engineering Insight: Data Quality Over Data Quantity
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Last reviewed: August 2026. Regulatory requirements may vary by national implementation. This content is for informational purposes and does not constitute legal or engineering advice.