With land fixed and both acquisition and relocation ruled out, the plan must increase treatment capacity within the existing footprint. As the consultant I would proceed:
Characterize the post-expansion load — project the 50%-larger flow and BOD5/TSS/nutrient loads from the expanded production rate, not just scale the current numbers linearly (some unit processes may not).
Audit for waste minimization / source reduction first — water reuse/recycling within the process, dry clean-up before wash-down, and process modifications can reduce the load the treatment plant must actually handle, buying capacity without new footprint.
Assess whether existing unit processes are under-loaded — a hydraulic or organic capacity audit (comparing actual vs. design loading) often reveals headroom the original design never used.
Intensify treatment within the existing tankage — convert a conventional activated-sludge basin to a higher-rate configuration (e.g. adding submerged fixed-film media — a moving-bed biofilm reactor retrofit — or switching to membrane bioreactor operation) to raise the biomass concentration and treatment rate per unit volume without adding new tanks.
Add equalization or optimize existing equalization — smooths peak loading so the intensified process is not sized for the worst instantaneous peak.
Consider going vertical or multi-level — package/compact treatment units (e.g. stacked clarifiers, membrane units) can add capacity on the same plan-area footprint.
Explore sending excess flow off-site under agreement — if a municipal WWTP has capacity, a pre-treatment-and-discharge (sewer-use) agreement moves part of the load off the industry's own land entirely.
Phase the upgrade and confirm regulatory approval — sequence construction to keep the plant operating, and confirm the intensified process can still reliably meet the discharge permit before committing capital.
