Sizing a dosing pump for four grease traps and 400 mL a day: why the smallest industrial pump is twenty-two times too big, why metering by time fixes that, why we threw out the solenoid-valve architecture, and why the tubing chose the pump.
An owner sent us both quotations and asked us to explain the gap. Most of it was scope, not margin ā and we will not tell him the cheap plant must be imported junk.
Most clients have no influent lab result, so the strength on the drawing is an assumption. Here is why we design the same plant at three wastewater strengths, what actually moves between them, and what we put in front of the client.
Nearly every first call asks how long a sewage treatment plant takes to build. Field notes from our Cebu jobs on what actually takes the time: civil works, the design basis nobody schedules, and the commissioning stage most contracts never write down.
An owner had three proposals with three different technologies on the cover. We quoted the same building all three ways ourselves. Field notes on what actually separated extended aeration, fixed film and a batch reactor on a Cebu site.
An owner in Cebu asked why he could not just enlarge his septic tank instead of building an STP. We sampled the tank first. BOD was down, solids were down, and ammonia came out higher than it went in. Field notes on what a septic tank does, what it cannot do, and how we kept his tank and built the plant around it.
A client put two quotations side by side and asked which one was cheaper. Neither of us could answer that from the cover page. Here is how we cost a sewage treatment plant per cubic metre treated, what sits inside that number, and where capital money buys running money back.
A plant that had passed the year before came back at BOD 82 against a Class C limit of 50, three weeks before its permit sampling. Field notes on why the TSS number answered most of it, the one extra laboratory number we ask for, and when this is a housekeeping fix and when it is a design problem.
A blower tripped on a Friday and nobody was on site until Monday. What we found in the tank, why BOD recovers in days and ammonia in weeks, what we did in order, and the design question underneath it.
Solids going over the clarifier weir usually are not a clarifier problem. Field notes on the three quite different things a thirty-minute jar test separates, and the order we work through them.
White billowy foam and thick brown foam look alike in a photograph and mean opposite things. Field notes on what we found underneath each one, and the order we work through it.
Small STPs fail more often than large ones, and not because they are cheap. Field notes from Cebu on why 5 cubic meters a day is harder to operate than 500 ā and how I design small sewage treatment plants differently now.
