Manure methanation: not a necessary evil, but a solution
Manure methanation is a knife that cuts both ways: replacing gray energy with green energy and reducing ammonia and methane emissions. The saying goes ‘necessity is the mother of invention and innovation’. Renewable energy from non-fossil fuels is a necessity. Emission reduction is a necessity.
Manure digestion is a proven and feasible innovation for the production of renewable energy and other valuable end product from manure. Anaerobic digesting manure from dairy cows at one’s own farm is an investment that can be overseen and is financially attractive. The challenge for the many agricultural entrepreneurs with a traditional stable floor, however, lies in making the stable (floor) suitable. Several Dutch stables have already been adapted with dense (rubber) low-emission floors and in certain regions, particularly in Brabant, and in a number of cases this is even a requirement.
“Manure methanation is a proven and feasible innovation for the production of renewable energy and other valuable end products from manure”.
Why a dense stable floor?
Manure digestion requires, or is desirable to say the least, that fresh manure is immedatiately transported from the stable to the digester. This is done using pipes ensuring fresh manure with a high gas potential is obtained. Research shows that quick storage of fresh manure in a sealed tank reduces methane and ammonia emissions from the manure cellar.
A special feature of the manure digestion project in Deurningen is that the stable floors have been transformed to dense low-emission floors using a rubber floor. This allows that fresh manure with a high gas production can be obtained and ammonia and methane emissions due to traditional storage are reduced.
The manure digester, the solution
The manure digestion is basically a gas-tight, heated, insulated tank with a mixer in which the manure is anaerobic digested and is converted into biogas in a controlled environment. This way, the methane is not released into the air and is even used optimally. By applying advanced technology, the biogas is upgraded to biomethane with the same characteristics as natural gas. This biomethane is suitable for injection into the natural gas network and is a very suitable and green alternative to heating, hot water and cooking with the fossil fuel natural gas. Then why does not every dairy farmer have a manure digester? This has to do with the scale, but also with the type of stable.
Realizing manure digestion at one’s own farm means that the digester is fed daily with fresh manure. This is fully automated process without any worry of the farmer. The challenge is to make the stable and floor suitable for the fresh manure supply from the stable to the digester. Fresh manure is a condition for optimal anaerobic digestion and biogas production due to the 30% higher gas yield compared to old manure. The calculation: a ton of fresh manure produces 35 Nm3 (cubic meters) of biogas, whereas a ton of old manure produces 20 to 25 Nm3 of biogas. The efficiency of the Microferm biomethane installation from HoSt is already optimal for dairy farms with a manure production from 8,000 m³.
Fresh manure has 30% more biogas potential than old manure.
A ton of fresh manure produces 35 Nm3 biogas. A tonne of old manure 10 Nm3 less.
The faster the manure is stored in a gas-tight storage, the higher the emission reduction.
Limiting stable emissions
Fully preventing methane and ammonia emissions may not be feasible or realistic, but limiting these emissions is. The Dutch dairy sector is 2018 consisted of around 17,000 dairy farms. Together these dairy farmers have 1.62 millions dairy cows. About half of the emissions coming from dairy farms is methane. A quarter of this is due to cold fermentation (digestion) of the manure due to storage under the stable, also known as the manure cellar or manure basement. Ammonia is also produced via this manure. The faster the manure is stored in a gas-tight tank, the higher the emissions reduction.
Manure digestion or manure methanation, in a controlled gas-tight environment, is a solution that is up for the grabs.