Method for acidification of manure

The invention relates to a method and a device for the acidification of manure.

Livestock production has intensified in many parts of the world due to an increasing demand for meat and meat products. The treatment, storage and transportation of livestock manure presents several environmental and social concerns. Besides the strong unpleasant odours or the presence of pathogens, other problems are for example the anthropogenic emission of methane, the emission of ammonia from animal barns and manure storage or the loss of nitrogen to the environment through air emissions or water effluents.

Methane has 25times and nitrogen dioxide 300times the global warming potential of carbon dioxide. The uncontrolled release of nitrogen compounds can cause

eutrophication of surface and ground water and contribute to particulate matter formation.

The acidification of manure is a well-known process to reduce the emission of ammonia and nitrous oxide gases and has also shown the potential to reduce emissions of methane.

Commonly the manure is mixed with solid or liquid acids to reduce the pH value.

Examples for these acids are lactic acid, sulfuric acid or nitric acid.

In US2013/0186823 A1 sulfuric or sulphurous acid is used to acidify manure.

US2006/225473 A1 mentions as well a list of mainly solid acids, which are suitable for the acidification of manure to reduce volatile organic compounds.

But the handling with mineral acids is dangerous and requires stringent regulations for equipment in the farms. It also requires trained persons to avoid dangerous situations or the pollution of the environment.

So, the task of the present invention is to provide a method for acidification of manure which is easier to handle and less dangerous for the handling persons and the environment.

The solution for this task is to use carbon dioxide for acidification. Using carbon dioxide in gaseous or liquid form is easier for handling. It is not characterized as a substance that is harmful to water. The risk to create excess acidity is not given anymore. Additionality it is less corrosive. It is not contributing to the amount of total dissolved solids in the manure.

Furthermore, it is more affordable compared to traditionally used acids.

The amount of carbon dioxide, which is injected into the manure is depending on the pH of the manure. Depending of the source of the manure, the pH is in range between 7,6 to 8.

After acidification the pH of the manure should be in range between 6,3 to 6,7. For dropping the pH by 1 unit around 10 g of carbon dioxide per liter manure is necessary. The treated manure can be liquid or a slurry with different content of solids and can be from different sources. The acidification can be carried out with different solid contents and independent of the way how farms collect and store their manure.

Depending on the amount of manure produced every day it would be useful to have an automatic acidification system. In a favourable system the acidification can be carried out continuously. In systems with less amount of manure per day the treatment can alternatively be carried out batch wise.

The treatment with acids can be carried out directly in the animal houses or in the manure stores or directly before the application to the soil.

One embodiment for the acidification of manure, comprises a tank for the manure, a gas cylinder, for storing carbon dioxide, at least one pH probe, for measuring the pH of the manure, a pH control unit, which is controlling the amount of carbon dioxide which is necessary to decrease the pH of the manure. In a preferred embodiment the tank is covered, because the excess carbon dioxide can be collected and recycled. In such a tank the carbon dioxide can be distributed in the tank, by a mat containing finely perforated aeration hoses or nozzles. For mixing the carbon dioxide with the manure it is preferred to place a mechanical agitation device in the tank.

After the treatment the acidified manure is pumped out of the tank. It can be stored in a different storage site.

In another embodiment the tank is a mobile tank, wherein the gas is injected to the manure directly before the manure is distributed to the soil. This mobile tank can also comprise a slurry mixer inside the tank or directly before the exit of the manure from the tank.

Further features and advantages of the invention are described in the following examples.

Figure 1 (Fig 1 ) shows a preferred set up for acidifying manure. The manure 6 is pumped into a covered treatment tank 5. The covered treatment tank 5 is equipped with a mat 4, which has aeration hoses or nozzles for distributing a gas from the bottom of the tank. Furthermore, the covered treatment tank 5 is equipped with a mechanical agitation device 8 and a pH probe 3.

The acidified manure 7 is pumped out of the covered treatment tank 5 by a pump. The carbon dioxide gas is provided by cylinder 1 and distributed through the mat 4 into the covered treatment tank. The necessary amount of gas is regulated by a pH regulation unit 2 which is contact with the pH probe 3. The acidified manure 7 can be pumped into a further storage compartment or directly into a truck for distribution on the soil.

Figure 2 shows another preferred embodiment. In this embodiment the manure is directly acidified before it is distributed to the soil. The manure is stored in a mobile tank 1. This mobile tank 1 is additionally equipped with a pH controller 2. The pH controller is connected to a not shown pH probe, measuring the pH of the manure, and to a gas cylinder 3, which is providing carbon dioxide. The pH controller regulates the necessary amount of carbon dioxide, which is added to the manure directly before the distribution to the soil. In the figure the acidified manure is applied to the soil by trailing hoses 4. As an example the mobile tank 1 can be moved by tractor 5, which in another preferred example includes a computer to control the acidification.