Odour at a food waste transfer station, a food waste treatment plant or a landfill leachate site is not one problem. Ammonia, hydrogen sulphide and sulphur compounds behave differently, respond to different products, and are generated at different points in the process. Sites that treat odour as a single issue end up dosing a general deodoriser and chasing the peak. Sites that separate the compounds can usually reduce total dosage, because each product is doing only the job it is good at.
Product referenced in this article
Biological Deodoriser for Food Waste — application notes, specification table and document downloads for this range.
Why food waste and leachate are harder than most odour sources
Two features separate these sites from a wastewater plant or a pet facility. The first is concentration: food waste is a high-strength stream with a high nitrogen content, and leachate from a landfill is frequently an order of magnitude more concentrated than municipal sewage. The second is the surface area presented to the air. A liquid stream can be contained; a tipping hall full of mixed refuse cannot, and odour escapes from the whole volume as it is disturbed.
On top of these, the composition changes through the day. A facility receiving commercial waste in the morning and household waste in the evening sees a different nitrogen and sulphur load in each shift. Any dosing strategy that is set once in the morning and not adjusted is going to be wrong by the afternoon, and the complaint will arrive at the worst possible time.
The three compounds and where they come from
Ammonia comes from the nitrogen in the waste. It is light, it rises, and it is the compound that carries furthest into the surrounding area and into neighbouring properties. At a tipping hall it is released at the point of unloading, which is why complaints often track the collection schedule rather than any treatment step.
Hydrogen sulphide is produced when sulphur-containing material breaks down without oxygen. A compacted, wet, anaerobic mass inside a bin or a compacted layer in a landfill cell is the ideal condition, and the note it produces is the one most people describe as sewage-like. It is heavier than air and concentrates low, in pits, in the receiving area and in the drainage system.
Sulphur compounds beyond hydrogen sulphide — the mercaptans, which include methanethiol — are produced in the same anaerobic environment but from a different pathway. They are the reason a site can be handling a hydrogen sulphide problem correctly and still have an objectionable note, and they are generally the hardest of the three to treat by biological means.
Botanical extracts: where they belong
A botanical extract deodoriser works by neutralising. The active fraction complexes with the odour-forming molecule and converts it into a non-odorous compound, and because the reaction is chemical rather than biological, it is immediate. The practical consequence is that a botanical product is the right tool when you have a short, high-concentration odour event and no time to wait: a tipping hall during a delivery, a covered area being opened after a period of closure, a temporary odour from a tanker or an unwashed bay.
They are also useful where the site is being treated as a problem by people who cannot be persuaded to accept a sustained biological control programme as sufficient. A visible, fast, neutralising action is easier to run past a neighbours' committee than a slow biological improvement, and in that context it has a real place.
What botanical extracts do not do is keep working. The reaction consumes the active fraction, and once the extracted material in the immediate area has been neutralised, the effect fades. That is not a drawback, but it does mean they are an event product rather than a base treatment, and using them as the base treatment is the most common misuse we see.
Biological and enzymatic routes: where they belong
Biological and enzymatic products work on the source rather than on the air. Enzymes break down the specific substrate that releases the odour — typically protein residues for the ammonia pathway and sulphur-bearing compounds for the faecal note — and do so at the source, so the odour is no longer generated rather than being masked after it has formed. Biological formulations go further: they establish a population that competes with the organisms producing the strongest odours and keeps the material on a less odorous pathway.
These routes need time. A biological product establishes a working population over days, and an enzyme product needs to be present when the substrate arrives. The payoff is that the effect persists as long as the material keeps arriving at a controlled rate, which is the normal operating condition of a plant rather than an event.
The combination is where most well-run sites end up. A base biological or enzymatic treatment across the process, with a botanical extract available for the peaks — the tipping bay during unloading, the discharge of a strongly loaded liquor, the emptying of a reception pit. The total daily dose is often no higher than a single-product approach, because each product is only being asked to do the job it is actually suited to.
Dosing practice that determines the result
Most disappointing results in this sector are dosing problems rather than product problems, and they share a pattern. The product is applied once, in a fixed line, at a fixed concentration, and not adjusted. The site generates a variable load, the dose does not follow it, and the peak is untreated.
Practical measures that make a real difference: apply at the point where odour is generated rather than at the boundary where it is complained about; adjust the dose to the delivery schedule rather than to a fixed daily volume; use a fine mist and let the droplets reach the material, because a coarse spray that lands on the floor treats the floor; and keep nozzles clear, since a blocked nozzle is the most common single cause of an under-dosed line.
Two things to settle before specifying. Whether the site needs immediate action at opening, in which case a neutralising product has a place in the first hour, or steady suppression across the day, in which case it does not. And what the complaints actually are — if a neighbouring complaint is a hydrogen sulphide note at a specific time, tracking the complaints against the site timeline will usually identify the source step before any product is chosen, and that answer is worth more than any product selection.
Frequently asked questions
- What is the difference between botanical extract and biological deodoriser?
- A botanical extract works by neutralising: it complexes with the odour-forming molecule and converts it into a non-odorous compound. The action is immediate but does not persist, so it suits short, high-concentration events. A biological or enzymatic product works on the source, breaking down the substrate that produces the odour or competing with the organisms that produce it. It needs a few days to establish but then persists as long as the load does.
- Which deodoriser works best for a waste transfer station?
- A combination. A base biological or enzymatic treatment across the process, with a neutralising botanical extract available for peaks such as the tipping bay during unloading. Because each product handles only the compound it suits, the total daily dose is often no higher than a single-product approach.
- How should we dose a food waste odour control system?
- Adjust the dose to the delivery schedule rather than to a fixed daily volume, apply at the point where odour is generated rather than at the site boundary, and use a fine mist so droplets reach the material. Fixed dosing set once a day will under-treat peaks, which is where complaints originate. Check nozzles regularly, since a blocked nozzle is the most common cause of an under-dosed line.
- Is a biological deodoriser a substitute for covering the material?
- No. Containment is the first control and chemical treatment is the second. At a transfer station the emission area dominates, and no product substitutes for keeping the material enclosed and disturbed as little as possible. A deodoriser reduces the odour generated at an inevitably open point, and it works far better once the obvious containment measures are in place.