Four Questions I Would Ask Before Signing for a Sewage Treatment Plant

A client called me the week before he was due to sign for a sewage treatment plant. Not to ask me to bid — he had already chosen someone else — but because his wife had asked him a question over dinner that he could not answer: "so what happens if it does not work?"

He read me the contract over the phone. Two pages. A list of tanks and pumps, a lump sum, a delivery schedule, and a payment schedule that had 90 per cent of the money paid before the plant ever saw a drop of sewage. Nothing about what the plant was supposed to achieve. Nothing about what happens if it does not achieve it.

He signed anyway. Different supplier, not us, and I only heard the ending two years later. But I have thought about that phone call many times since, because the questions he needed were not technical. They were four ordinary questions any owner can ask, in plain language, without knowing anything about biology.

These are the four I would ask if I were buying a plant instead of building one.

1. What exactly is arriving at this plant — every stream, not just the toilets?

This is the question that catches the most expensive mistakes, and almost nobody asks it, because everyone assumes the answer is obvious.

I reviewed a design last year for a commercial building where the specification said, on page one, that the plant would treat domestic sewage. Three pages later the same document listed a suspended solids concentration close to 1,500 milligrams per litre, coming from a bay where delivery trucks were washed. Both statements were in the same client document, written by different people, and the plant had been sized against the first one.

Ordinary domestic sewage arrives at somewhere around 200 to 250 milligrams per litre of suspended solids. The truck wash was six times that, in a stream nobody had counted, discharging in a short violent burst in the morning instead of spread across the day. The plant was not slightly undersized for that. It was designed for a different problem.

Different industries carry different parameters, and the ones that apply to you are not always obvious from the building's name — we keep a breakdown of the significant wastewater parameters DENR applies by industry for exactly this reason.

I have made this mistake myself, early on, and it cost me far more than it cost any client. A food processing plant, hams and hotdogs and beef jerky. I let the domestic sewage and the process wastewater from the production floor go into one line. It seemed tidy. What it actually did was two things: it pulled the whole plant under the stricter set of discharge parameters that apply to industrial effluent, and it fed the biology an emulsified fat load I had badly underestimated. I built that plant twice. The client only ever paid once.

So when you ask this question, do not accept "domestic sewage" as an answer. Ask specifically: is there a kitchen, and is it a canteen or a full commercial kitchen? Is there a laundry? Is anything washed with detergent on site — floors, vehicles, equipment? Is there a clinic? Does any production water, cooling blowdown, or floor washing find its way into the same line? Is stormwater properly separated, or does the plant flood every time it rains hard?

Then ask which of those streams the price in front of you is based on. Get it in writing before you discuss money, because every peso in that quotation follows from this answer.

2. What will this plant cost me every month — and how much of that has to be bought from you?

The purchase price is negotiated once. The operating cost is paid every month for the next fifteen years, and it varies more between technologies than most owners expect.

A well-run fixed-film biological plant lands somewhere near thirty pesos per cubic metre treated, all in — electricity, chemicals, sludge hauling, consumables. A chemical-intensive advanced oxidation train, on the same water, can run three times that. Both are legitimate plants. They are not the same plant to own, and the difference does not appear anywhere on the cover page of a quotation.

Ask for the number in pesos per cubic metre, and then ask for the arithmetic behind it. Which motors run continuously and at what kilowatt. How many kilograms of what chemical per day. How many cubic metres of sludge per month and what the hauler charges per trip in your area. If a supplier can hand you that breakdown without preparing it specially, they have done the calculation. If the figure appears out of nowhere and never gets broken down, it is a marketing number. If you want a starting figure to check any quotation against, our STP price estimator will give you one in about a minute.

Then ask the second half, which matters more than people realise: how much of that monthly cost has to be bought from the supplier?

I sell probiotics. Bacterial cultures for sewage treatment plants — it is part of our business and I believe in them for the situations where they genuinely help. And I will still tell you plainly: be careful of any plant whose compliance depends on a proprietary product that only one company sells.

I have seen plants that were designed short on tank volume and then propped up on a monthly dose of a branded culture, sold at a price the owner had no way to compare against anything. Stop dosing, and the effluent fails. That is not a treatment plant. That is a subscription with tanks attached to it. The same trap exists with proprietary media, proprietary chemical blends, and control panels locked so that only the supplier's technician can change a setting.

