The lagoon is taking more organic load than it can process

What is actually happening

A facultative or aerated lagoon runs a rough balance. Organic material arrives, resident organisms oxidise it, and oxygen is replenished by aeration, by wind and by algal photosynthesis at the surface. The balance holds while the arrival rate sits inside the treatment rate.

A shock load breaks that balance from one side. Two or three times the normal organic arrival consumes dissolved oxygen faster than it can be replaced, and the surplus material does not simply wait. It settles. What the water column cannot process in passing becomes an addition to the sludge blanket, which is why a plant that has taken repeated seasonal shocks often finds its capacity problem arrived years before anyone measured it.

Where it typically comes from

• Seasonal industrial discharge. Food processing, dairy, brewing and sugar campaigns concentrate a year of load into a few months, and a lagoon sized for the annual average is not sized for the season.
• Septage receiving. A hauled load is small in volume and very large in organic strength, and a receiving programme without a rate limit puts the whole of it into the lagoon in an afternoon.
• Wet weather and infiltration. Less an organic spike than a hydraulic one, but it shortens retention time, which reduces how much of the load is treated before it leaves.
• A failing upstream process. Where a primary or pretreatment step is not doing its job, the lagoon inherits the difference and the symptom appears where it is visible rather than where it started.

What biological treatment reaches

The mechanism is enzymatic hydrolysis of organic material. Protease, cellulase and lipase break complex organic solids into fragments small enough for bacterial cells to take up and oxidise, and published work shows mixtures of the three reduce total suspended solids by 30 to 50 per cent with improved settling. Applied to a lagoon under load, that means a larger share of what arrives is digested in the water column rather than settling to the bottom.

The honest scope of that: it lowers BOD, it degrades fats, oils and grease, it reduces what accumulates as sludge, and it improves settling. Those are all statements about what happens to material.

What it does not reach

• Oxygen. Biological product does not aerate a lagoon. Where dissolved oxygen is the binding constraint, adding organisms adds demand.
• Hydraulics. Short-circuiting, dead zones and lost retention time are physical problems, and no dose changes the path water takes through a cell.
• Ammonia and nitrogen. Nitrifying organisms do not survive drying, so a dry product cannot contain viable nitrifiers whatever its label implies. If a shock load is pushing ammonia towards a permit limit, that is not a problem this product line addresses.
• The septic conditions and the odour a sustained shock produces. We do not sell odour control and make no claim to it, and the claims policy sets out why that boundary sits where it does.

What to do about it

Establish whether the constraint is load or oxygen before spending anything. Dissolved oxygen readings across the cell, taken at the same points and depths on a repeatable basis, will usually separate the two within a fortnight, and they cost nothing but the walk. If oxygen holds up under load, the organic fraction is the useful place to intervene. If it collapses, aeration is the first call and biology is the second.

Where the load is seasonal and predictable, treatment ahead of the season is worth more than treatment during it. Building biomass capability before the campaign arrives is a different proposition from recovering a lagoon that has already gone anaerobic, and the second is considerably harder.