PROJECT DESCRIPTION
BACKGROUND
Pig farming is one of the main source of pollution in some specialised pig farming regions such as Brittany (France). The European Directive on nitrogen has determined a maximum level of organic nitrogen input per hectare (170 kg per year). The administrative areas where this level is not respected were classified as « Structural Excess Areas » : out of 74 areas identified in France, 71 were in Brittany. This was the result of an excessive specialisation in pig farming in that region (with 16 million pigs produced in 1997, Brittany represented 58% of French production), although similar problems can be encountered in the Benelux countries for example. Yet, farmers are keen to utilise this by-product for the fertilisation of their fields, and to avoid having to buy synthetic fertilisers that are also a threat for the environment. Another problem is the fact that the manure has a very offensive smell. Therefore, there is a need for a solution that allows the level of nitrogen in the manure to be adjusted to the needs of the farmers and of the environment, and that also reduces its smell to an acceptable level.
OBJECTIVES
To develop a process that allows for : - the optimisation of the level of nitrogen in pig manure - the deodorisation of this manure - and its disinfecting so that it can be spread onto fields. The aim of the project was to construct two pilot units, one at a fixed location and a mobile unit for the treatment of smaller quantities of manure.
RESULTS
The following results were obtained: 1. Removing the odours caused by sulphur compounds (mercaptans) contained in the manure liquids. The process was adapted from gasoline sweetening and other light fraction freedom sweetening, already used by IFP. It is based on the oxidation of mercaptans to disulphides. This reaction is activated by contacting the manure liquids with a lean oxygen air stream in presence of an homogeneous catalyst. 2. Reducing the nitrogen content of the manure liquids. Owing to accretion of the manure liquids, part of the ammonia, which is the main contribution to the nitrogen content of the manure liquids is stripped from the liquids. The fraction of the ammonia, in the vapour phase, which represents the amount one wants to remove, is oxidised into gaseous nitrogen and water. The reaction takes place on a solid phase catalyst. A supply of oxygen is required to match the oxygen consumption. Nitrogen introduced with the reaction oxygen, and nitrogen produced by the reaction are purged to the atmosphere. 3. Sterilising the manure liquids and the off-gas. The temperatures of the mercaptans liquid phase oxidation (around 900 C.) and of the vapour phase ammonia oxidation (over 2500 C.) have a strong bactericidal effect: strains of bacteria are destroyed. The treated liquid effluent can be spread on the soil without fear of contamination. 4. The gaseous phase ammonia oxidation is sufficiently exothermal that, once started, only a small external heat input is required. This contributes significantly to the low operating cost of the SMELOX process. Although the project met with several difficulties and failed to deliver the mobile unit in its life span, the demonstration of the feasibility of the process was achieved. The process is now marketed by one of the partners, APVCompost who had sold 3 units by the end of 2001. The Agence de l’Eau Loire Bretagne decided to add the SMELOX process to the list of treatment processes eligible for aid from the agency. Farmers who invest in the equipment will receive a grant, which should help the commercial development of this technology.The following results were obtained: 1. Removing the odours caused by sulphur compounds (mercaptans) contained in the manure liquids. The process was adapted from gasoline sweetening and other light fraction freedom sweetening, already used by IFP. It is based on the oxidation of mercaptans to disulphides. This reaction is activated by contacting the manure liquids with a lean oxygen air stream in presence of an homogeneous catalyst. 2. Reducing the nitrogen content of the manure liquids. Owing to accretion of the manure liquids, part of the ammonia, which is the main contribution to the nitrogen content of the manure liquids is stripped from the liquids. The fraction of the ammonia, in the vapour phase, which represents the amount one wants to remove, is oxidised into gaseous nitrogen and water. The reaction takes place on a solid phase catalyst. A supply of oxygen is required to match the oxygen consumption. Nitrogen introduced with the reaction oxygen, and nitrogen produced by the reaction are purged to the atmosphere. 3. Sterilising the manure liquids and the off-gas. The temperatures of the mercaptans liquid phase oxidation (around 900 C.) and of the vapour phase ammonia oxidation (over 2500 C.) have a strong bactericidal effect: strains of bacteria are destroyed. The treated liquid effluent can be spread on the soil without fear of contamination. 4. The gaseous phase ammonia oxidation is sufficiently exothermal that, once started, only a small external heat input is required. This contributes significantly to the low operating cost of the SMELOX process. Although the project met with several difficulties and failed to deliver the mobile unit in its life span, the demonstration of the feasibility of the process was achieved. The process is now marketed by one of the partners, APVCompost who had sold 3 units by the end of 2001. The Agence de l’Eau Loire Bretagne decided to add the SMELOX process to the list of treatment processes eligible for aid from the agency. Farmers who invest in the equipment will receive a grant, which should help the commercial development of this technology.
