One Drawing Decision Gave Them an Ammonia Problem They Never Needed

A meat processing plant we worked on had ammonia arriving at up to 200 mg/L. Ham, cured meats, a large staff, and a plant designed for 20 m³/day that was actually running about half of that.

Here is the part worth your attention: they did not need to treat ammonia at all.

Their process wastewater, on its own, would never have been measured on ammonia. The parameters that applied to it were about organic load and grease. But somewhere in the design, the domestic sewage from the toilets had been piped into the same treatment line as the production water.

Once those two streams are combined, they are one stream. And that combined stream now had to meet the stricter set of parameters — including ammonia.

Nobody bought equipment to create that problem. Somebody drew a line on a plan to keep the piping neat.

I have made this mistake myself

I am not writing this from a comfortable distance. Early in my career I did exactly the same thing on a food processing plant — combined the domestic and process streams into one line because it simplified the layout — and gave myself a nitrification problem I did not need to have, on a plant that was already fighting fats and already sitting on a second floor with neighbours close enough to smell every bad day.

It is an easy decision to make on a drawing and an expensive one to live with. That is why I now say it out loud in the design review: if we are combining these streams, this is the parameter that just got harder, and here is what it will cost to meet it.

The second problem, arriving at the same time

That meat plant also had heavy emulsified oil — cooking fats from the production process — plus a great deal of soap from washdown.

They had a grease interceptor. What that wastewater needed was dissolved air flotation. A grease interceptor catches free-floating grease; it does very little against oil that soap has already emulsified into the water, which is what you get when you wash down a hot kitchen with detergent.

So the fats that should have been intercepted went through, and everything landed on the biological plant instead — which was now also being asked to nitrify.

That combination is why ammonia kept failing.

What we did about it

The thing that saved us was that the plant had two aeration tanks rather than one. With a single tank this would have been a much harder job.

We kept the first tank as moving media. The media tumbles and effectively self-cleans, which matters when the water reaching it is still carrying fat.

We built the second tank out as fixed media, and made it robust, because that is where we wanted the ammonia work done. Bundles of polypropylene rope, made up rather like a jellyfish, roughly fifteen ropes to a bundle, hung down the full depth of the tank. These were circular stainless tanks about two metres across and five metres deep, so the bundles run the whole five metres. It is also the arrangement that has held up best for us when a plant loses its air for a few days.

Then two less visible things. We set the recycle so the plant was not throwing away its own alkalinity — converting ammonia is acid-forming and the buffer has to come back round. And we held the settled sludge at around 200 mL in the cone rather than letting it climb.

Since then that plant has not failed ammonia.

Two things to take from it

Ask what happens to your parameters before you combine streams. If you are designing a new facility, or extending an existing one, the decision to route toilets and production into one plant should be made deliberately, with the compliance consequence stated. Sometimes combining is still right — one plant is cheaper to build and operate than two. But it should be a decision, not a side effect of tidy plumbing.

Fix the front of the plant, not just the back. Where fat and grease are getting through, the biology carries a load it was never sized for, and the parameter that fails is often nowhere near the actual fault. Which parameters apply to you depends on your industry, and the answer changes the moment your streams change.

Every site is different. Two aeration tanks gave us options that a single-tank plant would not have had, and I would not promise the same route on a different layout.

If you are planning a facility and are not sure whether to combine your streams, that is a fifteen-minute conversation that can save a great deal later. Book a free 15-minute consultation.