Residents bothered by the smell of liquid manure, residents worried about the upcoming construction of a large pigsty, who hasn’t read this kind of news?
At a time when large pig farms are being built in many countries, the problem of odours is a challenge and even a hindrance to the development of the pork industry. In recent years, more and more importance has been attached to the problem of odour nuisance.
What exactly is a smell ?
Smell is the emanation of volatile bodies perceived by the organ of smell. It is made up of molecules whose chemical composition characterizes the odorous properties. The intensity of an odour depends on the concentration of odorous molecules in the air breathed and is expressed in ppm (parts per million). The perception of these effluents differs according to their concentration and specific environmental conditions (wind, humidity, temperature). The duration of the perception of odours carried by the air therefore depends on these parameters. For example, wind blowing in the same direction will continuously carry certain odours, such as that of applied liquid manure. The pleasant or unpleasant sensation varies from person to person, but some smells are universally perceived as nauseating. Liquid manure falls into this category. It should be noted that on average a human being breathes some 12 m3 per day, and that beyond the phenomenon of habituation, the ability to get used to an odour and no longer perceive it, some odours are persistent and remain unpleasant over time. Liquid manure falls into this category.
The smell of manure
In 2002, a study was conducted in Quebec (Groeneveld and Hébert, 2002) to determine how fertilizer waste odours were perceived on a scale of 0 to 10, with 10 being the most unpleasant odour. The odour rating for hog manure on feedlot was determined to be 8 out of 10, while solid cattle manure had a rating of 4 out of 10.
The odour of manure is the result of anaerobic decomposition. The main sources are :
The pig barn, barn, manure pit (storage) and land application.
Slurry has always had the same odour, however, over time, hog production has evolved from small operations to sites with large numbers of animals and increasing concentrations of slurry in large pits.
How to control, mitigate manure odours
Odours emanating from three main sources; barn, pit, spreading, different solutions specific to the source of these odours have been developed.
Here is a summary of the main odour reduction techniques.
Smells from the pigsty
Filtration technology. The air is filtered to remove odour-carrying dust. Depending on the type of filter applied, the reduction can be significant: from 50 to 90%.
Litter. The litter used includes enzymes that continuously compost litter and dejecta. However, the method can be expensive.
Feeding. The principle is based on the addition of feed additives, such as lemon oil, kelp extracts, which allow for better digestion and thus a reduction in odours.
Air deodorization. This consists of using ‘odour masks’ (e.g. certain oils) to reduce the intensity of odours.
Odours from the slurry pit
Management of slurry dumps: this technique consists of distributing the slurry input into the pit in small quantities on a regular basis, rather than massive inputs.
Aeration, an effective biological treatment technique based on oxygen supply and mixing, but little used in relation to its cost.
Filtration, the objective is to reduce the proportion of solids to lower the BOD (Biochemical Oxygen Demand). However, this method, which is close to liquid-solid separation, requires a large infrastructure (aerator, solid filter).
Anaerobic biological deodorization. Bacteria and/or enzyme cultures are added to achieve biochemical digestion to eliminate odours. According to various sources, this method is not very convincing.
Methanisation. The production of methan via an anaerobic digester reduces odours. However, odours may persist when the digestate is spread. In order to optimize methane production and reduce costs, in the case of pig manure, a liquid-solid separation should first be carried out.
Odor maskers. Aromatic oils are used to partially mask odours. The cost is usually high.
Chemical deodorizers. Peroxide, potassium permanganate are among the oxidizing agents that reduce odours.
Covering the pit with a floating barrier or by deploying a pit cover.
Odours related to manure spreading
It appears that the soil injection method is the most effective in terms of odour control. However, it cannot be applied to all crops and in some cases the nature of the soil does not allow this technique.
A solution that combines odour reduction and economy
The solutions mentioned above offer benefits in terms of odour control, but in most cases the problems related to manure management remain:Operating costs associated with spreading and Environmental Risks.
Solugen offers a solution that combines :
Odour control: 90 to 95% of storage and spreading odours are eliminated.
Limitation of environmental risks: the manure is treated continuously to extract the solid fraction, 84% pure water and fertilisers in liquid form. The pure water can be reused, phosphorus management is optimized because 85% of the phosphorus in the manure is found in the solid part, which now represents only 10% of the initial volume of manure, and drastic reduction of greenhouse gases.
Creation of a circular economy; for farms that generate at least 10,000 m3 of manure per year, operating costs are generally lower than those of conventional manure management and the liquid fertilizers recovered have a market value.