Process & Water Chemistry

Chemistry reacts in whole numbers of particles.

A balanced equation is a recipe, and its quantities are the big numbers written in front of the formulas: the coefficients.

That last word is worth a paragraph. V is not the water you added; it is the volume of everything in the vessel once the solute is in and dissolved.

Adding water to a solution adds no solute.

PV = nRT, read aloud P V equals n R T. P is the absolute pressure in pascals — absolute, not gauge, because a gas at zero gauge still has atmosphere in it. V is the volume in cubic metres, n the amount of gas in moles, T the absolute…

A reactor is almost never charged in exact proportion. One reactant is used up while some of the other is still there, and at that moment the reaction stops.

Two percentages share this lesson, and they answer completely different questions.

A titration is a mole count performed with a tap.

You are solving for whichever one the paper leaves out. Note where each number comes from, because that is how you tell them apart in a sentence.

This lesson is written in mg/L, million gallons per day and pounds per day, and it is written that way on purpose: it is the convention every North American operator certification exam uses, and the constant is the point of the lesson.

Chlorine gas is 100% chlorine. Nothing else on the pallet is, and forgetting that is the most expensive habit in this chapter.

Add chlorine to a water carrying ammonia and the residual does something no other chemistry does: it rises, then falls, then rises again.

The product CT comes out in mg·min/L, which is exactly the unit every regulator's table is printed in.

Put it the other way and the answer arrives negative, which is the equation telling you so.

The residual that leaves the plant is not the residual that arrives.

A water analysis lands on the desk: calcium 80, magnesium 25, bicarbonate 180, sulphate 60, all in milligrams per litre.

This lesson is authored in the trade's own units on purpose. Every softener controller sold in North America is programmed in grains, every resin is rated in grains, and every operator licensing exam asks in grains.

Alkalinity is not hardness and the two are easy to confuse because both get quoted as CaCO₃. Hardness is what scales — calcium and magnesium.

A conductivity meter measures how easily current crosses a centimetre of water. Ions carry that current, so the reading tracks how many ions are dissolved — but the meter cannot tell one ion from another, and it has never weighed anything.

Every softener calculation in this lesson is one idea in three costumes: the resin holds a fixed number of grains of hardness, the water spends them, and the regeneration puts them back.

An ion-exchange bed does not soften water a little. It takes hardness down to a fraction of a grain, and that is usually more softening than the building wants.

Regeneration is the reverse trade: a strong sodium chloride brine drives the calcium and magnesium back off the resin and down the drain, and sodium takes their places.

Ion exchange suits a building. A city softens by precipitation: add a cheap alkali, turn the dissolved hardness into a solid, and settle it out.

A cooling tower works by evaporating water. Vapour leaves pure — it carries no calcium, no chloride, no silica — so every mineral that came in with the makeup stays behind in a shrinking amount of water.

Water leaves a cooling tower by exactly three doors, and the makeup meter has to pay for all of them: M = E + B + D. M is the makeup, E the evaporation, B the blowdown or bleed, and D the drift.

Three thermometers describe a cooling tower, and the two differences you can make from them mean completely different things.

A dose is written as a concentration, but nobody can pour a concentration. Getting from the specification to the jug takes up to four steps, and each has its own relation.

Dose a closed loop and the chemical stays. Dose a cooling tower and it starts leaving immediately, because the tower is bleeding — and what bleeds out is treated water, at full strength.

Everything from the first two lessons transfers, with one substitution: steam is the boiler's evaporation.

Condensate is distilled water at a couple of hundred degrees that you have already bought, already treated and already heated.

Water either wants to put calcium carbonate down or wants to take it up, and which of those it wants decides a great deal about the inside of a pipe.

Langelier tells you which side of saturation a water sits on. Operators wanted something that also graded how far, on a scale that never went negative and that could be indexed straight into a dosing table.

Langelier and Ryznar both ask one question: can this water lay down calcium carbonate.

Everything so far has been a prediction from water chemistry. A coupon is different: a flat piece of the actual alloy, weighed, hung in the actual stream, pulled, cleaned to a written procedure and weighed again.

A corroding metal is a short-circuited battery. Iron dissolves at the anodic sites, giving up electrons; oxygen takes them at the cathodic sites a few micrometres away.

Cathodic protection makes the whole of a structure a cathode by supplying it with electrons from somewhere else — a metal that is willing to corrode instead.

Stainless steel does not resist corrosion by being thick; it resists by carrying a chromium oxide film two or three nanometres deep.

Every unit process in a plant is a promise about time.

A clarifier is not sized by its volume. It is sized by its surface, and there is a piece of physics behind that worth understanding once and never forgetting.

Three numbers are quoted for every settling basin, and you now have two of them. Detention time uses the tank's volume and says how long the water stays.

The overflow rate says how fast a particle must fall.

A rapid gravity filter is measured by three numbers, and they are all the same arithmetic wearing different hats.

Coagulant dose is not calculated from first principles — it is found, on a bench, in six beakers, and then scaled.

This lesson is authored in North American operator units — million gallons per day, milligrams per litre, pounds per day — because the constant at its centre is a convention of that system and does not survive translation.

Activated sludge is farming. There is a crop of bacteria in the basin, sewage is the feed, and the operator's job is to keep the herd the right size for the meal.

Half an hour, a litre of mixed liquor and a graduated cylinder will tell you more about a secondary plant than a day of paperwork.

Every separation in this chapter rests on one fact: put a liquid mixture in a warm vessel and the vapour standing over it is not the same mixture.

Before a single tray is counted, the split is already decided.

The balance decided what leaves. These two ratios decide what circulates, and circulation is where the energy bill lives.

Sizing a column by hand has been done the same way since the 1930s, and every step is a named paper. It works by bracketing the answer between two extremes that are cheap to compute and impossible to build.

McCabe and Thiele's construction is the only version of this problem you can see. Draw the equilibrium curve on a plot of vapour y against liquid x, add the 45° diagonal, then add three straight lines.

An absorber is a different animal from a still. Nothing is boiling; a solute is being washed out of a gas by a liquid that will dissolve it.

Put trays in the absorber instead of packing and the question changes from how many metres to how many stages.

Heat does not kill a population all at once. Hold a spore suspension at a fixed temperature and plot the survivors on semi-log paper, and what you get is a straight line going down.

The trade counts kill in logs, and the public reads it in percents.

D answers one question at one temperature.

A real cook is never one temperature. The vessel comes up, holds, and cools, and every minute of that history kills something — just at wildly different rates.

That scale was built for bacterial spores in low-acid canned food. Beer is a different product with a different enemy. It is acidic, alcoholic, hopped and carbonated, and the organisms that spoil it are feeble against heat.

Everything so far has been definitions. This lesson is the payoff, and it is the reason UHT milk exists. The rule, first, in one line: ten degrees hotter, one tenth the time — for an organism whose z is 10 C°.