A properly sized biological plant does not need to be fed a branded product every month to pass. It needs air, retention time, and someone who wastes sludge on schedule. Ask directly: if I stopped buying anything at all from you after the warranty, does this plant still comply? Watch how that question is received. The answer you get is less informative than the reaction.

And never let your compliance depend on a chemical that may not be available in this country next year. That is a rule I hold hard.

3. Where does the sludge go, and who is paying to move it?

Anyone who tells you their plant produces no sludge is telling you either that they do not understand the process or that they are counting on you not to.

The organic matter arriving at your plant does not vanish. Part of it is oxidised to carbon dioxide and water. The rest becomes bacterial cells — new biomass, growing every day the plant is fed. You can genuinely reduce how much of it you have to haul away by designing for a long sludge age and letting the population partly consume itself, which is what extended aeration does. That is real, and it is worth paying for. But it reduces sludge. It does not abolish it. Something always has to leave the plant.

So ask, before signing: how many cubic metres of sludge will this plant produce per month at design load? Where on this site does it go — drying beds, a holding tank, a dewatering unit? How often does a truck come? Is there room for that truck to reach it? Who is licensed to receive it in this province, and what do they charge?

I have seen new plants where the sludge drying beds existed on the drawing and were quietly deleted during construction to hold the price, and the owner discovered it eighteen months later when the aeration tank was so thick with solids that the effluent was carrying suspended matter over the weir and the operator had nowhere to put anything he wasted.

Hauling cost is real money and it is nearly always left out of the comparison between two bids. Put it in.

4. What happens on the day something fails and nobody who knows this plant is on site?

Every plant fails eventually. A blower seizes, a float switch sticks, a pump loses its seal, an operator resigns without notice. What matters is what that day looks like.

Ask whether there is a standby for the equipment that cannot stop. A blower is the one that cannot stop — take air away from an aeration tank and you have hours, not days, before the biology turns septic and you are looking at a recovery that takes weeks. A single blower with no standby saves money in the quotation and can cost you a full re-seeding.

Ask where the spare parts come from. We designed a leachate plant for a landfill on a remote island a few years back, and that question changed the whole equipment list. Anything with a two-week freight time and a customs clearance in front of it is not a spare part, it is a shutdown. We specified equipment we knew could be serviced with things obtainable domestically, and we shipped standbys with the plant. On a site with a ferry schedule between it and the mainland, that is not gold plating. It is the design.

Ask who trains your operator, for how long, and whether the training happens during commissioning when the plant is behaving or over the following months when it is not. A good operator can carry an average plant a long way. He cannot carry a bad design, and he cannot carry a plant nobody ever explained to him. If you already own a plant and your operator is working without that support, our operations and maintenance support exists for exactly that situation.

And ask the question that man on the phone could not answer. How is this plant accepted as complete? If the answer is "on delivery" or "on commissioning", that is not acceptance, that is a receipt. Acceptance should be laboratory results on the actual effluent, against the actual DENR parameters you are required to meet, taken after a stated stabilisation period — a biological plant needs weeks to build a stable population, so results on day three mean very little. Tie a meaningful part of the payment to that test. A supplier confident in the design will not fight you on it. That is the whole reason the term exists.

The pattern underneath all four

Read those four questions again and you will notice none of them are about equipment. Nobody needs to ask you what brand of blower is in the quotation. The four things that decide whether you are happy with this plant in year three are: what is really arriving at it, what it costs to run, where the solids go, and what happens when something breaks.

Those are the four places where an assumption can hide. And an assumption that nobody wrote down is always paid for by the owner, never by the person who made it.

You do not need to become an engineer before you sign. You need the assumptions on paper, in language you understand, with the numbers attached. Any supplier worth buying from will be relieved you asked, because a client who understands what he bought is a client who does not blame the plant for the building's growth three years later.

If you have a contract in front of you right now and you are not sure what it commits you to, send it over and I will read it with you. You can book a free 15-minute consultation with us — no obligation, and I have no interest in whether you buy from us or from one of the other wastewater companies in the Philippines. I would just rather you buy a plant that works.