What is your design basis?
Flow and COD are only part of the design basis. The asset duty also depends on how the load is generated, how it varies, the wastewater fractions present and the performance required across the site operating range.
Assess the site before the schematic.
Each note examines a factor that can change the route, scope or operating burden of a wastewater or reuse project. The stated parameters and proposed route may appear complete while a critical site condition remains unverified. These gaps often surface only after the scope is fixed, proposals are received or commissioning begins.
Design basis
An influent table does not define the complete operating basis. These notes address load generation, variability, sector conditions and assumptions that should be tested.
Does the design account for the sector behind the water?
Sites with similar headline flow and quality values can still require different treatment routes because source streams, chemical use, cleaning practices, solids, temperature and production schedules differ.
Is reuse the priority, or is disposal being managed?
Reuse requires a confirmed receiver, demand profile, quality limits, storage, monitoring, off-spec diversion and fallback supply. A project focused on disposal reduction may require a different asset.
Reuse & water portfolio
Recovery begins with stream segregation, confirmed demand, required quality, storage and an off-spec route. A percentage alone does not define reuse.
High-grade reuse is not just polishing
Advanced treatment depends on the feed it receives, upstream stability, fouling and scaling control, cleaning requirements and the water quality required at the reuse point.
How much water is being used, and what should return?
Recovery should be based on source streams, confirmed demand, required quality and residual handling, not on a percentage alone.
Is ZLD the answer, or an assumption made too early?
ZLD should not be the starting assumption. Before evaporation or crystallisation is selected, establish the production and treatment operating basis: site water balance, reuse demand, recoverable streams, salt and scaling load, concentrate and residue routes, utilities, cleaning, staffing and maintenance.
Treatment performance
Meeting targets at one condition does not demonstrate performance across the site operating range. These notes address variability, diagnostics and design-basis change.
The plant is running. Is it absorbing variability?
A plant can meet targets at steady or reduced load and still lose performance during cleaning, restart, product changeover, return streams or changes in wastewater chemistry and biological load.
Before replacing equipment, review the process logic
The unit showing the problem may not be the unit creating it. Its feed, upstream controls, hydraulic and mass loading, utilities and maintenance condition should be checked before replacement is selected.
How a design basis drifts, and why it is found late
The scope and operating basis can change while earlier assumptions remain in place. The mismatch may not become visible until procurement, commissioning or handover.
Sludge, odor & residuals
Residual volumes, dewatering, storage, transport and odor pathways can determine whether the route remains operable.
Sludge is not the end of treatment
A compliant effluent route can still be difficult to operate if sludge and residual handling are not designed. Dry-solids load, wet volume, conditioning, dewatering, return liquors, storage, odor and removal frequency belong in route selection.
Odor is a pathway problem, not a product problem
Odor control begins by identifying where compounds form, how they are released, the airflow or pathway to receptors and when exposure occurs. Treating only the most visible point can leave the controlling source unresolved.
Biosolids reuse needs a defined receiver
A beneficial-use route exists only when treated material meets regulatory and receiver criteria and a confirmed outlet can accept the required volume on the required schedule, including seasonal and upset conditions.
Monitoring & control
Measurements, alarms and control responses should identify deterioration early enough to protect the process and the receiving use.
Monitoring before spending more
More instruments do not improve control unless each measurement is located early enough, maintained, trusted and linked to a defined response.
Alarms are not automation
Alarms notify operators of abnormal conditions; automatic control executes predefined responses. A plant needs both rationalised alarms and control logic suited to the process duty.
Commissioning as performance verification
Mechanical completion and start-up do not demonstrate process performance. Commissioning and performance testing should verify the flow and load range, water quality, chemical and energy demand, residuals, controls and recovery from representative disturbances.
Supplier readiness
Supplier proposals become comparable only when duty, assumptions, scope boundaries, controls, commissioning and guarantees are normalised.
Why supplier bids are hard to compare
Two quotations may use different influent assumptions, scope boundaries, redundancy, controls, residual handling, commissioning and guarantee conditions. Price comparison requires those differences to be normalised.
Is the asset defined, or is the duty still open?
A well-built asset can still underperform if its duty, operating range and performance-test conditions were not fully defined.
Technology selection before due diligence
Selecting technology before source characterisation and route definition can force the design basis around a preferred option. References and catalogues can inform evaluation but do not replace site-specific due diligence.
Asset definition
Define the asset duty before the project is priced.
A comparable proposal needs a common duty: what must be treated, recovered and rejected; the operating range; residual and utility requirements; control responses; and how performance will be demonstrated.
Asset dutyDefine source streams, flow and load ranges, target quality, reuse or discharge duty, residuals, utilities and operating variability before the first schematic.
Control and verificationDefine routing, monitoring, interlocks, off-spec handling, commissioning and performance-test requirements rather than leaving them to supplier interpretation.
Basis for comparisonCompare scope, assumptions, CAPEX and OPEX implications, operating requirements, risks and guarantees against the same duty.