Why a lagoon sours: the anaerobic turn and hydrogen sulfide
A lagoon sours when its oxygen runs out and anaerobic bacteria take over the breakdown of the waste. Some of them reduce sulfate to hydrogen sulfide, the rotten-egg gas, and the water turns acidic and rank. Keeping the upper column aerobic shifts the breakdown back toward the path that makes no sulfide.
What’s actually happening in your water
A lagoon sours when its biology runs out of oxygen. The waste keeps arriving, the bacteria keep working, and once the oxygen is gone the breakdown carries on the anaerobic way, meaning without oxygen. That path does not break waste down cleanly. Sulfate-reducing bacteria give off hydrogen sulfide (H2S, the rotten-egg gas), other anaerobes give off ammonia and organic acids, and the water turns acidic and rank. The smell your neighbors call about and the sour reading you take are the same condition.
Souring tends to arrive with the warmth. A lagoon that held a load through cold months speeds up as it warms in spring, and the biology’s oxygen demand climbs faster than anything replaces it. The water can turn over a few warm weeks, which is why the worst of the odor often lands on roughly the same schedule each year.
The same anaerobic turn that sours the water also slows the digestion of solids, so they settle out as sludge and, at the surface, form a crust. Souring, sludge, and crust trace back to the one missing thing.
Why the usual fixes don’t hold
Pit additives and biological amendments are the common reach, and some help at the margin. None of them puts oxygen where the breakdown needs it, so the lagoon keeps running anaerobic underneath and sours again once the amendment is spent.
Surface aerators do add oxygen, and plenty of operators have one that ran the power bill up without settling the smell. The reason is transfer efficiency, how much of the oxygen you pay for actually dissolves. A large bubble races to the top in seconds and hands most of its oxygen back to the air. You pay for oxygen that never reaches the water.
Odor-masking agents treat the complaint and leave the anaerobic cause in place, which is the same surface logic that fails on a soured pond.
How restoration works here
Continuous nanobubble oxygenation keeps the upper column aerobic. Nanobubbles stay suspended and give their oxygen up in the water rather than the air, so the oxygen you pay for does the work. With the column aerobic, more of the waste breaks down the aerobic way, which produces no sulfide, so less hydrogen sulfide leaves the surface and the sour, acidic swing settles. It runs around the clock, and nothing about the operation stops.
The proof is operational, and operators already track it: odor-complaint counts before and after, hydrogen sulfide readings where you take them, and the condition of the water through a warm season, all against a baseline we measure before any commitment. The lagoon-duty unit is the N4, built for high organic loads with no fine passages to clog. A heavily loaded lagoon needs a system sized to its load, so we will not quote one too small to hold. What we measure and how is published, so the readings you show an inspector are ones we can both stand behind.
What to expect, and when
Weeks 1-2
Oxygen in the upper column rises, and the sulfide leaving the surface starts to ease as the top layer turns aerobic. Operators who track complaint calls or take gas readings tend to notice the change here first.
Weeks 3-12
As aerobic breakdown takes over the upper column, less hydrogen sulfide is generated and the sour, acidic swing settles. The pace depends on the load, the temperature, and how much fresh waste arrives.
Season and beyond
A full warm season shows whether the lagoon still turns on its old schedule, measured against the baseline we take before install. We keep the record either way, so the change is a number you can check.
The record
We don't have a published case file for this problem yet. Every Alchemal installation is instrumented from day one, so the first case files are being measured now, and until one is ready, our methodology shows exactly what we record and how we report it.
When this isn't the right fix
- Hydrogen sulfide released during agitation and pump-out is a recognized hazard around manure storage. Oxygenation lowers the standing sulfide load, but it does not remove the need for your operation's gas-monitoring and confined-space procedures, which govern on agitation days regardless.
- A lagoon is an engineered, permitted system. We integrate with your compliance framework and never replace it, and the readings we take are built to stand up in front of an inspector.
- A heavily loaded lagoon needs a system sized to its actual load. If the real issue is capacity, a lagoon undersized for the herd or the throughput, oxygenation helps but will not substitute for volume, and the assessment will say so.
Questions people ask
Why does my manure lagoon smell like rotten eggs?
The rotten-egg smell is hydrogen sulfide, a gas that anaerobic bacteria produce when they break down waste without oxygen. Once a lagoon's biology runs out of oxygen, sulfate-reducing bacteria take over part of the breakdown and give off that gas, so the smell is a sign the water has gone anaerobic rather than a passing nuisance.
What does it mean when a lagoon goes sour?
A soured lagoon is one whose oxygen demand has outrun its supply, so anaerobic bacteria dominate the breakdown. Their by-products, hydrogen sulfide and organic acids, make the water acidic and rank and slow the clean digestion of solids. Souring, odor, and slow breakdown are the same anaerobic condition seen from different angles.
Why is souring worse in spring?
A lagoon that carried a load through cold months warms in spring, and the biology speeds up while the oxygen supply stays low. The demand climbs faster than anything replaces it, so the water can turn sour as it warms. Holding oxygen in the upper column through that warm-up keeps the aerobic path ahead of the anaerobic one.
Is the hydrogen sulfide from a lagoon dangerous?
Hydrogen sulfide is a recognized hazard around manure storage, especially when agitation or pump-out releases it in a rush. Treat it as a safety matter governed by your operation's gas-monitoring and confined-space procedures. Oxygenation lowers the standing sulfide load in the water; it does not replace those procedures on an agitation day.
Will oxygen stop the souring for good?
Where the souring comes from the lagoon running anaerobic, holding oxygen in the upper column removes the conditions the sulfide-making bacteria need, and the souring eases. Where fresh waste arrives faster than any system can break it down, oxygen helps but the loading has to be matched too, which is what the assessment sizes for.
Tell us what your water is doing.
A specialist reads your description and replies with a plain answer: what it usually means and what we would measure first.