I Sell Probiotics. Here's When I Tell Clients Not to Buy Them.

Almost every week I get the same message, usually late at night, usually from a building administrator or a plant operator who has been getting complaints all day: "Sir, our STP is smelling. How many kilos of bacteria do we need?"

We sell probiotics. It would be easy for me to answer that question with a number and a delivery date. But I have been designing and fixing sewage treatment plants in the Philippines long enough to know that most of the time, the bag of bacteria is not what that plant needs. And if I sell it anyway, I will be back at the same site in three weeks, and the smell will still be there.

So here is how I actually think about it.

Sewage already comes with its own bacteria

This is the part that surprises people. Domestic wastewater is not sterile. It arrives at your plant loaded with the organisms that break it down, and given oxygen, time, and a place to hold on, they will multiply on their own. That is the whole idea behind activated sludge. You are not really buying bacteria; you are building a home for them and keeping them there.

A healthy plant grows more biomass than it needs. That is why we waste sludge. If a plant is running properly, it is producing bacteria, not consuming them. So when somebody tells me they have to buy bacteria every single month, forever, my first thought is not "they need a bigger dose." My first thought is: something in that plant is killing or flushing out the biomass faster than it can grow, and nobody has found it yet.

When I do recommend probiotics

There are real situations where dosing makes sense, and I want to be specific about them rather than vague.

Commissioning a new plant. A brand new tank with clean water and a fresh influent line can take four to eight weeks to build up a working population on its own. Seeding it shortens that considerably. On a project where the client has an occupancy permit inspection coming and a plant that has never seen sewage, that head start is worth paying for. I would rather seed properly at startup than explain a failed compliance sample later.

Restarting after a long shutdown. We saw a lot of this after the pandemic, and we still see it with resorts and schools that go quiet for months. The tank sat idle, the blower was off, the biomass starved and went septic. Re-seeding a dead tank is a legitimate use.

Recovery after a chemical shock. Somebody dumps a drum of bleach, or a cleaning contractor flushes disinfectant down a floor drain over a long weekend, and by Monday the mixed liquor has gone pale and the settling test looks like dirty water. The biomass is genuinely dead. Dosing shortens the recovery. But — and this matters more than the dose — you have to find out who dumped it and stop them, or you are buying bacteria again next month.

Fats, oils and grease that the plant was never sized for. Certain strains produce lipase and do help chew through grease in lines and traps. I have used this in kitchens and canteens to buy breathing room while the real fix is being fabricated. Notice the phrase: buy breathing room. It is a bridge, not a destination.

When probiotics will not save you, no matter how much you pour

Before I quote anyone a dose, I check five things. Four of them are free.

Oxygen. If the dissolved oxygen in your aeration tank is sitting below about 1.0 mg/L, adding aerobic bacteria is like sending guests to a house with no air. They will not work and they will not survive. Undersized blower, clogged diffusers, a blower running two hours a day because somebody was told to save on electricity — I have found all three. Fix the air first. Aeration is boring and it is usually the answer.

Sludge retention. Is there return sludge? Is the clarifier holding the solids, or is the blanket rising and washing MLSS straight out with the effluent? If your solids are leaving the plant, you are not treating anything. You are feeding the drain, and probiotics just make that a more expensive drain.

Hydraulic loading. If the tank is too small for the flow it is actually receiving — and on a lot of buildings the real flow is nothing like the design flow written on the as-built — the water leaves before the bacteria can eat. No product fixes a hydraulic retention time that is half of what it should be.

Ongoing toxicity. Disinfectant, strong acid or caustic from a cleaning routine, certain sanitizers, high salinity from a specific process line. If the poison keeps arriving, the monthly bacteria bill becomes permanent. That is not treatment. That is a subscription.

Nutrient balance. This one costs a lab test. Industrial and food streams are often heavy on organics and short on nitrogen and phosphorus. Bacteria need a rough balance to build cells. If the ratio is badly off, the population will not develop regardless of what you seed it with, and the answer is nutrient supplementation, not more organisms.

One more that deserves its own mention: if the parameter failing is ammonia, adding general-purpose bacteria will not help you at all. The organisms that remove ammonia are a different workforce with entirely different demands, and they are usually failing for a reason a product cannot reach.

The plant that taught me this

Early in IWSI's history we took on a food processing plant — hams, hotdogs, beef jerky. When we arrived, they were already dosing bacteria almost weekly. The previous contractor had sold them a standing order and then walked off the site after collecting most of his payment, which is a story for another day.

The odor was bad enough that complaints had gone past the neighbors to the Barangay, then to the City Health Office, and then to the DOH. The treatment area sat on the second floor, so there was nowhere for the smell to hide.

I will be honest about my own part in it. We underestimated the emulsified fats in that stream. Emulsified FOG does not behave like the floating grease a conventional interceptor is designed to catch — it passes straight through, arrives at the aeration tank, and coats everything. We had also allowed the domestic line and the process line to be combined, which pushed the whole flow into a stricter compliance category and made every parameter harder to hit. Both of those were design decisions, and both were mine to own.

No quantity of probiotics was ever going to fix that. The bacteria being dosed weekly were doing exactly what they were sold to do, and the plant still stank, because the problem was upstream of biology. It only stabilized after we changed the physical design: proper separation of the streams, the correct pre-treatment for an emulsified stream rather than a grease interceptor, and FBBR-style fixed-film media retrofitted into the aeration tank so the plant could hold a much larger population in the same volume.

We did dose during the re-seeding after that retrofit. Then we stopped, and the plant kept running. That is the shape of a correct probiotic application: a defined event with an end date, not a line item that renews forever.

For what it is worth, we did not bill that client again until the plant passed. Their trust had already been spent by somebody else, and the only way to get it back was to be on site at whatever hour the plant needed us, holidays included. We only had to do that once, because we never repeated those design mistakes.

Two questions worth asking your supplier

If someone is selling you a recurring monthly dose, ask them what is consuming the biomass. A plant that cannot hold its own population has a cause, and a supplier who has looked at the plant properly should be able to name it — low DO, solids washout, a toxic input, short retention time, nutrient deficiency. "Your bacteria just get used up" is not a cause.

And ask whether the product is proprietary to that supplier. Not because proprietary is automatically wrong, but because you should know in advance whether a routine consumable ties your plant to one company's price list for the next ten years. Among wastewater companies in the Philippines, that arrangement is common enough that it is worth asking about before you sign, not after.

What I tell people now

Probiotics are a genuine tool. Used at commissioning, at restart, after a shock, or as a bridge while a real fix is fabricated, they earn their cost and I am happy to supply them. Used as a monthly patch over an aeration problem or a design problem, they are the most expensive way I know to not solve anything.

Before you order another sack, spend an afternoon on the plant instead. Take a DO reading in the aeration tank. Do a 30-minute settling test in a one-liter cylinder and look at what settles and how clear the top is. Check whether the return sludge pump is actually running. Ask the housekeeping and maintenance staff — not the building admin, the people holding the hose — what gets poured down the drains and when. Those four things will tell you more than any product datasheet, and they cost nothing. What the plant smells like while you do it will tell you a fifth.

If you go through that and you are still not sure what you are looking at, send me what you found. I would rather sell one correct dose than twelve wrong ones. If you would rather have somebody looking at the plant on a schedule, we do O&M support as well.

Book a free 15-minute consultation with us and we will go through your plant's readings together — no charge, and no obligation to buy anything.