Why equalisation tanks get undersized on campaign-driven sites

Most equalisation tank sizing starts from an average daily flow figure — total daily volume divided by 24 hours, with a multiplier bolted on for safety. That approach works reasonably well for a site that actually runs close to steady state. It fails, predictably, on any site that runs in shifts, batches, or seasonal campaigns, which describes most industrial sites in Egypt.

The mistake

Take a food processing site running three shifts on weekdays and shutting down completely on Friday. An average-flow calculation smooths that pattern into a single number that never actually occurs on the plant floor. The real hydraulic and organic load arrives in spikes — heaviest during the first production hours after a shutdown, when cleaning-in-place and startup effluent both hit the drain at once.

A tank sized to average flow has no buffer for that spike. It either overflows, forcing an uncontrolled discharge, or the downstream biological stage gets hit with a load and flow rate it wasn't designed for, and treatment performance drops exactly when the discharge permit matters most.

What sizing against the actual schedule looks like

The fix isn't a bigger safety factor on the same average-flow calculation — it's building the tank against the site's actual production schedule: shift pattern, cleaning cycles, and any seasonal campaign variation, not just annual throughput. That means asking for (or measuring) hourly flow and load data across a representative production week, not a single average figure from a utility bill.

Two things fall out of that exercise, cheaply:

• The equalisation tank volume is set by the actual peak-to-average ratio for that specific site, not a generic industry rule of thumb.
• Dosing systems downstream (coagulant, pH correction, nutrients for biological treatment) get buffer capacity sized to the same spike, instead of running at a fixed rate that's wrong for most of the day.

It's a cheaper fix than it sounds — equalisation volume is one of the least expensive ways to buy resilience in a wastewater treatment train, and it's usually the first thing value-engineered out when a design is built against an average-flow number that never happens on site.