How much bacteria does a lagoon need?

The honest answer is not a figure you can look up

The question sounds as though it should have a tidy answer — a fixed amount of product for a given size of lagoon — and the category is full of pages that oblige. The honest answer is that a credible quantity does not exist until the lagoon has been characterised. It comes from the manufacturer's written dose table, applied to the specific lagoon and then reviewed by a person before it becomes an order. The dose table is the only legitimate source of a quantity; everything upstream of it is measurement and judgement, not arithmetic you can do from a symptom.

What actually sets the amount

Several properties of the lagoon and the load it carries feed the sizing, and none of them can be guessed from the outside. Begin with the water itself: the surface area of each cell and the water depth set the volume to be treated, and a system of several cells in series has to be taken cell by cell rather than as one pooled figure. Then the load passing through it. The influent flow rate and the organic strength of that influent — its biochemical oxygen demand — bear on how hard both the initial and the ongoing dose have to work, and taken together they give the hydraulic retention time, the average period a parcel of water spends in the cell. Retention time counts twice, because a lagoon that turns its water over too quickly can carry organisms out before they have acted — which decides whether biological treatment is viable at all, before it decides how much is needed.

Against that background sits the material to be reduced. The measured depth and distribution of the sludge set the volume of accumulated solids, and the pivotal input is the volatile — treatable — fraction of that material, because bioaugmentation acts on the organic share only: the inert fraction of grit, sand, silt and mineral solids is not biodegradable and remains at any dose. Water temperature and the standard of mixing and aeration then govern how the organisms are delivered and how active they are, since biological activity slows sharply in cold water and a poorly mixed cell starves the process of contact. The product and the objective close the calculation — a concentrated formulation is applied at a fraction of the mass of a standard one, a sinking solid and a soluble pouch place organisms in different parts of the water body, and whether the aim is to knock down an established blanket or to hold a maintained system steady moves the amount again. The manufacturer's dose table is what converts all of these inputs into a quantity; a symptom description cannot.

Where a quantity must not come from

Notice what is absent from that list. A quantity does not come from a rule of thumb, from a competitor's online calculator, from a concentration attached to a symptom, or from a case-study quantity reverse-engineered to fit your lagoon. Each of those produces a figure that looks authoritative and is disconnected from the material actually in the water. A figure of that kind is worse than no figure, because it invites an order that is confidently wrong.

Why identical lagoons can need different amounts

A lagoon of largely digestible organic material and a lagoon that has taken road grit and mineral load for years can share every external dimension and still need different amounts of product, because the treatable share of the sludge differs. Bioaugmentation acts on the volatile fraction, so the quantity of usable material — not the depth on a dipstick — is what the sizing turns on. No figure attached to dimensions alone can know that share, which is why the volatile fraction has to be measured or supplied before a quantity means anything.

Why a person reviews what the plan sizes

This is the reasoning behind how the dosing plan is built. It gathers what can be gathered — the format the duty calls for, the dimensions of the cell, the figures you already hold on depth and volatile fraction — and characterises the lagoon. It then sizes an indicative quantity from the manufacturer's method and hands it to a person, because the figure has to be read against the particular lagoon and because the judgement of whether biological treatment is even the right answer is not something to automate. An under-sized order is not a small error: to the operator it reads as a product that does not work, when the truth is that it was never sized to the material in front of it.

What SediLogic does, and what it does not

A boundary matters here. SediLogic does not perform, arrange or subcontract on-site sludge surveys, and it will not come and measure your lagoon for you — though it can test a sludge sample you send in. Where you already hold survey figures — a depth profile, a total accumulated volume, a volatile fraction from a laboratory — those make the sizing considerably more accurate, and the dosing plan is built to use them. Where you do not, the plan still characterises what it can and stays candid about the uncertainty that remains. Either way the destination is the same: the dosing plan sizes an indicative order from the manufacturer's method on the figures you enter, and a person reviews it before it becomes an order. That is what the dosing plan at /dosing-plan is for.