There is a strong smell of progress when it comes to converting manure into fertilizer and gas.
The nitrate content in the groundwater is too high as farmers distribute too much liquid manure on their fields. What can one do with 73 billion litres of liquid manure a year?
31/03/2017, by Wolfgang Kempkens
Germany could be put in the dock because the nitrate content of groundwater is too high in many parts of the country. Thus, the Federal Government is violating a requirement of the European Union. The cause of the misery are farmers, especially those who distribute manure on their fields. It is not possible to adjust the amount distributed to the needs of the cultivated plants: excess manure is washed away by rain into nearby streams or immediately into the groundwater. In order to escape this accusation, the Ministry of Agriculture is currently preparing an amendment to the Fertilizer Ordinance. Whether this will help, however, is questionable.
12.5 million cattle are currently found in Germany’s stables. Each produces 16 litres of liquid manure a day, so that is about 200 million litres daily or 73 billion litres a year. In addition, there is the liquid manure of 27.3 million pigs reaching about the same order of magnitude.
It is hopeless to distribute everything in the fields and expect the environment doesn’t suffer. However there are solutions. Manure Eco Mine is a research project, subsidized by the EU with 3.8 million Euros – Manure means fertilizer. Within this framework, two experimental plants for the treatment of liquid manure were established in the Netherlands and Spain. A process for the separation of liquid manure into water, fertilizer and pollutants is optimized at these plants.
Ultrafiltration or Reverse Osmosis
The first step is to separate the water, which accounts for 90 percent of the liquid manure. This is done by ultrafiltration or reverse osmosis. In both cases, fine-pored membranes are used, which allow only water molecules to pass through. In the case of ultrafiltration, this is accomplished without pressure; the reverse osmosis works with pressure, so the separation is faster.
What remains is a mixture of nitrate and phosphate, i.e. fertilizers, organic constituents and pollutants such as drug residues and pathogenic germs, which according to today’s practice simply land in the fields. According to the new process, this mixture is now fermented in a biogas plant. Some of the germs are killed. This produces a combustible gas, which can be used, among other things, for generating electricity. From what remains, the fertilizers are recovered; the rest can be burned.
The process could even be worthwhile despite the large manpower required. Europe’s farmers pay 15.5 billion Euros a year for nitrogen and phosphorus fertilizers. From only liquid manure and dung, fertilizers worth 10.7 billion Euros could be recovered annually estimates Professor Siegfried Vlaeminck from the University of Antwerp Belgium, who coordinates the Manure Eco Mine.
Using Manure Directly in Biogas Plants
There is also another method. The Finnish company Ductor recommends the direct conversion of manure in biogas plants, i.e. converting it into a gas that can be fed into the natural gas network after a processing step. This is a well-known method. However, the process only works currently when the proportion of liquid manure or dung is low. Otherwise, the bacteria producing the gas, surpass the produced amount of ammonia. Sometimes small amounts are enough, specifically: “Plants where excrements are recycled are more frequent,” says Joachim Krassowski, head of the biogas working group at the Fraunhofer Institute for Environmental, Safety and Energy Technology (Vigilance) in Oberhausen, who has examined the Ductor process.
The Finns have developed a system in which liquid manure and dung are pretreated. Here bacteria dissolve the nitrogen compounds contained therein and convert them into (gaseous) ammonia. With the help of the remaining suspension, the Ductor developers conduct air or steam, which entrains the ammonia. It can again be converted into nitrogen fertilizer.
More about this
The nitrogen-free suspension ultimately ends up in a biogas plant. Since no more ammonia can form, the bacteria work tirelessly on the utilization of the residuals. Pleasant secondary effect: Energy crops such as maize need not be added or are added just in small amounts. More than 800,000 hectares of usable area, where currently energy crops are cultivated in Europe, would then be free for food production, according to Ductor CEO Ari Ketola. The first large-scale plant, which converts 1400 tonnes of chicken manure per year, commenced operation at the end of 2016 in Tuorla, Finland. It generates 266,000 cubic metres of biogas and115 tonnes of ammonium sulphate, i.e. nitrogen fertilizers, and 640 tonnes of phosphorus fertilizer per year.