The most common question about a bacterial culture is how much to apply, and the honest answer is that a single figure is not useful because the same dose means different things in different volumes of water. What is useful is the ratio between the seeded population and the population already in the basin. Below is how that ratio is worked out, how often the dose is repeated, and which measurements should be used to judge the result rather than a subjective impression after two weeks.
Product referenced in this article
Wastewater Treatment Bacteria JY-AO2-02 — application notes, specification table and document downloads for this range.
Why a single number is not the answer
A dose expressed as a volume of product is meaningless on its own, because the same litre of culture is a negligible addition to a large basin and a significant one to a small tank. The meaningful quantity is the ratio of the seeded population to the population already present, because what matters biologically is whether the introduced organisms are numerous enough relative to the existing community to establish and to compete.
That is why the first two things we ask for are the volume of the reactor being treated and the mixed liquor solids concentration. The volume tells you the hydraulic scale, and the solids tell you the population density. With those, plus what the product's viable count is at the point of delivery, the seeded-to-existing ratio can be estimated rather than guessed.
Calculating a starting dose
The working method is to express the target as a ratio rather than as a volume. For a culture intended to establish and become the working population in a reactor, the practical starting point is a seeded population of roughly one to five percent of the existing biomass per application, repeated as needed. This is an order-of-magnitude figure for setting a trial, not a specification, and it will be adjusted once responses are seen.
Two corrections matter more than the base figure. Activity is the first: the same volume of product at a lower viable count is a smaller dose, which is why a count guaranteed at the end of the storage period matters and not one taken at manufacture. Retention time is the second: the seeded population has to survive long enough to establish, and in a reactor with a short retention time a large fraction of it leaves before it multiplies. Where retention time is short, either the ratio must be higher or the dose must be repeated more frequently, and this is the most common reason a first dose appears to do nothing.
How often to repeat
Frequency follows from establishment time and from how quickly the population declines. A culture in a healthy reactor with a working biological population usually establishes within a few weeks, and a single well-chosen dose is often enough. A reactor that is being repeatedly disturbed — a plant that is shocked regularly, or one where conditions fluctuate sharply — needs repeated dosing, because the population cannot establish if the conditions it depends on do not persist.
There is a specific case worth naming, because it is so common and so often handled in the wrong order. Where a plant is dosing a culture to recover from a shock, the culture should follow the correction of whatever caused the shock, not precede it. Adding biology to a plant that is still receiving a toxic influent is spending money on a population that cannot survive, and it is a frequent cause of the conclusion that the product does not work.
Judging the result by measurement
Four measurements, and none of them is an impression. Operational stability: the settling and sludge volume behaviour, which is usually the first thing to change because a healthier population aggregates better. Organic removal: the COD or BOD figures that existed before the dose, compared with the same figures afterwards, at the same sampling point and time of day. Nitrification: the ammonia figure, which responds more slowly and is the measure that separates a cosmetic change from a working population. Heterotrophic rate, where the plant runs a respirometry or similar routine, which is a direct measure and often the first to move.
Two cautions on how the results are read. Odour is not a measurement: operators adapt to a persistent smell, and a subjective improvement reported from within a plant is weak evidence in a way an ammonia figure is not. And a single improvement is not attributable without a comparison — ideally a period before and after, and ideally a second comparable reactor that was not dosed. Where no comparison reactor exists, the best available substitute is a sufficiently long baseline at consistent sampling.
What to send us, and what you get back
Five items and we can return a specific starting dose rather than a general recommendation: the reactor volume; the mixed liquor solids concentration; the retention time; the figures you are currently trying to move, with the sample point; and the problem itself in one sentence — a shock, a start-up, a chronic exceedance or a specific compound.
What you get back is a starting dose, the repeat interval we would suggest, and the measurements we would want to see at what times. What we will not do is guarantee a result for a plant we have not seen, and we will say so if the problem turns out to be something no biology addresses — an inhibitory influent, a hydraulic problem, or a design fault. Those cases are worth identifying early, because they are not dosing problems and no amount of culture fixes them.
Frequently asked questions
- How much bacteria culture should I add to my wastewater plant?
- A single volume figure is not useful on its own, because the same dose means different things in different reactor volumes. What is meaningful is the seeded-to-existing population ratio. As a starting point for a trial, a seeded population of roughly one to five percent of existing biomass per application is the order of magnitude we work to, adjusted for product activity and retention time. Send us the reactor volume, the solids concentration, the retention time and the current figures, and we will return a specific starting dose.
- How often should bacteria be dosed?
- It follows from establishment time and how fast the population declines. In a healthy reactor with a working biology, a single well-chosen dose usually establishes within a few weeks. Where the plant is repeatedly disturbed or conditions fluctuate sharply, the population cannot establish and the dose must be repeated. Where the dose is for recovery from a shock, it should follow the correction of the cause rather than precede it.
- How soon will I see a difference?
- The first thing to change is usually sludge settling behaviour and sludge volume, because a healthier population aggregates better. Organic removal figures typically move within a week or two. Ammonia responds more slowly, and it is the measure that distinguishes a cosmetic change from a working population. We agree a measurement plan before the dose so the result is readable rather than a matter of opinion.
- Can a culture fix a plant that keeps being shocked?
- Not on its own. A culture added to a plant still receiving a toxic influent is spending money on a population that cannot survive. Correct whatever is causing the shock first, then dose. If the cause cannot be corrected, the honest answer is that no biological product will hold the plant, and it is worth knowing that before buying rather than after.